Chapter 13 - Meiosis and Sexual Life Cycles

Asexual Reproduction

1. Results in offspring that are exact genetic copies of the parent

Genetics

1. Scientific study of heredity and variation

2. Heredity - Transmission of traits from one generation to the next

3. Variation - Differences in appearances between related individuals

Genes

1. Units of hereditary information that contains specific nucleotide sequences

2. Locus - A genes specific location on a chromosome

Gametes

1. Transmit the genes from parent to child

2. Sperm (23) and egg (23) combine to form a zygote (46)

3. Egg carries the X chromosome, sperm can carry X or Y

Somatic Cells

1. Body cells

2. Everything except sperm and egg

Sexual Reproduction

1. 2 parents producing offspring that have unique combinations of genes

Karyotype

1. Display of homologous (pairs) chromosomes

Autosomes

1. 1-22 of the chromosome pairs

2. The 23red pair are are the sex chromosomes

Sex Chromosomes

1. XX - Female (Homologous)

2. XY - Male (Only small parts are homologous)

Diploid

1. A cell that has two sets of chromosomes

2. 2n (2×23=46 for humans)

3. Somatic (body) cells

Haploid

1. A cell that has one pair of chromosomes

2. n (23 in humans)

3. Reproductive (Gametes) cells

Germ Cells

1. Undergo meiosis to make gametes

Meiosis Stages

1. Meiosis I - Homologs (pairs) come together and separate, which results in 2 haploid daughter cells with replicated chromosomes. The pairs themselves stay together

2. Meiosis II - Sister chromatids separate to make 4 haploid cells

3. Prophase I - Chromosomes condense, homologous chromosomes pair up aligned by genes, and then non-sister chromatids exchange DNA segments

Meiosis I

Meiosis II

Prophase I (Meiosis)

Tetrad

1. A group of four chromosomes formed in prophase I of meiosis

2. the chromosomes cross over to exchange DNA and form chiasmata (the location where DNA is exchanged)

Metaphase I (Meisosis)

1. Tetrads (pairs of 4 chromosomes) line up down the middle

2. Microtubules (spindles) attach to the center (kinetochore) of each chromosome

Prophase II (Meisosis)

1. Spindle apparatus forms

Metaphase II (Meisosis)

1. Sister chromatids are arranged in the middle

2. Sister chromatids are no longer identical because of crossing over

Anaphase II (Meisosis)

1. Sister chromatids separate (not homologous pairs like in anaphase I)

Telophase II

1. Chromosomes are on both ends of the cell and the cytoplasm begins to split (cytokinesis)

2. Nucleus reforms