Genetics exam 1
A/- or A-
"-" indicated that we have no clue what is there due to a lack of evidence
A/A or AA
"/" indicates same chromosome
A/A ; B/B or AA BB
";" indicates different chromosome (Non-homologous)
Discontinuous traits
"either-or" phenotypic differences between alternative alleles
Mutant allele
(1) an allele, or DNA variant, whose frequency is less than 1% in a population; (2) an allele that causes a phenotype seen only rarely in a population.
Huntingtons disease is (A) A haplo-sufficient gene, because the mutant allele is dominant (B) A haplo-insufficient gene, because the mutant allele is dominant (C) Neither, because the mutant allele is not a loss-of-function (If) allele
(C) Neither, because the mutant allele is not a loss-of-function (If) allele
Which genotype(s) below could NOT be a parent of a child with blood type A? (A) IA/IB (B) IA/i (C) IB/i (D) i/i (E) They could all be a parent
(E) They could all be a parent
DNA
(deoxyribonucleic acid) is a double-stranded polymer of nucleotides that carries genetic information. DNA strands are antiparallel (oriented in opposite directions) with 5' to 3' polarity.
RNA
(ribonucleic acid) is a polymer of nucleotides that is transcribed from DNA that is an intermediary in the synthesis of proteins
General molecular principles
- a specific gene determines a specific enzyme, whose activity may affect phenotype - A dominant allele usually determines a normally functioning protein - A recessive allele usually does not encode a functional protein.
haplo-sufficient
1 good copy of the gene (in a diploid) is sufficient for a normal phenotype - loss of 1 copy or a los of function (If) mutation in 1 copy is tolerated - Mutation is recessive
Haplo-insufficient
1 good copy of the gene is not sufficient for a normal phenotype - Loss of 1 copy or a If mutation in 1 copy leads to a mutant phenotype - Mutation is dominant.
Monohybrid cross
1-trait
How to recognize dominant traits in pedigrees
1. Affected children always have at least one affected parent (no hidden individual; no carrier) 2. As a result, dominant traits show a vertical pattern of inheritance 3. Two affected parents can produce unaffected children, if both parents are heterozygotes
How to recognize recessive traits in pedigrees
1. Affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous matings 2. All the children of two affected parents should be affected 3. Rare recessive traits show a horizontal pattern of inheritance 4. Recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population
Diakinesis
1. Chromatids thicken and shorten 2. At the end of prophase I, the nuclear membrane breaks down, and the spindle begins to form
Diplotene
1. synaptonemal complex dissolves 2. A tetrad of four chromatids is visible 3. Crossover points appear as chiasmata, holding nonsister chromatids together 4. Meiotic arrest occurs at this time in many species
When flipping a coin two times, what is the probability that the coin lands on heads and then tails
1/2
When rolling a single 6-sided dice, what is the probability of rolling a 4 or a 6?
1/3
When rolling two 6-sided die, what is the probability of rolling two 3s?
1/36
What proportion of the offspring of the monohybrid cross for gene A do you expect to show the fully recessive phenotype?
1/4
Round peas are dominate to wrinkled peas. Yellow peas are dominate to green peas. Pea plants with purple flowers are dominate to pea plants with white flowers. You cross Purple-flower Round Yellow pea plants with White-flower Green Wrinkled pea plants, and then you cross individuals in the first filial (F1) generation together) What proportion of F2 offspring do you expect to show the fully recessive phenotype?
1/64
In humans, how many ova develop from 100 primary oocytes?
100
One oak tree cell with 14 chromosomes undergoes mitosis. How many daughter cells are formed and what is the chromosome number in each cell? 1 daughter cell with 28 chromosomes 2 daughter cells with 28 chromosomes 2 daughter cells with 14 chromosomes 1 daughter cell with 14 chromosomes
2 daughter cells with 14 chromosomes
What type of phenotypic ratio does a monohybrid cross produce?
