Exam 2 Book Questions

Question 1

Which of the following factors did not contribute to Mendel’s success in his study of heredity?
- His use of the pea plant
- His study of plant chromosomes
- His adoption of an experimental approach
- His use of mathematics

Answer 1

His study of plant chromosomes

Question 2

What is the difference between a locus and an allele?

Answer 2

A locus is a place on a chromosome where genetic information encoding a characteristic is located. An allele is a version of a gene that encodes a specific trait.

Question 3

What is the difference between genotype and phenotype?

Answer 3

A genotype is the set of alleles possessed by an individual organism, and a phenotype is the manifestation or appearance of a characteristic.

Question 4

How did Mendel know that each of his pea plants carried two alleles encoding a characteristic?

Answer 4

The traits encoded by both alleles appeared in the F2 progeny.

Question 5

If the F1 plant depicted in Figure 3.6b is backcrossed to the parent with round seeds, what proportion of the progeny will have wrinkled seeds? (Use a Punnett square.)
- 3/4
- 1/2
- 1/4
- 0

Answer 5

0

Question 6

If the probability of being blood type A is 1/8
and the probability of being blood type O is 1/2, what is the probability of being either blood type A or blood type O?
- 5/8
- 1/2
- 1/10
- 1/16

Answer 6

5/8

Question 7

How are the principles of segregation and independent assortment related, and how are they different?

Answer 7

Both the principle of segregation and the principle of independent assortment refer to the separation of alleles in anaphase I of meiosis. The principle of segregation says that these alleles separate, and the principle of independent assortment says that they separate independently of alleles at other loci.

Question 8

A chi-square test comparing observed and expected numbers of progeny is carried out, and the probability associated with the calculated chi-square value is 0.72. What does this probability represent?
- Probability that the correct results were obtained
- Probability of obtaining the observed numbers
- Probability that the difference between observed and expected numbers is significant
- Probability that the difference between observed and expected numbers could be due to chance

Answer 8

Probability that the difference between observed and expected numbers could be due to chance

Question 9

What process causes the genetic variation seen in offspring produced by sexual reproduction?

Answer 9

Meiosis

Question 10

How does the heterogametic sex differ from the homogametic sex?
- The heterogametic sex is male; the homogametic sex is female.
- Gametes of the heterogametic sex have different sex chromosomes; gametes of the homogametic sex all have the same sex chromosome.
- Gametes of the heterogametic sex all contain a Y chromosome; gametes of the homogametic sex all contain an X chromosome.

Answer 10

Gametes of the heterogametic sex have different sex chromosomes; gametes of the homogametic sex all have the same sex chromosome.

Question 11

How do chromosomal, genic, and environmental sex-determining systems differ?

Answer 11

In chromosomal sex determination, males and females have chromosomes that are distinguishable. In genic sex determination, sex is determined by genes, but the chromosomes of males and females are indistinguishable. In environmental sex determination, sex is determined fully or in part by environmental effects.

Question 12

What is the phenotype of a person who has XXXY sex chromosomes?
- Klinefelter syndrome
- Turner syndrome
- Poly-X female

Answer 12

Klinefelter syndrome

Question 13

What was the genotype of the few F1 red-eyed males obtained by Bridges when he crossed a white-eyed female with a red-eyed male?
- X+
- XwX+Y
- X+Y
- X+X+Y

Answer 13

X+Y

Question 14

Hemophilia (reduced blood clotting) is an X-linked recessive condition in humans. A woman with hemophilia mates with a man who exhibits typical blood clotting. What is the probability that their child will have hemophilia?

Answer 14

All of their male offspring will have hemophilia, and none of their female offspring will have hemophilia, so the overall probability of hemophilia in their offspring is
1/2.

Question 15

What unusual feature of the Y chromosome allows some recombination among the genes found on it?

Answer 15

Eight large palindromes allow crossing over within the Y chromosome.

