Question

1)Consider a cell with a diploid chromosome number 2n=10, and two telocentric pairs, two metacentric pairs, and one acrocentric pair of chromosomes. Draw the cell in anaphase I of meiosis. Indicate one pair of sister chromatids by arrows. Indicate one pair of homologous chromosomes by stars. Don’t forget to draw the centromeres and the spindle.

(Hand drawing is OK for this question)

2) Describe how new combinations of alleles can be formed through the process of meiosis.

3) In corn, kernels are usually smooth due to the Su allele. The recessive su allele gives the kernel a wrinkled appearance. Likewise, kernel color in corn can either be colorless due to the recessive r allele or purple due to the dominant R allele. You wish to deduce the genotype of a smooth, purple kernel for your experiment. What are all the possible genotypes this corn kernel could be at the smooth and purple loci? What genotype and phenotype of corn should you use in order to do a testcross? What are the phenotypic ratios expected from this testcross for each of the possible mystery kernel genotypes?

4) List all the different gamete genotypes and the probability of observing each genotype that can be produced by an individual with the genotype AABbCcDD.

5) What is nondisjunction? What are the consequences if nondisjunction occurs during meiosis I?

Answer 1

1)

2) Meiosis I has four stages known as prophase I, metaphase I, anaphase I and telophase I. Prophase I has five sub stages known as leptotene , zygotene , pachytene , diplotene and diakinesis. In pachytene sub stage the non-sister chromatids cross each other and exchange of genes are take place. Thus new combination of alleles can be formed through the process of meiosis.

3)

4)