Genetics Meiosis

Sexual Life Cycles Alternation of meiosis and fertilization is common in most living organisms

Sexual Life Cycles of Humans

Meiosis diploid and haploid stages Meiosis II Meiosis I diploid Meiosis II haploid haploid

Meiosis I reduction division, separates homologues Meiosis II Meiosis I diploid Meiosis II haploid haploid

Meiosis I Interphase (precedes Meiosis) Meiosis I G1 , S, G2 Meiosis I prophase I, metaphase I, anaphase I, telophase I Cytokinesis (follows Meiosis)

Interphase precedes meiosis G1 first gap S synthesis G2 second gap

Prophase I longest phase synapses tetrad formation crossing-over chiasma

Metaphase I tetrads align at the metaphase plate

Anaphase I homologous chromosomes pull apart separation accomplished by disassembly of kinetochore microtubules elongation by nonkinetochore homologous chromosomes separate

Telophase I Chromosomes reach the poles each pole with haploid number cleavage furrow

Cytokinesis Division of cytoplasm animal cells form a cleavage furrow plant cells form a cell plate cleavage furrow

Meiosis II mitotic division, separates sister chromatid diploid Meiosis II haploid haploid

Meiosis II prophase II, metaphase II, anaphase II, telophase II Cytokinesis

Prophase II spindle apparatus forms

Metaphase II sister chromatids align at equator

Anaphase II sister chromatids separate

Telophase II daughter cells contain half the number of chromosomes the initial parent cell had 2n n diploid haploid

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Summary ghgnfn

Gametogenesis Spermatogenesis Oogenesis

Spermatogenesis

Oogenesis End product is ONE egg and 3 polar bodies

Some Zygote Possibilities single birth 1 sperm + 1 ovum = 1 zygote monozygotic (identical) twins dizygotic (fraternal) twins 2 sperm + 2 ova = 2 zygotes

Events that contribute to Variations independent assortment chromosomes random fusion of gametes crossing-over mutations

Independent assortment of chromosomes

Random fusion of gametes A gamete from one individual unites with a gamete from another individual 1 in 8 million x 1 in 8 million = 64 trillion 64 trillion combinations of chromosomes

Crossing-over Prophase I

Chromosomes human = 46 chromosomes (23 pairs) autosomal chromosomes = 44 (22 pairs) sex chromosomes = 2 (1 pair)

Female Sex Chromosomes female = XX all gametes carry X chromosome homogametic sex

Male Sex Chromosomes male = XY 1/2 of gametes carry X, 1/2 carry Y heterogametic sex Hemizygous

Activity Is this cell going through mitosis or meiosis? How do you know?

Is this cell going through mitosis or meiosis? How do you know? What specific stage is it in? What special process is going on? What is the importance of it? The End