2. Meiosis & Sexual Reproduction (10.1)
State Standard
2E. Compare the advantages of sexual reproduction and asexual reproduction in different situations.

3. Chromosomes & Chromosome Number
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Chromosomes & Chromosome Number
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes—one of two paired chromosomes, one from each parent

4. Chromosomes & Chromosome Number Cont’d
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Chromosomes & Chromosome Number Cont’d
Homologous Chromosomes have…
Same length
Same centromere position
Carry genes that control the same inherited traits

5. These chromosomes
Have not replicated
These chromosomes
have replicated

6. Haploid and Diploid Cells
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Haploid and Diploid Cells
An organism produces gametes to maintain the same number of chromosomes from generation to generation.
Gametes are haploid. The contain half the normal # of chromosomes for the organism. (n)
Human gametes = 23 chromosomes
All other body cells (aka somatic cells) are diploid. They contain the normal # of chromosomes for the organism. (2n)
Human body cells = 46 chromosomes.

7. Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis
Meiosis is a special type of cell division that produces gametes.
Gametes are haploid (n) cells
When 2 gametes combine during fertilization, the
normal (2n) number of chromosomes is restored.

8. Human meiosis reduces the cell from 46 to 23 chromosomes.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Stages of Meiosis
Involves two consecutive cell divisions called Meiosis I and Meiosis II
Meiosis reduces the chromosome number (2n) to half (n) through the separation of homologous chromosomes
Human meiosis reduces the cell from 46 to 23 chromosomes.

9. Chromosomes replicate.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I - Interphase
Chromosomes replicate.
Chromatin condenses.
Interphase

10. Pairing of homologous chromosomes occurs. (called synapsis)
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I – Prophase I
Pairing of homologous chromosomes occurs.
(called synapsis)
Each chromosome consists of two chromatids.
Prophase I
The nuclear envelope breaks down.
Spindles form.

11. Meiosis I – Prophase I Cont’d
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I – Prophase I Cont’d
During Prophase I, crossing over creates genetic variation.
Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

12. Chromosome centromeres attach to spindle fibers.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I – Metaphase I
Chromosome centromeres attach to spindle fibers.
Metaphase I
Homologous chromosomes line up at the equator.

13. Entire homologous chromosomes separate and move
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I – Anaphase I
Entire homologous chromosomes separate and move
to opposite poles of the cell.
Anaphase I

14. The spindles break down.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I – Telophase I
The spindles break down.
Telophase I
Chromosomes uncoil and form two nuclei.
The cell divides.
There is no interphase following Meiosis I

15. Meiosis II – Prophase II
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II – Prophase II
A second set of phases begins
as the spindle apparatus forms and the
chromosomes condense.
Meiosis II is like mitosis.
Prophase II

16. Meiosis II – Metaphase II
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II – Metaphase II
A haploid number of chromosomes
line up at the equator.
Metaphase II

17. Meiosis II – Anaphase II
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II – Anaphase II
The sister chromatids are
pulled apart at the centromere by spindle
fibers and move toward the opposite poles
of the cell.
Anaphase II

18. Meiosis II – Telophase II
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II – Telophase II
The chromosomes reach the poles, and
the nuclear membrane and nuclei reform.
Telophase II

19. Meiosis II - Cytokinesis
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II - Cytokinesis
Cytokinesis results in four haploid cells, each with n number of chromosomes.
The 4 daughter cells are genetically unique.
Cytokinesis

20. The Importance of Meiosis
Chapter 10
Sexual Reproduction and Genetics
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

21. Other Concepts in Sexual Reproduction
Fertilization
- the joining of a sperm & egg to form a fertilized egg cell called a zygote.

22. This process is aided by wind & animals
Other Concepts in Sexual Reproduction
Pollination in Plants
- when pollen grains (sperm cells) from a seed plant land on the female reproductive structure of the plant. This leads to fertilization & seed formation.
This process is aided by wind & animals

23. Other Concepts in Sexual Reproduction
Conjugation
- A process in which two cells (prokaryotic or protist) connect to each other and exchange genetic information – thereby increasing genetic variation.

