29. Heredity

Distinguish between the following paired terms: 

(c) simple inheritance and polygenic inheritance.

Recessive X-linked traits 

(a) Are passed from fathers to their sons

(b) Are more likely to be expressed in males

(c) Always affect some aspect of the reproductive system

(d) Are never expressed in females

(e) Cannot be passed from mothers to daughters

Indicate the type of inheritance involved in each of the following situations. 

(c) The trait is expressed more commonly in sons than in daughters. 

Hemophilia A, a condition in which blood does not clot properly, is a recessive trait located on the X chromosome (Xʰ). Suppose that a woman who is heterozygous for this trait (XXʰ) has children with a normal male (XY). What is the probability that the couple will have daughters with hemophilia? What is the probability that the couple will have sons with hemophilia?

Distinguish between the following paired terms: 

(b) heterozygous and homozygous, 

Match the following types of inheritance (key terms a–f) with

the descriptions below:

Key:

(a) dominant-recessive

(b) incomplete dominance

(c) multiple-allele

(d) polygene

(e) sex-linked

(f) extranuclear

____ (1) only sons show the trait

____ (2) homozygotes and heterozygotes have the same phenotype

____ (3) heterozygotes exhibit a phenotype intermediate between those of the homozygotes

____ (4) phenotypes of offspring may be more varied than

those of the parents

____ (5) inheritance of ABO blood types

____ (6) inheritance of stature

____ (7) reflects activity of mitochondrial DNA

Describe the important mechanisms that lead to genetic variations in gametes.

Suppose that the ability to taste PTC (phenylthiocarbamide) depends on the presence of a dominant gene T; nontasters are homozygous for the recessive gene t. This would be a case of classical dominant-recessive inheritance.

(a) Consider a mating between heterozygous parents producing three offspring. What proportion of the offspring are likely to be tasters? What is the chance that all three offspring will be tasters? Nontasters? What is the chance that two will be tasters and one will be a nontaster?

(b) Consider a mating between Tt and tt parents. What is the anticipated percentage of tasters? Nontasters? What proportion can be expected to be homozygous recessive? Heterozygous? Homozygous dominant?

A woman with blood type A has two children. One has type O blood and the other has type B blood. What is the genotype of the mother? What are the genotype and phenotype of the father? What is the genotype of each child?

In skin color inheritance, what will be the relative range of pigmentation in offspring arising from the following parental matches?

(a) AABBCC × aabbcc

(b) AABBCC × AaBbCc

(c) Aabbcc × aabbcc