3:1
One oak tree cell with 14 chromosomes undergoes meiosis. How many cells will result from this process, and what is the chromosome number in each cell? 4 cells, each with 14 chromosomes 2 cells, each with 14 chromosomes 2 cells, each with 7 chromosomes 4 cells, each with 7 chromosomes
4 cells, each with 7 chromosomes
In humans, how many sperm develop from 100 primary spermatocytes?
400
What proportion of the offspring from a cross between 2 dihybrids for genes A and B do you expect to show 1 dominant trait and 1 recessive trait?
6/16
Suppose the intermediate called Colorless precursor 2 in the pathway in Fig 3.16 was blue instead of colorless. What is the phenotypic ratio seen in progeny of the A/a ; B/b X A/a ; B/b dihybrid cross?
9 : 3 : 4
Round peas are dominate to wrinkled peas. Yellow peas are dominate to green peas. You cross Round Yellow with Green Wrinkled, and then you cross individuals in the first filial (F1) generation together. What proportion of the F2 offspring do you expect to show the fully dominant phenotype?
9/16
What type of phenotypic ratio does a dihybrid cross produce?
9:3:3:1
Rare allele
<1% is considered a mutant allele
Assume that a series of compounds has been discovered in Neurospora. Compounds A-F appear to be members of a biosynthetic pathway. Several mutations in converting these compounds have been identified. Mutant strains 1-5 each contain a single mutation. Growth of each strain on minimal medium with one of the compounds A-F added is shown by (+); no growth is shown by (o) Which compound is the furthest upstream in the pathway?
A
Polymorphic
A gene with two or more distinct wild-type alleles in a population
What is the primary determinant of maleness?
A single gene called SRY which is the sex determining region of Y
What is the genotype of each individual in a monohybrid cross for gene A?
A/a
What are alternative forms of a single gene?
Alleles
Allele
An alternative form of a gene.
Base pairs in DNA
C-G A-T
Zygote
Cell formed by the fertilization of the egg by the sperm during sexual reproduction; in humans, eggs and sperm are haploid and zygotes are diploid.
Haploid
Cells, such as gametes of diploids, that contain one set of chromosomes
Metacentric chromosome
Cetromere is in the middle
Telophase
Chromosomes decondense and are enclosed in two nuclei
Leptotene
Chromosomes thicken and become visible, but the chromatids remain invisible. - Centrosomes begin to move toward opposite poles
What do DNA molecule and proteins assemble into?
Chromosomes. Each chromosome contains many genes.
3:1 phenotypic ratio
Complete dominance
What is the correct order of events that describe the central dogma of biology?
DNA transcribed to RNA, RNA translated to protein
Which of the following describes the central dogma of biology? DNA transcribed to protein, protein translated to DNA RNA translated to DNA, DNA transcribed to protein RNA translated to protein, protein transcribed to DNA DNA translated to RNA, RNA transcribed to protein DNA transcribed to RNA, RNA translated to protein
DNA transcribed to RNA, RNA translated to protein
The central Dogma of Biology
DNA-transcription-RNA-translation-protein
Chromosomes
DNA/protein structures that contain genes
What does a 12:3:1 ration in F2 progeny of a dihybrid cross indicate?
Dominant epistasis
Mendel's Law of Independent Assortment
During gamete formation, different pairs of alleles segregate independently of each other
In the above feeding experiment, which compound is the furthest downstream in the pathway?
E
True or False: Most loss-of-function mutations are dominant.
False
Complementarity
G-C and A-T base pairing in DNA through hydrogen bonds
During what phase does most cell growth occur?
G1 and G2 phase
What are the three parts of interphase?
Gap 1 (G1) phase Synthesis (S) phase Gap 2 (G2) phase
Carriers
Heterozygous individuals that display a normal phenotype that have a recessive allele for a trait
Zygotene
Homologous chromosomes enter synapsis - The synaptonemal complex forms
A slash (/) separates genes and their alleles that are on ... (
Homologs
What happens in metaphase I and anaphase I?
