Module 1-3 Genetics Exam 1

Genes are on Chromosomes

diploid organism -> haploid gamete-> fusion of haploid gamete-> new diploid organism Up until this point... we were assuming -Two alleles assort into gametes independently of one another (segregates maternal and paternal lineages) >- we thought about the offspring are going to inherit one of A possible 2 copies from parents and then upon Fusion of the 2 haploid gametes into a diploid cell that number would go back up to 2 -Each gene assorts independently of other genes -Offspring have predictable phenotypic ratios (3:1 OR 9(dom for two genes):3 (dom,recessive):3(same):1(homo recc)) for mono- and dihybrid crosses respectively (irrespective of sex) >- for sex, animals not plants, the male and female would be 50-50% -What if we notice that a pattern of inheritance in one sex of offspring is different than the other sex? -- we assumed that every Organism that is formed through fertilization to gametes is going to carry 2 copies of each gene - one from mom and one from dad -during independence assortment part of these chromosomes produces

Randomly assorting chromosomes

- When chromosome pairs align during metaphase one it is a cis confirmation meaning all the paternal chromosomes are located on the left hand side and all the maternal on the right hand side - Trans confirmation is the opposite of the first homologous pair it is a mix of the maternal and paternal on both sides it has ends up resulting in multi genetic possibilities it is an inverse of the maternal and paternal on each side

Summary of Mitosis - mitosis occurs in all diff types of cells

- Asexual method reproducing- no genetic change from the parent cell to the daughter cells - Produces genetically Identical daughter cells - Duplicates genome, separates two identical genomes into two daughter cells - during one round of cell division - Can occur in cells of any chromosome number (the number o copies of each chromosome in the cell) (ploidy) o 2n->2n o n->n o 5n->5n o Always end up with the same number of chromosomes you started off with o If you start with diploid you end with diploid because you genetically identical - For instance, humans of diploid meaning there are two copies of each chromosome one copy from mom and one from dad for each chromosome - Its diploid so when cell undergoes mitosis it starts with 46 chromosomes it undergoes duplication and division producing another genetically identical cell with 23 pairs - Humans have 23 pairs of chromosomes meaning 46 total chromosomes

Meiosis 2: just like mitosis sister chromatids separate

- In Meiosis two we usually don't have sister chromatids that are not identical because the crossing over that occurs during prophase one - In prophase two we have condensed sister chromatids we pair them up and nuclear envelope is degraded - in metaphase 2 the paired chromatids line up - between metaphase 2 an anaphase 2 there is not the same colors, so it indicates that each individual chromatin is not represented by each of the parent cells - in anaphase two uhm we segregate the chromosomes and is going to be a mix of both the maternal and paternal line because of the segregation and synapses of prophase one - In this image the top cells as well as the bottom cells create two genetically unique daughter cells - neither of these cells will represent the parent cell

Meosis- reduction of chromsome number

- Meiosis is what is cell looks like after replication but before we get into a cell division components of meiosis - Before we separate these chromosomes we're not only going to pair up the sister chromatids that are the result of the genome duplication from S phase and interface, we're going to pair up the homologous chromosomes. - Long chromosome from the maternal and paternal link will link up and form a tetrad for all the individual chromosomes -Each diploid cell has two copies of each chromosome: One from "MOM" and one from "DAD"- one long, short, and medium -has 6 chromosomes, three homo pairs, which is diploid - humans have 23 pairs of these chromosomes sets with 46 total chromosomes

Molecular Basis of Dominance

- The locus for flower color is associated with an allele sequence that is starts with C in is responsible for producing an enzyme that is going to synthesize the purple payment within a flower - While the allele for white Flowers is made up of gene sequence that is almost identical to the allele for purple Flowers however the first nucleotide is different an is an A this results in production of no functional enzyme for pigment color - the first nucleotide is important for the functionality of the enzyme that's responsible for producing the pigment in Flowers - the locus for the flower colors are on the same gene - the white allele does not produce any pigment so for a heterozygous individual with traditional complete dominance from medallion inheritance, the purple allele is producing enzyme that produces enough payment that corresponds to the purple flow in pea plants and this production of pigment as the same exact production of pigment for a homozygous dominant allele - Dominantly allele there is not a difference in quantity of pigment produce if an Organism has two copies of the dominant allele versus just one copy of the dominant allele - Put a heterozygous individual they have inherited both a dominant and recessive copy of a particular gene

Dominant Epistasis in Squash- two genes

- Whereby two jeans are going to control the complete expression of pigment in a squash plant - this inhibits the activity of enzyme one which is the W gene which is responsible converting compound A to compound B - The Y gene is responsible for converting compound B to compound C Ratio of offspring from WwYy x WwYy: 12:3:1 White W_Y_ 9 W_yy 3 If W is functional, Enzyme I is inhibited Green wwyy 1 W is non-functional Enzyme I is not inhibited Enzyme II (Y) is non-functional Yellow wwY_ 3 W is non-functional Enzyme I is not inhibited Enzyme II(Y) is functional -W protein inhibits function of "enzyme 1" -Y protein enables function of "enzyme 2" -W - dominant allele (W) is epistatic to Y - the only way to get full expression of the pathway we have to have two recessive copies of W gene at least one dominant copy of the Y gene= B->C - Because the W gene is in its dominant allele arrangement as a responsible for inhibiting part of this pathway this is a dominant epistaxis - so we can see that the Genotype from 2 heterozygous crossed together produces any number of copies of the dominant W gene the arrangement of the alleles for the Y gene doesn't matter because this particular activity in the biosynthetic pathway comes before the activity of the Y and G gene - So this Case we would produce two different genotypes for white squash, it would either be one dominant copy of the W gene and one dominant copy of the Y gene, or one dominant copy of the W gene and two recessive copies of the Y gene - Either version we're not going to get conversion of A to B - so all the squash will be white - in order to get green squash we have to have no function copies of the W gene and no functional copies of the Y gene meaning we can produce compound be but we cannot convert compound B to C - W is epistatic to y gene and it is dominant epistatic to y because it is the dominant allele arrangement, it is Marking the activity of the Y gene

Goal and overview of mitosis

- asexual reproduction - Process of cell producing a genetically identical daughter cell - how does the cell ensure that all the genetic information DNA gets into both daughter cells? o Cell copies all (DNA) that evenly divides the copies - In order to duplicate into two- replicate all the genetic material in the cell. This is the photocopy part. so you have a bunch of DNA in the nucleus, you want to 1st copy all the DNA and once you copy that DNA you have to independently you have independent genomes you separate those genomes then you can perform cytokinesis - From the one parent cell (one chromosome) it turns into two independent, identical daughter cells

Objectives Module 1 topic 1

- review and master usage of genetic terms - Describe the central dogma of molecular biology -> describe the functions of DNA. RNA, and protein in cell function -> compare and contrast the function of transmission and expression of DNA sequence -Compare and contrast the types of cell division including: -> the goal of division -> mechanism of division including the stages- each stage of meiosis and mitosis included -> major factors promoting genetic diversity during cell division - Product of division for each mode of cell division

