1. MEIOSIS
& Sexual Reproduction

2. Meiosis-
cell division in which the daughter cells receive only half the number of chromosomes present in the parent cells
Homologous chromosomes-
pairs of similar chromosomes (same size, shape, & carrying alleles [genes] for the same trait)
1. Humans have 46 chromosomes (22 pairs of homologous chromosomes & one pair of sex chromosomes)
2. Autosomes- are the chromosomes other than the sex chromosomes ex) somatic or body cells

3. Diploid cells- contain the full # of chromosomes (2n)
Haploid cells- gametes that contain half the # of chromosomes (n); no homologous pairs
Gametes- specialized sex cells
Female gametes = egg cells or ova (ovum is singular; egg cell)
Male gamete = sperm cell
Fertilization- the fusion of sperm & ova nuclei to form a zygote

4. Stages of Meiosis- "reduction division" in specialized cells for reproduction. IPMATPMAT
It is a process which prepares sex cells.

6. A. Prophase I
1. Each chromosome has already replicated & consists of 2 chromatids
a. Synapsis results in 4 chromatids joining together to form a tetrad
2. Each chromosome lines up relatively close with its homologous chromosomes & become attached at their centromeres. This process is called SYNAPSIS.
3.while tetrads form, CROSSING OVER occurs, which is the exchange of segments between chromatids

9. Metaphase I
1. Centromeres are attached by the spindle fibers
2. Tetrads line up at the equatorial plane
Anaphase I
1. DISJUNCTION- separation of tetrads into homologous chromosomes
NON DISJUNCTION - is the failure to separate homologous chromosomes (very bad)

12. Telophase I
1. Cytokinesis occurs forming daughter cells
2. Nuclear membrane reappears around the nuclei.
3. No further replication of chromosomes takes place, but the remainder of the division is exactly like mitosis

13. Prophase II
[both daughter cells divide]
[homologous chromosome line up on the equator]
Metaphase II
Anaphase II
[homologous chromosomes separate]
[4 different haploid cells are produced, these (n) are gametes]
Telophase II

14. Number of daughter cells Number of cell divisions
COMPARISON CHART
MITOSIS vs. MEIOSIS
Characteristic
Mitosis
Meiosis
Number of daughter cells
Number of cell divisions
Chromosome number in daughter cells
Comparing daughter cells and parent cell
Type of reproduction 2 4 2 1
Same as parent
One-half of parent
identical
different
sexual
asexual

15. Sexual Reproduction
Advantages
1. Offspring are not identical to either parent
2. Variations that increases adaptability in a changing environment
3. Individuals are able to move into new environments
4. By making population more varied helps to ensure survival of the species

16. Sexual Reproduction in Simple Organisms- CONJUGATION (permits the recombination of hereditary material, to form new variety of organisms)
A. Spirogyra- the flow of cell material between 2 cells through a conjugation tube and the formation of a zygospore (protective wall)
B. Paramecium- formation of a protoplasmic bridge between 2 and the exchange of material.
Don't have sexes, but different mating types positive/negative isogametes.
C. Bacteria

18. Sexual Reproduction in Animals
specialized organs that produce gametes
Gonads-
Ovaries-
female that produce ova (egg cells)
Testis-
male that produce sperm cells
contain both ovaries and testes
Hermaphrodism -

19. Gametogenesis -
production of gametes
Oogenesis –
production of ova in the ovaries
Meiotic division that produces 3 polar bodies and one mature ovum
production of sperm in the testes
Spermatogenesis –
Meiotic division that produces 4 sperm
cells

22. Comparison of egg and sperm
Egg cells contain yolk, and are larger than sperm
Sperm is motile, eggs are sessile

23. fusion of sperm and egg nuclei to form a zygote
Fertilization -
1. Diploid (2n) chromosomes restored
takes place outside of body - more eggs are produced
2. External fertilization -
a. Amphibians
b. fish
takes place inside body, less eggs are produced
3. Internal fertilization -
a.Mammals
b. birds

24. Parthenogenesis –
the development of an unfertilized egg into an adult animal
1. Bees
2. Ants
3. Aphids