Keystone Review - Genes Alleles and Meiosis1. C – the original number of

chromosomes (60)is halved by the end of meiosis I (30) and remains constant through the end of meiosis II (30).

2. C – One allele for each gene is found on each chromatid in a tetrad.

3. D – At the beginning of prophase I of meiosis and prophase of mitosis the full set of chromosomes is present and they have replicated their DNA to form identical sister chromatids.

4. D – The two alleles for a gene in an animal body cell, which contains homologous pairs of chromosomes, may have either the same of different DNA sequences. Therefore choices A and B are incorrect. Each allele is located on one of the homologous pairs of chromosomes. Therefore, choice C is incorrect, and choice D is correct.

Keystone Review - Genes Alleles and Meiosis

Constructed Response:A. Any two of the following phases should be identified:– Prophase: nuclear envelope dissolves and chromosomes

condense– Metaphase: the chromosome or tetrads align at the center of

the cell– Anaphase: chromatids or homologous chromosomes separate

and are pulled to opposite sides.– Telophase: the nuclear envelope reforms around the two

separated sets of chromosomes.

Keystone Review - Genes Alleles and Meiosis

Constructed Response:B. In meiosis, homologous chromosomes pair and crossing-over occurs between them. Homologs separate, producing haploid daughter cells. All the stages of mitosis occur twice in meiosis.

Keystone Review - Genes Alleles and Meiosis

Constructed Response:C – Daughter cells resulting from meiosis have half the normal chromosome number (haploid) and can function as gametes. The daughter cells all differ in the genetic information (alleles) they contain, while mitosis produces identical daughter cells which are diploid.

Keystone Review - Genes Alleles and Meiosis