Inheritance Mechanism Horizontal Transmission

-(Prokaryotes only; not affiliated with cell division process) -> bacterial method of swapping DNA without regard to generations -> we will cover this in the HGT lecture - not affiliated to cell division process - strictly when bacteria swap DNA sequences and it can happen within a species, btw two species without regard to generation - NOT typical type of inheritance where call is passing genetic info during cell division - this is a specialized type of DNA transmission that occurs regardless of generation of cells

Autosomal Recessive Inheritance

-- Autosome recessive inheritance is where a gene is inherited on Autosome meaning nonsex chromosome - in this in the case of this a trade is only expressive the individual has homozygous recessive Geno type - There are two types of inheritance -Ex. Skin pigmentation characteristic-this is the characteristic or gene we are investigating -Trait: Albinism-lack of presence of pigment in the hair, skin, and eyes -Gene is located on an autosome (non-sex chromosome) -Trait is expressed ONLY if individual is homozygous recessive genotype -- Albino trait is only seen phenotypically when an individual inherits 2 copies of that specific recessive allele an Organism that inheritance at least one copy of the dominant or normal skin pigmentation on, these individuals will not show characteristics albino - heterozygous produces carrier's meaning they are capable to pass on the albino gene/allele to future generations but they do not exhibit the trait

Understanding of Genetics in 1850s - very limited

-1850s (Pre-Civil war era in US; Victorian era in Europe) -No concept of genes, DNA, chromosomes, alleles, etc.-nor how many copies of each gene -No concept of dominant or recessive traits -Most of this information was not discovered until 1910 -Structure of DNA not known until 1950s!

Predicting Offspring

-3 ways of sex-linked inheritance (3 crosses) via X chromosome

Human Karyotype: 46 total chromosomes (2n); 23 pairs (n) - 4 chromatids per tetrad per chromosome

-After S phase, EACH chromosome is replicated...just like in MITOSIS, BUT during Meiosis, maternal and paternal "versions" of the chromosomes PAIR UP. Forms a TETRAD = 4 chromatids - This is this is a replicated mitotic cell and what it looks like before it goes into meiotic cell division - Each of the chromosomes are represented by two copies and each copy of the chromosome which has two sister chromatids or identical copies - the homologous chromosome forms of tetrad 2 chromatids that make up maternal and two chromatids that make up paternal - This is a human karyotype - meaning all the genetic information that is present within cell after S phase of genome replication but before we divide any of the chromosomes into individual daughter cells

Sex Linkage—Violation of Mendel's Assumptions

-Calvin Bridges (an undergraduate researcher!) working in the Morgan lab at Columbia University notices a sex-associated segregation of F2 offspring during a mating experiment in Drosophila (fruit flies)-found presence of a gene on an actual sex chromo -Discovers genes can violate the law of independent assortment IF the gene locus is found on a sex chromosome -Females inherit two copies of X chromosome >XX -diploid for all the genes on X -Males inherit one copy of X and one copy of Y >XY -haploid for all the genes on X and Y

Outline Topic 1

-Central dogma of genetics -transmission of genetic material -> modes of inheritance -vertical/ horizontal transmission - sexual/ asexual transmission -Mitosis and meiosis -> goal of cell division -> mechanism -> Stages -Genetic diversity in meiosis

Recessive Lethal Alleles—Yellow Coat Color

-Coat color in mice is controlled by a single gene "A" >Agouti allele A—produces brown coat phenotype (agouti)-- Have to have two recessive copies of the AGOUTIA allele >Mutant yellow allele A^Y—produces yellow coat color-- Any number of copies of the yellow allele will result in the yellow coat color in mice Mutant allele (A^Y) >Behaves dominantly to normal allele to control coat color >Behaves as homozygous recessive lethal allele Genotype homozygous recessive A^YA^Y genotype does not survive

Gene Interaction- two genes

-Commonly seen in biosynthetic pathways—multiple genes required to make a final product (pigment) - where the first gene is necessary for a conversion of an initial starting compound and the second gene is further down in the pathway -Genes Y and C interact because the alleles determine the function of enzymes in a biochemical pathway -So in this case using the example the first gene is the Y gene and that codes for an enzyme called phinosinthesis and its responsible for converting a precursor compound to the compound phiosinthesis - the second gene is further down on the pathway it codes for the enzyme CC synthase it is responsible for the production of red and yellow pigment from an intermediate compound called violaxanthin - if the Organism doesn't have a functional copy of it of cc synthase they Aren't capable of producing the final step which is the conversion of violaxanthin into the red pigment - so the two individuals here the homozygous recessive produces no pigment while the Organism that inherits at least one dominant copy or functional copy of each Y and C gene is going to produce the full expression of the pathway where we get generation of the Peach and orange intermediate we're either the Y gee or the C gene is not functional - So in this case if an Organism is going to inherit 2 copies of the recessive allele for why that enzyme is not functional that means this Organism is not capable of converting the precursor compound to that intermediate phyotene Compound and therefore is not capable of producing any pigment which is where the cream color comes from

Mendels Experiment

-Crossed true-breeding plants with different phenotypes (purple and white) -- Had to produce organisms that were backcross where they would only pass one version of a particular trait -- he breeded purple with purple creating two true breeding and also did this for white as well this was to get his F1 generation -Observed (F1) offspring phenotype-- Once he got his true breeding for both colors >All purple >White trait "disappears" -- because there is was White Mendel came up with that both parents in the parental generations donate the molecule of inheritance to the F1 generation . However the white trait is masked by the purple trait phenotypes -Crossed F1 x F1 -- when we do this white trait is restored -Observed F2 phenotypes >75% purple >25% white (trait reappears) -- so the white trait does not get inherited in F1 generation however is not saying you too in hearings in the purple trait

Pre Mitosis -DNA synthesis

-During interphase cell initiates DNA replication (S phase) -duplicates entire genome -generates two identical genomes within the parent cell -objective is to separate two genomes into daughter cells -identical chromosomes sister chromatids stick together before separation - they line up together then pull apart into individual offspring daughter cells

Many Observable Characters

-Each character has only two possible traits -Ex. Flower color is EITHER purple or white - let him know dominant pattern over recessive traits

Mendels experiment Mendel concluded:

-Each parent contributes one trait per character -Ex color flower: one gets white one gets purple >For each characteristic, each organism has two copies of the gene -If the traits differ (for specific gene like color), the "dominant" trait masks the recessive -Recessive traits are observed only in the absence of the the dominant-when organism gets two copies of recessive allele -Results in ability to predict phenotypic ratios -75%, 25% >3:1 dominant : recessive IF you start with two heterozygote parents -and cross them

Autosomal Dominant Inheritance -- That means the genes we're considering is located on the Autosome or nonsex chromosome but that the AutoZone will trade exhibits a dominant pattern of inheritance

-Ex. Stature-the gene we are considering -Trait: Achondroplasia/Dwarfism -Gene is located on an autosome (non-sex chromosome) -Trait is expressed in individuals who have any number of copies of the dominant allele-exibits a dom pattern of inheritance >Meaning any Organism who inhibits at least one copy of this little will show the trait in the phenotype for ACHONDROPOASIA -Unaffected individuals are homozygous recessive -- associated with very short stature in humans - only individuals who received 2 copies of the recessive trait are going to exhibit normal or typical stature

