Question 1

The principle of independent assortment is not true for:
A) incomplete dominance.
B) mutations.
C) heterozygotes.
D) homozygotes.
E) linked genes.

Accepted Answer

The principle of independent assortment does not apply to linked genes because they are located close to each other on the same chromosome and tend to be inherited together, rather than assorting independently.

Question 2

The sex of most mammals, birds, and insects is determined by:
A) the temperature.
B) the external environment.
C) sex chromosomes.
D) chance.
E) the internal envronment.

Accepted Answer

The sex of most mammals, birds, and insects is determined by sex chromosomes, such as the XY system in mammals and the ZW system in birds.

Question 3

A brown-eyed couple already has a child with blue eyes.What is the probability that their next child will have blue eyes, assuming that the brown eye allele is dominant and the blue eye allele is recessive?
A) 0
B) 1/4
C) 1/2
D) 3/4
E) 1

Accepted Answer

The brown-eyed couple must both be carriers of the recessive blue eye allele in order for their first child to have blue eyes. Therefore, each parent must have the genotype Bb (B for brown eye allele and b for blue eye allele). When they have another child, there is a 25% chance that both parents will pass on the recessive blue eye allele to the child, resulting in the child having blue eyes. This is because the parent's gametes can combine in four different ways (BB, Bb, bB, bb), and only one of these ways (bb) results in blue eyes. Thus, the probability of their next child having blue eyes is 1/4 or 25%.

Question 4

A lizard with a striped tail is crossed with one having a spotted head, producing normal looking (no stripes or spots) lizard progeny.What progeny would be expected to be produced by mating these progeny with each other, if the genes conferring stripes and spots were on different chromosomes?
A) equal numbers of normal, striped, spotted and striped, and spotted
B) 3 striped : 1 spotted
C) 9 striped and spotted : 3 spotted : 3 striped : 1 normal
D) 9 striped : 3 spotted : 1 striped or spotted
E) 9 normal : 3 striped : 3 spotted : 1 striped and spotted

Accepted Answer

The answer of A lizard with a striped tail is...

Question 5

The sex of a human is determined by:
A) the number of chromosomes.
B) the number of autosomes.
C) the presence of only one X chromosome.
D) the number of sex chromosomes.
E) the presence of a Y chromosome.

Accepted Answer

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

Question 6

A brown-eyed couple heterozygous for eye color are planning on having two children.What is the probability that both children will have blue eyes, assuming brown eyes is dominant and blue eyes is recessive?
A) 0
B) 1/32
C) 1/16
D) 1/4
E) 1/2

Accepted Answer

First, we need to represent the genotypes of the parents. We'll use B and b to represent the alleles for brown and blue eyes, respectively. Since the parents are heterozygous for eye color, their genotypes are Bb.

We can use a Punnett square to determine the possible genotypes of their offspring:

|   | B  | b  |
|---|---|---|
| B | BB | Bb |
| b | Bb | bb |

From this, we can see that there is a 25% chance (1 out of 4) that each child will inherit the bb genotype and therefore have blue eyes (since blue eyes is recessive). To find the probability that both children will have blue eyes, we multiply the probabilities:

1/4 x 1/4 = 1/16

Therefore, the probability that both children will have blue eyes is 1/16 or choice C.

Question 7

Why is color-blindness more common in males than in females?
A) Because females would have to receive one copy of the recessive color blindness gene to actually express the trait.
B) Because a male only needs to receive the recessive gene from his mother to be color-blind.
C) Because color-blindness is an Y-linked trait.
D) Females are hemizygous
E) Males are never hemizygous

Accepted Answer

Color-blindness is an X-linked recessive trait, so males, having only one X chromosome, will express the trait if they inherit the recessive gene from their mother.

Question 8

If a couple is planning on having three children, what is the probability that only one will be male?
A) 0
B) 1/4
C) 3/8
D) 1/2
E) 3/4

Accepted Answer

The probability of having a male child is 1/2 and the probability of having a female child is 1/2. 
The probability of having only one male child and two female children can occur in three ways: 
1) male-female-female 
2) female-male-female 
3) female-female-male
The probability of each of these events is (1/2) * (1/2) * (1/2) = 1/8, and there are three such events. 
Therefore, the total probability of having only one male child is 3 * (1/8) = 3/8.

Question 9

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 the alien couple will have a child that is heterozygous for eye color?
A) 1
B) 1/2
C) 1/4
D) 3/4
E) 0

Accepted Answer

The homozygous Martian has two alleles for red eyes (RR), and the heterozygous Martian has one allele for red eyes and one for purple (Rr). The possible offspring genotypes are RR and Rr, with a 50% chance (1/2) of being heterozygous (Rr).

Question 10

A couple has already had 3 girls with cystic fibrosis, and were hoping to have a normal child for their fourth.What are the chances that the fourth child will be a normal male?
A) 0
B) 1/8
C) 1/4
D) 3/8
E) 1/2

Accepted Answer

Cystic fibrosis is an autosomal recessive disorder. The parents are both carriers, since they have had 3 affected children. The probability of having a normal male child is 1/4.

Question 11

Genes that tend to be inherited together are said to be:
A) associated.
B) related.
C) similar.
D) linked.
E) alleles.

Accepted Answer

Genes that are inherited together are said to be "linked" because they are located close to each other on the same chromosome, reducing the likelihood of being separated during recombination.

Question 12

An organism with the genotype of AaXx can produce gametes containing __________ if the two genes are unlinked.
A) either Aa or Xx
B) either AX, Ax, aX, ax
C) AaXx
D) AX or ax
E) A,a,X,x

Accepted Answer

If the two genes are unlinked, the organism can produce gametes containing either AX, Ax, aX, or ax.

