Chapter 15

Question 1

how can you locate a particular gene

Answer 1

a particular gene can be seen by tagging isolated chromosomes with a fluorescent dye that highlights the gene

Question 2

wild type

Answer 2

phenotypes that are common

Question 3

mutant phenotypes

Answer 3

traits alternative to the wild type

Question 4

XX

Answer 4

female

Question 5

XY

Answer 5

male

Question 6

How do x and y chromosomes behave in meiosis in males?

Answer 6

short segments at the ends of the Y chromosomes are homologous with the x chromosome

Question 7

What is responsible for the development of testes in an embryo?

Answer 7

A gene on the y chromosomes called SRY

Question 8

sex-linked gene

Answer 8

gene that is located on either sex chromosome

Question 9

y-linked genes

Answer 9

genes on the y chromosome

Question 10

x–linked genes

Answer 10

genes on the x chromosome

Question 11

difference between x-linked and y-linked

Answer 11

x chromosomes have genes for many characters unrelated to sex, most y-linked genes are related to sex determination

Question 12

for a recessive x-linked trait to be expressed

Answer 12

A female needs two copies of the allele (homozygous)
A male needs only one copy of the allele (hemizygous)
x-linked recessive disorders are much more common in males than in females

Question 13

Some disorders caused by recessive alleles on the X chromosome in humans

Answer 13

Color blindness (mostly X-linked)
Duchenne muscular dystrophy
Hemophilia

Question 14

X Inactivation in Female Mammals

Answer 14

In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development
The inactive X condenses into a Barr body
If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character

Question 15

linked genes

Answer 15

genes located on the same chromosome that tend to be inherited together

Question 16

genetic recombination

Answer 16

the production of offspring with combinations of traits differing from either parent

Question 17

parental types

Answer 17

Offspring with a phenotype matching one of the parental phenotypes

Question 18

recombinant types, or recombinants

Answer 18

Offspring with nonparental phenotypes (new combinations of traits)

Question 19

what percent frequency of recombination is observed for any two genes on different chromosomes

Answer 19

50%

Question 20

crossing over

Answer 20

Morgan discovered that genes can be linked, but the linkage was incomplete, because some recombinant phenotypes were observed

Question 21

new combinations of alleles; variation for natural selection

Answer 21

Recombinant chromosomes bring alleles together in new combinations in gametes
Random fertilization increases even further the number of variant combinations that can be produced
This abundance of genetic variation is the raw material upon which natural selection works

Question 22

what is more likely the farther apart two genes are?

Answer 22

the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency

Question 23

linkage map

Answer 23

is a genetic map of a chromosome based on recombination frequencies

Question 24

map units

Answer 24

Distances between genes can be expressed

Map units indicate relative distance and order,not precise locations of genes

Question 25

genes that are far apart on the same chromosome

Answer 25

can have a recombination frequency near 50%

Such genes are physically linked, but genetically unlinked, and behave as if found on different chromosomes

Question 26

alteration of chromosome number or structure

Answer 26

Large-scale chromosomal alterations in mammals often lead to spontaneous abortions (miscarriages) or cause a variety of developmental disorders
Plants tolerate such genetic changes better than animals do

Question 27

nondisjunction

Answer 27

pairs of homologous chromosomes do not separate normally during meiosis
As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy

Question 28

Aneuploidy

Answer 28

results from the fertilization of gametes in which nondisjunction occurred
Offspring with this condition have an abnormal number of a particular chromosome

Question 29

monosomic

Answer 29

zygote has only one copy of a particular chromosome

Question 30

trisomic

Answer 30

zygote has three copies of a particular chromosome

Question 31

Polyploidy

Answer 31

is a condition in which an organism has more than two complete sets of chromosomes
Triploidy (3n) is three sets of chromosomes
Tetraploidy (4n) is four sets of chromosomes
Polyploidy is common in plants, but not animals
Polyploids are more normal in appearance than aneuploids

Question 32

deletion

Answer 32

removes a chromosomal segment

Question 33

duplication

Answer 33

repeats a segment

Question 34

inversion

Answer 34

reverses orientation of a segment within a chromosome

Question 35

translocation

Answer 35

moves a segment from one chromosome to another

Question 36

down syndrome

Answer 36

is an aneuploid condition that results from three copies of chromosome 21
It affects about one out of every 700 children born in the United States
The frequency of Down syndrome increases with the age of the mother

Question 37

Klinefelter syndrome

Answer 37

result of an extra chromosome in a male xxy

Question 38

Turner syndrome

Answer 38

monosomy just X in female