Dihybris Cross - two genes

-For two independently assorting genes: >Treat cross like you are performing two monohybrid crosses at the same time >Assortment of alleles from gene 1 has no impact of assortment of alleles for gene 2 -Two independently assorting genes are considered: >Seed color: Yellow is dominant to green - 2alleles >Seed shape: Round is dominant to wrinkled - 2 alleles >Cross two plants heterozygous for BOTH genes and determine the genotypes, phenotypes, and phenotypic ratio of the offspring

Monohybrid Cross - one gene

-Fruit color in tomato plants is controlled by a single gene where red (one allele) is dominant to yellow (2nd allele) -Scenario: A tomato plant is homozygous for red fruit color. Another tomato plant is homozygous for yellow fruit color. - What is the character being assessed? -Assign a dominant and recessive trait -Perform a cross of the true-breeding plants -What do you expect to see in the F1 and F2 generations? -Genotype and phenotype ratios

Mechanisms for Recessive Epistasis

-Gene "B" -protein makes melanin pigment(synthesizing)-its going to get deposited into the hair of the dogs -Gene "E" -protein deposits pigment(made from gene B) into the hair shaft >E is recessively epistatic to B because: -> _ _ ee genotype masks the production of melanin from gene B- none of the pigment from gene B will get deposited if we have two recessive ee's

Overview of Meiosis II

-Genome is NOT replicated again -Sister chromatids are still paired -Sister chromatids are separated during second cell division ->Replicated chromosome (2 chromatids) split into unreplicated chromosomes ->**Meiosis II is VERY similar to Mitosis** - The only replication that occurs is during interphase, S phase - After that the cell moves immediately into meiosis one then meiosis 2 - the goal is to take replicated version of each chromosome and make a daughter cell that represents unreplicated versions of each chromosome - no replication between meiosis one and two - so moving from meiosis one to two all we're doing is separating the sister chromatids that remain as the product of meiosis one

Overview of Meiosis I

-Genome is replicated- replicating all chromosomes -Sister chromatids AND homologous chromosomes pair -Paternal and maternal chromosomes are divided during meiosis one ->Each daughter cell only inherits one of each chromosome ->Thus, one copy of each gene (n) -> Haploid daughter cells they don't contain homologous pairs they do contain sister chromatid pairs but they are haploid - Image: Interphase- we want to replicate all chromosomes in this phase > we start homo pairs that is unreplicated > then replication which results in two sister chromatids per chromosome > we still have tow chromo which represents one homo pairs Meiosis 1: -Goal is to segregate the paternal versions of this chromosome from the maternal versions of this chromosome -Now each daughter cell will contain either the paternal or the maternal

Mitosis Summary asexual cell division - VT -> you wont introduce any genetic diversity in this cell division, its strictly one cell divided itself into two cells

-Goal: Produce a genetically identical daughter cell from parent cell -> Used for Tissue growth or repair ->NOT used to increase genetic diversity -Mechanism: One round of DNA replication followed by one round of cell division -> generates new copies of DNA and then we divide the two copies of DNA present within cell into two new cells in one round of cell division -Stages: ->DNA synthesis (interphase)- two complete genomes ->Prophase, metaphase, anaphase, telophase & cytokinesis -Result: ->Two genetically identical daughter cells -> cell will take two genomes into two daughter cells and then the cell will split down the middle becoming two cells with two identical genomes

Module 1 topic 2: History of mendels Experiments

-Gregor Mendel—Father of genetics- inheritance >Wanted to be a physics teacher, but kept failing the exam >Became an Augustinian monk in the 1850s-2nd carrier path >Allowed him to investigate mechanisms of inheritance in agriculturally-important organisms (sheep, pea plants, etc.) -Pioneered the investigation of patterns of inheritance >Up until this point in history, inheritance was thought of as "blending" of traits-- Mom and dad organisms would produce offspring's that had a blending of specific characteristics from both parents or parental generations >The practice of artificial selection had been used for thousands of years in agriculture-although not known -- is when you selectively breed organisms with favorable traits together over a series of generations and then that trait becomes fixed within that population >Selective breeding of organisms with "favorable" traits to increase the chances that offspring will also have those traits -- in animals and plants - like dog breed -artificial selection for all dog breeds they are the same species so they can all interbreed with each other, but organisms that have specific traits that people want are bread over generation to generation to maintain that trait

Before Division In meiosis

-Just like in mitosis, the first step in meiotic cell division is to replicate the genome - this happens in any cell division -"S" synthesis phase occurs before the start of meiosis (interphase)- replicates during this in S phase of Interphase -Replicates whole genome- creates this -Sister chromatids link together (prophase I)- like in mitosis **In meiosis, the cell also must join the homologous chromosome pairs** ->Links the same chromosomes inherited from different parents into "tetrads" (prophase I) - For every chromosome in a diploid Organism there are two copies - from mom and dad. So not only did the sister chromatids have to link and form sister chromatids pairs, but the homologous pairs also have to link up and produce these tetrads image: sisters chromatids to homologous chromosomes pairs

Animal Life Cycle- - The human life cycle is homologous to all animal life cycles especially mammalian

-Meiosis occurs in the germ cells (gonads) of the male and female organism ->Produces haploid (n) gametes from diploid (2n) cells -Gametes fuse during fertilization forming new diploid cell (n+n=2n) -of the gonad tissue -> Each gamete have half the number of chromosomes that is present in ovary and testicular tissue- becoming single cell with single nucleus -Diploid cell undergoes TONS of mitosis to become multicellular diploid organism -> - to become adults sexually mature organisms that will go on to produce the next round comma

Modes of Inheritance Inheritance Mechanisms

-Vertical transmission-> one cell replicates its DNA and then cell divides into two daughter cells (typical parent to offspring cell division)- in this case genetic material is specifically tied to cell division -> anytime this happens you are taking one cell, replicating DNA, dividing cell into two cells and through this you are getting vertical transmission of the DNA from parent to offspring -> through two cell division processes (both produce two versions of VT) - Mitosis -Asexual Reproduction - Meiosis- Produces cells used for sexual reproduction- genetically unique cells made

Review of Mendelian Principles

-Mendel's two laws hold up to scrutiny in many cases: >Genes are on chromosomes >Genes assort independently during meiosis >Alleles segregate during meiosis -2n->n to make gametes - The difference between this medallion tray insects tray is that oftentimes we have jeans that are located on the sex chromosome and male inherit a different pairing of sex chromosomes than females do so the phenotypic outcome is going to be different than a traditional mendelian outcome >New organisms are formed during fusion of haploid genomes during fertilization - n+n->2n >Predictable phenotypic outcomes >if we know the genotypes of the organism that we started with in the P generation