Homologs move to opposite poles - Centromeres do not divide and sister chromatids are not separated
Dosage compensation
Human females have two X chromosomes and males have only one In female cells, one X chromosome in inactivated - The inactive X chromosome is condensed into a Barr body
A pure-breeding wild legume with white flowers and long pods is crossed to a pure-breeding wild legume with purple flowers and short pods. The F1 offspring are allowed to self-fertilize, and the F2 generation has 301 long purple, 99 short purple, 612 long pink, 195 short pink, 295 long white, and 98 short white. How are the traits being inherited? Incomplete dominance for flower color, incomplete dominance for pod shape Complete dominance for flower color, complete dominance for pod shape Complete dominance for flower color, incomplete dominance for pod shape Incomplete dominance for flower color, complete dominance for pod shape
Incomplete dominance for flower color, complete dominance for pod shape
Chromosome loss
Lagging chromatid that is not pulled to either spindle pole at mitotic anaphase
What are the genotypes of the parents for a microcephalic child?
M/m both parents give a little m
Karyotype
Micrograph of stained chromosomes arranged in homologous pairs
A semicolon (;) separates genes and their alleles that are on ...
Non-homologous chromosomes
Y-linked
Only in males
Stages of Mitosis
Prophase Prometaphase Metaphase Anaphase Telophase
Round peas are dominate to wrinkled peas. Yellow peas are dominate to green peas. What is the genotype of an individual that is pure-breeding for both dominate phenotypes?
R/R ; Y/Y
Round peas are dominant to wrinkled peas. What is the best answer for the parental genotypes of a cross that gave all round pea progeny?
R/R x -/-
Round peas are dominate to wrinkled peas. Yellow peas are dominate to green peas. If you cross Round Yellow with Green Wrinkled, what is the genotype of the first filial (F1) generation?
R/r ; Y/y
During what phase does chromosomes replicate to form sister chromatids?
S phase
Homogametic sex
Sex with one type of gamete (XX females in humans)
What happens during meiosis II?
Sister chromatids separate and move to opposite poles
Anaphase
Sister chromatids separate and move to opposite poles Centromeres of all chromosomes divide simultaneously Kinetochore microtubules shorten and pull separated sister chromatids to opposite poles
what can cause dramatic effects in the genome?
Small changes
Prometaphase
Spindle forms and sister chromatids attach to microtubules from opposite centrosomes Nuclear envelope breaks down - Microtubules from centrosomes invade the nucleus and connect to kinetochores in centromere of each chromatid - Sister chromatids attach to microtubules from opposite poles - Mitotic spindle forms from three kinds of microtubules (astral, kinetochore, and polar)
Pachytene
Synapsis is complete - crossing-over, genetic exchange between non sister chromatids of a homologous pair, occurs.
What determines the three-dimensional shape of the protein?
The amino acid sequence
What does Meiosis I reduce?
The chromosomes from 2n to n
Cytokinesis
The cytoplasm divides and produces two daughter cells - begins during anaphase but not completed until after telophase - parent cells split into two daughter cells with identical nucei
S phase
The stage of the cell cycle from the birth of a new cell until the onset of chromosome replication, each chromosome doubles to produce identical sister chromatids
Which of the following statements applies to homologous chromosomes? (select one) They contain the same genes in the same order but may have different alleles of some genes They segregate from each other at anaphase of mitosis They are attached to the same centromere They are genetically identical
They contain the same genes in the same order but may have different alleles of some genes
True or False: Loss-of-function mutations in haplo insufficient genes are usually dominant.
True
What is now known as genes?
Units o inheritance
What is the causative gene for microcephaly?
WDR62
Which one of the following questions is best solved by the product rule? What is the probability of rolling a 6 or a 7 using a 9-sided die? What is the probability of rolling a 6 using an 8-sided die? What is the probability of rolling a 6 twice in a row using a 12-sided die?
What is the probability of rolling a 6 twice in a row using a 12-sided die?
Can Nucleotide sequences of DNA be copied?
YES
Can mitosis occur in a cell whose genome is haploid?
