Question

biology exam 5

1. the phenotype is caused by a ...... allele, because the

a. recessive; male is unaffected by the phenotype.
b. dominant; male is heterozygous for the phenotype.
c. dominant; female is heterozygous for the phenotype.
d. recessive; female is unaffected by the phenotype.

1. phenotype is influenced by many factors, including the chromosome upon which a gene

is located, ranges of dominance, and...
a. karyotype
b. pedigree
c. environment
d. phenotype

1. the wide range of eye color indicates that eye color is...

a. sex - linked
b. recessive
c. polygenic
d. epistatic

1. suppose a mouse is homozygous for alleles that produce black fur and homozygous for

alleles of an epistatic gene that produces albinism. what color fur will the mouse have?
a. white
b. black
c. gray
d. spotted

1. which pair of genes in the figure below would be most likely to have a genetic linkage?

a. a and c
b. c and d
c. e and a
d. b and d

1. two genes on a linkage map are 9 map units apart. this means that in 9 percent of the

offspring, the phenotypes from those genes will...
a. appear codominant
b. disappear
c. be cloned
d. not appear together

1. sex - linked disorders appear more often in males because the y chromosome...

a. does not carry sex - linked genes.
b. codes for all genotypic mutations.
c. has genes only for sex determination.
d. is not really a chromosome at all.

Explanation:

1. Recessive alleles often show a pattern where an individual can be heterozygous (carrying one recessive and one dominant allele) and not show the phenotype. If a male is heterozygous and unaffected, and the allele is recessive, it fits the description.
2. Phenotype is influenced by the environment, the chromosome location of genes, and ranges of dominance.
3. A wide range of eye - color (a continuous variation) is often due to polygenic inheritance (multiple genes contributing).
4. Epistasis occurs when one gene masks the expression of another. If there is an epistatic gene for albinism (which would result in no pigment production), even if the mouse has alleles for black fur, it will be white.
5. Genes that are closer on a chromosome (like C and D in the figure) are more likely to have genetic linkage (inherited together).
6. If two genes are 9 map units apart, there is a 9% chance of recombination. So, in 9% of the offspring, the phenotypes from those genes will not appear together (due to recombination).
7. The Y chromosome does not carry many sex - linked genes (compared to the X). So, males (XY) are more likely to show sex - linked disorders (which are often on the X) because they have only one X and the Y does not carry a counter - acting allele.

Answer:

1. a
2. c
3. c
4. a
5. b
6. d
7. a