1. Levels of Organization in DNA
Double helix
Chromatin with nucleosome packaging via histone proteins
Chromosome

2. Outcome of Mitosis
Result: two DIPLOID cells that are identical to one another
Diploid: describes a cell or nucleus that contains two complete sets of paired chromosomes, one from each parent
Haploid: describes a cell or nucleus that contains only one set of unpaired chromosomes
Animation for Review:

3. Centromere
Homologous chromosomes: pair of chromosomes with the same general structure, and sequence of genes ; one chromosome comes from mom, the other from dad
Sister chromatids: either of the two identical copies of a replicated chromosome ; one half of the duplicated chromosome

4. Locus/loci: the specific location or position of a gene on a chromosome (Ex: gene for eye color vs. enzyme A vs. cytochrome C)

5. How do chromosomes differ? Alleles
Allele: specific form or variation of a gene ; you inherit one from mom, and one from dad ; source of variation in traits
Alleles differ from other alleles by one to few bases (nucleotides)
Example 1: alleles for blue eyes vs. brown eyes for the gene of eye color
Example 2: alleles for A blood-type vs alleles for B blood type for gene of blood type

6. Meiosis
Meiosis: process where a single diploid cell divides to produce four cells containing half the original amount of DNA (haploid)
Produces gametes (eggs and sperm) – also called “sex cells”
Only occurs in sex organs (testes or ovaries)

7. How Meiosis Works: http://highered. mheducation
Stages of Meiosis:

8. How does meiosis contribute to the variation in traits?
Crossing Over during Prophase I:
Parts of non-sister chromatids cross over and exchange genetic material
Produces chromatids with a new combination of alleles (recombinants)
Can occur along any part or length of the chromosome
Independent (or Random) Assortment during Metaphase I:
Chromosomes line up randomly
The inheritance of one gene/trait is independent of the inheritance of another trait (this means that an allele of one chromosome has an equal chance of being paired with any allele on another chromosome) **ONLY FOR NON-LINKED TRAITS
2^23 combinations in humans

9. What is synapsis?
Synapsis: Pairing of homologous chromosomes

10. What is a tetrad?
Tetrad: two pairs of homologous chromosomes next to each other
“Homologous chromosomes in a tetrad cross over each other, resulting in sister chromatids with a different set of alleles.”

11. Variation due to Crossing Over
Chiasma/Chiasmata: specific location where alleles cross over
Recombinant (HL Only): allele combinations that were not present in the original parents ; result from crossing over

12. Recombinant Chromosomes After Crossing Over

13. Variation Due to Independent Assortment

14. Outcome of Meiosis
Gametes (sperm or egg cells) that are unique in their genetic composition, and haploid nuclei

15. Why is meiosis considered a “reduction division”?
Meiosis consists of two divisions. DNA is replicated before the first division, resulting in two diploid cells. DNA is not replicated before the second division, which causes resulting daughter cells to have haploid nuclei.

16. Meiosis in Testes vs. Ovaries
Spermatogenesis
Oogenesis

17. Formation of Gametes in Testes vs. Ovaries

18. Stages of Gamete Development

19. Gamete Formation in Ovaries (Oogenesis)

20. Gamete Formation in Testes (Spermatogenesis)

21. Overview of Spermatogenesis

22. Overview of Oogenesis

23. These cells (spermatogonia) then undergo a period of growth
 Outline the processes involved in spermatogenesis within the testes, including mitosis, cell growth, the two divisions of meiosis and cell differentiation
Spermatogenesis describes the production of spermatozoa (sperm) in the seminiferous tubules of the testes
The first stage of sperm production requires the division of germline epithelium by mitosis
These cells (spermatogonia) then undergo a period of growth
This is followed by two meiotic divisions that result in four haploid daughter cells
These haploid cells then differentiate to form sperm cells
The developing sperm cells are nourished throughout by the Sertoli cells

24.  Outline the processes involved in oogenesis within the ovary, including mitosis, cell growth, the two divisions of meiosis, the unequal division of cytoplasm and the degeneration of polar body
Oogenesis describes the production of female gametes (ova) within the ovary
The process begins during foetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth
These cells begin meiosis but are arrested in prophase I until puberty
At puberty, some follicles continue to develop each month is response to FSH secretion
These follicles complete the first meiotic division to form two cells of unequal size
The cell with less cytoplasm is a polar body (which degenerates), while the larger cell forms a secondary oocyte
The secondary oocyte begins the second meiotic division but is arrested in prophase II (until fertilisation)
It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis
The second meiotic division will produce an ovum and a second polar body