Yes
amino acid structure
a carboxyl group, amine group, and R group
Complementation group
a collection of mutations that do not complement each other
Epistasis
a gene interaction in which the effects of an allele at one gene hide the effects of alleles at another gene
Recessive episasis
a gene interaction in which the effects of recessive alleles of one gene hide the effect of alleles at another gene
Monomorphic
a gene with only one wild-type allele in a population
X-linked inheritance
a genetic condition that is associated with mutations in genes on the X chromosome. If present in males, they will be affected because they only carry one X chromosome. However, females, if only carrying the mutation on one gene, will generally go unaffected because they have 2 X chromosomes.
Multi-hybrid crosses
a mating of two hybrids in which two heterozygous loci are considered (AaBb x AaBb)
X chromosome inactivation
a mechanism of dosage compensation in which all X chromosomes in a cellular genome but one are inactivated at an early stage of development through the formation of heterochromatic Barr bodies.
Complementation table
a method of collating data that helps visualize the relationship among a large group of mutants
Prototroph
a microorganism that does not require any organic growth factors
Autotroph
a mutant microorganism that can grow on minimal medium only if it has been supplemented with one or more nutrients not required by wild-type strains.
Heterogeneous trait
a mutation at any one of a number of genes can give rise to the same phenotype
homologous chromosomes (Homologs)
a pair of chromosomes containing the same linear gene sequence, each derived from one parent
Redundant gene action
a phenomenon where dominant, functional alleles of either one or the other of two genes is required in a pathway
Dominant epistasis
a phenomenon where the effects of a dominant allele at one gene hide the effects of alleles at another gene
Heterogenous trait
a phenotype caused by a mutation in any one of a number of different genes
Locus heterogeneity
a property of a trait where mutations in any one of two or more genes results in the same mutant phenotype
Karotype
a visual description of the complete set of chromosomes in one cell of an organism; usually presented as a photomicrograph with the chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type
Mutant
allele, or DNA variant, whose frequency is less than 1% in a population or an allele that cause a phenotype rarely seen in a population (usually but not always written as a lowercase letter e.g. y)
Modifier genes
alter the phenotypes produced by alleles of other genes - can have major effect or more subtle effects
Alleles
alternative forms of a single gene (made by a mutation in the gene's sequence)
Dominant inheritance
an abnormal gene from one parent that can cause the disease.
recessive lethal allele
an allele that prevents the birth or survival of homozygotes, though heterozygotes carrying that allele survive.
Wild-type
an allele, or DNA variant, whose frequency is more than 1% in a population or an allele that dictates the most frequently observed phenotype in a population (usually but not always written as a capital letter e.g. Y)
Alkaptonuria
an inborn error of metabolism
Reciprocal recessive epistasis
an interaction between alleles of two different genes where the homozygous recessive genotype of each gene prevents the phenotypic expression of (is epistatic to) the dominant allele of the other gene
Biochemical pathway
an orderly series of chemical reactions within a cell in which molecules are converted stepwise into a final product
Oogonia
are diploid germ cells in the ovary of female embryos that undergo one mitotic event, then meiosis I (arrests until after birth), and then at puberty, one primary oocyte per month (ovulation) completes meiosis I (arrests at meiosis II until fertilization!). 1 oocyte only produces 1 haploid mature ovum.
prototrophs
can grow in minimal media without any nutritional supplements
Nonhomologs
cary completely unrelated sets of genes
Diploid
cells carrying two matching sets of chromosomes
Acrocentric chromosome
centromere is near one end
G1 phase
chromosomes are not duplicating or dividing - Length of time varies in different cell types
Prophase
chromosomes condense and become visible - Centrosomes move apart toward opposite poles nucleoli begin to disappear
Non Homologous chromosomes
chromosomes in a single genome that are not homologs—they do not have similar DNA sequences and do not pair during meiosis.
