1. What is the role of meiosis in reproductive varability?
SB2. Students will analyze how biological traits are passed on to successive generations
c. Using Mendel’s laws explain the roles of meiosis in reproductive variability
What is the role of meiosis in reproductive varability?

2. LEQ#4: What is the role of meiosis in reproductive variability?
What is the role of meiosis in reproductive varability?

3. What is the role of meiosis in reproductive varability?
Vocabulary to Know:
Meiosis
Gametes
Fertilization
Zygote
Crossing over
Meiosis I
Meiosis II
Sex cells
Sperm
Egg
Genetic recombination
synapsis
Embryo
Haploid
Diploid
Parent Cell
Daughter Cell
Heredity
Genetic variation
Variability
Sexual reproduction
Homologous Chromosomes
Independent assortment
What is the role of meiosis in reproductive varability?

4. What do you remember about mitosis?
What is mitosis?
Why is mitosis important?
What kind of cells does it produce?
What type of cells are produced?
Diploid or haploid
What is the role of meiosis in reproductive varability?

5. What is the role of meiosis in reproductive varability?
What is meiosis?
Process of cell division in sexually reproducing organisms that reduces the number of chromosomes in reproductive cells from diploid to haploid
Produces gametes
Sex cells
Sperm (male)
Egg (female)
What is the role of meiosis in reproductive varability?

6. What is the role of meiosis in reproductive varability?
Diploid vs. Haploid
Diploid
Total number of paired chromosomes found in each somatic cell
Humans 46
Represented by 2n
Haploid
Number of chromosomes found in each sex cell
Humans 23
Represented by n
What is the role of meiosis in reproductive varability?

7. Mitosis vs. Meiosis
Similar to mitosis, but there are some important differences
Mitosis
Produces 2 genetically identical cells
Undergoes 1 cell division
Meiosis
Produces 4 genetically different cells
Undergoes 2 cell divisions
Meiosis I, Meiosis II
What is the role of meiosis in reproductive varability?

8. What is the role of meiosis in reproductive varability?
Stages of Meiosis
Meiosis I
Homologous chromosomes (paired chromosomes) pair up in process called synapsis
Prophase I crossing over occurs
Chromosome segments are broken off and exchanged between homologous chromosomes
Leads to additional genetic variation in offspring
What is the role of meiosis in reproductive varability?

9. What is the role of meiosis in reproductive varability?
Meiosis I Continued….
Metaphase I homologous pairs line up randomly
Called independent assortment
Anaphase I paired homologous chromosomes are pulled toward opposite ends by spindle
Cell divides during Telophase I to produce two daughter cells
What is the role of meiosis in reproductive varability?

10. What is the role of meiosis in reproductive varability?
Stages of Meiosis
Meiosis II
Nearly identical to mitosis
Two daughter cells undergo cell division and produce 4 haploid cells
Each with unique chromosomes
Genetically different
What is the role of meiosis in reproductive varability?

11. What are 2 similarities between mitosis and meiosis?
What is the role of meiosis in reproductive varability?

12. What are 2 differences between mitosis and meiosis?
What is the role of meiosis in reproductive varability?

13. Comparison of Divisions
Mitosis
Meiosis
Number of divisions 1 2
Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction

14. What is the role of meiosis in reproductive varability?
Concept Check:
Meiosis produces human cells with how many chromosomes? 44 23 46 15
What is the role of meiosis in reproductive varability?

15. What is the role of meiosis in reproductive varability?
Concept Check:
2. Which of the following is an important factor in increasing variety among sexually reproducing organisms?
a. testcross
b. gene linkage
c. crossing over
d. synapsis
What is the role of meiosis in reproductive varability?

16. What is the role of meiosis in reproductive varability?
Concept Check
3. What event takes place during anaphase II of meiosis II?
a. Nuclear membrane breaks down
b. Spindle fibers disassemble
c. Sister chromatids separate
d. Cytoplasm divides
What is the role of meiosis in reproductive varability?

17. What is genetic variability?
What is the role of meiosis in reproductive varability?

18. What is the role of meiosis in reproductive varability?
Introduction
Offspring acquire genes from parents by inheriting chromosomes
Each chromosomes contains thousands of genes.
Half of the genes come from the mother
Half of the genes come from the father.
What is the role of meiosis in reproductive varability?

19. What is the role of meiosis in reproductive varability?
What are genes?
Genes are traits that are found on chromosomes
Genes determine an organisms traits
characteristics
Genes are passed on from one generation to the next
There are multiple versions of every gene
Called alleles
Each gene is located in a specific place on a specific chromosome
Each chromosomes contains thousands of genes
Homologous Chromosomes
Genes (Trait A and Trait B)
What is the role of meiosis in reproductive varability?

20. What is the role of meiosis in reproductive varability?
Genetic Variability
There is variability between all living organisms.
The degree to which differences exist among a population
To understand how meiosis affects genetic variability we must first look at fertilization
What is the role of meiosis in reproductive varability?

21. Meiosis Meiosis creates sperm and egg cells.
Oogenesis- formation of egg cell
Spermatogenesis-formation of sperm
What is the role of meiosis in reproductive varability?

22. Spermatogenesis Occurs in the testes
Two divisions produce 4 spermatids
Spermatids mature into sperm
Men produce about 250,000,000 sperm per day

23. Spermatogenesis

24. Oogenesis Occurs in the ovaries
Two divisions produce 3 polar bodies that die and 1 egg
Polar bodies die because of unequal division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte matures into an ovum (egg) every 28 days

25. Oogenesis Meiosis I Mitosis Mature egg Oogonium (diploid) Ovum (egg) aX a X a X
Meiosis I a A X
Mitosis
Mature
egg
Oogonium
(diploid) A X A X
Ovum (egg) A X

26. What is the role of meiosis in reproductive varability?
Fertilization
Union of male (sperm) and female (egg) gametes to create a zygote
Organism’s first cell
During fertilization the zygote receives one set of chromosomes from each parent’s gamete
The chromosomes from each parent then match up together to form homologous chromosomes
What is the role of meiosis in reproductive varability?

27. What is the role of meiosis in reproductive varability?
Each human gamete has 23 chromosomes (haploid) During fertilization the two gametes fuse to from a zygote containing 46 chromosomes (diploid)
Zygote
What is the role of meiosis in reproductive varability?

28. Role of Meiosis in Genetic Variability
During meiosis independent assortment and crossing over occur between pairs of homologous chromosomes.
Because of this each gamete formed during meiosis contains a different mixture of genes/traits.
The recombination of these genes during fertilization produces an offspring with a combination of traits from both parents
Genetic recombination
All of these factors contribute the genetic variability seen in living things.
What is the role of meiosis in reproductive varability?

29. What is the role of meiosis in reproductive varability?
Concept Check
4. Two similar chromosomes that you inherit from your parents ( one from your mother, one from you father) are called
a. homologous chromosomes
b. sister chromatids
c. sex chromosomes
d. homozygous alleles
What is the role of meiosis in reproductive varability?

30. What is the role of meiosis in reproductive varability?
Concept Check
5. Which of the following cell types is diploid?
a. sex cell
b. gamete
c. sperm cell
d. zygote
What is the role of meiosis in reproductive varability?