Transcript Genetics Review

 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%