Autosomes
chromosomes not involved in sex determination. The diploid human genome consists of 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (the X and Y chromosomes)
Non-homologous chromosome
chromosomes that are not members of the same pair
The two strands of the double helix are what?
complementary and have opposite orientation
Centrioles
core or centrosome, not found in plant cells
What is the final stage of cell division?
cytokinesis
Aneuploidy
describes a cell or an organism whose chromosome sets are not all complete - usually results in multiple abnormalities or lethality - caused by nondisjunction
Monosomic
describes an individual lacking one (1) chromosome from the diploid number for the species (2n -1)
Euploidy
describes cells containing only complete sets of chromosomes
Triploid
describes cells or organisms with three complete sets of chromosomes (3x)
Monoploid
describes cells, nuclei, or organisms that have a single set of unpaired chromosomes. For diploid organisms, monoploid and haploid are synonymous (1x)
Epistasis tests
describes how gene interactions can affect phenotypes
Trisomic
describes individuals having one extra chromosome in addition to the normal diploid set (2n + 1)
cross-fertilize
different plant
9:3:3:1 phenotypic ratio
dihybrid cross/ 2 unlike genes
Spermatogenia
diploid germ cell in the testes that undergo one mitotic event, then meiosis to produce 4 haploid sperm
Spermatogonia
diploid germ cells found only in testis, divide by mitosis for form primary spermatocytes After puberty, maturation begins to form sperm - Primary spermatocytes undergo symmetrical division at meiosis I to produce two secondar spermatocytes - Secondary spermatocytes undergo symmetrical division at meiosis II to produce two spermatids - Spermatids mature to become sperm - Equal numbers of X and Y sperm are produced.
Dominant epistasis I
dominant allele of one gene hides effects of both alleles of another gene - Ratio: 12:3:1
Dominant epistasis II
dominant allele of one gene hides effects of dominant allele of another gene - Ratio: 13:3
S phase
duplication of chromosome into sister chromatids
9:4:3 phenotypic ratio
epistasis of 2 genes in a pathway
mitotic nondisjunction
failure of sister chromatids to separate during anaphase of mitosis
Pure-breeding (lines)
families of organisms that produce offspring with specific parental traits that remain constant from generation to generation.
X-linked
gene or trait that is carried on the X chromosome
Conserved
genes that are shared in different organisms
The molecular explanation for Mendel's pea shape is that the R allele encodes the Starch branching enzyme (Sbe1), but the r allele does not make the enzyme. R is dominant over r, such that R/r individuals make enough branched starches to make round peas. But r/r individuals cannot make branched starches, leading to the wrinkled peas phenotype. Since the loss-of-function allele r is recessive, the Sbe1 gene is ...
haplo-sufficient
Amphidiploid
has two diploid genomes, each from a different parental species
Mutation
heritable alteration in DNA sequence
complete dominance
hybrid resembles one of the two parents
Allopolyploid
hybrids in which chromosome sets come from distinct, but related, species - usually infertile because different chromosome sets cannot easily pair and segregate properly
Sister chromatids
identical copies of a replicated chromosome
2 sister chromatids
identical copies of the same chromosome
Sex Chromosomes
in humans, the X and Y chromosomes, which determine the sec of an individual
1:2:1 phenotypic ratio
incomplete dominance or codominance
Vertical Pattern
indicates a rare dominant trait - Every affected person has at least one affected parent - Mating between affected person and unaffected person is effectively a testcross.
Horizontal pattern
indicates a rare recessive trait - parents of affected individuals are unaffected but are heterozygous (carriers) for the recessive allele
Heterozygote
individual that has two different alleles for a given gene or locus (e.g. Y/y)
Homozygote
individual that has two identical alleles for a given gene or locus (e.g. Y/Y or y/y)
Parental (P) generation
individuals whose progeny in subsequent generations will be studied for specific traits
Monohybrids
individuals with two different alleles for a single trait
What are the substages of prophase I?
leptotene, zygotene, pachytene, diplotene, diakinesis
Protein
linear polymer of amino acids translated from RNA that folds into a particular shape and are required for the structure, function, and regulation of the body's cells, tissues, and organs.
