Meiosis

Chromosome Number The two sets of chromosomes are homologous, each chromosomes from the male parent has a corresponding chromosome from the female. Fruit flies have 8 chromosomes. 4 came from the fly’s male parent, and 4 came from the female parent.

Diploid & Haploid Diploid: cell with 2 sets of chromosomes. Diploid: 2N Fruit Fly: 2N=8 Humans: 2N=46 Haploid: cell with 1 set of chromosomes, i.e. gametes. Haploid: N Fruit Flies: N=4 Humans: N=23

Meiosis 1 Diploid cell  4 haploid cells Chromosome no. is halved Separate homologous chromosomes

Meiosis I Interphase I: copy chromosomes Prophase I: pair homologous chromosome, form a tetrad Metaphase I: spindle fibers attach to chromosome. Anaphase I: fibers pull homologous chromosomes toward opposite ends. Telophase I & Cytokinesis: nuclear membranes form. Cell separates into 2 cells.

Metaphase I Anaphase I Telophase I

Meiosis II Prophase II: 2 haploid cells, with ½ the number of chromosomes. Metaphase II: chromosomes line up in the middle. Anaphase II: sister chromatids separate and move toward opposite ends. Telophase & Cytokinesis: result in 4 haploid (N) cells.

Mitosis Meiosis 2 Cells Identical Diploid 4 Cells Not Identical Haploid

Gene Linkage Chromosome: group of linked genes. Traits appear to be inherited together. Chromosomes assort independently, not genes.

Cross-over Cross-over Creates genetic diversity separate & exchange linked genes new combination of alleles Creates genetic diversity

Cross-over

Gene Maps The further apart two genes are, the more likely they are to be separated by crossover. The rate of separation/recombination are used to create a map of the distances between genes. Gene Map: shows the relevant location of each known gene on a chromosome.

Gene Map