1. Review of chromosome structure and intro to meiosis
Sexual Reproduction and Meiosis
Review of chromosome structure and intro to meiosis

2. What is a chromosome? Contains genetic information
Made of genes which are made of DNA
Chr. genes  DNA (Large => Small)
Let’s look at the structure: chromatid, centromere, double stranded chromosome

4. CHROMATIN thin uncoilded strands of DNA

6. CHROMATID each side of chromosome

7. What are homologous chromosomes?
Homologous chromosomes are sets of double strand chromosomes that are in all cells in your body.
You get one set from mom and one set from dad
Karyotype

8. HOMOLOGOUS CHROMOSOME the same shape and size carry genes for same traits

10. Karyotype What gender is this individual?

11. What can you tell me about this karyotype?

12. Diagnosis the individual…

13. DIPLOID cells with TWO sets of chromosomes (2n)

14. Haploid only ONE set of chromosomes (n)

15. Reproduction and Development
What is reproduction?

16. Reproduction To make more of its own kind:
A) asexual – 1 parent, identical offspring
B) sexual – 2 parents, NOT identical offspring

17. MEIOSIS: GAMETE CELL DIVISION
Recall that GAMETES are the REPRODUCTIVE (SEX) cells of the body. (Sperm and Egg)
The purpose of Meiosis is to produce gametes
SEXUAL REPRODUCTION occurs when two different individuals ( 1 male & 1 female) produce a HYBRID OFFSPRING (a combination of both parents) by each contributing 1 GAMETE cell.
Male cell: SPERM CELL
Female cell: EGG CELL
FERTILIZATION occurs when the two cells meet and form ONE new cell called the ZYGOTE. (This is the very FIRST cell of any sexually reproducing organism)
The zygote will then divide OVER AND OVER again VIA MITOSIS until it grows into fully developed individual.

18. GAMETOGENESIS: The making of gametes
GAMETE - SEX CELL (SPERM OR EGG)
GENESIS - TO MAKE OR CREATE
2 TYPES:
SPERMATOGENESIS - Makes MALE sperm cells
OOGENESIS - Makes the FEMALE egg cells
Both processes use MEIOSIS as their type of cell division, HOWEVER the results are quite different.

20. In order for a sexually reproducing organism's chromosome number to stay the same generation after generation (for example: Humans- 46 chromosomes) the gamete's chromosome number must be HALF of the normal number.
(Human gamete - 23 chromosomes)
To make such cells requires a different type of cell division called MEIOSIS

21. MEIOSIS I:
Interphase: Copies of the chromosome pairs are made leaving the cell with 92 chromotids
PROPHASE I: Same as prophase of mitosis EXCEPT
Once chromosome are formed, they PAIR UP with their MATCHING COUNTERPART. (ALSO CALLED SYNAPSIS)
*REMEMBER! You have 2 copies of each of the 23 chromosomes (1 from mom, 1 from dad), this adds up to make 46 total.
This is called a HOMOLOGOUS PAIR – during meiosis they form tetrads
CROSSING OVER occurs between the homologous chromosomes
(GENES can FLIP-FLOP from one chromosome to its partner)
Crossing over creates endless gene combinations and GREATLY increases GENETIC DIVERSITY

23. Crossing Over
Crossing over - portions of chromatids break off and attach to adjacent chromatids on homologous chromosome
Crossing over allows for the random mixing of genes (genetic recombination) which adds genetic variety to a species so that no two individuals are exactly the same.

24. Crossing over in Prophase 1
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

25. Crossing Over Metaphase I Prophase I: Tetrad formation/ crossing over
Anaphase I
Telophase I
Because of crossing over, every gamete receives a unique set of genetic information.
Telophase II

26. Crossing over animation

27. METAPHASE I:
Same as metaphase of mitosis EXCEPT. . .
HOMOLOGOUS PAIRS line up in the middle, instead of INDIVIDUAL chromosomes.
ANAPHASE I:
SISTER CHROMATIDS are NOT pulled apart
HOMOLOGOUS PAIRS are pulled apart "BUTTERFLIES" are still intact
TELOPHASE I:
Same as telophase of mitosis EXCEPT. . .
At this point the CHROMOSOME NUMBER has been reduced from 92 to 46 in the
daughter cells. (From DIPLOID to HAPLOID)

30. Meiosis II
The events that take place in MEIOSIS II are exactly the same as MITOSIS, EXCEPT that there are only 23 chromosomes being separated INSTEAD of 46.

31. IMPORTANT DISTINCTION
NOTE: There is NO interphase between meiosis I and meiosis II.
Why is this important?
So that each new cell will only have half (haploid) the number of chromosomes as the original parent cell.
Meiosis II is not preceded by the copying of DNA

32. Stages Of Meiosis - Meiosis II
Prophase II - Cells do not go into interphase between meiosis I and II, thus chromosomes are already condensed
Metaphase II - Chromosomes line up at the equator of the two haploid cells produced in meiosis I
Anaphase II - Chromosomes made up of two chromatids split to make chromosomes with one chromatid which migrate to the poles of the cells
Telophase II - Cytokinesis and reformation of the nuclear membrane in four haploid cells each with one set of chromosomes made of one chromatid

35. Meiosis goes through TWO sets of division (not ONE): MEIOSIS I and II
SIMILARITIES:
The order of phases ( P > M > A > T ) and major events that occur at each are the same for the most part
PROPHASE- formation of chromosomes, centrioles, & spindle fibers
METAPHASE- chromosomes line up on equator
ANAPHASE- pulling apart of chromosomes
TELOPHASE- separation completes, cytokinesis occurs
DIFFERENCES:
Meiosis goes through TWO sets of division (not ONE): MEIOSIS I and II
Meiosis produces FOUR daughter cells (not TWO)
Daughter cells have been reduced to HAPLOID (N) cells (23 chromosomes) instead of DIPLOID (2N) (46 chromosomes)
Daughter cells are NOT IDENTICAL to the PARENT cell or EACH OTHER

36. Secondary Spermatocytes
SPERMATOGENESIS
Happens in the TESTES
GERM CELLS in the testes are DIPLOID (2N, 46) just like the rest of the body cells.
Initial germ cells are called PRIMARY SPERMATOCYTES
1 round of spermatogenesis produces FOUR healthy sperm cells. Every sperm cell contains a unique combination of genes. (NO TWO ARE ALIKE!) 46 23
Primary Spermatocyte
Secondary Spermatocytes
Spermatids
Mature Sperm Cells 2N m1 1N
(1 chromosome = 1pair of sister chromatids – still connected) m2 1N

37. Initial germ cells are called PRIMARY OOCYTES
OOGENESIS:
Happens in the OVARIES
GERM CELLS in the ovaries are DIPLOID (2N, 46) just like the rest of the body cells.
Initial germ cells are called PRIMARY OOCYTES
1 round of Oogenesis produces ONE healthy egg cell (OVUM), and THREE POLAR BODIES. The polar bodies serve NO PURPOSE in the body.
Primary Oocyte
1 Ootid
Mature Egg Cell (OVUM) 46 23
3 Polar Bodies X
Secondary Oocytes 2N m1 1N
(1 chromosome = 1pair of sister chromatids – still connected) m2 1N 23

38. Sperm production begins at puberty and continues throughout life
Sperm production begins at puberty and continues throughout life. An average of 300,000,000 sperm cells are made every day.
Females start releasing ONE mature egg every month beginning at puberty and ending at MENOPAUSE (late 40s to 50s) .
Why the difference?! Why do males make so much sperm and females make so few eggs?