Chapter 11-4 Meiosis

Meiosis Vocabulary

• Diploid

• Haploid

• Gametes

• Homologous chromosomes

• Crossing over

• Tetrad

So lets talk about making a person

• So who do you look like?• What holds the genetic information?• How is this genetic information passed to

the next child?• How many sets of chromosomes do you

have?• What are homologous chromosomes?• Where do you get your sets of

chromosomes?

Meiosis

• Most cells have two sets of chromosomes– This is called diploid (2 sets of 23)– 2n = diploid #, humans 2n = 46

• Gametes have one set of chromosomes– This is called haploid cell (1 set of 23)– n = haploid #, humans n = 23– Sperm, egg, pollen are examples

• Meiosis is the process of making haploid cells from diploid cells

• Haploid + haploid = diploid /fertilization

Meiosis

• Meiosis has two divisions – meiosis 1 – meiosis 2

• Meiosis 1– First division separates the homologous

chromosomes– Crossing over of genetic material can take

place• Meiosis 2

– 2nd division separates the sister chromatids into individual chromosomes

– Process is like mitosis• Except for the number of chromosomes

• Each division has same 4 ‘steps’– Prophase, metaphase, anaphase, telophase

Meiosis I

Interphase I Prophase I Metaphase I Anaphase I

Cells undergo a round of DNA replication, forming duplicate Chromosomes.

Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Spindle fibers attach to the chromosomes.

The fibers pull the homologous chromosomes toward the opposite ends of the cell.

Section 11-4

Figure 11-15 Meiosis

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Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Mitosis vs Meiosis

• Mitosis – 1 division– 2 daughter cells– Exact copies of

parent cells– Diploid to diploid– Purpose

• Growth • Repair• Asexual

reproduction

• Meiosis– 2 divisions

• 1st separates pairs

– 4 daughter cells– Each unique– Diploid to haploid– Purpose

• Make gametes/ sex cells

• Leads to genetic variation due to crossing over