bio chap 17

Question 1

Genes located along the X chromosome:

Answer 1

are called X-linked genes.

Question 2

During meiosis in the male, sex chromosomes segregate to produce two types of sperm: X-bearing sperm and Y-bearing sperm.

Answer 2

true

Question 3

The group represented by a large proportion of the progeny, deriving from maternal gametes containing alleles present in the same combinations as found in the mother’s X chromosomes, is called the ______________________ group.

Answer 3

nonrecombinant

Question 4

Which of the following statements regarding sex ratios are true?

Answer 4

Sex ratios are dynamic and can change over time; the ratio of males to females at birth may be different from that during adolescence and adulthood.

Question 5

A woman is at the train station and sees a family with five boys. The occurrence of five boys in this family is likely the result of a mutation in one of the X chromosomes of the mother that impacts the survival of female embryos in the womb.

Answer 5

false

Question 6

Which one of the following statements does not accurately describe segregation of the sex chromosomes?

Answer 6

In humans, the sex at each birth is not a random process because there are often large families with either all girls or all boys.

Question 7

Sons of a cross between a white-eyed male and a red-eyed female always have red eyes.

Answer 7

false

Question 8

The group that represents a small proportion of the progeny, deriving from maternal gametes containing combinations of alleles not found in either X chromosome of the mother, is called the _______________ group.

Answer 8

recombinant

Question 9

Which of the following events occur during anaphase I of meiosis?

Answer 9

In males, the X chromosome is segregated from the Y chromosome.

Question 10

Nondisjunction could be the reason for a red-eyed male offspring from a cross between a red-eyed male and a white-eyed female.

Answer 10

true

Question 11

Why are the female progeny from the F1 cross shown in Figure 17.9 not used for linkage analysis?

Answer 11

All F2 females have a wild-type phenotype of red eyes and cross-veined wings.

Question 12

During meiosis in the female, sex chromosomes segregate to produce two types of eggs: X-bearing eggs and Y-bearing eggs.

Answer 12

false

Question 13

Which of the following statements explains why all of the F1 females from a cross between a red-eyed homozygous female and a white-eyed male are heterozygous?

Answer 13

The male parent provides them with a white-eye allele on the X, and the female parent provides them with a red-eye allele on the X.

Question 14

Daughters of a cross between a white-eyed male and a red-eyed female always have red eyes.

Answer 14

false

Question 15

What kind of eye color would be expressed in male progeny from a white-eyed female and a red-eyed male?

Answer 15

All males would have white eyes.

Question 16

Most chromosomes are paired and are both inherited from either the mother or the father.

Answer 16

false

Question 17

Which of the following statements regarding both the X and Y chromosomes are true?

Answer 17

All organisms on Earth―whether insects, birds, mammals, etc.―have both X and Y chromosomes.
If an organism of any species is male, it must possess a Y chromosome.
The Y chromosome of any species is always smaller than the X chromosome.
The X and Y chromosomes are similar across all species, given the evolutionary relationship between these chromosomes.
all of these are false**

Question 18

All organisms have either an X or Y chromosome, as these chromosomes are solely responsible for determining the sex of an individual. Mendel’s failure to identify X and Y chromosomes in his pea plants invalidated a portion of the data he collected.

Answer 18

false

Question 19

For rare X-linked traits, most of the affected individuals are males.

Answer 19

For rare X-linked traits, most of the affected individuals are males.

Question 20

In a male fruit fly, the white-eye gene is carried on the Y chromosome.

Answer 20

false

Question 21

A wild-type fruit fly:

Answer 21

exhibits the most common phenotype in the population.

Question 22

In Figure 17.5a, none of the F2 females has white eyes. Why?

Answer 22

The allele for red eyes is dominant over white eyes, and these F2 females are either homozygous dominant (red-eye allele) or are heterozygous.

Question 23

Which one of the following statements does not accurately describe the sex chromosomes?

Answer 23

The relative size and gene content of the X and Y chromosomes is very similar across species.

Question 24

The frequency of recombination is expressed as the ratio of recombinants to the total number of progeny.

Answer 24

true

Question 25

Imagine that a researcher is looking at the movement of sperm in a vial. He notices that although all the sperm tend to move upward, there is a group that consistently moves faster and reaches the top of the vial first. This may be the result of differences in which sex chromosome―either the YXor Y―the sperm contain. As X chromosomes are larger than Y chromosomes, Y-chromosome–bearing sperm may move faster.

Answer 25

true

Question 26

The ratio of recombinants to total number of progeny can be simplified to a percentage, and 1% recombination is equal to 1 __________________, which represents the distance between two linked genes.

Answer 26

map unit

Question 27

Two genes, A and B, are found on the same chromosome. One homologous chromosome carries alleles A and B, whereas the other homologous chromosome carries alleles a and b. If genes A and B are so closely linked that the recombination frequency is 0%, only AB and ab gametes will be produced during meiosis.

Answer 27

true

Question 28

Genetic variations in DNA sequences in human populations, such as single nucleotide polymorphisms (SNPs), have been used to map “disease genes” by determining whether the SNP is linked to the mutant gene.

Answer 28

true

Question 29

An X chromosome carrying the allele for white eyes is transferred from a male to a female of the next generation and in the next generation is transmitted back to the male again. This is called:

Answer 29

crisscross inheritance.

Question 30

Which one of the following statements does not accurately describe segregation of the sex chromosomes?

Answer 30

In humans, the sex at each birth is not a random process because there are often large families with either all girls or all boys.

Question 31

The small area near the centromere is the most likely location for recombination between two homologous chromosomes.

Answer 31

false

Question 32

n humans and other mammals, XX individuals are female and XY individuals are male.