Mendelian Inheritance Patterns

-Mendelian inheritance patterns Occurs when only two alleles are considered for a single character -One will be Recessive phenotype—must have two copies of allele to show phenotype (no masking) -One will be Dominant phenotype—must have only one copy of allele to show phenotype - one recessive and one dominant in this case of complete dominance which is what Mendelian inheritance describes

Polygenic Inheritance - two genes

-More than two genes interact to produce a single characteristic-three or more gene interact to produce single characteristics -Produces a spectrum of phenotypes -Depicted as a bell curve >Extreme phenotypes represented as the least prevalent

Multiple Phenomena—ABO blood groups - one gene -its at one time, we can see more than one phenomena in one gene at a time

-Multiple alleles and co-dominance -One gene, three alleles A, B, O(six possible genotypes)-controls blood type >Alleles A and B are codominant-- Meaning it cell is hetero for A&B the cell will produce both sugar molecules A&B so blood type will be a B >Alleles A and B are both completely dominant to allele O - so if there is a hetero for allele A and allele O, or allele B and allele O then A allele or B allele is going to be completely dominant to the O allele. In this case homo or hetero for little A and O produces a phenotype of A blood group same for B - only time when individual can have type O blood is In the absence of either dominant allele so a little A and B cannot be present in order to produce phenotype O

Pleiotropy- one gene

-Multiple different disparate effects from presence of one allele -Example: Sickle Cell Anemia >Results from presence of the sickle-cell allele for hemoglobin gene (H) (sickle or normal alleles) >HSHS and HSHN(hetero) result in "sickle cell disease"- some form of it -MANY symptoms that arise from presence of allele *Lethargy *Inefficient O2 transport *Damage to cardiovascular system *Pain *Swelling of extremities - The reason for these symptoms is because the inheritance of these sickle cell allele causes the shape of the red blood cells to change - these are pointing in shark causing pain and damage Inside the blood vessels it is hard to transport oxygen, there are swelling, and leaking of the blood vessels

Bridges' Experiment

-One gene (R) controls eye color in flies iF RED (r) IS DOMINANT TO WHITE (r): >- So his assumption is if an Organism inherits 2 copies of this gene then they can become home oh for red allele they can be home up for wide a little and they can be hetero or they could be hit around - if the experiment followed mendelian rules whatever Organism has at least one dominant allele would show the dominant phenotype -F1 results are expected: 50% male and 50% female -F2 cross :Rr x Rr Results: all females are red, 50% red and 50% white males -What would you expect the F2 ratios to be IF laws of independent assortment were obeyed? 3 red : 1 white ~50/50 male:female for each phenotype -But instead of forming a nice 3:1 phenotypic ratio with 50% represents males 50% represents female, he gets in the F2 generation all of the red flies are going to be female, none of the white are female so he saw a sexually different distribution in the F2 generation

Multiple Alleles- one gene

-One gene controls one phenotype or one characteristic -Each organism inherits two alleles BUT... >More than two possible alleles exist for the gene >Example: Variegation of clover leaves >Gene/character = leaf pattern (L) >Allele/trait = 22 phenotypes possible -7 possible alleles present for that gene >Produced through various combinations of seven possible alleles (A-H)

Monohybrid Cross - tomato plants are diploid organisms

-P generation: RR x rr (red x yellow) -F1 Offspring: Rr (red) -hetero -F1 cross: Rr x Rr (red x red) -Gametes of F1 R or r -Cross: results: 3:1

Multiple Phenomena—Sickle Cell Anemia- one gene

-Pleiotropy and co-dominance -One gene, two alleles (three possible genotypes) -just Sickle cell alleles= homozygous sickle cell allele results in very extreme pleiotropic symptoms -sickle cell allele and normal allele = heterozygous genotype; codominant alleles, symptoms not as extreme as homozyote - homozygous for sickle cell, hetero where we have one healthy one sickle cell, or homologous for normal or unaffected allele - These alleles are codominant so there are actually producing individuals who have normal shaped red blood cells and sickle cell blood cells and while they exhibit some symptoms of sickle cell is not as bad as homozygous for sickle cell (they can resist infection with a malaria parasite)

Recessive Epistasis - two genes

-Recessive allele arrangement of gene "E" masks any allele arrangement of gene "B" -Example: Character = Lab coat color -Two genes B and E -Produces 3 phenotypes Geno Pheno Ratio B_E_ Black 9 bbE_ Brown 3 __ee Yellow 4 -the blue part doesn't matter

Variable Expressivity & Penetrance

-Some genes vary in their ability to express the associated phenotype -Variable expressivity—individuals with genotype produce varying levels of phenotype-deals with single individual >None, slight, moderate, high, extreme degrees of phenotype Variable penetrance >Proportion of population who are positive for genotype and show any degree of the phenotype >Represented as a percentage-deals with pop -- Does not associate with individuals that don't show phenotype that should be associated with of Genotype

Terminology is important

-What is a gene? -Heritable factor, a discrete unit of hereditary information made of a specific nucleotide sequence -What is a gene locus? -Place on a chromosome where gene found/located -- When Organism inherits 2 copies of a particular gene the locus for that gene is found on the same place for homologous pair of chromosome - so if a gene locus for flower color is located on the chromosome #5 that gene locus is the same for both homologous chromosome -What is an allele? -An alternative form of a gene -Version of the gene -Described as a trait

Meiosis I—First Round of Division

-Starts with replicated diploid genome -First round of cell division separates homologous pairs -Results in ½ reduction of # of chromosomes -Does NOT reduce the number of sister chromatid pairs (replication value remains the same) -Ex: Start with 10 total chromosomes -How many chromosomes after replication? 10 chromo and 5 homo pairs present -How many after Meiosis I? 5 chromo -Are they replicated or unreplicated? -- After we're done with this each daughter cell produced from the Reduction in meiosis one should have five chromosomes- one of each of the Homologous pairs either maternal or paternal copy from each pair - The starting cell has not been replicated you have 5 red chromosomes and five blue chromosomes because each chromosome is replicated by one chromatin that is why it hasn't been replicated yet - after replication we now have each chromosome that is represented by two sister chromatids

Meiosis 2 - sound round of division

-Starts with replicated haploid cell- two of them so its represented by two sister chromatids ->** Does NOT undergo another round of replication between I and II -Goal is to separate sister chromatids- going to segregate the sister chromatids from each other ->Replicated -> unreplicated state- haploid cells ->Very similar to mitosis

Genetics Central Dogma What is genetics?

