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Biology 210 Assignment 1
1. Find an article or website about a genetic disease or trait in humans (include the link). Is the
trait dominant or recessive (or something else)? Provide some measure of how common or rare
it is in general (or in a specific population). [2 marks]
b) Using Mendel’s first law, explain the pattern of inheritance you would expect to see for the
trait above. [2 marks]
c) Suppose you have a family with one affected parent. Draw out a hypothetical pedigree for
your selected disease/trait, including (and labelling): 3 generations, males and females in each
generation, those with the trait and those that are unaffected carriers. [4 marks]
2. Suppose the following cross in some sexually reproducing organism produces 200 progeny:
AABbCc × AaBbcc. Assume all the genes are unlinked and that the uppercase letters
represent completely dominant alleles. [4 marks]
a. How many offspring are expected to have the genotype Aabbcc?
b. How many offspring are expected to have the genotype AaBbCC?
c. How many offspring are expected to express the dominant phenotype for each gene?
d. How many offspring are expected to express the dominant phenotype for gene A if it were
to have a penetrance of 80%?
3. Name and describe checkpoints that occur prior to S-phase and before G2? Why is it so
important that the cell not pass either of these checkpoints until it is ready (specifically, what
would be possible outcomes for daughter cells)? [4 marks]
4. In the Meiosis figure below, a cell contains two pairs of homologous chromosomes. [6 marks]
(a) Color the indicated gene on the first chromosome. In following steps, colour all
corresponding position(s) of that allele (follow it through the process). Assume no crossing over
takes place.
(b) Fill in the “(b)” labels on the figure from the following choices (not all apply):
Fission, Meiosis I, Meiosis II, Mitosis, centromeres, sister chromatids, homologous pair, barr
body
(c) Indicate the ploidy (eg. 2n) of the cells at each step “(c)”.
7. In diploid organisms, what are the two processes that produce genetic variation in gametes?
Explain how each results in a “shuffling of the deck” when it comes to which genes are
inherited. [4 marks]
8. You catch 2 snakes from a meadow. One’s scales are a striped pattern and the other is
spotted. Eventually one snake lays eggs and when hatched you find all striped baby snakes. You
release them, keeping 2 baby snakes. When they produce baby snakes, you observe 8 striped
and 2 spotted.
(a) Suggest a possible model to describe the inheritance of scale patterns. Define genotypes
and phenotypes for the Parental, F1, and F2 snakes. Verify your model with a chi square test.
SHOW ALL YOUR WORK. [6 marks]
(b) Suppose instead that the F1 generation all had mottled scales (neither striped nor spotted)
and their offspring (F2) were striped, mottled, and spotted. What type of dominance would this
be and what ratio of offspring would you expect in the F2 generation? [2 marks]
9. Hemophilia in humans is X-linked recessive. A non-bleeder woman whose father has
hemophilia is having a child with a man who does not exhibit hemophilia.
(a) Use a Punnett square to show what proportions of their possible sons and daughters are
expected to exhibit hemophilia.
(b) The father-to-be is colour-blind, which is also X-linked recessive. Add this annotation to your
Punnett square to show the additional possible genotypes and phenotypes. Could any of the
children be colour blind?
(c) The couple finds out they are having twins. If they are dizygotic twins (fraternal), what is the
probability they with both be hemophiliacs? What is the probability if they are monozygotic
(identical) twins? Explain.
10. Suppose that a compound attractive to pollinators is produced by a plant in a pathway
encoded by genes one (O) and two (T). You have obtained two pure lines of plants, one that
produces the compound and one that does not (OOTT and oott, respectively). You cross them
to obtain F1 plants that are heterozygous at both loci.
(a) Use a branch diagram to visualize the possible outcomes of a cross between two F1 plants.
(b) Calculate the expected proportion of offspring that will produce the attractant if this is a
case of duplicate recessive epistasis.
(c) What is the expected proportion of offspring that will produce attractant if this is a case of
duplicate dominance?
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