Exam 4: Modification of Mendelian Ratios

Expressivity is the term used to describe the balanced genetic output from a hemizygous condition.

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

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

With incomplete dominance,a likely ratio resulting from a monohybrid cross would be ________.

Provide an example of sex-influenced inheritance.

Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white,aaBB or aaBb gives yellow,and aabb produces green.Crosses among heterozygotes give a 12:3:1 ratio.What type of gene interaction would account for these results?

Because of the mechanism of sex determination,males of many species can be neither homozygous nor heterozygous.Such males are said to be ________.

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.

Which types of ratios are likely to occur in crosses (F₂)when one is dealing with two interacting,epistatic gene pairs?

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

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

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?

In a mating between individuals with the genotypes I^AIO X I^OIO, ,what percentage of the offspring are expected to have the O blood type?

Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A,such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual.If heterozygotes are phenotypically normal,we would say that the mutant allele is recessive to its normal allele.

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?

State a significant difference between X-linked and sex-influenced inheritance.

A 9:7 ratio indicates incomplete dominance.

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?

With both incomplete dominance and codominance,one expects heterozygous and homozygous classes to be phenotypically identical.