NameLS7B Week 2 Lab Worksheet
Part 1. Modeling Meiosis
Draw the chromosomes as they would appear in each cell shown in the diagram below. Include Gene A and Gene D in
your drawings and be sure to designate which genes/alleles are present in each cell. Double check that the alignment
for the chromosomes is accurate during metaphase I and metaphase II, assume no crossing over.
Gene Durian
Yellow chromosomes,
alleles labeled “D” and “d”.
Gene Apple
Red chromosomes,
alleles labeled “A” and “a”
1. Explain Mendel’s principles of segregation and independent assortment.
2. Assuming no crossing over, does segregation of alleles occur in meiosis I or II? Explain your reasoning.
3. Assuming no crossing over, does assortment of genes take place in meiosis I or II? Explain your reasoning.
Part II Modelling Non-Disjunction – In the following cells model what would result if the larger
chromosome (with the A and a alleles) experienced NDJ in Meiosis I. (Assume no crossing over)
Modelling Non-Disjunction – In the following cells model what would result if the larger chromosome
(with the A and a alleles) experienced NDJ in Meiosis II. (Assume no crossing over)
1. How many different allele combinations in the gametes are produced when meiosis occurs without NDJ
compared to when NDJ occurs, in the larger chromosome (the smaller chromosome proceeds through meiosis
correctly) in Meiosis I and Meiosis II?
Part 3. Using Punnett squares, determine the phenotypes of offspring that the following parents could produce. For
some situations, there could be more than one genotype for at least one of the parents. In these cases, be sure to
include Punnett squares for all possibilities.
1. An autosomal recessive trait with an unaffected XX parent and an affected XY parent.
2. An autosomal dominant trait with an affected XX parent and an unaffected XY parent.
3. An X-linked recessive trait with an unaffected XX parent and an affected XY parent.
4. An X-linked dominant trait with an unaffected XX parent and an affected XY parent.
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