Ch. 4 Concept Check & Comprehension Questions

Question 1

Which of the following statements is true?
A. Not all inheritance patterns follow a strict dominant/recessive relationship.
B. Geneticists want to understand both inheritance patterns and the underlying molecular mechanisms that cause them to happen.
C. Different inheritance patterns are explained by a variety of different molecular mechanisms.
D. All of the above are true.

Answer 1

D. All of the above are true.

Question 2

Which of the following is not an example of a wild-type allele?
A. Yellow-flowered elderflower orchid
B. Red-flowered elderflower orchid
C. A gray elephant
D. An albino (white) elephant

Answer 2

D. An albino (white) elephant

Question 3

Dominant alleles may result from mutations that cause..

Answer 3

• the overexpression of a gene or its protein product
• a protein to inhibit the function of a normal protein
• a protein to be inactive and 50% of the normal protein is insufficient for abnormal phenotype

Question 4

Polydactyly is a condition in which a person has extra fingers and/or toes. It is caused by a dominant allele. If a person carries this allele but does not have any extra fingers or toes, this is an example of..

Answer 4

Incomplete penetrance

Question 5

The outcome of an individuals traits is controlled by..

Answer 5

Genes and the environment

Question 6

A pink-flowered four-o’clock is crossed to a red-flowered plant. What is the expected outcome for the offspring?

Answer 6

1 red : 1 pink

Question 7

A person which type AB blood has a child with a person with type O blood. What are the possible blood types of the child?

Answer 7

A and B

Question 8

A cross is made between a white-eyed female fruit fly and a red-eyed male. What would be the reciprocal cross?

Answer 8

Female is X^W+X^W+ and the male is X^WY

Question 9

Hemophilia is a blood clotting disorder in humans that follows an X-linked recessive pattern of inheritance. A man with hemophilia and a woman without hemophilia have a daughter with hemophilia. If you let H represent the normal allele and h the hemophilia allele, what are the genotypes of the parents?

Answer 9

Mother is X^HX^h and father is X^hY

Question 10

A female cow with scurs and a male bull with no scurs have an offspring. This offspring could be..

Answer 10

A female with no scurs or a male with scurs

Question 11

The Manx phenotype in cats is caused by a dominant allele that is lethal in the homozygous state. A Manx cat is crossed to a normal cat. What is the expected outcome for the surviving offspring?

Answer 11

1 normal offspring : 1 Manx offspring

Question 12

Which of the following is a possible explanation for pleiotrophy?

Answer 12

All of them

• the expression of a single gene can affect cell function in more than one way
• a gene may be expressed in different cell types in a multicellular organism
• a gene may be expressed at different stages of development

Question 13

Two different strains of sweet peas are true-breeding and have white flowers. When these strains are crossed together, the F1 offspring all have purple flowers. This phenomenon is called ..

Answer 13

Complementation

Question 14

If the F1 offspring from question 1 are allowed to self-fertilize, what is the expected outcome for the F2 offspring?

Answer 14

9 purple to 7 white

Question 15

Both yellow and red flowers are common in natural populations of the elderflower orchid, and both are considered wild-type.

Why are both of these colors considered to be wild type?

Answer 15

Because both of them are prevalent in natural populations.

Question 16

A comparison of protein levels among homozygous (PP or pp) and heterozygous (Pp) genotypes.

Does a PP individual produce more of the protein encoded by the P gene than is necessary for the purple color?

Answer 16

Yes. The PP homozygote probably makes twice as much of the protein that is needed for purple pigment formation.

Question 17

Which individual(s) in this pedigree exhibit(s) incomplete penetrance?

Answer 17

III-2

This individual is heterozygous but does not exhibit polydactyly.

Question 18

What are the two main factors that determine an organism’s traits?

Answer 18

Genes and the environment determine an organism’s traits

Question 19

At the molecular level, what is the explanation for why the flowers are pink instead of red?

Answer 19

50% of the functional enzyme is not enough to give a red color

Question 20

At which level is incomplete dominance more likely to be observed-at the molecular/cellular level or at the organism level?

Answer 20

It is often easier to observe incomplete dominance at the molecular/cellular level.

Question 21

Inheritance of sickle cell disease

Why does the heterozygote have an advantage?

Answer 21

In this case, the heterozygote is resistant to malaria

Question 22

Which of these three scenarios explains overdominance with regard to the sickle cell allele?
A. Disease resistance
B. Homodimer formation
C. Variation in functional activity

Answer 22

A.

Question 23

Which allele is an example of a loss-of-function allele?

Answer 23

The i allele

Question 24

What features of this pedigree indicate that the allele for Duchenne muscular dystrophy is X-linked?

Answer 24

Only males are affected with the disorder. Also, carrier females often have affected brothers.

Question 25

Explain why the reciprocal cross yields a different result from the first cross.

Answer 25

Because females carry two copies of an X-linked gene, whereas males have only one.

Question 26

Why are the homologous regions of the X and Y chromosome important during meiosis?

Answer 26

For chromosome synapsis (pairing)

Question 27

What is the phenotype of a female cow that is heterozygous?

Answer 27

Would not have scurs

Question 28

What is the molecular explanation for sex-limited inheritance?

Answer 28

Certain traits are expressed only in males or females, possibly due to differences in the levels of sex hormones or other factors that differ between the sexes.

Question 29

Manx cat, which carries a lethal allele

Why do you think the heterozygote survives with developmental abnormalities, whereas the homozygote dies?

Answer 29

The heterozygote has one normal copy of the gene, which allows for development to proceed in a way that is not too far from normal. Having two mutant copies of the gene probably messes up development to a degree that is incompatible with survival.

Question 30

Epistasis-

Answer 30

The alleles of one gene mask the phenotypic effects of the alleles of a different gene.

Question 31

Complementation-

Answer 31

Occurs when two strains exhibiting the same recessive trait produce offspring that show the dominant trait. This usually means the alleles for the recessive trait are in two different genes.

Question 32

Explain why a single gene knockout does not have an effect on the phenotype.

Answer 32

In some cases, a single gene knockout does not have an effect due to gene redundancy. Other explanations are also possible.

Question 33

At the molecular level, explain why the ttvv homozygote has an ovate capsule phenotype.

Answer 33

The two genes are redundant. Having one normal copy of either gene produces a triangular capsule. If both genes are inactive, an ovary capsule is produced.