Chapter 12 notes

Chapter 12 notes - Chapter 12 Meiosis I How Does Meiosis...

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Chapter 12 – Meiosis I. How Does Meiosis Occur a. Meiosis is nuclear division that leads to a halving of chromosome number. It precedes the formation of eggs and sperm. It consists of two cell divisions meiosis I and meiosis II i. During meiosis I, the diploid parent cells produces two haploid daughter cells made up of two identical sister chromatids. ii. During meiosis II, sister chromatids from each chromosome separate. iii. The outcome of meiosis is a reduction in chromosome number. iv. The four haploid daughter cells go on to form egg and sperm cells via a process called gametogenesis b. Homologous chromosomes – pairs of the same chromosome c. Gene – a section of DNA that influences one or more hereditary traits in an individual. i. Alleles are different versions of a particular gene, homologous chromosomes carry the same genes, but each homolog may contain different alleles. d. Karyotype – the number and types of chromosomes present in an individual e. Diploid – organisms with two versions of each type of chromosome in humans diploid number is 46 f. Haploid – organisms with one type of each chromosome, the letter n stands for the number of distinct types of chromosomes in a given cell. Haploid number for humans is 23 g. Ploidy – the combination of a number and n i.e. humans ploidy is 2n h. Polyploidy species may have three or more of each type of chromosome in each cell i. Zygote – the diploid cell that results from fertilization j. Homologous chromosomes are referred to as either maternal or paternal in origin.
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