Question 1

It is predictable that half of the human babies born will be male and half will be female because

Accepted Answer

The answer of It is predictable that half of the...

Question 2

Use the following to answer questions:
Cleft chin is an X-linked dominant trait. Assume that a man with a cleft chin marries a woman with a round chin.
-What percent of their male progeny will show the cleft chin trait?

Accepted Answer

Since cleft chin is an X-linked dominant trait, and the man has a cleft chin, he has the dominant allele on his X chromosome. The woman with a round chin has two recessive alleles. All male progeny inherit their X chromosome from their mother, who has the recessive allele, so 0% of the male progeny will have a cleft chin.

Question 3

The blue sclera allele has 90 percent penetrance for producing blue sclera, 60 percent penetrance for fragile bones, and 40 percent penetrance for deafness. If these probabilities of penetrance are independent, _______ percent of individuals with the blue sclera allele will have deafness, blue sclera, and fragile bones.

Accepted Answer

To find the percentage of individuals with all three traits, multiply the penetrance probabilities: 0.90 (blue sclera) * 0.60 (fragile bones) * 0.40 (deafness) = 0.216 or 21.6%, which rounds to 22%.

Question 4

How many autosomes do humans have?

Accepted Answer

Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (XX for females and XY for males) for a total of 46 chromosomes. Autosomal chromosomes are non-sex chromosomes and occur in identical pairs in both males and females.

Question 5

A dominant allele K is necessary for normal hearing. A dominant allele M on a different locus results in deafness no matter which other alleles are present. If a kkMm individual is crossed with a Kkmm individual, _______ percent of the offspring will be deaf.

Accepted Answer

The answer of A dominant allele K is necessary for...

Question 6

In tomatoes, tall is dominant to short, and smooth fruits are dominant to hairy fruits. A plant homozygous for both dominant traits is crossed with a plant homozygous for both recessive traits. The F₁ progeny are tested and crossed with the following results: 78 tall, smooth fruits; 82 dwarf, hairy fruits; 22 tall, hairy fruits; and 18 dwarf, smooth fruits. These data indicate that the genes are

Accepted Answer

The phenotype ratios in the offspring indicate that the two genes are linked and show 20 percent recombination. This is because the observed double recombinant class (tall, hairy and dwarf, smooth) adds up to 40 individuals out of a total of 200 (20 percent). If the genes were unlinked or not showing recombination, the two double recombinants would not exist, and the other two phenotypic classes would have equal numbers. If the genes were linked and showing only 10 percent recombination, the frequency of the double recombinants would be too low compared to the observed data.

Question 7

White eyes is a recessive sex-linked trait in fruit flies. If a white-eyed female fruit fly is mated to a red-eyed male, their offspring should be

Accepted Answer

In sex-linked traits, males inherit their X chromosome from their mother. A white-eyed female (XwXw) crossed with a red-eyed male (X+Y) will produce all white-eyed males (XwY) and all red-eyed females (X+Xw).

Question 8

Despite the law of independent assortment, when two loci are on the same chromosome, the phenotypes of the progeny sometimes do not fit the predicted phenotypes due to

Accepted Answer

When two loci are on the same chromosome (i.e. they are physically linked), they do not assort independently. This means that the alleles at these loci tend to be inherited together more often than if they were on different chromosomes. This phenomenon is known as linkage, and it can result in offspring phenotypes that do not match the predicted ratios based on Mendelian genetics.

Question 9

A human male carrying an allele for a trait on the X chromosome is

Accepted Answer

Males only have one X chromosome, so they cannot be homozygous or heterozygous for traits on the X chromosome. Instead, they are hemizygous, meaning they only have one copy of the allele.

Question 10

The complete phenotype of an organism is dependent on

Accepted Answer

The complete phenotype of an organism is dependent on the genotype, which is the genetic makeup of the individual. However, the expression of those genes can be influenced by penetrance, which refers to the proportion of individuals with a specific genotype that actually exhibit the expected phenotype, and expressivity, which refers to the variation in phenotype among individuals with the same genotype. Additionally, some traits may be controlled by polygenes, or multiple genes that contribute to the phenotype, further complicating the relationship between genotype and phenotype. Therefore, all of the factors listed in choices A through D can influence the complete phenotype of an organism.

