Genetics

Independent Assortment

During gamete formation, Alleles assort independently, meaning the gamete's chance/prob of getting one allele for a given trait is not affected by the prob/chance of getting a certain allele for a DIFFERENT trait

Homozygous

a genotype in which the 2 copies of the gene are the same allele Homozygote: individual with identical alleles for a give gene or locus

Codominance (lec 4) 2 key points

a heterozygote that expresses BOTH parents' traits simultaneously ex? IAIB blood type from ABO blood type (simultaneous expression of the traits of both parents in a heterozygote)

Genetic Hypothesis

a hypothesis about the deviation between the expected and observed results, based on the underlying genetics

Gene

a locus of DNA that encodes a particular RNA or protein

Mapping Function

a mathematical formula that corrects for the multiple cross over events that do NOT result in genetic recombination cM= -50ln(1-2p)

Auxotroph (lecture 9)

a microorganism that requires an organic molecule in order to grow ex) amino acid auxotroph: needs to supplied with the amino acid in order to grow

Asexual Reproduction

a mode of reproduction in which the offspring arise from a single parent, and are genetically identical to the parent and each other.

Mutation

a permanent change in a gene such that it specifies a different phenotype

Mitosis

a process of nuclear division in eukaryotic cells that occurs when a parent cell divides to produce two identical daughter cells of the same ploidy

Genotype

a specific set of alleles inherited at a given locus

Complementation Test "cis/trans test"

a test to discover whether two mutations are allelic (in the same gene) or non-allelic (in separate genes) -allelic: do not complement each other, produce mutant -non allelic: complement, produce wt phenotype

Allele

a variant/alternative form of a single GENE.

Chi-Squared Analysis (lec 3)

statistical method; tests the probability that the null hypothesis is true; x^2= summation of (o-e)^2/e OHHEEEEEEEE (tests whether or not deviation is due to chance) -Null Hypothesis: the deviation between observed and expected is due to chance alone (null= chance)

Chiasmata

the OBSERVABLE regions in which non-sister chromatids of homologous chromosomes exchange genetic material/cross over

Null Hypothesis

the deviation between what is expected and what is observed is due to chance alone

Chromatid

one of the two daughter strands of a replicated chromosome

Sister Chromatid

one of the two identical copies of a replicated chromosome plural: two identical copies of a replicated chromosome joined together by a common centromere

Measuring Recombination Frequency in 3 point mapping (lecture 7)

p= probability of crossover --> For double crossover: p1p2 (between AB (p1) and BC (p2)

Incomplete Dominance

partial/semi; occurs when a heterozygote's phenotype is an intermediate between those of the parents

Blended Inheritance

pre-mendelian theory that states that the offspring's genetic material is a uniform blend of that of the parents (genetic makeup is blend/intermediate of parents')

p (lecture 7)

probability of crossing over p= probability of CO p^2= probability of DCO (2 crossovers) 1-p= probability of NO crossovers (NCO)

Poisson Distribution

probability of occurrence of exactly m events when your mean is m events P(n)= m^n e^-m/n! (em = mean expectation)

CentiMorgan; cM (lecture 7)

probability of recombination x 100 (p x 100) ex) p= .35 , cM= 35 cM cM= -50ln(1-2p)

Coefficient of Coincidence

ratio of Observed DCO/Expected DCO *observed is what we actually saw *expected is always on bottom

Autosomal

refers to non-sex chromosomes, or the genes on these chromosomes

Genetic Map (lecture 7)

*mirror images ignored, ABC vs CBA (genes) -RF between 2 close genes is low, and vice versa. Because low probability of getting a crossover. -So a genetic map gives us the relative ORDER of genes on a chromosome, and does not correspond to the physical distance across the chromosome. -Graphical way of representing recombination frequency data, but not the physical distance.

Chromosome

-a threadlike strand of DNA that carries genes -a strand of DNA that is encoded with genes

Interference

1. Crossovers that do not occur independently (occurrence of one crossover event reduces the likelihood that another crossover will occur in an adjacent part of the chromosome) 2. 1- C (E-O)/(E) think: crossover interferes or affects the other one *negative interference possible if more observed than expected.. A situation where the number of observed double crossover events in progeny is less than what is expected by the number of SCO events

3-Point Mapping (lecture 7)

1. Determine gene order first before "measuring recombination frequencies by counting progeny" 2. Testcross triple heterozygote (cis?) with tester strain (triple recessive homozygote) 3. 8 recombinant classes. Frequent ones are SCOs. Rare ones are DCOs. 4. Allele of the MIDDLE gene: -does not separate from the parentally-linked alleles in the frequent class -SEPARATES from the parentally-linked alleles in the rare class 5. Alleles of flanking/outer genes: -Frequent class: do not separate from parentally-linked center allele -Rare class: separate from parentally-linked center allele Basically, COMPARE the recombinant allele order to the parental allele order.