-Study of the transmission and expression of (DNA sequence->into RNA-> sometimes protein-> cell function) genetic material (instructions for all cellular process) -Expression? -> Gene sequences in DNA language are modified to RNA and protein to carry out all cellular function- Expression of a phenotype -Transmission? -> Inheritance of genetic material through cell division or Horizontal gene transfer -> How DNA is replicated and passed to offspring through cell division or horizontal gene transfer- portion or all DNA transferred to one cell to another regardless of generation

Mendel's Model Organism

-Sweet pea plants-they produce gametes through meiosis -Sexually reproduce through meiosis -Qualities of sweet pea model organism -Easy to grow -Easy creation of true-breeding strains (?)-homo for a particular alleles(traits) -Easily controlled matings: self-fertilization or cross-fertilization-using a paint brush -Grow to maturity in one season -Observable characteristics with two distinct forms-either characteristic trait 1 or trait 2 would show -Produce many offspring per generation

Overview of the Stages of Meiosis

-Synthesis (replicates genome)- during interphase -Meiosis I (2n->n): first division cycle - Go from a diploid cell meaning 2 copies of every chromosome to a haploid cell -> condense DNA ->Joins sister chromatids ->Joins homologous chromosomes - Chromosome from mom and dad that are homologous won't go in together to form a tetrad- - We want two haploid daughter cells and each cell will either contain chromosome for mom or chromosome from dad but none of the daughter cells will contain more than one copy of each chromosome ->Separates homologous chromosomes (2n->n)- during Metapahse >This is the reduction step diploid->haploid > starting cell are already haploid > this is the goal > each chromosome is represented by 2 copies, two sister chromatids Meiosis II (n->n): ->Segregates sister chromatids (like mitosis) ->Replicated "n" to unreplicated "n"

Common Misconception

-Terms dominant and recessive have NOTHING to do with the frequency of the allele within a population -- They only have to do with what happens in a hetero individual so in a hetero Organism is the trait you're investigating dominant or recessive? so if you couple a dominant and recessive alleles what is the phenotypes in an Organism ? -Dominant is not necessarily more > not higher frequencies necessarily -Recessive is not necessarily less > not lower frequencies in pop necessarily -** Achondroplasia is perfect example -- Even out of 100 people it is unlikely that someone would have Achondroplasia most will have homozygous recessive or be normal but if someone gets one or more copies for this trait will exhibit a dominant phenotype

Expected genotypic Ratios

-Three possible genotypes produced: -Homozygous dominant (PP) -Heterozygous (Pp) -Homozygous recessive (pp) -PP and Pp produce dominant phenotype -pp produces recessive phenotype -3:1 ; 2 getero gynotypes: 1 homo reccessive: 1 homo dominant

Crossing Over / Synapsis - genetic diversity

-Trading of genetic material from maternal to paternal or paternal to maternal between homologous chromosomes -Occurs in regions of exact DNA sequence homology...more on that later - none of the cells will look 100% like the paternal or maternal line

Co dominance - one gene

-Two alleles exist for a single gene BUT... -Both alleles are expressed in the cell -Heterozygous genotype produces a third phenotype >"patches" of both of two parental phenotypes produced >Same abbreviation format as incomplete dominance ->Letter = gene/character ->Superscript = allele/trait -ex: cow result is a miz btw two patrents- heterozygous -produces while and brown allele

Incomplete Dominance - one gene

-Two alleles exist for a single gene BUT... -Neither allele is completely dominant -Heterozygous genotype produces a third phenotype - Represents an intermediate between both parents phenotypes ->Intermediate phenotype is a "blend" of the two parental phenotypes ->New abbreviation format >Letter = gene/character >Superscript = allele/trait -- Therefore when we cross two true breeding P generations organisms together we will generate hetero Genotypes in the F1 generation and this phenotype will be the third phenotype in this example the flower ends up being pink

Gene Interaction without Epistasis- two genes

-Two genes interact to produce four phenotypes for a single characteristic Geno Pheno Ratio Y_C_ Red 9 Y_cc Peach 3 yyC_ Orange 3 yycc Cream 1 How is this ratio different from the ratio produced from a typical Mendelian dihybrid cross ? -we are not looking at two diff phenotypes, we are looking at one phenotype

Gene Interactions—Two genes interact - two genes

-Two genes interact to produce specific phenotypes for one characteristic -Two classes of gene interactions >Without epistasis (no gene masking)-neither gene is going to mask the production of the other gene >Epistasis: One gene's allele masks the phenotype of the other gene's alleles -Dominant epistasis—when the dominant allele of gene A masks the effects of either allele in gene B >Ex. Squash color -Recessive epistasis—when the recessive allele of gene A masks the effects of either allele gene B >Ex. Coat color in Labrador retrievers

Dihybrid independent Assortment

1) Genotypes of Hetero. parents: YyRr x YyRr yellow, round- 2 genes 2) Gametes allele combinations for each parent: YR Yr yR yr Each gamete has an allele for EACH gene 3) Perform cross where all gamete possibilities are represented by egg and sperm -because each parent is the same genotype we can do this one time -each gamete is going to contain an allele for each gene -2 different genes are going to be present in each gamete 4) Assign common genotypes, phenotypes, and pheno. ratio Genos phenos ratio - 4 phenotypes Y_R_ yellow, round 9 yyR_ green, round 3 Y_rr yellow, wrinkled 3 yyrr green, wrinkled 1

Mendels Law

1. Law of segregation: 2 alleles for a character separate from each other during gamete formation >When does this occur? -- During meiosis we will separate the homologous pairs from each other. during anaphase one would performing the reduction division such that the daughter cells are going to only contain one of the alleles present in the parental generation so when we are making the gametes we're going to separate the diploid homologous chromosome into haploid cells. - so the parental cell starting off in segregation contains 2 copies of each gene. The daughter cells resulting from meiosis one of the gamete formations are only going to contain one of them each of those alleles 2. Law of independent assortment: 2 or more genes assort independently of each other during gamete formation >When does this occur? -- We talked about this in the cell lecture where we talked about the orientation of homo pairs that are set up during metaphase one are independent of each other so if a homologous pair lines up in one in one orientation for the first chromosome set that has no bearing of the orientation of the second chromosome set or the third chromosome set - meaning a maternal gene can be inherited for one daughter cell for one gene and a paternal gene can be inherited for that same daughter cell for a different gene - genes assort independently -meaning the orientation of 1 gene has no bearing over the orientation of another gene, when the home all is pairs lineup in metaphase one of meiosis one

Reviewing Mendel's Assumptions

1.Alternative forms of alleles account for variations in inherited characters 2.For each character, organism inherits 2 copies of a gene, 1 from each parent 3.If 2 alleles at a locus differ, then the dominant trait is responsible for the disappearance of the recessive trait >What if more than two alleles exist for a specific gene?

