1. 3C Meiosis

2. Cell Division
MITOSIS is the division of one cell into TWO IDENTICAL DIPLOID cells
Identical to each other
Identical to the original cell
Same number of chromosomes

3. Cell Division
MEIOSIS is the division of one cell into FOUR genetically DIFFERENT HAPLOID GAMETES (known as sex cells)
Different from each other
Different from the original cell
HALF the number of chromosomes

4. Sexual Reproduction When a sperm fertilizes an egg…
Does the fertilized egg have twice as many chromosomes?
Why not?
Because the sperm and the egg have HALF the chromosomes of a normal cell

5. Chromosome Pairs Humans have 46 chromosomes
Each of our 46 chromosomes has a “twin”
23 sets of “twins”

6. Chromosome Pairs HOMOLOGOUS PAIRS
Two chromosomes with same genetic info
Mom’s gene for hair color match up with dad’s gene for hair color to determine your hair color
23 chromosomes come from mom
23 chromosomes come from dad
= 46
23 HOMOLOGOUS PAIRS = 46 total chromosomes

7. Sexual Reproduction GAMETE – any reproductive cell Egg or sperm
Gametes are haploid (23)
HAPLOID = 1 set of unpaired chromosomes
HA = Half
PLOID = Chromosomes

8. Sexual Reproduction
MEIOSIS is the cell division in which the resulting cells (gametes) have half the number of chromosomes as the original cell
FERTILIZATION
Haploid + Haploid = Diploid
Egg + Sperm = Fertilized Egg

9. Meiosis Meiosis has two parts:
Meiosis I – separation of homologous chromosomes
Meiosis II – separation of sister chromatids

10. Meiosis Overview Very similar to mitosis Here are the differences…
Starts as diploid (2n)
Ends as haploid (1n)

11. Genetic Variation: Crossing Over

12. Crossing Over – also known as homologous recombination

13. Tetrad

22. Meiosis Video

23. Meiosis

24. Sources of Genetic Variation
ONE – Mutations (Replication)
As discussed in last unit, mutations can occur in cells
If mutations occur during replication in gametes, mutation will be passed to offspring leading to potentially new traits in offspring

25. Sources of Genetic Variation
TWO – Mutations (Environmental Factors)
Again - As discussed in last unit, mutations can occur in cells
If mutations caused by environmental factors occur in gametes, they can also be passed to the offspring

26. Sources of Genetic Variation
THREE - Meiosis
New genetic combinations from meiosis
Partially due to the separation of homologous pairs (each gamete is haploid)
Also due to crossing over – aids in every gamete being genetically unique

27. Nondisjunction
In addition, some genetic disorders are due to failure of meiosis to occur properly
Nondisjunction – failure of meiosis to properly separate chromosomes in gametes

28. Nondisjunction Gametes end up with too few or too many chromosomes
Examples:
Down’s Syndrome (Trisomy 21)
Klinefelter’s Syndrome (XXY)
Turner’s Syndrome (X)
TURNER
short stature (usually under 5' tall) is the most common feature of TS
narrow, high-arched palate
retrognathia (lower jaw not prominent)
ears protruding outward, and/or low set, and/ or rotated toward neck low hairline
webbed neck (excess or stretched skin) which may include a lowered hairline
droopy eyes
strabismus (lazy eye)
broad chest
cubitus valgus (arm turns slightly out at the elbow)
scoliosis (curvature of spine)
flat feet
small and narrow fingernails, toenails that turn up
short fourth metacarpal (bone in hand under knuckle)
edema (swelling or puffiness) or hands and feet, especially at birth
KLINEFELTER
Boys and teenagers
Taller than average stature
Longer legs, shorter torso and broader hips compared with other boys
Absent, delayed or incomplete puberty
After puberty, less muscular bodies and less facial and body hair compared with other teens
Small, firm testicles
Small penis
Enlarged breast tissue (gynecomastia)
Weak bones
Low energy levels
Shyness
Difficulty expressing feelings or socializing
Problems with reading, writing, spelling or math
Attention problems
Men
Infertility
Small testicles and penis
Decreased facial and body hair
Enlarged breast tissue
Decreased sex drive