Answer 32

a

Question 33

The human X and Y chromosomes are different lengths and contain different genes, except for small regions of homology that allow the two chromosomes to pair in meiosis.

Answer 33

a

Question 34

Segregation of the X and Y chromosomes during male meiosis results in half of the sperm receiving an X chromosome and half a Y chromosome so that random union of gametes predicts a 1:1 female:male sex ratio at the time of fertilization.

Answer 34

a

Question 35

Morgan studied a mutation in the fruit fly Drosophila melanogaster that resulted in fruit flies with white eyes rather than normal red eyes. In this species, as in mammals, females are XX and males are XY.

Answer 35

a

Question 36

In a cross of a normal red-eyed female with a mutant white-eyed male, all of the male and female progeny had red eyes. When brothers and sisters of this cross were mated with each other, all of the females had red eyes, but males were red-eyed and white-eyed in a 1:1 ratio.

Answer 36

a

Question 37

This pattern of inheritance is observed because the gene Morgan studied, called white, is located in the X chromosome. The nonmutant w+ allele is dominant to the mutant w– allele, and the gene is present only in the X chromosome and not in the Y chromosome.

Answer 37

a

Question 38

X-linked genes show a crisscross inheritance pattern, in which the X chromosome with the mutant gene that is present in males in one generation is present in females in the next generation.

Answer 38

a

Question 39

Bridges observed rare fruit flies that did not follow the usual pattern for X-linked inheritance and inferred that these exceptional fruit flies resulted from nondisjunction, or failure of homologous chromosomes to segregate, in male or female meiosis. His observations provided evidence that genes are carried in chromosomes.

Answer 39

a

Question 40

In humans, X-linked inheritance shows a pattern in which affected individuals are almost always males, affected males have unaffected sons, and a female whose father is affected can have affected sons.

Answer 40

a

Question 41

Genes that are close together in the same chromosome are linked and do not undergo independent assortment.

Answer 41

a

Question 42

Recombinant chromosomes result from crossing over between genes on the same chromosome and show a nonparental combination of alleles.

Answer 42

a

Question 43

Nonrecombinant chromosomes have the same configuration of alleles as one of the parental chromosomes.

Answer 43

a

Question 44

In genetic mapping, the observed proportion of recombinant chromosomes is the frequency of recombination and can be used as a measure of distance along a chromosome. A recombination frequency of 1% is one map unit.

Answer 44

a

Question 45

Gene linkage and mapping are used to identify the locations of disease genes in the human genome.

Answer 45

a

Question 46

In humans and other mammals, the Y chromosome contains a gene called SRY that results in male development.

Answer 46

a

Question 47

In Y-linked inheritance, only males are affected and all sons of an affected male are affected. Females are never affected and do not transmit the trait.

Answer 47

a

Question 48

Most Y-linked genes show complete linkage, which allows their evolutionary history to be traced.

Answer 48

a

Question 49

Mitochondria and chloroplasts have their own genomes, which reflect their evolutionary history as free-living prokaryotes.

Answer 49

a

Question 50

Mitochondria in humans and other mammals show maternal inheritance, in which individuals inherit their mitochondrial DNA from their mother.

Answer 50

a

Question 51

Because mitochondrial DNA does not undergo recombination and is maternally inherited, it can be used to trace human ancestry and migration

Answer 51

a

Question 52

Explain how the human X and Y chromosomes can pair during meiosis even though they are of different lengths and most of their genes are different.

Answer 52

The X and Y chromosomes can pair during meiosis through regions of homology located near the tips of the chromosomal arms.

Question 53

Describe the biological basis for the 1:1 ratio of males and females at conception in mammals.

Answer 53

Meiosis in the mammalian egg cell results in X-bearing eggs only. In contrast, meiosis in the sperm cell results in a 1:1 ratio of X-bearing and Y-bearing cells. Random fertilization of the egg results in a 1:1 ratio of female to male offspring.

Question 54

Explain why linked genes do not exhibit independent assortment.

Answer 54

Linked genes do not exhibit independent assortment because they are located sufficiently close together on the same chromosome.

Question 55

Describe how recombination frequency can be used to build a genetic map.

Answer 55

The closer, or more tightly linked, that two genes are to each other, the smaller the frequency of recombination because it is less likely that a crossover event would take place in the interval between them. The further two genes are from each other the greater the frequency of recombination because there would be a greater chance that a crossover event would happen in the interval between the genes. The frequency of recombination can be used as a measure of distance between the genes.

Question 56

Describe the pattern of inheritance expected from a Y-linked gene in a human pedigree.

Answer 56

For a Y-linked gene, only males are affected with the trait. Females never inherit or transmit the trait, and all sons of affected males are affected. This is due to the fact that males get their Y chromosome from their father only.

Question 57

Describe the pattern of inheritance expected from a gene present in mitochondrial DNA in a human pedigree.

Answer 57

A gene present in mitochondrial DNA is transmitted from the egg cell (mother) to the offspring. Both males and females can show the trait, all offspring from an affected female show the trait and males never transmit the trait to their offspring.

Question 58

Explain how Y-chromosome and mitochondrial DNA data can be used to trace ancestry.

Answer 58

Y-linked genes show complete linkage, and mitochondrial DNA does not undergo recombination and is maternally inherited. For these reasons, Y-linked and mitochondrial DNA are good traits to use when tracing ancestry.

Question 59

Which of the following events occur during anaphase I of meiosis?

Answer 59

In males, the X chromosome is segregated from the Y chromosome.

Question 60

A single point mutation in a mitochondrial gene involved in protein synthesis that affects oxidative phosphorylation is an example of a maternal inheritance pattern that is characteristic of mitochondrial diseases.

Answer 60

true