Reviewing Mendel's Assumptions

1.Alternative forms of alleles account for variations in inherited characters -- Each characteristic there are different phenotypes that can arise from different alleles. Each allele is a different trait in each characteristic has multi traits that can be inherited 2.For each character, organism inherits 2 copies of a gene, 1 from each parent 3.If 2 alleles at a locus differ (hetero individual), then the dominant trait is responsible for the disappearance of the recessive trait- also known as masking >Not always the case --in mendelian extensions it is not always the case so in the case with a hetero individual where the two alleles at a specific locus differ one is not necessarily dominant over one completely recessive allele

Mendels Assumptions - from his experimental data

1.Alternative forms of genes (AKA alleles) account for variations in inherited characters -- So if you were to look at a population of humans for any given characteristic there are various forms of each characteristic trait -- ex eye color: there is a lot of different alleles that account for eye color in that leads to a variation within population 2. For each character, the organism inherits 2 copies of a gene, 1 from each parent -- so a diploid Organism is going to inherit a copy of every gene and a copy of every gene from dad 3. If 2 alleles at a locus differ (hetero for a particular gene), then the dominant trait is responsible for the disappearance of the recessive trait >The recessive allele is masked by the complete dominant allele

Cell divides sister chromatids

As so moves through division phase (mitosis stages) 1. the sister chromatid pairs aligned in the center of the cell 2. sister chromatids are pulled apart by spindle fibers 3. cell undergo cytokineses 4. two identical daughter cells are produced a. each sister chromatid is now an individual chromosome b. segregation of chromatids into daughter cells

Prophase 1

Before Prophase: Interphase- Duplication of ALL DNA in the cell; this forms the sister chromatids STAGE: Prophase I- 1. Chromatin condenses 2. Sister chromatids join- pair them up 3. Replicated HOMOLOGOUS PAIRS stick together (form TETRADS)- maternal and paternal 4. Crossing over/genetic swap happens! Homologous chromosomes physically trade segments of DNA Improves genetic diversity! > snapsis occurs- - Is good for that maternal and paternal homologous pairs to mix and match sequences creates diversity so that the results are neither 100% maternal or paternal - genetic sequences is being swapped from maternal to paternal and vice versa

Whn is the DNA copied?

Cell cycle has many phases - interface - not concerned with cell division, make sure everything is working right o G1 o S DNA copied - manufacturing knew material- new sequence of DNA that an exact copy of existing sequence o G2 - mitotic phase o mitosis o cell division

Coat Color in Mice

Consider two traits controlled by a single gene >Survival -AA; A^Y survives -A^YA^Y dies Coat color -AA agouti color -AA^Y yellow color -A^YA^Y yellow color—does not survive

Variable Expressivity and Penetrance

Crazy kitty toes-polydactyly (extra toes) Variable expressivity: genes can have varying degrees of expression: >Describes the degree of expression of the phenotype >None, some, extreme? - If an Organism has the phenotype for producing extra toes, it for being a polydactylist we can see varying degrees of expression Variable penetrance: The proportion of individuals in a population who have an allele AND express any degree of the phenotype >If 100 cats have the allele for polydactyly, but only 80 cats have extra toes (80% penetrant) -- Not all the organisms that have the Genotype for polydactyl have a phenotype for it

Stages of Mitosis part 1

During interphase- G2 - within nucleus you have a bunch of chromatin that has already been replicated and all the genetic information is found within nuclear envelope - on outside nucleus you have now duplicated the centrosomes - occurs after replication of the genome - G2: duplicated genomes in "loose" chromatin state Prophase - Chromatin condense, sister chromatids pair - Condense all info from the chromatin state into chromosome states - we pair up each genetic sequence within its matching identical sequence that makes up sister chromatids prometaphase - Nuclear envelope degrades, spindle fibers attached to sister chromatids at kinetochore- mostly in animal cells - Kinetochore are attached centromere to each chromatid

Incomplete Dominance part two -genotypic ratio and phenotypic ratio for incomplete dominant is the same

F1 x F1 heterozygous cross produces three genotypes AND three phenotypes >CRCR = Red 1 >CRCW = Pink 2 >CWCW = White 1 Molecular mechanism is generally due to difference in gene dosage >Two red alleles = max pigment >One red, one white = medium pigment >Two white alleles = no pigment -- In the case of complete dominance whether an Organism had one allele that was dominant or two alleles that were dominant the production of the phenotype is exactly the same in a homozygous dominant versus a heterozogous - In the case of incomplete dominance we get a difference in gene dosage. In case of red Snapdragon these organisms have two copies of the red alleles meaning they produce maximum pigment or two times the amount of pigment that let's say the pink Organism made, so if the pink Organism only has one copy of the red producing allele, we are going to get medium pigment the pink

Meiosis Summary- Sexual cell division sexual reproduction

Goal: Produce a genetically unique daughter cells from single parent cell- such that non of the daughter cells are identical ->Used for increasing genetic diversity in a population Mechanism: ->One round of DNA replication followed by two rounds of cell division Stages: ->DNA synthesis (interphase)- s phase-(identical to what occurs in mitosis) ->(Meiosis 1) - Prophase I, metaphase I, anaphase I, telophase & cytokinesis I ->(Meiosis 2) - Prophase II, metaphase II, anaphase II, telophase & cytokinesis II (this phase is almost identical to mitosis Result: Four genetically unique daughter cells- from one parent cell

Three Contributors to Genetic Diversity

I.Random assortment of chromosomes ->Meiosis I (Metaphase I) II.Crossing over/synapsis ->Meiosis I (Prophase I) III.Random fertilization (post meiosis)-- Is where after the games have been made after meiosis it's a random choice of gametes ->Male Haploid gamete ->Female haploid gamete ->Fertilization produces a DIPLOID organism that is genetically distinct from either parent! -- After we get cell division we get haploid gametes (eggs and sperm) and those gametes are going to go on to undergo a fertilization event - No way determine which gaming to fertilize which other gaming it is random

Results of Meiosis 1 Division

Image: - we have replicated diploid cell -we have preformed meiosis 1 reduction division - in end result we have two haploid daughter cells, each cell contains one chromo from each homo pair - these two haploid cells are the inverts of one another- one gets maternal and one gets paternal

Mitosis

Interphase - Before cell can divide it must first duplicate the chromosomes stored in nucleus - During chromosome duplication, several bubble up in chromosomes - then bubbles (two) merged together so now each chromosome consists of two identical copies called sister chromatids -the sister chromatids are made of DNA that there are roundup of small proteins called histones Prophase - Outside nucleus centrosomes move away from each other to opposite sides of cell - microtubules extend from the centromere forming mitotic spindle - while Dina is condensing to become a shorter and thicker chromosome consisting of two sister chromatids - as chromosomes continued to condense, the nuclear envelope breaks apart. chromosomes fully condensed at this point - chromosomes attached to spindle fibers metaphase - chromosomes end up at center of cell on plate anaphase - Sister chromatids are split from each other becoming chromosome, they are pulled to opposite poles of cells and move along spindle fibers - this pulls spindle fibers farther apart Telophase and cytokinesis - Once chromosomes reach destination, they become less condensed, two nuclear envelopes form completing mitosis, creating two genetically identical daughter nuclei - the cytoplasm divides by the process of cytokinesis forming two daughter cells

Which cell perform meiotic division?

