Question 1

What are the predicted phenotypes of the female children from the union of a woman who is heterozygous for hemophilia and a man who has normal blood clotting characteristics? (Use the Punnett square to verify your answer.)

Accepted Answer

Hemophilia is a sex-linked recessive trait. When a heterozygous woman (X^HX^h) mates with a man with normal blood clotting (X^HY), their female offspring can either be carriers (X^HX^h) or not carriers (X^HX^H). This results in a 1:1 ratio of homozygous healthy to carrier female children.

Question 2

The sex of most mammals, birds, and insects is determined by

Accepted Answer

Sex chromosomes determine the sex of most mammals, birds, and insects. In these organisms, specific combinations of sex chromosomes (such as XX for females and XY for males in many species) are responsible for the development of sexual characteristics.

Question 3

The cells of female mammals, including humans, contain two __________.

Accepted Answer

The answer of The cells of female mammals, including humans,...

Question 4

Blood types A, B, AB, and O are controlled by how many alleles representing a single locus?

Accepted Answer

Blood types A, B, AB, and O are controlled by three alleles at a single locus: IA, IB, and i.

Question 5

What is the probability that two lizards heterozygous for stripes on their tails (Ss) will produce homozygous offspring with no stripes (ss)?

Accepted Answer

The probability is calculated using a Punnett square for two heterozygous parents (Ss x Ss). The possible genotypes for the offspring are SS, Ss, Ss, and ss. Only one of these four possibilities is ss (homozygous with no stripes), so the probability is 1/4.

Question 6

If a couple is planning on having two children, what is the probability that both will be male?

Accepted Answer

The probability of having a male child is 1/2. For two independent events (each birth), the probabilities multiply: 1/2 * 1/2 = 1/4.

Question 7

The sex of a human is determined by the

Accepted Answer

The presence of a Y chromosome determines male sex in humans, as it carries the SRY gene responsible for male development.

Question 8

A couple who does not have cystic fibrosis but are both heterozygous has already had three girls with cystic fibrosis, and are hoping to have a healthy child for their fourth. What are the chances that the fourth child will be a healthy male?

Accepted Answer

The probability of having a healthy child for two heterozygous parents is 3/4, since one out of four children is expected to have cystic fibrosis (25%) and three out of four are expected to be healthy (75%). The probability of having a male child is 1/2, assuming equal probability of having a male or female child. Therefore, the probability of having a healthy male child is the product of these two probabilities: 3/4 (chance of being healthy) * 1/2 (chance of being male) = 3/8. Previous children do not affect the probability of the traits of future children due to independent assortment.

Question 9

A heterozygous fruit fly with normal wings and a gray body ( VvBb ) is crossed with homozygous flies with vestigial wings and black bodies ( vvbb ). Out of 800 total F₁ progeny, 296 are normal gray, 328 are vestigial black, 99 are normal black, and 77 are vestigial gray. What is the best explanation for this result?

Accepted Answer

The distribution of phenotypes suggests that the genes for wing length and body color are linked (on the same chromosome), leading to non-Mendelian ratios in the offspring. This linkage disrupts the expected 1:1:1:1 ratio for independent assortment, resulting in an uneven distribution of phenotypes.

Question 10

What are the possible genotypes of a female child from the union of a woman who is heterozygous for hemophilia and a man who has normal blood clotting characteristics?

Accepted Answer

Hemophilia is a sex-linked recessive trait. A heterozygous woman (X^HX^h) and a normal man (X^HY) can produce a female child with either the genotype X^HX^H (normal) or X^HX^h (carrier).

Question 11

A Barr body in a mammalian female cell represents a(n)

Accepted Answer

A Barr body represents an inactivated X chromosome in the nuclei of female cells, a process that occurs to dosage compensate for the double set of X chromosomes females have compared to males.

Question 12

What are the predicted phenotypes of the male children from the union of a woman who is heterozygous for hemophilia and a man who has normal blood clotting characteristics? (Use the Punnett square to verify your answer.)

Accepted Answer

Hemophilia is a sex-linked recessive trait. The mother, being heterozygous, carries one allele for hemophilia (X^h) and one normal allele (X^H). The father, with normal blood clotting, has only the normal allele on his X chromosome (X^H) and a Y chromosome. When they have male children, the sons receive their X chromosome from their mother and their Y chromosome from their father. Therefore, there is a 50% chance (1:1 ratio) that a male child will inherit the X^h chromosome from the mother and have hemophilia, and a 50% chance he will inherit the X^H chromosome and be healthy.

Question 13

Which of the following refers to the expression of an intermediate phenotype in heterozygous individuals?

Accepted Answer

Incomplete dominance refers to a genetic situation in which one allele does not completely dominate another allele, resulting in a new phenotype that is a blend of the two.

Question 14

Color blindness is more common in males than in females because

Accepted Answer

Color blindness is more common in males because it is a sex-linked trait, specifically linked to the X chromosome. Males have only one X chromosome (XY), so inheriting one copy of the recessive allele from their mother (on the X chromosome) is enough to express the trait. Females (XX) would need to inherit two copies of the allele, one from each parent, to express the trait.

Question 15

In genetics, map units express the distance between

Accepted Answer

Map units, or centimorgans, are used to express the distance between two loci on a chromosome, reflecting the frequency of recombination between them.

Question 16

Which describes the interaction between genes such that the presence of certain alleles in one locus affects the expression of certain alleles in the other locus?

Accepted Answer

Epistasis occurs when the expression of alleles at one gene locus is dependent on the presence of alleles at another locus, effectively masking or modifying the phenotypic expression of the alleles at the second locus.

Question 17

All calico cats are female because

Accepted Answer

The calico phenotype in cats is due to the random inactivation of one of the two X chromosomes in females, leading to the expression of different color genes on the active X chromosomes in different cells. This phenomenon does not occur in males, as they have only one X chromosome.

Question 18

Two Martians fall in love and marry. One Martian is homozygous for red eyes and the other is heterozygous. The recessive eye color is purple. What is the probability that they will have a child with purple eyes (assuming Martians have similar genetics to humans)?

Accepted Answer

Since one parent is homozygous for red eyes (RR) and the other is heterozygous (Rr), all their children will have at least one dominant allele for red eyes (R), making it impossible for them to have purple eyes, which would require two recessive alleles (rr).

Question 19

The ability of a single gene to have multiple effects is known as _____.

Accepted Answer

Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. This is a common phenomenon in genetics where a single gene can affect multiple traits in an organism.

Question 20

If a couple is planning on having three children, what is the probability that only one will be male?

Accepted Answer

The probability of having a male (M) or female (F) child is 1/2 for each child. The scenarios where only one child is male are: MFF, FMF, and FFM. Each of these scenarios has a probability of (1/2)^3 = 1/8. Since there are three such scenarios, the total probability is 3 * 1/8 = 3/8.

Quiz 11: The Basic Principles of Heredity