Biology Ch. 9
Whether an allele is dominant or recessive depends on..
whether it or another allele determines the phenotype when both are present.
Words synonymous with homozygous..
True-breeding, purebred
What is a genotype?
the genetic makeup with a genome.
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?
1/4 will be boys suffering from hemophilia, and 1/4 will be female carriers.
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?
9/16
Why do more men than women have colorblindness?
A male only needs one recessive colorblindness allele to show the trait, a female must inherit the allele from both parents, which is less likely.
If a version of a gene is dominant, then..
A single copy of it will produce its trait.
A man with type B blood and a woman who has type A blood could have children of which of the following phenotypes?
A, B, AB, or O
What is a phenotype?
An observable trait.
Homozygous dominant
BB
Heterozygous genotype
Bb
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?
Black short haired parent rabbit is BBSS. Genotype of the brown long haired parent rabbit is bbss. The F1 rabbits will all be black and short-haired, BbSs. The F2 rabbits will be black short haired, black long haired, brown short haired, and brown long haired, in a proportion of 9:3:3:1.
Both Tim and Jan have a widow's peak, but Mike has a straight hairline. What are their genotypes?
Both Tim and Jan are heterozygous, and Mike is homozygous recessive. The probability of the next child having freckles is 3/4. The probability of the next child having a straight hairline is 1/4. The probability of the next child having freckles and a straight hairline is 3/4 x 1/4= 3/16
Provide an example of a phenotype
Brown hair
How did her professor know her father was colorblind too? Why did he not say the same thing to the colorblind males in the class?
Her father has only one X chromosome which he passes on to all his daughters. A male only needs to inherit the colorblindness allele from a carrier mother.
Words synonymous with heterozygous..
Hybrid, carrier
A fruit fly with a gray body and red eyes is mated with a fly having a black body and purple eyes. What ratio of offspring would you expect if they body-color and eye color genes are on different chromosomes? 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?
If the genes are not linked, the proportions among the offspring will be 25% gray red, 25% gray purple, 25% black red, and 25% black purple. The actual percentages show that the genes are linked. The recombination frequency is 6%.
Two genes located near each other on the same chromosome will..
Often be inherited as a set.
Which extension of Mendel's model accounts for the hereditary variation in human skin color?
Skin color appears to be a quantitative trait resulting from polygenic inheritance, like human height.
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 for different combinations of alleles. Which are parent gametes, which are recombinant gametes, and how are the recombinants produced.
The parent gametes are WS and ws. Recombinant gametes are Ws and wS, produced by crossing over.
Homozygous, recessive
bb
Edward was found to be heterozygous for sickle-cell trait. The alleles represented by the letters S and s are..
on homologous chromosomes.
