Human body cells have 46 chromosomes

1
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Chromosomes and Chromosome Number

• Human body cells have 46 chromosomes

• Each parent contributes 23 chromosomes

• Homologous chromosomesone of two paired
  chromosomes, one from each parent

2
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Homologous chromosomes

• Same length

• Same centromere position

• Carry genes that control the same inherited traits

3
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Haploid and Diploid Cells

• An organism produces gametes to maintain the same
  number of chromosomes from generation to
  generation.

• Human gametes contain 23 chromosomes.

• A cell with n chromosomes is called a haploid
  cell.

• A cell that contains 2n chromosomes is called a
  diploid cell.

4
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• The sexual life cycle in animals involves meiosis.

• Meiosis produces gametes.

5
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Stages of Meiosis I

• Reduces the chromosome number by half through the
  separation of homologous chromosomes

• Involves two consecutive cell divisions called
  meiosis I and meiosis II

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Interphase

• Chromosomes replicate.

• Chromatin condenses.

Interphase
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Prophase I

• Pairing of homologous chromosomes occurs.

• Each chromosome consists of two chromatids.

Prophase I

• The nuclear envelope breaks down.

• Spindles form.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Prophase I

• Crossing over produces exchange of genetic
  information.

• Crossing overchromosomal segments are exchanged
  between a pair of homologous chromosomes.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Metaphase I

• Chromosome centromeres attach to spindle fibers.

Metaphase I

• Homologous chromosomes line up at the equator.

10
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Anaphase I

Anaphase I
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Telophase I

• The spindles break down.

Telophase I

• Chromosomes uncoil and form two nuclei.

• The cell divides.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Prophase II

Prophase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Metaphase II

Metaphase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Anaphase II

Anaphase II
15
Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Telophase II

Telophase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Cytokinesis results in four haploid cells, each
  with n number of chromosomes.

Cytokinesis
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
The Importance of Meiosis

• Meiosis consists of two sets of divisions

• Produces four haploid daughter cells that are not
  identical

• Results in genetic variation

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis Provides Variation

• Depending on how the chromosomes line up at the
  equator, four gametes with four different
  combinations of chromosomes can result.

• Genetic variation also is produced during
  crossing over and during fertilization, when
  gametes randomly combine.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Sexual Reproduction v. Asexual Reproduction

• Asexual reproduction

• The organism inherits all of its chromosomes from
  a single parent.

• The new individual is genetically identical to
  its parent.

• Sexual reproduction

• Beneficial genes multiply faster over time.

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CDQ 1
Sexual Reproduction and Genetics
Chapter 10
Chapter Diagnostic Questions
Which symbol is used to represent the number of
chromosomes in a gamete?

2. x
3. r
4. n

1. A
2. B
3. C
4. D

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FQ 3
Sexual Reproduction and Genetics
Chapter 10
10.1 Formative Questions
How does the number of chromosomes in gametes
compare with the number of chromosomes in body
cells?

1. Gametes have 1/4 the number of chromosomes.
2. Gametes have 1/2 the number of chromosomes.
3. Gametes have the same number of chromosomes.
4. Gametes have twice as many chromosomes.

1. A
2. B
3. C
4. D

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FQ 4
Sexual Reproduction and Genetics
Chapter 10
10.1 Formative Questions
What type of organisms only reproduce asexually?

1. bacteria
2. protists
3. plants
4. simple animals

1. A
2. B
3. C
4. D

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FQ 9
Sexual Reproduction and Genetics
Chapter 10
10.3 Formative Questions
Two genes on the same chromosome may become
separated during meiosis.

1. true
2. false

1. A
2. B

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CAQ 1
Sexual Reproduction and Genetics
Chapter 10
Chapter Assessment Questions
How many chromosomes would a cell have during
metaphase I of meiosis if it has 12 chromosomes
during interphase?

1. 6
2. 12
3. 24
4. 36

1. A
2. B
3. C
4. D

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CAQ 2
Sexual Reproduction and Genetics
Chapter 10
Chapter Assessment Questions
Which stage of meiosis is illustrated?

1. prophase I
2. interphase
3. anaphase I
4. anaphase II

1. A
2. B
3. C
4. D

26
CAQ 3
Sexual Reproduction and Genetics
Chapter 10
Chapter Assessment Questions
What is the next step for the chromosomes
illustrated?

1. Chromosomes replicate.
2. Chromosomes move to opposite poles.
3. Chromosomes uncoil and form two nuclei.
4. Chromosomes line up at the equator.

1. A
2. B
3. C
4. D

27
STP 1
Sexual Reproduction and Genetics
Chapter 10
Standardized Test Practice
What is this process called?

1. fertilization
2. gamete formation
3. inheritance
4. reproduction

1. A
2. B
3. C
4. D

28
STP 2
Sexual Reproduction and Genetics
Chapter 10
Standardized Test Practice
Before meiosis I, the sister chromatids of this
chromosome were identical. What process caused a
change in a section of one chromatid?

1. DNA replication
2. crossing over
3. synapsis
4. telophase

1. A
2. B
3. C
4. D

29
STP 3
Sexual Reproduction and Genetics
Chapter 10
Standardized Test Practice
At what stage is the chromosome number reduced
from 2n to n?

1. prophase I
2. metaphase I
3. anaphase I
4. meiosis II

1. A
2. B
3. C
4. D