Prophase of Meiosis - Zoology - Quiz, Exercises for Zoology. All India Institute of Medical Sciences
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ayushmati23 December 2012

Prophase of Meiosis - Zoology - Quiz, Exercises for Zoology. All India Institute of Medical Sciences

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Prophase of Meiosis, Metaphase of Meiosis, Diploid Parent Cell, Homologous Pairs, Chromosomes, Sister Chromatids, Metaphase Plate, Haploid Cells, Anaphase of Meiosis, Unlinked Genes. Sometimes quiz are helpful in prepari...
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Diploid cell

Meiosis - A Quick Review homologous pair 1 Start with a diploid parentcell 2n = 4 chromosomes, (2 homologous pairs of chromosomes) homologous pair 2 Prior to meiosis, the DNA replicates to form 4 duplicated chromosomes Prophase of Meiosis I

- The chromosomes condense; each chromosome consists of 2 sister chromatids.

- Each homologous pair consists of tetrad 4 chromatids which form a tetrad. (Crossing over can occur in this stage) Metaphase of Meiosis I - Homologous pairs align randomly at the metaphase plate: or

Then, the homologous pairs separate in anaphase of Meiosis I.

At the end of Meiosis I - two haploid cells are formed, sister chromatids are still together.

In Meiosis II - sister chromatids separate (similar to mitosis).

At the end of of Meiosis II, four haploid gametes are formed, each with n = 2 chromosomes:

or

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Case 1 - Unlinked genes. Two genes with two alleles (A,a and B,b). Genes A and B are on different chromosomes. The parent genotype is AaBb. In the diagrams below, fill in the alleles of genes A and B on the chromosomes of the parent cell in metaphase of Meiosis I , and in each of the possible gamete types at the end of meiosis.

or This is an example of independent assortment. With respect to genes A and B, How many different gamete types can be formed? Is each type equally likely to be formed? What is the probability of each type?

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Case 2 - Linked genes, no crossing over. Two genes with two alleles (A,a and B,b). The parent genotype is AaBb. Genes A and B are on the same chromosome (they are linked) as follows: allele A is linked to B and allele a is linked to b. Fill in the alleles of genes A and B on one homologous chromosome pair of the parent cell in metaphase of Meiosis I , and all the possible gametes types at the end of meiosis. Assume there is no crossing over during meiosis. (Note that the second homologous pair is not shown for simplicity.)

In this case, the alleles of A and B do not show independent assortment because the genes are linked. With respect to genes A and B, How many different gamete types can be formed? What is the probability of each type? Which of the gamete types that were formed in Case 1 were not formed in this case?

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Case 3 - Linked genes, with crossing over. Two genes with two alleles (A,a and B,b). The parent genotype is AaBb. Genes A and B are on the same chromosome with allele A linked to B and allele a linked to b. Genes A and B are separated by a short distance and there is a 10% probability that crossing over occurs between gene A and gene B. Fill in the alleles of genes A and B on chromosome 1 of the parent cell in metaphase of Meiosis I (after crossing over has occurred), and in all possible gamete types at the end of meiosis.

In this case, the alleles of A and B do not show independent assortment because the genes are still linked, but there is some recombination of alleles that results from crossing over. How many different gamete types can be formed? Identify the parental type gametes and the recombinant types in the diagram above. Which types (parental or recombinant) have the greater probability of being formed? What is the probability of each type?

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