Locating a Gene by 3 point Cross (lecture 7) like #4 on problem set

1. Know Gene Order 2. List possible genotypes (8) and possibilities of getting each. Example: ABC gamete (parental)..probability (1-p1)(1-p2) -SCO in region 1: p1-p1p2 -SCO in region 2: p2-p1p2 -DCO: p1p2 (measuring recombination between genes) 3. Measure recombination events between A and B add SC+ DC progeny probabilities/ total= p1 -Measure between B and C SC+DC progeny probabilities/2= p2 -Between A and C: ALL probabilities of the 8 genotypes= p1+p2

Determining Gene Order in 3 point cross (draw the crossover pictures for practice) (lecture 7)

1. Test cross a triple heterozygote with homo recessive: A/a B/b C/c x a/a b/b c/c --> non-recombinants: A/a B/b C/c , a/a b/b c/c (ABC, abc) ***? --> recombinants: 6--> A, B, C, AB, BC, AC (rarest types are the ones from DCO) *recognize DCO because rarest progeny *outside markers remain together, middle markers switch partners *8 categories of progeny from 3 point crosses (2 classes of non-recombinants, 6 of recombinants (less numerous than parental, least numerous is the DCO pair)

Tetrad

1. The assemblage of four haploid spores (ascospores) of yeast in a single ascus 2. A pair of synapsed homologous chromosomes during prophase I homologous chromosomes: x (1 paternal, 1 maternal) PAIR of homologous chromosomes: XX

Haploid

A cell or an organism that has a single set of chromosomes

Testcross

A cross between an individual with dominant phenotype of a trait and an individual that is homozygous recessive for that trait in order to determine the genotype/zygosity of the dominant individual.

Dihybrid Cross

A genetic cross between two individuals that are heterozygotes for two traits/genes, resulting in a characteristic phenotypic ratio of 9:3:3:1 in the offpsring ex) AaBb x AaBb a cross between two individuals that are both heterozygous for two traitsa cross between two individuals that are both heterozygous for two traits

Linkage Group

A linkage group is a group of genes that recombine with probabilities less than 0.5

Gamete

A mature, haploid reproductive cell (3)

Prototroph

A microorganism that has the ability to synthesize all of its metabolites from inorganic material

Sexual Reproduction

A mode of reproduction involving the fusion of female gamete and male gamete, which forms a zygote that potentially develops into genetically distinct offspring

Tetratype

A tetrad containing 4 different genotypes: -2 parental genotypes -2 recombinant genotypes

Ditype

A type of tetrad (4 haploid spores from single meisis in ascus of fungi) that contains two different genotypes

Mendelian Genetics (his assumptions) EDIT THIS

DAST I: 1. Assumed Complete Dominance: A dominant allele completely masks the effect of the recessive allele, and produces the same phenotype in hetero/homozygotes 2. Allele number: Each organism has two alleles that make up the genotype for a given trait (2 alleles/gene) 3. Survival: all alleles are equally viable or have the same chance of survival 4. Trait: 1 gene determines only 1 trait. 1) Each genotype produces an equal number of gametes 2) All gametes are equally likely to interact with one another, regardless of genotype 3) All progeny of each genotype are equally viable 4) Alleles assort independently, meaning the gamete's chance of getting one allele for a given trait is not affected/influenced by the chance of getting a particular allele for a different trait 5) gene is stable unit of inheritance VEGAS

Dominant Epistasis

Dominant allele of one gene masks the phenotypic expression of the other gene 12:3:1 phenotypic ratio

Pedigree

a genetic representation of a family tree that diagrams the inheritance of a trait or disease though several generations

2-point cross (mapping, measuring probability of recombination) (lecture 7)

SCO--> recombinants DCO--> non-recombinants Larger 2 pt crosses are error prone (unaccounted for/invisible DCOs that cancel the first crossover, yielding non-recombinants)

Partial Dominance

Same as incomplete -occurs when a heterozygote's phenotype is an intermediate between those of the parents

Reciprocal Cross

a cross with the phenotype of each sex reversed as compared with the original cross, to test the role of parental sex on inheritance pattern; a cross where you interchange the genotypes of both parents in order to test the role of parental sex on the inheritance of the trait

