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Biology 3

Ch 6 Cell Division

Dr. Terence Lee

Telomeres

� The telomere is like a protective cap at the end of the DNA.

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Three Types of Cell Division

• Asexual Reproduction

– Binary fission and mitosis

are the primary means of

reproduction in single cell

organisms.

• Sexual Reproduction

– Combining of genetic information from two parents.

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The Cell Cycle

The Cell Cycle

• Interphase

– The longest phase

– Also called the growth phase

– Prepares for next cell division.

• Mitosis

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Mitosis

• Prophase

1. Chromosomes condense

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Sister Chromatids

Early Prophase

Prophase

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Metaphase

Anaphase

1. The chromosome breaks in

half

2. Each sister chromatid is now a

new daughter chromosome.

Telophase

1. Spindle fibers disassemble

2. Nuclear membrane re-forms

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Cytokinesis

• Process during which …

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Cell Division and Sexual

Reproduction

• Why sexual reproduction when asexual reproduction

(mitosis) gets the job done?

Cell Division and Sexual

Reproduction

Humans have two sets of chromosomes

Cell Division and Sexual

Reproduction

• Haploid

• Diploid

• Gametes

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Meiosis I

Overview

Meiosis I

• Prophase I

1. Chromosomes condense

2. Spindle and spindle fibers form

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Meiosis I

• Metaphase I

Meiosis I

• Anaphase I

1. Homologous chromosomes

separate from each other

2. Chromosomes move toward

cell’s poles

Meiosis I

• Telophase I

1. Spindle fibers disassemble

2. Chromosomes uncoil

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Meiosis I

Review

Meiosis II

• Prophase II

1. Chromosomes condense

2. Spindle and spindle fibers

form

Meiosis II

• Metaphase II

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Meiosis II

• Anaphase II

– Chromatids separate as

chromosomes begin to

move to cell’s poles

Meiosis II

• Telophase II

1. Nuclear membrane re-forms

2. Chromosomes uncoil

Review

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Sex Determination

• Autosomes

– Non-sex chromosomes (1-22)

• Sex Chromosomes

– XX and XY (23)

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6.16 The sex of the offspring is determined in a variety of ways

in other species.

The sex of the offspring is determined in a variety of ways

in other species.

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The sex of the offspring is determined in a variety of ways

in other species.

Chromosome Number

• Normal person has 23 pairs of chromosomes

• Downs Syndrome or

trisomy 21 is caused by

nondisjunction