Homework 10 - KEY
BIO 2
1.
Mark has a recessive mutation (b) in a gene required for normal red-green color vision on his
X chromosome. He is also a carrier (heterozygote) for cystic fibrosis, a disease caused by a
recessive mutation (c) in a gene located on chromosome 7. He inherited both mutations from
his mother.
Below is a drawing of Mark’s sex chromosomes and copies of chromosome 7 as they would
appear on the metaphase plate in mitosis. Note how the chromosomes and alleles are labeled.
a.
Using the same system of drawing and labeling the chromosomes as used above, draw Mark’s
sex chromosomes and copies of chromosome 7 as they would appear on the metaphase plate
during metaphase of meiosis I. Underline the recessive alleles to clearly distinguish them
from the dominant alleles.
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b.
Draw Mark’s sex chromosomes and copies of chromosome 7 as they would appear on the
metaphase plate during metaphase of meiosis I. Label the chromosomes and alleles very
clearly.
2.
Hyenas have a diploid chromosome number of 40. Calculate how many different types of eggs
can be produced by a female hyena due to the independent assortment of her paternal and
maternal chromosomes during meiosis. Show your calculation.
There are two different ways that each homolog pair can line up during meiosis and
there are 20 different homolog pairs.
220 = 1,048,576
Would this number be different for male hyenas? Explain.
No. Both female and male hyenas carry exactly 20 different homolog pairs. In the
female, the two X chromosomes are homologs for the sex chromosomes. They are
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not identical. In the male, the X and Y chromosomes are homologs for the sex
chromosomes and are also not identical.
3.
MUST BE HAND-DRAWN
A species of haploid algae is growing on a glacial moraine in Southern Alaska. Two different
strains of the algae are found on the moraine:
Strain 1:
Black hyphae (B), black asexual spores (S), fast-growing (F)
Strain 2:
White hyphae (b), white asexual spores (s), slow-growing (f)
Strain 1 is not thriving because its black hyphae and black spores can easily be seen by
predators against the gray background of the moraine. However, it has survived because it is
able to partially compensate for the high predation rate by growing very quickly. Strain 2 isn’t
thriving either. While it has the advantage of being nearly invisible to predators, it grows very
slowly.
Although the two stains of algae have historically been separated by a large lake, the lake has
recently frozen over so that they are now in contact with one another.
Complete the diagram on the next page, showing how fertilization of a haploid cell from one
strain by a haploid cell of the other can lead to a zygote, which can then undergo meiosis to
produce “daughter” algae that thrive on the moraine. Assume that the haploid chromosome
number of the algae is 3 and that the genes controlling the three traits (hyphae color, asexual
spore color, and growth rate) are located on different chromosomes.
In your drawing, show the chromosomes and the alleles of each gene through the process of
fertilization and meiosis. Since the genes are located on different chromosomes, the only
phases of meiosis you need to show are metaphase I and II. Distinguish between the
chromosomes as demonstrated in the drawing of the two haploid cells from each strain (top of
drawing).
4.
List and briefly describe the three different ways that sexual reproduction creates offspring
that are genetically unique.
a.
Independent assortment. The paternal and maternal homolog pairs line up
independently from one another on the metaphase plate in meiosis I. Some gametes
get more paternal homologs while some get more maternal homologs.
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b.
Crossing over. Paternal and maternal homologs line up and exchange parts during
prophase of meiosis I. This mixes and matches existing combinations of alleles in the
maternal and paternal contributions.
c.
Fertilization. Fertilization brings together unique gametes to create a diploid
organism with additional genetic diversity.
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