Microcephaly is a recessive disease, what is the genotype of the child?
m/m
Continuous (quantitative) traits
many genes interact like human height or skin color
Consanguineous mating
mating between genetic relatives sharing a recent common ancestor
Which type(s) of cell division reduce(s) the chromosome number by half? Note: Sister chromatids are identical, so they count as one chromosome meiosis I and meiosis II mitosis and meiosis I meiosis II meiosis I mitosis mitosis and meiosis II
meiosis I
Complementation test
method of discovering whether two mutations are in the same or separate genes. Two mutant strains with the same mutant phenotype are crossed if the progeny areas wild type, the strains had mutations in different genes; if the progeny are a mutant, the strains had mutations in the same gene.
Centrosome
microtubule organizing center near the nuclear envelope
Which type(s) of cell division can be classified as equational (the parent cell has the same number of chromosomes as each daughter cell?) Note: Sister chromatids are identical, so they count as one chromosome meiosis I and meiosis II mitosis and meiosis I meiosis II meiosis I mitosis mitosis and meiosis II
mitosis and meiosis II
Restrictive conditions
mutant allele has defective functions
Permissive condition
mutant allele has wild-type functions
Auxotrophs
mutants that cannot grow without supplements being supplied
x-linked recessive
mutation never passes from father to son. However, daughters of affected males are carriers. 1/2 of sons of carriers will inherit the trait.
Conditional lethal
mutations are lethal only under some conditions - Permissive condition - Restrictive condition
Heterogenous traits
mutations in different genes can cause the same phenotype
Phenotype
observable characteristic (e.g. yellow or green peas)
Redundancy
only one dominant allele of either of two genes is necessary to produce phenotype - Ratio: 15:1
Pedigree
orderly diagram of a family's relevant genetic features, extending through as many generations as possible.
Genotype
pair of alleles present in an individual (e.g. Y/Y or Y/y)
.Pleiotropy
phenomenon in which a single gene determines a number of distinct and seemingly unrelated characteristics.
Phenocopy
phenotype arising from an environmental agent that mimics the effect of a mutant gene - not heritable - can be deleterious or beneficial
Cochicine treatment
prevents spindle formation and results in doubling of chromosome numbers
Product rule
probability of 2 independent events occurring TOGETHER = PRODUCT (multiplication) of their individual probabilities
Sum rule
probability of either 2 mutually exclusive events occurring = sum (addition) of their individual probabilities.
Translation
process in which the codons carried by RNA direct the synthesis of polypeptides from amino acids according to the genetic code
Mitosis
process of division that produces daughter cells that are genetically identical to each other and to the parent cell
Branched-line diagrams
progeny phenotypes for each gene are shown in different columns.
Allele frequency
proportion of all copies of a gene in a population that are of a given allele type - Most common allele is usually the wild-type allele
Round peas are dominate to wrinkled peas. Yellow peas are dominate to green peas. What is the genotype of an individual that is pure-breeding for both recessive phenotypes?
r/r ; y/y
2:1 phenotypic ratio
recessive lethal allele
In four-o'clocks, the allele for red flowers in incompletely dominant to the allele for white flowers, so heterozygotes have pink flowers. If you specifically want to produce pink flowers, which of these crosses would be most efficient?
red x white
Expressively
refers to the degree or intensity with which a particular genotype is expressed in a phenotype
CFTR Protein
regulates the passage of chloride ions across the cell membrane. Heterozygous individuals produce enough CFTR for normal lung function.
Incomplete dominance
relationship between two alleles of a gene where the heterozygote has a phenotype intermediate between that of the two homozygotes - genotypic ratio = phenotypic ratio - 1:2:1 - hybrid resembles neither parent
Codominance
relationship between two alleles of a gene where the heterozygote has the trait of both homozygotes - Hybrid shows traits from both parents
Pax6 gene
required for eye development in insects, mice, and humans
Self fertilize
same plant
Heterogametic sex
sex with two different kinds of gametes (XY males in humans, ZW females in birds)
Homologs
similar chromosomes - one comes from one parent and the other comes from the other parent
RNA
single strand complementary to DNA strand on the right
Gametes
specialized cells (eggs or sperm) that carry genes between generations
Genes
specific segment of DNA in a discrete region of a chromosome that serves as a unit of function by encoding a particular RNA or protein.