Question 13

In a two-point test cross, 36 of the offspring were recombinant types.The remaining 64 offspring were parental types.How many map units separate the two loci?
A) 28
B) 36
C) 64
D) 78
E) 100

Accepted Answer

Since 36 offspring were recombinant, and 64 were parental, the total number of offspring is 100. This tells us that the two genes are located on different chromosomes or are far apart on the same chromosome. Thus, each recombinant offspring represents a crossover event between the two genes. 
Therefore, the percentage of recombinant offspring indicates the distance between the two genes in map units. To calculate this, we divide the number of recombinant offspring (36) by the total number of offspring (100) and multiply by 100 to get the percentage of recombinants:
36/100 x 100 = 36%
Therefore, the two loci are 36 map units apart. This corresponds to answer choice B.

Question 14

A __________ is best used to demonstrate the linkage of two genes.
A) monohybrid cross
B) dihybrid cross
C) monohybrid test cross
D) two-allele test cross
E) two-point test cross

Accepted Answer

A two-point test cross is specifically designed to analyze the linkage between two genes by crossing an individual heterozygous for both genes with an individual homozygous recessive for both genes, allowing for the observation of recombinant and parental genotypes.

Question 15

The offspring of two heterozygous gray-bodied, normal-winged flies should be 50% gray-bodied/normal wings (BbRr) and 50% black-bodied/vestigial wings (bbrr) because these alleles are linked.If a small number, say 15%, of the offspring are instead black-bodied with normal wings, this is most likely the result of:
A) crossing-over.
B) incomplete dominance.
C) codominance.
D) an error in meiosis.
E) mutation.

Accepted Answer

Crossing-over during meiosis can result in new combinations of alleles, leading to offspring with unexpected phenotypes, such as black-bodied with normal wings.

Question 16

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 are the chances that the alien couple will have a child with red eyes?
A) 1
B) 1/2
C) 1/4
D) 3/4
E) 0

Accepted Answer

The homozygous Martian has two alleles for red eyes (RR), and the heterozygous Martian has one allele for red eyes and one for purple (Rr). All offspring will inherit at least one R allele from the homozygous parent, resulting in a 100% chance of having red eyes.

Question 17

A lizard with striped tails is crossed with one having a spotted head, producing normal looking (no stripes or spots) progeny.What progeny would be expected to be produced by mating one of these lizards with another that had a striped tail and spotted head, if the genes conferring stripes and spots were close together on the same chromosome?
A) equal numbers of normal, striped, spotted and striped, and spotted
B) 3 striped : 1 spotted
C) mostly progeny that are striped or spotted
D) mostly progeny that are normal or striped and spotted
E) 9 normal : 3 striped : 3 spotted : 1 striped and spotted

Accepted Answer

The answer of A lizard with striped tails is crossed...

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?
A) 1/1
B) 1/2
C) 1/4
D) 3/4
E) 0

Accepted Answer

The answer of Two Martians fall in love and marry.One...

Question 19

The probability that two genes will be separated by crossing-over is related to:
A) the phenotype that they control.
B) how far the two genes are from the centromere.
C) the distance between the two genes on the chromosome.
D) whether the two genes are located on a sex chromosome.
E) how far the genes are from the kinetochore.

Accepted Answer

The probability of two genes separating by crossing-over is directly proportional to the distance between the two genes on the chromosome. The farther apart two genes are, the more likely they are to be separated by crossing-over during meiosis. This is because crossing-over occurs more frequently in regions of the chromosome where there is more physical space for the DNA strands to break and reattach. Therefore, choice (C) is the best answer. The other choices (A, B, D, and E) are not directly related to the probability of crossing-over.

Question 20

In genetics, map units express the distance between:
A) chromosomes during metaphase.
B) two loci on a chromosome.
C) alleles.
D) polar bodies.
E) homologous chromosomes.

Accepted Answer

Map units, also known as centimorgans, express the distance between two loci (positions) on a chromosome. This distance is proportional to the frequency of genetic recombination between the two loci. One map unit is equivalent to a 1% recombination frequency, meaning that two loci that are 1 map unit apart will have a 1% chance of undergoing a crossover event during meiosis.

Quiz 11: The Basic Principles of Heredity

The principle of independent assortment is not true for:

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

A brown-eyed couple already has a child with blue eyes.What is the probability that their next child will have blue eyes, assuming that the brown eye allele is dominant and the blue eye allele is recessive?

A lizard with a striped tail is crossed with one having a spotted head, producing normal looking (no stripes or spots) lizard progeny.What progeny would be expected to be produced by mating these progeny with each other, if the genes conferring stripes and spots were on different chromosomes?

The sex of a human is determined by:

A brown-eyed couple heterozygous for eye color are planning on having two children.What is the probability that both children will have blue eyes, assuming brown eyes is dominant and blue eyes is recessive?

Why is color-blindness more common in males than in females?

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

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 the alien couple will have a child that is heterozygous for eye color?

A couple has already had 3 girls with cystic fibrosis, and were hoping to have a normal child for their fourth.What are the chances that the fourth child will be a normal male?

Genes that tend to be inherited together are said to be:

An organism with the genotype of AaXx can produce gametes containing __________ if the two genes are unlinked.

In a two-point test cross, 36 of the offspring were recombinant types.The remaining 64 offspring were parental types.How many map units separate the two loci?

A __________ is best used to demonstrate the linkage of two genes.

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 are the chances that the alien couple will have a child with red eyes?

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?

The probability that two genes will be separated by crossing-over is related to:

In genetics, map units express the distance between: