1. Meiosis and Sexual Reproduction Notes
To be used with Meiosis and Sexual Reproduction Guided Notes

2. Genes and Heredity Heredity -
the passing of traits from parents to offspring.
Genetics -
the study of heredity (the passing of traits)
Each human cell contains 30 thousand different genes

3. Karyotype Karyotype is a chart of an organism’s chromosomes.
All 30,000 genes are located on 23 pairs of chromosomes.

4. Genes and Heredity Genes:
Factors that control organism traits or characteristics.
Part of a chromosome containing the genetic code
Passed on from parent to offspring.

5. Alleles T t t T Alleles: part of a gene that is located on a
chromosome.
Example:
Height(gene):
tallness or shortness(alleles)
The alleles determine
how each gene is expressed.
At least two alleles for one gene.
Locus: Location of gene on
a chromosome. T T t t

6. Meiosis
Meiosis:
A type of cell division where the chromosome number is reduced to half.
The process in which cells undergo two dividing phases to form gametes.
Meiosis only produces sex cells (gametes).

7. Meiosis Gametes are your sex cells. Your egg and sperm cells.
Sexual reproduction
(sperm + egg)produces a zygote.

8. Meiosis

9. Diploid vs. Haploid
Diploid Number (2n): the number of chromosomes found in all body cells.
Humans 46.
Haploid Number (n): 1/2 the diploid number of chromosomes. Humans 23.
found in the egg and sperm cells of a species
DIPLOID
HAPLOID

10. Diploid vs. Haploid Organism Diploid # Haploid # Human 46
Chimpanzee 48
Dog 78
Fruit fly 8
Garden pea 14
Adder’s fern 23 24 39 4 7
630

11. Terms Gametes: eggs or sperm Gonads:
specialized organs in higher animals where the gametes are made
Ovaries:
female gonads
Testes:
male gonads

12. Meiosis Interphase Preparation phase Organelles & cell grows
Chromatin duplicates
Non dividing phase

13. Chromatin-Chromosome-Homologous Chromosome
Sister
Chromatid
Chromosome
Homologous Chromosome

14. Homologous Chromosomes:
-a pair of chromosomes that contain genes for the same traits.
-one chromosome is from mom the other from dad.
-same size & centromeres are in same location.

15. Homologous chromosomes pair up according to: 1. same genes 2. size 3. centromere loci

16. Prophase I Homologous chromosomes become visible & pair up
Prophase I Homologous chromosomes become visible & pair up. The nuclear membrane starts to disappear. Centrioles are present.

17. Prophase I Synapsis: the meeting of homologous chromosomes
Tetrads: the two pairs of homologous chromosomes
Crossing Over: the exchange of chromosome pieces
Crossing over increases the variability of the offspring
This is why the offspring of sexual reproduction show many variations
- Crossing over occurs only during prophase

18. Metaphase I Centrioles move to poles extending spindle fibers
Metaphase I Centrioles move to poles extending spindle fibers. Homologous chromosomes attach to spindle fibers in middle of cell.

19. Anaphase I Cell is egg shaped Homologous chromosomes pull apart.

20. Telophase I/Cytokenesis Complete cell division Cell is figure eight in shape.

23. End of Meiosis I Cytokenesis - cytoplasmic division of the cell occurs
ends the first stage of meiosis
At the end of meiosis I there are two cells
each daughter cell contains the diploid number of chromosomes

24. Meiosis II
Meiosis II:
Similar to mitosis but no interphase & chromosome replication.
No pairing of homologous chromosomes. Single chromosomes line up during metaphase II.
Diploid (2n) is reduced to haploid (n)

25. Meiosis

26. Mitosis vs. Meiosis

27. Problems during Meiosis
Normally, homologous chromosomes separate and move toward opposite poles of the cell.
Problems during anaphase: this disorder is called non Disjunction
Nondisjunction: the failure of homologous chromosomes to separate

28. Nondisjunction
Down's syndrome: results from the nondisjunction of chromosome 21
individual has an extra 21st chromosome

29. Down’s Syndrome Rates

30. Mistakes in Mitosis can be Good
polyploidy:
having an entire extra set of chromosomes
Will result in the 3n or 4n number of chromosomes
- Many plants are a result of polyploidy; banana & day lily

31. Summary Meiosis is very similar to two divisions of mitosis.
The diploid number (2n) of chromosomes is reduced by half to the haploid number (n)
Eggs and sperm are formed
Crossing Over occurs—lots of variation
Variations rarely occur in MITOSIS
Variations often occur in MEIOSIS
Gaccione likes little boys and girls on Tuesdays only

32. Results of Meiosis
Mitosis is associated with growth, replacement and asexual reproduction
Meiosis is associated with sexual reproduction & reduces the # of chromosomes in half
Spermatogenesis: the production of sperm
Produces 4 sperm
Oogenesis: the production of ova or eggs
Produces one egg and three polar bodies
Penis