GgTt pea plants can produce _____ type(s) of gametes, but a ggtt plant can produce ______ type(s) of gametes.

four....one

Huntington's disorder is due to an autosomal dominant allele. If a heterozygous male marries a normal female, what percentage of the offspring will have Huntington's?

50%

Various procedures can be used to detect genetic disorders before birth. Among the tests discussed in this chapter, _____ is the least invasive, while ___ and ___ allow the chromosomes of the fetus to be examined.

ultrasound imaging...chorionic villus sampling...amniocentesis

In people with sickle-cell disease the red blood cells break down, clump, and clog the blood vessels. The blood vessels and the broken cells accumulate in the spleen. Among other things this leads to physical weakness, heart failure, pain, and brain damage. Such a suite of symptoms can be explained by ____.

the pleiotropic effects of the sickle-cell allele

Cystic fibrosis can be inherited even if neither parent has the disease. This is because the disease _____.

is caused by a recessive allele

The results of a testcross (that is, the offspring of this cross) were 50% phenotypically dominant and 50% phenotypically recessive. The genotype of the phenotypically dominant parent in this cross was _____.

Heterozygous

The genetic disease cystic fibrosis is caused by a defective allele that _____.

encodes a defective chloride-channel membrane transport protein

In a cross between two heterozygotes (A), the next generation will be _____.

in the ratio 1:3 homozygotes to heterozygotes

Flower color in snapdragons is an example of incomplete dominance. If a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with a pink-flowered plant, the progeny plants will be

25% red, 50% pink, and 25% white

A = big apples; a = small apples; R = red apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half the offspring trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents?

AArr and aaRr

In general, the frequency that crossing over occurs between two linked genes depends on ____.

how far apart they are on the chromosome

Human males are much more likely to have hemophilia (a failure of the blood to clot properly) than human females. This is the case because _____.

the gene for hemophilia is sex-linked

If a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction, the resulting chromosomal abnormality is called ____.

an inversion

A particular allele can have different effects if it is inherited from a male rather than a female. This phenomenon is known as _____.

genomic imprinting

If hair color, eye color, and the presence or absence of freckles were consistently inherited together, the best explanation would be that _____.

the genes for these traits are linked on the same chromosome

The Y chromosomes of mammals contain genes that code for ______.

"maleness" and few other traits

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.

nondisjunction

Four genes (A, B, C, and D) are on the same chromosome. The crossover frequencies below are obtained. Which is the correct sequence of genes? A-B 19% B-C 14% A-C 5% B-D 2% A-D 21% C-D 16%

ACBD

If a couple's first child is a boy, what is the probability that their next child will be a girl?

50%