Exam 4: Modifications of Mendelian Ratios

A typical epistatic ratio is 9:3:4.

One result of X -linkage is a crisscross pattern of inheritance in which sons express recessive genes of their fathers and daughters express recessive genes of their mothers.

Genomic imprinting occurs when one allele converts another.

Pattern baldness and hen/cock feathering in fowl are examples of X -linked inheritance.

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

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: Assign gene symbols for the genetic control of coat color on the basis of these data. Diagram the last two matings.

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 genes for zeste eyes and forked bristles are located on the X chromosome in Drosophila melanogaster. Both genes are recessive. A cross is made between a zeste -eyed female and a forked -bristled male. a() If 200 offspring from this cross were obtained, present the expected number, sex, genotype, and phenotype in each class of the F1. b() If the F1 offspring were crossed to produce 800 flies of an F2 generation, present the expected number, sex, and phenotype in each class. Assume no crossing over.

Provide an example of sex -influenced inheritance.

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

The term expressivity defines the percentage of individuals who show at least some degree of expression of a mutant genotype.

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 son will have hemophilia?

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.

With multiple alleles, there can be more than two genetic alternatives for a given locus.

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

The enzyme glucose -6 -phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man. a() What fraction of their sons would be expected to have G6PD? b() If the husband had G6PD, would it make a difference in your answer in part (a)?

A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is _.

Assume that a dihybrid F2 ratio, resulting from epistasis, was 9:3:4. If a double heterozygote is crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

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?

In a mating between individuals with the genotypes IAIO × IOIO, what percentage of the offspring are expected to have the O blood type?