Metaphase
stage of mitosis or meiosis during which the chromosomes are aligned along the equatorial plate of the cell
G2 Phase
stage of the cell cycle from the completion of chromosome replication until the onset of cell division
Nucleotide
subunit of the DNA (or RNA) macromolecule - - A, G, C, or T (U for RNA). Composed of - Phosphate group - Deoxyribose sugar - Nitrogenous base (Adenine, Cytosine, Guanine, or Thymine)
G2 phase
synthesis of proteins required for mitosis
What does the 9:3:3:1 ratio suggest?
that 2 genes both influence something
Transcription
the conversion of DNA-encoded information to its RNA-encoded equivalent
Expressivity
the degree or intensity with which a particular genotype is expressed in a phenotype - can be variable or unvarying
Genome
the entire collection of chromosomes in each cell of an organism Human genome: - 24 kinds of chromosomes - 3x10^9 base pairs - around 27,000 genes
Nondisjunction
the failure in chromosome segregation during cell division, when either chromatids or homologs do not seperate properly
law of independent assortment
the law that states that genes separate independently of one another in meiosis - viewable in dihybrid crosses
Dosage compensation
the mechanism that equalizes the levels of X-linked gene expression independent of the number of copies of the X chromosome; in mammals, the dosage compensation mechanism is X chromosome inactivation.
Progeny ratio
the outcome of Mendel's law of segregation
Penetrance
the percentage of individuals with a particular genotype that show the expected phenotype - can be complete or incomplete
Complementation
the process in which heterozygosity for loss-of-function mutant recessive alleles for two different genes produces a normal phenotype
Meiosis
the process of two consecutive cell divisions in the progenitors of gametes. In the first division, pairs of homologous chromosomes (sister chromatids) segregate into two different daughter cells; in the second division, the sister chromatids of each homolog segregate into two different daughter cells. A diploid (2n) cell produces four haploid (1n) gametes by meiosis.
F1 (first filial) generation
the progeny of the parental generation in a controlled series of crosses
Genetics
the science of heredity of biological information.
G1 phase
the stage of the cell cycle from the birth of a new cell until the onset of chromosome replication at S phase
Mendel's law of segregation
the two alleles for each trait separate during gamete formation and the two gametes, one from each parent, unite at random at fertilization
Sex chromosome aneuploidy
tolerated due to X-chromosome inactivation
Dominant
trait appears in the F1 progeny
Recessive
trait is hidden in the F1 progeny
X-linked dominant
trait seen in every generation. Affected male will produce affected daughters and unaffected sons
Dominant trait
trait that appears in the F1 hybrids (heterozygotes) resulting from a mating between pure-breeding parental strains showing antagonistic phenotypes
Recessive trait
trait that remains hidden in F1 hybrids (heterozygotes) resulting from a mating between pure-breeding parental strains showing antagonistic phenotypes
Multifactorial traits
traits determined by several different genes, or by the interaction of genes with the environment
sister chromatids
two identical copies of a chromosomes that exist immediately after DAN replication. Sister chromatids are identical, so they carry the same alleles for all genes.
9:7 phenotypic ratio
two unlinked genes operate in a pathway
autosomal monosomy
usually lethal
Recessive inheritance
when both genes in a pair must be abnormal to cause a disease
reciprocal recessive epistasis
when homozygous, recessive allele of each gene masks the dominant allele of the other gene - ratio: 9:7
Recessive Epistasis
when homozygous, recessive allele of one gene masks both alleles of another gene - ratio: 9:3:4
Dominance series
when the dominance relations of all possible pairs of alleles are arranged in a linear order