Question 16

How many Barr bodies does a male with XXXYY chromosomes have in each of his cells?

Answer 16

Two Barr bodies.

Question 17

If an F1 eggplant (Pp) in Figure 5.2 is used in a testcross, what proportion of the progeny from this cross will be white (pp)?
- All the progeny
- 1/2
- 1/4
- 0

Answer 17

1/2

Question 18

How do complete dominance, incomplete dominance, and codominance differ?

Answer 18

With complete dominance, the heterozygote expresses the same phenotype as one of the homozygotes. With incomplete dominance, the heterozygote has a phenotype that is intermediate between those of the two homozygotes. With codominance, the heterozygote has a phenotype that simultaneously expresses the phenotypes of both homozygotes.

Question 19

How does incomplete dominance differ from incomplete penetrance?
- Incomplete dominance refers to alleles at the same locus; incomplete penetrance refers to alleles at different loci.
- Incomplete dominance ranges from 0% to 50%;
- incomplete penetrance ranges from 51% to 99%.
- In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, heterozygotes express phenotypes of both homozygotes.
- In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype.

Answer 19

In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype.

Question 20

A cross between two green corn plants yields 2/3
progeny that are green and 1/3 progeny that are yellow. What is the genotype of the green progeny?
- WW
- Ww
- ww
- W_ (WWandWw)

Answer 20

Ww

Question 21

How many genotypes are possible at a locus with five alleles?
- 30
- 27
- 15
- 5

Answer 21

15

Question 22

How does gene interaction differ from dominance?

Answer 22

Gene interaction is interaction between genes at different loci. Dominance is interaction between alleles at a single locus.

Question 23

A number of all-white cats are crossed, and they produce the following types of progeny: 12/16 all-white, 3/16 black, and 1/16 gray. What is the genotype of the black progeny?
- Aa
- Aa Bb
- A_ B_
- A_ bb

Answer 23

A_ bb

Question 24

Brindle (tiger-striped appearance) is a recessive trait in bulldogs and in Chihuahuas. What types of crosses would you carry out to determine whether the brindle genes in bulldogs and in Chihuahuas are at the same locus?

Answer 24

Cross a bulldog homozygous for brindle with a Chihuahua homozygous for brindle. If the two brindle genes are allelic, all the offspring will be brindle:bb×bb→ allbb(brindle). If, on the other hand, brindle in the two breeds is due to recessive genes at different loci, then none of the offspring will be brindle:a+a+bb×aa b+b+→a+a b+b.

Question 25

How do sex-influenced and sex-limited characteristics differ from sex-linked characteristics?

Answer 25

Both sex-influenced and sex-limited characteristics are encoded by autosomal genes whose expression is affected by the sex of the individual organism possessing the genes. Sex-linked characteristics are encoded by genes on the sex chromosomes.

Question 26

How might you determine whether a particular trait is due to cytoplasmic inheritance or to genetic maternal effect?

Answer 26

Cytoplasmically inherited traits are encoded by genes in the cytoplasm, which is usually inherited only from the female parent. Therefore, a trait due to cytoplasmic inheritance will always be passed through females. Traits due to genetic maternal effect are encoded by autosomal genes and can therefore be passed through males, although any individual organism’s trait is determined by the genotype of the maternal parent.

Question 27

What type of epigenetic mark is responsible for genomic imprinting?

Answer 27

Methylation of DNA.

Question 28

How can you determine whether a phenotype such as reduced eyes in fruit flies is due to a recessive mutation or is a phenocopy?

Answer 28

Polygeny refers to the influence of multiple genes on the expression of a single characteristic. Pleiotropy refers to the effect of a single gene on the expression of multiple characteristics.

Question 29

What is the difference between polygeny and pleiotropy?

Answer 29

Polygeny refers to the influence of multiple genes on the expression of a single characteristic. Pleiotropy refers to the effect of a single gene on the expression of multiple characteristics.