Wild-type Allele

The allele that encodes the most common phenotype in a particular natural population

Sex linkage

The condition in which a gene responsible for a specific trait is located on a sex chromosome, resulting in sexually-dependent inheritance of the trait. incompletely sex-linked: found on BOTH sex chromosomes

Crossing Over

The exchange of genetic material between the nonsister chromatids of homologous chromosomes

Ascus (lecture 9)

The sac that contains all 4 haploid products/spores of a single meiotic event in fungi

Heterogametic Sex

The sex of a species possessing dissimilar sex chromosomes, such that the gametes produced may contain either kind of sex chromosome

Suppression

When a suppressor mutation (dominant or recessive) cancels the effect of an abnormal allele at a different locus, thus restoring normal/wildtype phenotype in double mutants (relief of a mutant phenotype by a 2nd mutation) *the interaction between two gene products such that the expression of one of the genes is changed

Segregation of allele pair; Law of Segregation

When two different alleles for a particular gene segregate during meiosis so that each gamete acquires only one of the two alleles

Complementary Gene Action

When two genes are required to produce a wild type phenotype

Diploid

a cell that contains two copies of each chromosome

Punnett Square

a diagram that shows the genotypes two individuals can produce when crossed

Allele Series (lecture 4)

all the possible alleles for a given gene ex) fruit flies eye color gene white^cherry white^apricot white^1 white^+ white^eosn

Dominant

an allele that completely controls the phenotype regardless of whether the individual is homozygous or heterozygous for that allele

Neomorphic Allele

an allele that produces a gene product whose function is in some way different from the function of the wild-type gene product (altered product)

Hypomorphic Allele

an allele that produces a less functional gene product than the product of the wild-type allele (sub-active product)

Null Allele

an allele that results in completely nonfunctional product

Recessive

an allele whose phenotype is not expressed in a heterozygote

Phenotype

an individual's observable traits

Breeding True

an organism that always passes down certain phenotypic traits to its offspring parents with a particular phenotype produce offspring only with the same phenotype. -exclusively produce offspring with the same phenotype for a particular trait *an individual that always produces offspring with the same phenotype as them

Linked Genes

genes that are located on the same chromosome and have a recombination frequency of less than 50%

Redundant Genes

genes whose products serve the same function in a pathway, thus requiring only one dominant allele at either locus for wild-type phenotype

Expressivity (Lecture 4)

the extent or degree to which a phenotype is expressed in each person of a particular genotype high: distinct phenotype, low= variable phenotype (variable expression of phenotype) the degree/extent to which an individual with a certain genotype expresses the associated phenotype

Penetrance

the fraction/number of people in a population with a given/particular genotype, who show the associated/expected phenotype (high--> all people affected and show the phenotype) (low--> some affected- all may have the allele for the mutation but only some actually exhibit the phenotype)

Recombination Frequency

the percentage of recombinant progeny; can be used to indicate gene linkage

Product Law of Probability

the probability of independent events occurring together is the product of their individual probabilities

Inheritance

the transmission of characteristics from one generation to the next

Meiosis *be more specific

two consecutive cell divisions ultimately resulting in 4 haploid daughter cells/gametes

Synthetic Phenotype

when a double mutant exhibits a novel phenotype not apparent in either single mutant (dies, individuals carrying either mutation alone, survive)

Hemizygous

when an individual has only one allele for a given gene (For example, the male is hemizygous for most X chromosome genes)

Recombination

when offspring have a different combination of alleles than both parents; the formation of nonparental combinations of genes in a gamete or an individual

Haploinsufficient

when one copy of the wild-type allele does not provide enough gene product activity to produce a wild-type phenotype (ex: incomplete dominance, also, null+wt allele-->still no wt phenotype, then wt allele is haploinsufficient. If phenotype is similar to null homo, then null allele is dominant. partway phenotype between the two then partial dominance) *haploinsufficient allele cannot be fully dominant

Duplicate Genes (lecture 5)

when the expression of only ONE dominant allele at either locus is necessary to produce wild-type phenotype 15:1 phenotypic ratio (15 wt, 1 mutant) *2 loci produce products with overlapping or identical functions

Recessive Epistasis

when the recessive alleles (aa) of one gene MASK the phenotypic expression of the other gene (masking of a gene by the recessive allele of another gene) *9:3:4 phenotypic ratio ex: (wt, intermediate, mutant) wt=both dominant, int=a dom, b rec, mut: a is rec --the masked alleles of B gene only expressed when epistatic locus A has dominant alleles