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Problem 1
Complete this concept map to help you review some key concepts of genetics.
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a.
b.
c.
d.
e.
f.
Problem 2
Whether an allele is dominant or recessive depends on
a. How common the allele is, relative to other alleles
b. Whether it is inherited from the mother or the father
c. Whether it or another allele determines the phenotype when both are present
d. Whether or not it is linked to other genes
Problem 3
Edward was found to be heterozygous (Ss) for sickle-cell trait. The alleles represented by the letters S and s are
a. Linked
b. On homologous chromosomes
c. Both present in each of Edward's sperm cells
d. On the same chromosome but far apart
Problem 4
Two fruit flies with eyes of the usual red color are crossed, and their offspring are as follows: 77 red-eyed males, 71 ruby-eyed males, 152 red-eyed females. The allele for ruby eyes is
a. Autosomal (carried on an autosome) and dominant
b. Autosomal and recessive
c. Sex-linked and dominant
d. Sex-linked and recessive
Problem 5
A man with type B blood and a woman who has type A blood could have children of which of the following phenotypes?
a. A or B only
b. AB only
c. AB or O
d. A, B, AB, or O
- Tim and Jan both have freckles but their son Mike does not. Show with a Punnett square how this is possible. If Tim and Jan have two more children, what is the probability that both will have freckles?
Problem 6
Problem 7
Both Tim and Jan have a widow's peak (see Module 9.8), but Mike has a straight hairline.
What are their genotypes?
What is the probability that Tim and Jan's next child will have freckles and a straight hairline?
- In rabbits, black hair depends on a dominant allele, B, and brown hair on a recessive allele, b. Short hair is due to a dominant allele, S, and long hair to a recessive allele, s. If a true-breeding black short-haired male is mated with a brown long-haired female, describe their offspring. What will be the genotypes of the offspring? If two of these F1 rabbits are mated, what phenotypes would you expect among their offspring? In what proportions?
Problem 8
Problem 9
A fruit fly with a gray body and red eyes (genotype BbPp) is mated with a fly having a black body and purple eyes (genotype bbpp).
What ratio of offspring would you expect if the body-color and eye-color genes are on different chromosomes (unlinked)?
When this mating is actually carried out, most of the offspring look like the parents, but 3% have a gray body and purple eyes, and 3% have a black body and red eyes.
Are these genes linked or unlinked?
What is the recombination frequency?
Problem 10
A series of matings shows that the recombination frequency between the black-body gene and the gene for dumpy (shortened) wings is 36%. The recombination frequency between purple eyes and dumpy wings is 41%. What is the sequence of these three genes on the chromosome?
Problem 11
A couple are both phenotypically normal, but their son suffers from hemophilia, a sex-linked recessive disorder.
What fraction of their children are likely to suffer from hemophilia?
What fraction are likely to be carriers?
- Why do more men than women have colorblindness?
Problem 12
Problem 13
In fruit flies, the genes for wing shape and body stripes are linked. In a fly whose genotype is WwSs, W is linked to S, and w is linked to s. Show how this fly can produce gametes containing four different combinations of alleles.
Which are parental-type gametes?
Which are recombinant gametes? How are the recombinants produced?
- Skin color in humans is at least partially hereditary; dark-skinned parents tend to have dark-skinned children. But humans come in a range of skin tones. Which extension of Mendel's model accounts for the hereditary variation in human skin color?
Problem 14
- Heather was surprised to discover she suffered from red-green colorblindness. She told her biology professor, who said, 'Your father is colorblind, too, right?' How did her professor know this? Why did her professor not say the same thing to the colorblind males in the class?
Problem 15
- In 1981, a stray black cat with unusual rounded, curled-back ears was adopted by a family in Lakewood, California. Suppose you owned the first curl cat and wanted to breed it to develop a true-breeding variety. Describe tests that would determine whether the curl gene is dominant or recessive and whether it is autosomal or sex-linked. Explain why you think your tests would be conclusive. Describe a test to determine that a cat is true-breeding.
Problem 16
Problem 17
The breakthrough that led Bateson and Punnett to recognize the existence of linked genes was the appearance of unexpected results after they crossed double heterozygous pea plants (PpLl) with each other. Imagine that you have a group of Labrador retrievers that are all heterozygous for both coat color and blindness (BbNn). If you used this group of dogs to produce 160 puppies, how many puppies of each phenotype do you expect to get if the genes are not linked? How would the results differ if the genes are in fact linked?