Question 11

In guppies, fan tail is dominant to flesh tail, and rainbow color is dominant to pink. F₁ female guppies are crossed with flesh-tailed, pink-colored males, and the following progeny are observed: 401 fan-tailed, pink-colored; 399 flesh-tailed, rainbow-colored; 98 flesh-tailed, pink-colored; and 102 fan-tailed, rainbow-colored guppies. Assuming that the F₁ female guppies have both dominant alleles on one chromosome, the map distance between these two genes is

Accepted Answer

The map distance between two genes is calculated as the percentage of recombinant offspring. In this case, the recombinant offspring are the flesh-tailed, pink-colored and fan-tailed, rainbow-colored guppies. The total number of offspring is 401 + 399 + 98 + 102 = 1000. The number of recombinant offspring is 98 + 102 = 200. Therefore, the map distance between the two genes is 200/1000 * 100 = 20 cM.

Question 12

Use the following to answer questions:
Cleft chin is an X-linked dominant trait. Assume that a man with a cleft chin marries a woman with a round chin.
-What percent of their female progeny will show the cleft chin trait?

Accepted Answer

Since cleft chin is an X-linked dominant trait, all daughters of a man with a cleft chin will inherit the dominant allele from their father and will show the cleft chin trait.

Question 13

Very few genes have been located on the Y chromosomes. Y-linked genes include a gene called testis-specific protein Y. A male with this gene will

Accepted Answer

Y-linked genes are only passed from father to son, as females do not have a Y chromosome. Therefore, a male with the testis-specific protein Y gene will only pass it to his sons.

Question 14

Sex in humans is determined by

Accepted Answer

Sex in humans is determined by the presence or absence of a gene called SRY found on the Y chromosome. If this gene is present, the individual will develop as male, while its absence will result in female development.

Question 15

An organism that produces either male gametes or female gametes, but not both, is called

Accepted Answer

A dioecious organism produces either male or female gametes, but not both. Monoecious organisms produce both male and female gametes. Heterozygous and homozygous refer to genetic types, not reproductive strategies. Parthenogenesis is a type of asexual reproduction.

Question 16

If Mendel's crosses between spherical-seeded tall plants and wrinkled-seeded short plants had produced many more than ¹/₁₆ wrinkled-seeded short plants in the F₂ generation, he might have concluded that

Accepted Answer

If Mendel had seen many more wrinkled-seed short plants in the F1 generation, it would have suggested that the spherical seed and tall traits are linked. This is because he would have expected a 9:3:3:1 ratio of the four possible combinations of traits (spherical-tall, spherical-short, wrinkled-tall, wrinkled-short), but instead would have seen mostly one of the combinations (wrinkled-short). This would indicate that the two traits (spherical seed and tall) are usually inherited together and are located on the same chromosome.

Question 17

Which of the following observations support the idea that the gene controlling maleness is located on the Y chromosome?

Accepted Answer

The presence of a Y chromosome is necessary for maleness. XO individuals are female because they lack a Y chromosome. XXY individuals are male because they have a Y chromosome, but they are sterile because they have an extra X chromosome. XXX individuals are female because they have three X chromosomes. Some men are XX but have a small piece of the Y chromosome attached to another chromosome. This is called a translocation. The presence of the Y chromosome, even a small piece of it, is necessary for maleness.

Question 18

When a dihybrid black, straight-winged fly is crossed to a double-recessive brown, curly-winged fly, the frequency at which black curly-winged and brown straight-winged flies are seen in the progeny is called the _______ frequency.

Accepted Answer

The frequency at which black curly-winged and brown straight-winged flies are seen in the progeny is a result of recombination of alleles during meiosis, thus the correct term is recombinant frequency.

Question 19

A linkage group corresponds to

Accepted Answer

A linkage group corresponds to a group of genes on the same chromosome that are physically linked together and tend to be inherited together.

Question 20

When reciprocal crosses produce identical results, the trait is

Accepted Answer

Reciprocal crosses involve switching the sexes of the parent organisms. If identical results are produced, it indicates that the trait is not sex-linked, meaning it is not associated with sex chromosomes. This does not necessarily mean that it is not inherited through autosomes.

Quiz 12: Inheritance, Genes, and Chromosomes