1. MEIOSIS

2. Parents can produce many types of offspring
Families will have resemblances, but no two are exactly alike

3. Eukaryotic DNA is organized in chromosomes.
Genes have specific places on chromosomes.
Gene-carry information that go toward determining your traits. Genes control the TRAITS of the individual
Trait - A physical characteristic, you inherit from your parents; this means your parents pass some of their characteristics on to you through genes. Examples of traits are height, eye color, and the ability to roll your tongue.

4. Every cell has a nucleus
Every nucleus has chromosomes
The number of chromosomes depends on the species
Ex. Humans have 46

5. Chromosomes come in matching sets -these are called homologous pairs

6. Chromosomes and Chromosome Number
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes—one of two paired chromosomes, one from each parent
Pairs 1-22
Humans have 23 pairs of homologous chromosomes pairs of autosomes
1 pair of sex chromosomes

7. Homologous chromosomes
Same Length
Same centromere position
Carry genes that control the same inherited traits

8. Homologous Chromosomes
eye color
locus
hair color

9. FIND THE HOMOLOG!

10. A somatic cell is any biological cell forming the body of an organism, somatic cells make up all the internal organs, skin, bones, blood, and connective tissue.
By contrast, gametes are cells that fuse during sexual reproduction, for organisms that reproduce sexually. Sperm and egg cell.

11. Fertilization n=23 egg 2n=46 zygote
The fusion of a sperm and egg to form a zygote
A zygote is a fertilized egg
n=23
egg
sperm
n=23
2n=46
zygote

12. A haploid cell has only one set of chromosomes N
A diploid cell has two sets of chromosomes 2N.
In human, the somatic cells are diploid, and the gametes are haploid.
Human cheek cells have 46 chromosomes. (Diploid)
Human sex cells have 23 chromosomes. (Haploid)

13. Cells in your body have a complete set (all 46) - they are called DIPLOID  
Sex cells (sperm and eggs) only have half (23)  - they are called HAPLOID

14. ---During Meiosis diploid cells are reduced to haploid cells
In humans, a diploid cell contains a total of 46 chromosomes, while haploid cells have 23 homologous chromosome pairs
All sex cells must reduce their chromosome number as they divide. This reduction division is called meiosis and changes the chromosome number from Diploid to Haploid.
---During Meiosis diploid cells are reduced to haploid cells
Diploid (2n)  Haploid (n)
When mitosis produces 2 identical daughter cells, both the parent and daughter cells referred to as diploid while in meiosis a diploid cell divides twice to produce 4 daughter cells that are considered haploid.

15. What is the difference between Diploid and Haploid?
Haploid cells contain only one set of chromosomes and diploid cells contain two sets of chromosomes.
• Haploid cells are produced by meiosis, and diploid cells are produced by mitosis.
• Diploid cells have the same number of chromosomes as the parent cell, and haploid cells have only a half of the number of chromosomes as the parent cell.
• Diploid cells are genetically identical to the parent cell, and haploid cells are not genetically identical to the parent cell.
• Haploid cells are important in sexual reproduction, and diploid cells are important in growth, asexual reproduction and genetic stability.

16. The process of creating a gamete (sex cell) is called MEIOSIS
It is similar to mitosis, but  will produce 4 daughter cells that are each haploid.

17. Why do we need meiosis?
Meiosis is necessary to halve the number of chromosomes going into the sex cells
Why halve the chromosomes in gametes?
At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

18. Mitosis vs Meiosis Mi-two-sis Mei-one-sis
Produces body cells-Somatic cells
Daughter cells are diploid 2N
2 Daughter cells are produced
Daughter cells are genetically IDENTICAL to parent
One nuclear division
Produces cells for growth and repair
Produces sex cell-Gametes
Daughter cells are haploid N
4 Daughter cells are produced
Daughter cells have one half of the genes from the parent cell.
Two nuclear divisions
Produces cells for sexual reproduction
Generates genetic diversity through crossing over

19. Homologous chromosomes
Meiosis
Diploid germ cell
Chromosome #: 46
DNA content: 2n
Homologous chromosomes 2n 4n 1n
Chromosome #: 46
DNA content: 4n
Reduction
division
Chromosome #: 23
DNA content: 2n
Mitotic
division
Chromosome #: 23
DNA content: 1n
Haploid
gametes

21. Meiosis
Has 2 stages
Meiosis 1, This is the stage where the chromosomes nuber is halved
Includes 4 stages
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Meiosis 2

22. Chromosomes replicate.
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis I
Interphase
Chromosomes replicate.
Chromatin condenses.
Interphase

23. Each chromosome consists of two chromatids.
Section 1
Sexual Reproduction and Genetics
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.

24. Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis I
Prophase I
Crossing over produces exchange of genetic information. Extremely IMPORTANT!!! It is during this phase that crossing over can occur.
Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

25. When homologous chromosomes hang out so close to each other they swap parts!
This is called “crossing over”
Crossing over increases genetic diversity

26. Chromosome centromeres attach to spindle fibers.
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis I
Metaphase I
Chromosome centromeres attach to spindle fibers.
Metaphase I
Homologous chromosomes line up at the equator.

27. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis
Mitosis
The first (and distinguishing) division of meiosis

28. Homologous chromosomes separate and move
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis I
Anaphase I
Homologous chromosomes separate and move
to opposite poles of the cell.
Anaphase I
Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis)

29. The spindles break down.
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis I
Telophase I
The spindles break down.
Telophase I
Chromosomes uncoil and form two nuclei.
The cell divides.
Cytokinesis occurs Spontaneously with Telophase 1
Results in 2 haploid daughter cells

31. Figure 13.7 The stages of meiotic cell division: Meiosis I

32. After Meiosis 1… Homologous chromosomes have been separated
Two non-identical daughter cells have been formed
The chromosomes number has been cut in half

33. Meiosis 2 is similar to Mitosis
Two identical daughter cells are formed from each of the cells created in Meiosis 1
Includes 4 stages
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

34. A second set of phases begins
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis II
Prophase II
A second set of phases begins
as the spindle apparatus forms and the
chromosomes condense.
Prophase II
Nucleolus/Nuclear Envelope breaks down

35. A haploid number of chromosomes
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis II
Metaphase II
A haploid number of chromosomes
line up at the equator.
Metaphase II

36. The sister chromatids are
Section 1
Sexual Reproduction and Genetics
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

37. The chromosomes reach the poles, and
Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis II
Telophase II
The chromosomes reach the poles, and
the nuclear membrane and nuclei reform. Spindle fibers disappear.
Telophase II

38. Section 1
Sexual Reproduction and Genetics
Meiosis
Meiosis II
Cytokinesis results in four haploid cells, each with n number of chromosomes.
Cytokinesis

39. Figure 13.7 The stages of meiotic cell division: Meiosis II

40. The Importance of Meiosis
Section 1
Sexual Reproduction and Genetics
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

41. Mitosis vs. Meiosis