10_Meiosis and Sexual reproduction
Overview of Meiosis and Sexual Life Cycles
Living organisms can reproduce their own kind.
Heredity involves the transmission of traits.
Variation is evident in offspring compared to parents and siblings.
Genetics studies heredity and variation.
Concept 10.1: Inheritance of Genes
Offspring inherit genes via chromosomes.
Genes are units of heredity made of DNA segments.
Genes passed through gametes (sperm and eggs).
Humans have 46 chromosomes in somatic cells; 23 in gametes.
Each gene has a specific locus on a chromosome.
Asexual vs. Sexual Reproduction
Asexual reproduction involves one individual passing genes without gametes.
Results in genetically identical individuals (clones).
Sexual reproduction involves two parents and unique gene combinations.
Concept 10.2: Fertilization and Meiosis in Life Cycles
Life cycle: generation-to-generation reproductive stages.
Human somatic cells have 23 chromosome pairs (homologous chromosomes).
Karyotype displays pairs; homologs carry genes for the same characters.
Human Chromosomes
Sex chromosomes are X and Y.
Females: XX; Males: XY.
Remaining 22 pairs are autosomes.
Each somatic cell has 46 chromosomes (diploid, 2n).
Gametes are haploid (n), containing 23 chromosomes.
Meiosis Overview
Meiosis reduces chromosome sets from diploid to haploid.
Two divisions: meiosis I and meiosis II; results in four daughter cells.
Each daughter cell has half the chromosomes of the parent cell.
Phases of Meiosis
Meiosis I: homologous chromosomes separate.
Meiosis II: sister chromatids separate.
Prophase I includes crossing over and synapsis via synaptonemal complex.
Genetic Variation and Evolution
Genetic diversity arises from mutations, crossing over, independent assortment, and random fertilization.
Independent assortment leads to different combinations of chromosomes.
Crossing over creates recombinant chromosomes.
Random fertilization results in diverse diploid combinations.
Sexual reproduction promotes genetic variation beneficial for evolution.