10 2 Meiosis Diploid Haploid Cells Chromosomes in

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10. 2 Meiosis

10. 2 Meiosis

Diploid & Haploid Cells • Chromosomes in body cells occur in pairs. • Diploid

Diploid & Haploid Cells • Chromosomes in body cells occur in pairs. • Diploid – a cell with two of each kind of chromosome (2 N) • Gametes have single chromosomes. • Haploid – a cell with one of each kind of chromosome (N)

Homologous Chromosomes • Paired chromosomes with genes for the same traits are called homologous.

Homologous Chromosomes • Paired chromosomes with genes for the same traits are called homologous. • Genes are arranged in the same order on homologous chromosomes.

Why Meiosis? • Human somatic cells (body cells) are diploid. • Gametes (sperm and

Why Meiosis? • Human somatic cells (body cells) are diploid. • Gametes (sperm and egg) are haploid • Meiosis – a type of cell division that produces four gametes, each with half the number of chromosomes as a body cell.

Meiosis • Meiosis occurs in two separate divisions, meiosis I and meiosis II. •

Meiosis • Meiosis occurs in two separate divisions, meiosis I and meiosis II. • Meiosis starts with one 2 N cell and ends with four N cells. • Meiosis is necessary for sexual reproduction.

Meiosis cont.

Meiosis cont.

Whiteboards • • What are homologous chromosomes? What does diploid mean? What does haploid

Whiteboards • • What are homologous chromosomes? What does diploid mean? What does haploid mean? What is the difference between gametes and somatic cells? • What would happen if gametes were diploid instead of haploid?

Meiosis I • Crossing Over – nonsister chromatids of homologous chromosomes exchange genetic material.

Meiosis I • Crossing Over – nonsister chromatids of homologous chromosomes exchange genetic material. • Homologous chromosomes are separated into two new cells.

Meiosis II • Sister chromatids are separated • Results in four cells, each with

Meiosis II • Sister chromatids are separated • Results in four cells, each with one copy of each chromosome.

Meiosis Provides Variation • Meiosis makes cells that are not identical. • Meiosis results

Meiosis Provides Variation • Meiosis makes cells that are not identical. • Meiosis results in a variety of different gametes. • Gametes are randomly fertilized, producing very large numbers of possible unique offspring. • Crossing over in Meiosis I adds more variation.

Mistakes in Meiosis • Nondisjunction – failure of homologous chromosomes to separate. • Results

Mistakes in Meiosis • Nondisjunction – failure of homologous chromosomes to separate. • Results in gametes that are missing chromosomes or that have extra chromosomes.

Mistakes in Meiosis cont. • Trisomy – organism has three chromosomes instead of a

Mistakes in Meiosis cont. • Trisomy – organism has three chromosomes instead of a pair.

Mistakes in Meiosis cont. • Monosomy – one chromosome instead of a pair. •

Mistakes in Meiosis cont. • Monosomy – one chromosome instead of a pair. • Triploidy – three copies of ALL chromosomes, resulting from complete nondisjunction.

Whiteboards • What is crossing over? • How does crossing over generate variation? •

Whiteboards • What is crossing over? • How does crossing over generate variation? • At the end of Meiosis how many cells are produced, and are they identical or different? • What is non disjunction?