1. Sexual reproduction is
Meiosis…

2. Mitosis Review Mitosis was cell division.
This is how you get more cells and how you grow bigger.
Mitosis is also important for asexual reproduction.

3. Mitosis
When human cells divide, the daughter cells have how many chromosomes???
If we reproduced like amoebas, we could just divide continually, and each daughter cell would have the same number of chromosomes (46).
However, we reproduce sexually.

4. Sexual Reproduction
Definition-process that creates a new organism by combining the genetic material of two organisms; it occurs both in eukaryotes and in prokaryotes.

5. How Do Organisms Sexually Reproduce?
DNA from both parents needs to be recombined!
A female gamete and a male gamete, must come together and form a zygote.

6. VARIATION is genetic diversity
Sexual reproduction has two parents, so the offspring are genetically different, and this creates variation among a species.

7. Genetic Differences
Sometimes it can be really difficult to see the genetic variation among individuals.
They may look the same, but they actually have lots of variety in their genes.

8. Sperm Cells All cells in our body have 46 chromosomes (23 pairs)
Sperm cells do not have 46 chromosomes. They have half the number of chromosomes (only 23), so they are called HAPLOID cells.

9. Egg Cells All cells in our body have 46 chromosomes (23 pairs)
Eff cells do not have 46 chromosomes. They have half the number of chromosomes (only 23), so they are called HAPLOID cells.

10. Sperm and Egg Sperm cells and egg cells are HAPLOID
They are also called our gametes.
2 gametes are needed to make a baby.

11. Fertilization Definition-an egg is penetrated by a sperm cell.
The haploid information of the gametes combines into one!
Now the cells are called a ZYGOTE

12. ZYGOTES A zygote is made from 2 gametes.
A zygote has half of its chromosomes from a female parent, and half of its chromosomes from a male parent.
Since a zygote has 46 chromosomes, it is a DIPLOID cell (not haploid)

13. Embryos
How does a zygote grow until it becomes big enough to be an embryo?

16. How are egg and sperm cells made?
If all of our cells have 46 chromosomes, how do egg and sperm cells end up with only 23?
Haploid Cell Diploid Cell

17. Meiosis!!!
Meiosis is the process that produces gametes with half the number of chromosomes.

18. Meiosis 1 Each of your 46 chromosomes replicates, so that you have 92.
Each chromosome pairs up with its exact replicate and is joined by a centromere.

19. Homologous Pairs
The sister chromatids from mom and the sister chromatids from dad for the same chromosome are a HOMOLOGOUS PAIR

20. We have 4 of each chromosome!
There are 4 copies of chromosome 12 here.
How many sex cells (gametes, haploids) are we going to be able to make???

21. Before chromosomes split…
Crossing Over Occurs!
The homologous pairs exchange genetic information.

22. Results of crossing over…
You will end up with crossed-over homologous pairs.
The sister chromatids are no longer identical!

23. Prophase 1
Homologous chromosomes pair up, crossing over occurs.

24. Metaphase 1
Homologous chromosomes pair up at the equator of the cell.

25. Anaphase 1
Homologous chromosomes separate and are pulled to opposite poles by the spindle fibers. The sister chromatids do not separate yet!

26. Anaphase 1
It doesn’t matter which pair goes to which side! Some cells will get more “mom” genetic information. Some cells will get more “dad” genetic information. This is called INDEPENDENT ASSORTMENT.

27. Telophase 1
The homologous pairs are completely separated to separate poles, which will become separate cells.

28. Interkinesis
We now have 2 cells, each with 46 chromosomes, but they are nothing like their parent cells!! Crossing over and independent assortment made them very different!
The cells grow now and make proteins, but there is no reason to make DNA.
interkinesis

29. Meiosis 2
We have 46 chromosomes in the two cells we created. We only want 23 in the gametes though.
We now have to split up the sister chromatids that are in each cell!

30. Prophase 2
The sister chromatids hang out in their cell, while spindle fibers start to form.

31. Metaphase 2
The sister chromatids form a single line across the middle of the cell.

32. Anaphase 2
Sister chromatids are pulled apart. They move to opposite poles.
Once they separate, they can be called chromosomes again.

33. Telophase 2
Spindle fibres begin to disappear, and a nuclear membrane forms around each set of chromosomes.

34. Cytokinesis
The two daughter cells are finally separated. How many are there? How many chromosomes in each? (Don’t say 2!)

35. More independent assortment.
It doesn’t matter how the sister chromatids separate! (As long as there is one of each of the 23 chromosomes in each cell)

36. Variation How did the 4 gamete cells become different from each other?
Crossing over
Independent assortment of homologous pairs (anaphase 1)
Independent assortment of sister chromatids (anaphase 2).

37. Example of Crossing Over
Hair color and eye color are on the same gene.
That is why so many people are blonde with blue eyes.
If people have black hair with blue eyes, that gene would have had to cross over in the middle!

38. Mutations
Remember that many different types of mutations can happen to your DNA and your chromosomes.
Insertion
Deletion
Substitution
Inversion
Duplication

39. What if the sister chromatids do not separate properly??

40. Examine a karyotype.
Geneticists make karyotypes by lining up chromosomes from people’s cells that are undergoing simple mitosis.

41. What’s wrong with this karyotype?

42. Down Syndrome
There are 3 copies of chromosome 21! (2 copies from one parent, 1 copy from the other parent)
This is called a trisomy.

43. What’s wrong with this karyotype?

44. Edwards Syndrome.
There is a trisomy on the 18th chromosome.

45. Other Genetic Disorders
Chromosome
22q11.2 deletion syndrome
22q
Angelman syndrome 15
Canavan disease
17p
Coeliac disease
Charcot–Marie–Tooth disease
Color blindness X
Cri du chat 5
Cystic fibrosis 7q
Down syndrome 21
Duchenne muscular dystrophy Xp
Haemochromatosis 6
Haemophilia
Klinefelter syndrome
Neurofibromatosis
17q/22q/?
Phenylketonuria
12q
Polycystic kidney disease
16 (PKD1) or 4 (PKD2)
Prader–Willi syndrome
Sickle-cell disease
11p
Tay–Sachs disease
Turner syndrome
We already learned about recessive disorders on the XY chromosome in males.
Other genetic disorders include: