Topic 4: Mendelian Genetics

A couple has six children- all daughters. If they have a seventh child, what is the probability that the seventh child will be a daughter?

• 6/7

• 1/7

• 1/36

• 1/2

If genes R and S are on two different chromosomes and the probability of allele R segregating into a gamete is 1/4, while the probability of allele S segregating into a gamete is 1/2, what is the probability that both will segregate into the same gamete?

• 1/4 x 1/2

• 1/4 $\div$ 1/2

• 1/4 + 1/2

• 1/4 + 1/4

In llamas, coat color is controlled by a gene that exists in two allelic forms. If a homozygous yellow llama is crossed with a homozygous brown llama, the offspring have gray coats. If two of the gray-coated offspring were crossed, what percentage of their off-spring would have brown coats?

• 0%

• 25%

• 50%

• 75%

Which of the following descriptions does not apply to meiosis?

• During the first division, the sister chromatids travel to opposite end of the cell.

• The chromosome number of the daughter cells is half that of the parent cell.

• The homologous chromosomes synapse and form tetrads before the first division.

• The cytoplasm of the cell and all its organelles are divided approximately in half.

In rabbits, the gene for short hair (S) is dominant, and the gene for long hair (s) is recessive. The gene for green eyes (G) is dominant and the gene for blue eyes (g) is recessive. A cross between two rabbits produces a litter of six short-haired rabbits with green eyes and two short-haired rabbits with blue eyes. What is the most likely genotype of the parent rabbits in this cross?

• ssgg X ssgg

• SSGG X SSGG

• SsGg X SsGg

• SsGg X SSGg

In humans, hemophilia is an X-linked recessive trait. If a man and a woman have a son who has hemophilia, which of the following is definitely true?

• The mother carries an allele for hemophilia

• The father carries an allele for hemophilia

• The boy's paternal grandfather has hemophilia

• Both parents carry an allele for hemophilia.

If a woman has type A blood, and her child has type O blood, the father must have which of the following blood type?

• A, B or O

• AB or A

• AB or B

• O only

Which of the following is true for both meiosis II and mitosis?

• Sister chromatids separate

• Homologous chromosomes separate

• DNA replication precedes the division

• Haploid cells are produced

X-linked conditions are more common in men than in women because

• the genes associated with the X-linked conditions are linked to the X chromosome, which determines maleness.

• men need to inherit only one copy of the recessive allele for the condition to be fully expressed.

• women simply do not develop the disease regardless of their genetic composition.

• the sex chromosomes are more active in men than in women.

In regard to the baby's colorblindness, a sex-linked recessive trait, you explain that

• colorblindness often appears randomly, even if neither parent is colorblind.

• the baby's father must have a recessive allele for colorblindness

• because colorblindness is sex-linked, a son can inherit colorblindness if his mother has the recessive colorblindness allele.

• the eggs must have been accidentally switched because males inherit sex-linked traits only from their fathers.