Meiosis

Making Gametes

Mitosis ReviewMitosis: Division of the Nucleus

Prophase Metaphase Anaphase Telophase

How many times does the nucleus divide in mitosis? ONE

Mitosis ReviewThink in your head:

What are the four stages of mitosis?

What is the purpose of mitosis?Prophase – Metaphase-Anaphase-Telophase

The first purpose of mitosis is growth. The second function of mitosis is repair. Cells are constantly wearing out and getting damaged and unless an organism replaces them at least as fast as they are lost, a gradual deterioration will occur.

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Meiosis

Making Gametes

Introductory Vocabulary1. Somatic cell: body cell a. EX: skin or bone cell2. Diploid: two sets of chromosomes; 2n a. EX: humans have 2 sets of chromosomes in

each body cell; 1 set came from the sperm & the other set came from the egg

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Mitosis results in 2 diploid cells

Diploid (2n) somatic cell

About Meiosis1. Purpose of meiosis: produce haploid gametes.2. Haploid: having 1 set of chromosomes; 1n

3. Gametes- special cells used in sexual reproduction.

a. EX: egg and sperm cells b. Gametes are ONLY produced by meiosis4. Meiosis occurs in reproductive organs

(ovaries and testes)

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Overview of Meiosis

1. Interphase: cell duplicates its chromosomes

2. Chromosomes are only duplicated ONCE

3. Cell divides 2 times to produce genetically different 4 cells

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Stages of Meiosis ISlide # 11

Prophase I1. Chromatids pair up with

their Homologous pair forming a tetrad.

2. Crossing over is a process where pieces of two homologous chromosomes switch places.

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Replicated Chromosome

Sister Chromatid

Sister Chromatid

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Tetrad

Maternal chromosome replicated

Paternal chromosome replicated

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These chromosomes are homologous

T tongue rolling t non tongue rolling

F1 M1

Crossing Over: Occurs in Prophase I1. Homologous chromosomes : a. Pair up alongside each other lengthwise b. Swap bits and pieces of their chromosomes, shuffling

the genome 2. Crossing over ONLY happens in Prophase I & results in

NEW chromosomes that did not exist before in either parent

3. Why crossing over is important: a. It creates the genetic diversity of ALL sexually

reproducing organisms b. Yes, this means you too!

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Metaphase I: Tetrads line up in center

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Anaphase I: Tetrads separate

Telophase I & cytokinesis

Meiosis I

Stages of Meiosis IISlide # 19

Meiosis IISlide # 15

Prophase II: Chromatid pairs move to center

Metaphase II: The chromatids line up

at center of the cell

Anaphase II: chromatid pairs

separate

Telophase II: cells divide, producing 4

haploid cells

Meiosis occurs in the testes and is called spermatogenesis and in

the ovaries of female and is called oogenesis.

Human Inheritance

Karyotypes, Nondisjunction, and Chromosome Disorders

Karyotypes

1. Karyotypes show the 23 homologous pairs for the person in which the cells were taken.

2. The pairs are put in order from longest to shortest and numbered from 1 to 23.

3. Pairs 1-22 are autosomes.4. Pair 23 are sex chromosomes What is the sex of this

individual?

Male

Nondisjunction Nondisjunction caused by an error during meiosis I

when homologous pairs fail to separate.

One gamete will end up with one extra chromosome, and another gamete will be left with one less chromosome.

What is aneuploidy?

1. Aneuploidy: When chromosomes fail to separate properly during meiosis, the gamete will have an abnormal number of chromosomes

• Monosomy: one gamete has 22 chromosomes and the other has 23; the zygote ends up with 45 chromosomes

• Trisomy: one gamete has 24 chromosomes and the other has 23; the zygote ends up with 47 chromosomes

Down Syndrome1. Cells contain one extra copy of

chromosome # 21.2. This results in:

a. characteristic facial featuresb. short staturec. mental retardation d. shorter life-spane. Increased risk for heart

problems, immune system problems, and cancer.

Turner Syndrome1. This female has only one X

chromosome. 45,X 2. This results in a. a female who cannot

have children because the ovaries do not fully develop.

b. Short in stature c. Webbed neck d. Some mental disability

Klinefelter Syndrome1. Results in a male who has

one extra X chromosome.47,XXY

2. This results in a. Sterile b. mental retardation. c. true male, but can have

some female characteristics.