24. Sexual vs. Asexual Reproduction
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Sexual vs. Asexual Reproduction
Asexual reproduction
The organism inherits all of its chromosomes from a single parent.
The new individual is genetically identical to its parent.
Advantages: Doesn’t require a partner, faster,
works well in a stable environment.
Disadvantages: No genetic variation. A major
environmental change can wipe out a species.

25. Sexual vs. Asexual Reproduction
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Sexual vs. Asexual Reproduction
Sexual reproduction
The organism inherits different genetic info from each parent.
The new individual is genetically unique from its parents.
Advantages: More genetic variation means
possible survival in a changing environment.
Disadvantages: Slower, 2 parents & mating
required.

29. In rabbits, gray fur (G) is dominant to black
Chapter 10
Sexual Reproduction and Genetics
10.2 Formative Questions
In rabbits, gray fur (G) is dominant to black
fur (g). If a heterozygous male is crossed with
a heterozygous female, what is the phenotypic
ratio of the possible offspring?
1:1
1:2:1
2:1
3:1 A B C D
FQ 7

30. Which explains how the shuffling of genes
Chapter 10
Sexual Reproduction and Genetics
10.3 Formative Questions
Which explains how the shuffling of genes
during meiosis results in billions of possible
combinations?
crossing over
gene linkage
genetic recombination
independent segregation A B C D
FQ 8

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

32. What is the term for an organism that has one
Chapter 10
Sexual Reproduction and Genetics
10.3 Formative Questions
What is the term for an organism that has one
or more sets of extra chromosomes in its cells?
diploid
gamete
hybrid
polyploid A B C D
FQ 10

33. How many chromosomes would a cell have
Chapter 10
Sexual Reproduction and Genetics
Chapter Assessment Questions
How many chromosomes would a cell have
during metaphase I of meiosis if it has 12
chromosomes during interphase? 6 12 24 36 A B C D
CAQ 1

34. Which stage of meiosis is illustrated?
Chapter 10
Sexual Reproduction and Genetics
Chapter Assessment Questions
Which stage of meiosis is illustrated?
prophase I
interphase
anaphase I
anaphase II A B C D
CAQ 2

35. What is the next step for the chromosomes illustrated?
Chapter 10
Sexual Reproduction and Genetics
Chapter Assessment Questions
What is the next step for the chromosomes illustrated?
Chromosomes replicate.
Chromosomes move to opposite poles.
Chromosomes uncoil and form two nuclei.
Chromosomes line up at the equator. A B C D
CAQ 3

36. What is this process called?
Chapter 10
Sexual Reproduction and Genetics
Standardized Test Practice
What is this process called?
fertilization
gamete formation
inheritance
reproduction A B C D
STP 1

37. Standardized Test Practice
Chapter 10
Sexual Reproduction and Genetics
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?
DNA replication
crossing over
synapsis
telophase A B C D
STP 2

38. At what stage is the chromosome number reduced from 2n to n?
Chapter 10
Sexual Reproduction and Genetics
Standardized Test Practice
At what stage is the chromosome number reduced from 2n to n?
prophase I
metaphase I
anaphase I
meiosis II A B C D
STP 3

39. To which step in this process does the law of segregation apply?
Chapter 10
Sexual Reproduction and Genetics
Standardized Test Practice
To which step in this process does the law of segregation apply?
grows into plant
gamete formation
fertilization
seed development A B C D
STP 4

40. 1/4 1/2 1 For human eye color, brown is dominant and
Chapter 10
Sexual Reproduction and Genetics
Standardized Test Practice
For human eye color, brown is dominant and
blue is recessive. If a husband is heterozygous
and his wife has blue eyes, what is the
probability that their child will have blue eyes?
1/4
1/2 1 A B C D
STP 5