Exam 4: Modification of Mendelian Ratios

Alleles that are masked by an epistatic locus are said to be hypostatic to the genes at that locus.

Hemizygosity is the term used to describe the state of a gene that has no allele on the opposing chromosome.

Assume that a dihybrid cross is made in which the genes' loci are autosomal,independently assorting,and incompletely dominant.How many different phenotypes are expected in the offspring?

The following coat colors are determined by alleles at one locus in horses: palomino = golden coat with lighter mane and tail cremello = almost white chestnut = brown The following table gives ratios obtained in matings of the above varieties: $\text { Cross }$ $\quad$$\quad$$\text { Parents }$ $\quad$$\quad$$\quad$$\text { Offspring }$ 1 cremello cremello all cremello 2 chestnut chestnut all chestnut 3 cremello chestnut all palomino 4 palomino palomino 1/4= chestnut 1/2= palomino 1/4= cremello Assign gene symbols for the genetic control of coat color on the basis of these data. Diagram the last two matings.

Two forms of hemophilia are determined by genes on the X chromosome in humans.Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man.What is the probability that their first daughter will have hemophilia?

What is meant by the term epistasis? Distinguish between epistasis and dominance.Do not use examples in answering this question.

How many different alleles can a gene have?

In the mouse,gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of pigment,resulting in an albino.Gene B gives agouti (wild-type fur); its allele b gives black fur. (a)Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse. (b)What would be the expected phenotypic ratio in the progeny?

The ABO blood group locus in humans provides an example of epistasis.

Regarding the ABO blood group system in humans,if an individual is genetically I^BIO and yet expresses the O blood type,which genotype is the individual likely to have?

A typical epistatic ratio is 9:3:4.

Below is a pedigree of a fairly common human hereditary trait in which the boxes represent males and the circles represent females.Shading symbolizes the abnormal phenotype. Given that one gene pair is involved: (a)Is the inheritance pattern X-linked or autosomal,recessive or dominant? (b)Give the genotype of each individual in the pedigree.If more than one genotypic possibility exists,present all possible alternatives.

Sex-limited inheritance is the same as sex-linked inheritance.

A mutant gene that produces brown eyes (bw)is located on chromosome 2 of Drosophila melanogaster,whereas a mutant gene producing bright red eyes,scarlet (st),is located on chromosome 3.Phenotypically,wild-type flies (with dull red eyes),whose mothers had brown eyes and whose fathers had scarlet eyes,were mated.The 800 offspring possessed the following phenotypes: wild type (dull red),white,scarlet (bright red),and brown.Most of the 800 offspring had wild-type eyes,whereas those with white eyes were the least frequent. (a)Using standard symbolism,diagram the cross from the P generation (brown-eyed mothers X scarlet-eyed fathers)and the F₁ generation.Be certain to provide the alleles of the mutant genes. (b)From the information presented above,how many white-eyed flies would you expect in the F₂ generation?

Pattern baldness is determined by a single autosomal gene pair.When females are homozygous for this gene pair,can they show pattern baldness?

Name three modes of inheritance that are influenced by the sex of individuals.

A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila.All of the resulting offspring were phenotypically wild type.Offspring of the F₂ generation had the following phenotypes: Sex Phenotupe Number male wild 96 male yellow 99 female wild 197 Based on this information: (a)Is the mutant gene for yellow body behaving as a recessive or dominant gene? (b)Is the yellow locus on an autosome or on the X chromosome?

Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance.What phenotypic and genotypic ratios are expected in the offspring?

With which of the following would hemizygosity most likely be associated?

Assume that a dihybrid cross (AaBb X AaBb)is made in which the gene loci are autosomal,independently assorting,and incompletely dominant.What phenotypic ratio would you expect from such a cross? Just provide the ratio,not the phenotypes.