Meiosis Meiosis Process of reduction division in which

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Meiosis • Meiosis: Process of reduction division in which the number of chromosomes per

Meiosis • Meiosis: Process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell • Two distinct divisions: Meiosis I and Meiosis II • Meiosis is the formation of human sex cells: sperm and egg

Chromosome Number • Each individual has sets of chromosomes • Homologous: term used to

Chromosome Number • Each individual has sets of chromosomes • Homologous: term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex partner • A cell that contains both sets of homologous chromosomes is said to be diploid, which means “two sets – Represented by 2 N – Have two homologues of each chromosome – Has chromosomes found in pairs

Chromosome Number • Haploid: term used to refer to a cell that contains only

Chromosome Number • Haploid: term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes – Represented by N • Egg and Sperm=Haploid Cells • Fertilized Egg=Diploid Cell

Meiosis I • Cells begin to divide in a way that looks similar to

Meiosis I • Cells begin to divide in a way that looks similar to mitosis • Differences between Meiosis and Mitosis: – In prophase of Meiosis I, each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad » 4 chromatids in a tetrad – As homologous chromosomes pair up and form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing-over » Exchange of alleles from new genes

Meiosis I • Differences between Meiosis and Mitosis: – During anaphase I, chromatids do

Meiosis I • Differences between Meiosis and Mitosis: – During anaphase I, chromatids do not separate at the centromere and pull the homologous chromosomes toward the ends of the cell

Meiosis II • Two cells produced in Meiosis I now enter a second meiotic

Meiosis II • Two cells produced in Meiosis I now enter a second meiotic division • No interphase in second meiotic division (no DNA replication) • Paired chromatids separate in this second division in anaphase II • Result: Four daughter cells containing just 2 chromosomes each and are haploid (N)

Human Genes • 23 Pairs of chromosomes – 44 Autosomes » Autosome is a

Human Genes • 23 Pairs of chromosomes – 44 Autosomes » Autosome is a chromosome that is not a sex chromosome – 2 Sex Chromosomes • Can see the process of mitosis and meiosis along with the 23 pairs of chromosomes by examining a karyotype – Photograph of chromosomes grouped in order in pairs

Comparing Mitosis and Meiosis • Mitosis results in the production of two genetically identical

Comparing Mitosis and Meiosis • Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells

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