Meosis

Front 1

genes

Back 1

hereditary units (segments of dna)encoded with info

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locus

Back 2

a genes specific location along the length of a chromosome

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asexual reproduction

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a single individual is the sole parent and passes copies of all its genes on to its offspring. gives rise to a clone.

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sexual reproduction

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two parents give rise to offspring that have unique combos of genes inherited from the 2 parents= genetic variation

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life cycle

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generation to generation sequence of stages in teh reproductive hsitory of an organism, from conception to reproduction

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karyotype

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chromsomes arranged in pairs (homologous chroms), starting with the longest chroms.

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autosomes and sex chroms

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sex chroms (female=xx, male=xy), all of the rest are autosomes

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gametes

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sperm and ova, have 22 autosomes plus a single chrom, either x or y. these cells are haploid because they only have 23 chroms.

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diploid cells

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like a zygote, have 46 chroms

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meiosis

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2 stage cell division in sexually reproducing organisms that results in gametes with half the original number of chroms.

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alternation of generations

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sporophytes (multicellular diploids) produce haploid cells called spores, which give rise to multicellular individuals. divides mitotically to generate a multicellular haploid stage called gametophyte. makes gametes by mitosis.

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meosis I: interphase I

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chroms replicate=2 identical sister chromatidsattached at centromeres

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meosis I: prophase I

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homologous chroms come together in pairs. they hold onto eachother by crossings called chiasmata and trade segments. centromeres separate, microtubules come about, chroms move to metaphase plate. this takes up 90% of time for meiosis.

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meosis I: metaphase I

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kinetechores attach to one of each pair, opposite pole microtubules attach to the other

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meosis I: anaphase I

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chroms move towards poles by spindle, sister chromatids move as a single unit, homologous one moves to the other

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meosis I: telophase I and cytokinesis

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each pole now has a haploid chrom set, but each chrom still has 2 sister chromatids

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meosis II: prophase II

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spindle apparatus forms, chroms move towards metaphase II plate

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meosis II: metaphase II

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on center line, kinetechores of sister chromatids going to opposite poles

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meosis II: anaphase II

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centromeres of sisters separate, and now individual chroms move towards poles

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meosis II: telophase II and cytokinesis

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nuclei form at opposite poles, there are 4 daughter cells, each with a haploid number of unreplicated chroms

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synapsis

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during prophase I, the duplicated chroms pair with their homoloques

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summary

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meosis I separates homologous pairs of chroms, meosis II separates sister chromatids of individual chroms

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sources of genetic variability

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1. independent assortment of homologous chromosomes
2. crossing over
3. random fertilization of ovum by sperm