Meiotic Animal Cells? ->Gonad Tissue—- Predominantly responsible for making the haploid gametes through meiosis - haploid cell generated here is eggs - haploid cell generated here is sperm -Ovaries and Testes (diploid 2n)2 - these two haploid cells will fuse creating a diploid Organism ->Produces haploid (n) gamete cells that will produce next generation through fusion (fertilization) Meiotic Plant Cells? ->Sporangia (diploid) 2n tissue produces haploid (n) spores ->Spores (n) undergo mitosis to produce (n) gametes ->Gametes fuse to produce next generation through fertilization - Meiotic plant cells creates haploid spores through diploid sporangia tissue in the spore will undergo mitosis to produce haploid game mates and then those gametes confuse together to produce the next generation through fertilization - sporangia will undergo meiosis to produce haploid spores and then those spores will go through mitosis to produce haploid gametes

Stages of Mitosis part two

Metaphase - Sister chromatid pairs align on metaphase plate - complete disintegration of the nuclear envelope - At each sister chromatin there is a kinetochore - At metaphase plate (also know as equator)- we are organizing our distinct units of our genomic info so that we can separate these two copies of genome into two daughter cells - There is no more nucleus in the cell at this point - Ex: 6 chromosomes Anaphase - Sister chromatids are pulled apart by spindle fibers - They get shorter- and now each chromatin is its each individual chromosome - Each chromosome is an identical copies of its sister chromatins - Ex: now its 12 chromosomes Telophase and cytokinesis - Genomes separated, decondense, cell splits - Two daughter cells from one parent cell, cell keeps dividing - In this each resulting daughter cell will have one centrosome from the pole, one copy of genome that genome is identical to parent genome, nuclear envelope will start to form again It has a cleavage furrow form which is protein (actin) ring on inside cell and pinch inside cell so plasma membrane will fuse to itself

Which cells perform Mitotic division

Mitotic Animal Cells?- cells that need to be turned over quickly or cells that will come into contact with outside world alot ->Epithelial tissue (skin, digestive system, immune cells, liver cells, etc.)- go through it a lot with frequent replenishment ->Cells subject to tissue damage or short life span are highly mitotic Cells that are slowly mitotic—not subject to high turnover -> want to go through alot of asexual cell division ->Ex: Neurons, muscle cells, adipose tissue (fat) Mitotic Plant Cells? ->Apical meristems perform nearly unlimited mitosis ->Roots (anchor plants and provide nutrients), shoots (helps it grows tall so plant will be able to preform photosynthesis), buds (needed for growth)( produces flowers and fruit) - regions of plant that go through high turnover- apical - plants start small then get big that is because of the apical meristem known as the roots, shoots, and buds

Non-Mendelian Patterns of Inheritance Lethal Alleles

Mutations in essential genes-- Meaning not only is it required to produce some phenotype in an individual but is also necessary for a pathway that is going to Keep the individual alive -Lethal allele >Has potential to cause death of organism >Alleles are result of mutations in essential genes Recessive lethal allele- must be homo recessive >MUST HAVE TWO COPIES OF ALLELE TO BE LETHAL >Death can be before birth, immediately after, or eventual >Ex. Cystic fibrosis-- Has to have two mutated copies of this allele Dominant lethal allele >Presence of one copy of allele results in death >Example: Huntington's disease -Usually takes a long time to become lethal...that's why it continues to be inherited

Goal and overview of Meiosis

Sexual reproduction ->Promotes genetic diversity by producing unique daughter cells that contain ½ the genetic information from the parent cell Different from mitosis: ->Reduction of # of chromosomes by HALF - Maternal from the paternal chromosomes- from each parent cell- so we will segregate our homologous pairs of chromosomes - we're going to pair up those homologous chromosomes then physically pull them apart during meiosis one ->Must divide number of chromosomes to make gametes because fertilization results in the fusion of two cells - we want haploid gamete with haploid gamete to produce diploid Organism ->If cells did not perform reduction before fertilization, the chromosome number would double with each new generation ->Two rounds of cell division (Meiosis I and Meiosis II) ->Produces genetically distinct daughter cells (4) Promotes genetic diversity- in three diff ways - but we maintain this diploid number

Metaphase, anaphase, telophase 1

Stage: Metaphase I- 1. HOMOLOGOUS PAIRS line up at equator- on metaphase plate -move tetrads that are undergoing crossing over - The lining up to homologous pairs is going to allow us to separate those homologous pairs STAGE: Anaphase I- 1. HOMOLOGOUS PAIRS- use spindle fibers separate- fibers pull them apart 2. Cell has undergone chromosomal REDUCTION- - so when our daughter cells are being formed each cell has one copy of each chromosome STAGE: Telophase I- 1. Cells complete division Each cell now has ONE copy of each chromosome **Each chromosome is a mix up of maternal and paternal gene sequences** - divide cell into two daughter cells

Product of DNA Replication and Condensation

Step one: replicate the genome - S phase of interface -occurs is unconvincing a loose chromatin step two: compensation of DNA into chromosomes -occurs during prophase of mitosis -condense the chromatin down into individual chromosomes -have to physically do this Step 3: physical linkage of identical chromatids and sister pairs -each pair of sister chromatids equals 1 chromosome -twin sister chromatids- we have to pair up these individual sequences so they can be divided equally between two daughter cells - during first phase of mitosis we condense the DNA we will pair up the individual chromatids into sister chromatid pairs - each Pair of sister chromated is considered one chromosome identical DNA sequences - Identical DNA sequences

Gene Interaction with Epistasis- two genes

Two genes interact to produce a single characteristic, but one gene allele MASKS the other-in a specific allele orientation Two types: >Dominant masking—Dominant allele arrangement of gene "A" masks any allele arrangement of gene "B" >Recessive masking—Recessive allele arrangement of gene "A" masks any allele arrangement of gene "B"

Meiosis Promotes Genetic Diversity -- Mitosis doesn't have sexual reproduction or genetic diversity

Two ways genetic diversity is promoted during meiosis: Random assortment ->Orientation of homologous pairs at the equator leads (- which genes are inherited by daughter cells) ->Orientation of one homologous pair on metaphase plate does NOT impact orientation of other pairs ->In humans the number of assortment combinations is 223! (two possible orientations for 23 pairs of chromosomes = 8,388,608 possibilities! >- each chromosome pair can either be maternal on the left in or paternal on the right or swapped Crossing over ->Shuffling of alleles between homologous chromosomes before reduction ->Prophase I -during synapsis - none of the chromatin from the tetrad represent 100% of maternal or the paternal chromosome -newly assorted genes from that chromosome

Review of Mendelian Principles :module 2 topic 2

Up until this point... •Two alleles assort into gametes independently of one another (segregates maternal and paternal lineages)-during anaphase 1 of meiosis 1 •Each gene assorts independently of other genes >meaning that one daughter cells gets assortment of maternal and paternal genes in one orientation that doesn't affect the orientation or segregation of maternal and paternal genes in the next homo pair •Offspring have predictable phenotypic ratios 50% parental phenotypes(looks like parent), 50% recombinant phenotypes (When genes are not linked)(produced from a test cross homo x hetero) •We will explore the phenomenon of autosomal gene linkage, which results in a deviation from the law of independent assortment -This will result in a change of the phenotypic ratios seen

Sex linkage practice female: hetero male: unaffected

•A female who is a carrier (heter) for hemophilia (X-linked blood clotting disorder) is planning on having children with a male who has "normal" blood clotting abilities •Assign the genotypes to these individuals •What is the probability that they will produce a child with hemophilia? •What is the probability they will produce a son with hemophilia? •Can the produce a daughter who shows abnormal blood clotting? Why or why not?

