Meiosis – Chapter 10

Meiosis – Chapter 10 - MeiosisChapter10...

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Meiosis – Chapter 10 05:09 Sexual Reproduction and Meiosis Asexual reproduction: single parent splits, buds, or fragments to produce two or more individuals. o Mitotic division* - genes are inherited traits are like those of parents. o Clones – genetically similar organisms. Sexual Reproduction : union of two sex cells: gametes to form single cell: zygote. o Egg and sperm = gamete , fertilized egg = zygote (in case of animals ) o Genetic variation – offspring are not genetically identical to the parents. Disadvantage: offspring may not be able to survive as well as parents. o Types of chromosomes: Chromosomes in somatic cells (body cells) have partner chromosomes. Homologous chromosomes: similar in size, shape, and position of their centromeres. 46 chromosomes in human cells constitute 23 homologous pairs. Carry info about same genetic traits * Can be contrasted with the two members of a pair of sister chromatids Set of chromosomes = one of each kind of chromosome One member of each homologous pair Diploid: 2 sets of chromosomes ( 2n) Haploid : single set of chromosomes ( n) Humans: each gamete= haploid, after ferilization zygote is diploid. Most human body cells are diploid Polypoid : three or more sets of chromosomes
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Dominantly seen in plants Meiosis- cell division that reduces number of chromosomes: “to make smaller” o Diploid cell undergoes two divisions producing 4 haploid cells. o Stages are similar to mitosis: “1. Two successive nuclear and cytoplasmic divisions, producing 4 cells” “2. DNA and other chromosome components duplicate ONLY once (during interphase preceding first meiotic division” “3. Each of the 4 cells has haploid chromosome number – only one chromosome set containing only one representative of each homologous pair” “4. Each homologous chromosome pair is shuffled, so the resulting haploid cells each have a virtually unique combination of genes” o Meiosis I : members of each homologous chromosome pair join and then separate and move into different nuclei Chromosomes duplicate in S phase of interphase Prophase I : s ynapsis occurs: homologous chromosomes come to lie lengthwise side by side: “fastening together” Maternal homologue: one member of each homologous pair. Originally inherited from the female parent during the formation of the zygote. Paternal homologue: other members of the homologous pair. Inherited from the male parent. Synapse associates 4 chromatids called a tetrad . Synaptonemal complex : proteinaceous structure that holds the synapsed homologues together Crossing-over: enzymes break and rejoin DNA molecules, allowing paired homologous chromosomes to exchange genetic material (DNA) o genetic recombination : new combinations of traits occur – genetic variation* spindle forms – microtubules and other components.
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