Meiosis IB Biology

Match up the key words to their definitions and copy them into your notes! Definitions Chromosome pairs, one from each parent, that are similar in length, gene position and centromere location. A cell that contains one complete set of chromosomes. A cell that contains two sets of chromosomes. One set of chromosomes is donated from each parent. Location of a gene on a chromosome Different forms of the same gene Sex cells that unite during sexual reproduction to form a new cell called a zygote Homologous pair Haploid Diploid Gene locus (loci) Allele Gamete

Spermatogenesis 2n=46 human sex cell diploid (2n) n=23 meiosis I n=23 sperm haploid (n) meiosis II

Interphase I mitosis Similar to mitosis interphase. Chromosomes(S phase). Chromosomes replicate (S phase). chromosome chromatidscentromeres Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres. Centriole Centriole pairs also replicate.

Interphase I Nucleusnucleolus Nucleus and nucleolus visible. nuclear membrane nucleolus cell membrane chromatin

Meiosis I (four phases) Cell division chromosome one-half. Cell division that reduces the chromosome number by one-half. four phases four phases: a.prophase I b.metaphase I c.anaphase I d.telophase I

Prophase I Longest and most complex phase (90%). Longest and most complex phase (90%). Chromosomes Chromosomes condense. Synapsis homologous chromosomes tetrad Synapsis occurs: homologous chromosomes come together to form a tetrad. Tetradchromosomeschromatids Tetrad is two chromosomes or four chromatids (sister and nonsister chromatids).

Prophase I - Synapsis Homologous chromosomes sister chromatids Tetrad

Homologous Chromosomes chromosomesmaternalpaternal Pair of chromosomes (maternal and paternal) that are similar in shape and size. (tetrads) Homologous pairs (tetrads) carry genes controlling the same inherited traits. locus(position of a gene) Each locus (position of a gene) is in the same position on homologues. homologous chromosomes. Humans have 23 pairs of homologous chromosomes. autosomes a.22 pairs of autosomes sex chromosomes b.01 pair of sex chromosomes

Homologous Chromosomes PaternalMaternal eye color locus eye color locus hair color locus hair color locus

Crossing Over Crossing over (variation) chromatidschiasmata Crossing over (variation) may occur between nonsister chromatids at the chiasmata. Crossing overchromatids chromatid Crossing over: segments of nonsister chromatids break and reattach to the other chromatid. Chiasmata (chiasma) crossing over Chiasmata (chiasma) are the sites of crossing over.

Crossing Over - variation nonsister chromatids chiasmata: site of crossing over variation Tetrad

Sex Chromosomes XX chromosome - femaleXY chromosome - male

Prophase I centrioles spindle fiber aster fibers

Metaphase I Shortest phase Shortest phase Tetradsmetaphase plate Tetrads align on the metaphase plate. INDEPENDENT ASSORTMENT OCCURS: INDEPENDENT ASSORTMENT OCCURS: 1. Orientation of homologous pair to poles is random. 2. Variation 3. Formula: 2 n Example:2n = 4 then n = 2 thus 2 2 = 4 combinations thus 2 2 = 4 combinations

Metaphase I metaphase plate OR metaphase plate

Question: In terms of Independent Assortment -how many different combinations of sperm could a human male produce? In terms of Independent Assortment -how many different combinations of sperm could a human male produce?

Answer Formula: 2 n Formula: 2 n Human chromosomes:2n = 46 Human chromosomes:2n = 46 n = 23 n = = ~8 million combinations 2 23 = ~8 million combinations

Anaphase I Homologous chromosomes Homologous chromosomes separate and move towards the poles. Sister chromatids centromeres Sister chromatids remain attached at their centromeres.

Anaphase I

Telophase I haploidchromosomes Each pole now has haploid set of chromosomes. Cytokinesis Cytokinesis occurs and two haploid daughter cells are formed.

Telophase I

Meiosis II No interphase II No interphase II DNA replication (or very short - no more DNA replication) Remember: Meiosis II mitosis Remember: Meiosis II is similar to mitosis

Prophase II prophasemitosis same as prophase in mitosis

Metaphase II metaphasemitosis same as metaphase in mitosis metaphase plate

Anaphase II anaphasemitosis same as anaphase in mitosis sister chromatids separate sister chromatids separate

Telophase II telophasemitosis Same as telophase in mitosis. Nuclei form. Cytokinesis Cytokinesis occurs. Remember:four haploid daughter cells produced. Remember:four haploid daughter cells produced. gametes = sperm or egg

Telophase II

Meiosis 2n=4 sex cell diploid (2n) n=2 meiosis I n=2 sperm haploid (n) meiosis II

Variation Important to population as the raw material for natural selection. Important to population as the raw material for natural selection. Question: Question: What are the three sexual sources of genetic variation?

Answer: 1. crossing over (prophase I) 2. independent assortment (metaphase I) 3. random fertilization Remember: variation is good!

Question: 20 chromosomes(diploid) chromosomes A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

Answer: 10 chromosomes (haploid) 10 chromosomes (haploid)

Fertilization spermeggzygote The fusion of a sperm and egg to form a zygote. A zygote is a fertilized egg n=23 egg sperm n=23 2n=46 zygote

Question: 40 chromatids chromosomes A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

Answer: 10 chromosomes 10 chromosomes

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