Exam 4: Modifications of Mendelian Ratios

How many different alleles can a gene have?

Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations, whereas genetic imprinting occurs when gene expression varies depending on parental origin.

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

Typical ratios resulting from epistatic interactions in dihybrid crosses would be

What distinguishes sex -limited from sex -influenced inheritance?

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?

A 9:7 ratio indicates incomplete dominance.

A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.

The presence of more than two alternative forms of a given gene would be called

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

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

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

Assume that a dihybrid F2 ratio, resulting from epistasis, was 15:1. If a double heterozygote is crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

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

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

The trait of medium -sized leaves in iris is determined by the genetic condition PP'. Plants with large leaves are PP, whereas plants with small leaves are P'P'. A cross is made between two plants each with medium -sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?

A maternal effect, or maternal influence, occurs when the offspring's phenotype is under the control of the mother's nuclear gene products that are present in the egg.

Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose -comb chicken is crossed with a walnut -comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single. a() What are the probable genotypes of the parents? b() Give the genotypes of each of the offspring classes.

Penetrance specifically refers to the expression of lethal genes in heterozygotes.