Sex linkage pratice part two

•A female who is a carrier for hemophilia (X-linked blood clotting disorder) is planning on having children with a male who has "normal" blood clotting abilities •Assign the genotypes to these individuals •Female carrier XBXb •"Normal" Male XBY -1/4 that they will produce a child with hemophilia -gene is not present on Y

Examples of Sex-linked (X) traits - This is a sex linked gene specifically located on the X chromosome there is also Y linked genes but its less common

•Affects males more often than females because females have two copies of the X chromosome (compensates for loss-of-function in a single allele) •Red green colorblindness •Duchenne's Muscular dystrophy •Hemophilia >- Affect males because they only inherit one allele for each one of the genes. Like if it's got the X chromosome from the mother and she has a red green colorblind gene then the Male will get it - males only need to inherit one copy of it and then they will have it •Males CANNOT be homo- or heterozygous for X- linked genes males can't be heterozygous because that implies they are inheriting 2 copies of 1 gene •Can only be hemizygous (haploid for that gene!) -they get the one copy of gene from mother - people can survive without Y chromosome but they can if they don't have their X chromosome. This is because there are a lot of genes on the X chromosome that are necessary for survival - The Y chromosome is mostly there for fraternity and sperm production so someone can survive without it

Mechanism of Sex-linked Inheritance

•Because female flies carry two copies of R gene, they can donate either the R or r allele to offspring •Notation is different XX or XY (chromosome) •Superscript denotes the allele •Females inherit one copy of X from both parents •Males inherit X from mother and Y from father •If R gene is located on X chromosome, heterozygous female will show dominant phenotype •Males will show ONLY allele phenotype (hemizygous) •White female must be homozygous recessive (rr) -The next generation the female will inherit an X chromosome and for the male it will inherit a Y chromosome -males only inherit X chromosome from the mothers so the mothers are responsible for the different genes for the male - males can't be heterozygous because that implies they are inheriting 2 copies of 1 gene

X inactivation - inactivation of one of those chromosomes that is inherited in the female

•Each cell in a female inactivates one of the X chromosomes FOREVER! •has 2 copies of the gene for fur color so it's heterozygous but Occurs early in embryonic development •The X that is "turned off" is chosen at random •Ensures that each cell only produces gene product from ONE X chromosome •Maintains gene dosage equivalent with male levels - these cats do not produce this color of bird pigment due to codominance they only do it for X inactivation- not codominance - males can only be orange or black not both - so the gene for coat color is on the X chromosome - all calico cats are female so they inherit 2 copies of the X chromosome Looking at the image the Organism the cat starts to develop when we get these cluster cells that are going to rise from ether the sale that turned off the orange chromosome or the cell that turned off the black chromosome > so everywhere on the cat that shows orange fur on the fur results from a parent cell that very early on turned off the black little carrying chromosome and vice versa for black -so the group of cells that were the progeny of the parent cell originally turned off the orange chromosome - happens at random - The reason only female cats can show this type of fur color pattern is because male cats can't do X inactivation because they don't have another X to inactivate

What happens in female?

•Females posses gene transcripts that are twice the number of X chromosomes as males •Do female express twice the quantity of gene product (RNA) for all the genes found on the X chromosome? •Is the gene "dosage" different in males and females? -NO! even though is twice the doses as males because females have twice the number of copies on all the genes located on their X chromosomes •Why or why not? •NO! Gene dosage is the same in males and females because one X is inactivated in female cells! -we have a mechanism in female cells to make the amount of gene product that Is being generated into male cells and female cells equivalent - we basically have to cut the gene dosage for x linked genes in half - This is where is X inactivation females perform inactivation of one of their X chromosomes that they inherited from mom or dad - so in any given cell only One X chromosome in a female cell is actually producing gene product the other X chromosome is completely turned off

Sex-linkage via Y Chromosome

•Inherited directly from father to son •All sons of affected father will be affected •Females are completely unaffected (do not inherit a Y chromosome) •Traits are typically associated with incomplete development of male characteristics and or sperm production > cause most genes associated with Y chromo is associated with fertility

Puffins

•Puffin clutch size (number of eggs laid) is affected by sex •Is this trait sex-limited or sex-influenced? -sexlimited=female •What question do you have to ask yourself to answer this? - The question for us is do both sexes perform a specific trait? - Do both males and females like eggs? The answer is no - males can't express this specific trait they inherit gene to determine clutch size they just don't use it

Sex-Influenced Traits

•Same genotype has different phenotype dependent on sex of organism-or environment that is under •Goat beards •Males only require ONE copy of the beard allele Bb •Females require TWO copies of the beard allele BbBb •Same genotype gives different phenotype - sexually dimorphic trait -females can produce a beard but it difficult - female doesnt produce beard phenotype if its hetero

Not sex linked But....

•Sex-limited -> Milk production-cause the gene is located on an autosome or non sex chromo •Both sexes have the gene, but only one sex produces the sex characteristic ->Males do not produce milk for offspring, so high fat phenotype is not seen in male cows.- only female cows •Sex-influenced -> Male patterned baldness •Trait is influenced by environment it is expressed in ->Gene-testosterone interaction, high testosterone= baldness trait expressed; low testosterone environment (women), baldness trait not expressed

Sex Linkage Practice part three

•What is the probability that they will produce a child with hemophilia?-recessive b -25% chance "affected"- male will have the phenotype for this disorder 75% chance "unaffected"- 50 percent female, 25 percent male •What is the probability they will produce a son with hemophilia?-ignore females just look at males •1:2 (50%) sons will be affected •Can the produce a daughter who shows abnormal blood clotting? Why or why not? •No, father will not contribute the hemophilia allele, so there is no chance that the female will be homozygous for hemophilia - you dont produce a homo affected daughter offspring

X-Inactivation Mechanism

•XIST gene is present on the X chromosome-so it on the X linked gene •XIST is expressed—producing an RNA molecule •XIST RNA wraps itself around the X chromosome that is not producing the RNA-at random •Results in silencing of the X chromosome - So whichever X chromosome turns on the Xist gene first wins - and then for the rest of their life about cell in all of that cells progeny, that particular X is going to express the gene whereas the other X is going to be totally genetically inert meaning silenced - males on the other hand happy XIST gene because they do inherit one copy of the X chromosome. The gene is present but it doesn't do anything and it doesn't have a function, never gets turned on -so they would behave like normal - In the image you have an XIST gene being produced ,this XIST RNA produced by left side is going to functionally attach the other chromosome ,so it winds it up so it makes it condensed which makes it functionally inert inside the cell , so the genes are available but they are never expressed

Sex Linkage Nomenclature

•X^W+X^W or X^W+Y - the + means wildtype •X or Y denotes the chromosome gene is linked to •Superscript denotes trait of recessive allele (white eyes) • + denotes dominant allele (W+ is red and dominant) •Wild type (WT) means dominant trait •**Only use this nomenclature in sex-linkage crosses, not in any other crosses •Terms •"Affected" (show phenotype) vs "unaffected" (doesnt show phenotype) describes phenotype of trait •"Carrier" only heterozygous females males cant be acrriers Ex: color blindness