Sexual Reproduction & Meiosis

Sexual Reproduction Reproduction that combines genetic information from two individuals. Produces variation in a gene pool.

Sexual Reproduction in Animals Requires 2 parents Gonads are organs which produce gametes. Ovary & Testes Gametogenesis: process of producing gametes. Egg & Sperm

Diploid vs. Haploid Diploid (2n): Full set of DNA (46 Chromosomes) Haploid (n): Half set of DNA (23 Chromosomes) n= number of chromosomes Somatic Cells: Diploid Gametes: Haploid 2n Examples: Humans: 46 Chromosomes Bull Frogs: 26 Fruit Fly: 8

Chromosomes of each pair in a diploid cell are homologous chromosomes.

Meiosis Cell division that produces gametes containing half the number of chromosomes as a parent’s body cell. Produces haploid cells (n) Not identical to any parent cell

Meiosis Phases Meiosis I Prophase II Metaphase II Anaphase II Meiosis II Interphase Prophase I Metaphase I Anaphase I Telophase I & Cytokinesis Prophase II Metaphase II Anaphase II Telophase II & Cytokinesis

Interphase DNA replicates in preparation for gametogenesis.

Prophase I Sister chromatids partner with their homologous pair. Nuclear membrane disappears. Spindle fibers form. Crossing Over: Exchange of genes between homologous chromosomes Results in offspring with a mixture of parent characteristics.

Metaphase I Homologous chromosomes line up in middle of cell at the metaphase plate. Spindle fastens to the centromere.

Anaphase I Homologous chromosomes split & move to opposite ends of the cell.

Telophase I & Cytokinesis Nuclear membrane reforms. End of the 1st division. The cytoplasm divides forming TWO daughter cells.

Prophase II Nuclear membrane breaks down. Daughter cells form new spindle. (2 cells because we divided once already. These cells are diploid.)

Metaphase II Sister chromatids line up at metaphase plate. Spindle connects to centromere.

Anaphase II Sister chromatids split apart and move towards the poles.

Telophase II & Cytokinesis Both daughter cells divide forming FOUR haploid cells (n). Nuclear membrane reforms.

Errors in Meiosis

Nondisjunction Homologous chromosomes don’t fully separate. Error: Too many or too few chromosomes.

Polyploidy Extra set(s) of chromosomes. In animals, almost always results in death of the zygote. Frequently occurs in plants. Ex: Sterile banana plant

Chromosomal Abnormalities Deletion – Part of chromosome is missing. Insertion – Extra part of chromosome added. Deletion Insertion