1. MEIOSIS and SEXUAL REPRODUCTION

2. TERMS

3. Gametes – specialized cells involved in sexual reproduction (male and female)
Fertilization – fusion of the nuclei of the male and female gametes
Zygote – the single cell that results from fertilization

4. Meiosis – cell division that results in ½ the number of chromosomes of the parent cell

5. Somatic cells – all cells of the body except the sex cells
Homologous chromosomes – chromosomes in the cells that are arranged in pair of similar size, shape, and genetic content

6. Diploid cells – cells that contain homologous chromosomes
Haploid cells (monoploid) – cells that contain only one of each of the homologous pairs of chromosomes (gametes)

7. Synapsis – the pairing of the duplicated homologous pairs joined at the centromeres
Tetrad – the group of four chromatids (duplicated homologous pair)

8. Crossing over - the exchange of parts of chromatids that occurs during synapsis

9. Disjunction – the process of separation of the tetrads (during anaphase I.)

10. THE STAGES OF MEIOSIS

11. INTERPHASE the original cell has 6 chromosomes 3 chromosome pairs
chromosomes duplicate

12. PROPHASE I chromosomes already duplicated
chromosomes match up with its homologous pair
four chromatids are fastened at their centromere
four chromatids are called a “tetrad”
crossing over and exchange of segments may occur
nuclear membrane disappears
spindles form
tetrads move toward the equator

13. METAPHASE I Centromeres of the tetrads line up at the equator
Spindle microtubules fasten on to the centromeres

14. Homologous chromosome tetrad separate “disjunction”
ANAPHASE I
Homologous chromosome tetrad separate “disjunction”

15. Cytokinesis occurs – two daughter cells produced
TELOPHASE I
Cytokinesis occurs – two daughter cells produced

16. Daughter cells form spindles Chromosomes move toward the equator
PROPHASE II
Daughter cells form spindles
Chromosomes move toward the equator

17. Spindle attaches to centromeres Chromosomes line up at the equator
METAPHASE II
Spindle attaches to centromeres
Chromosomes line up at the equator

18. ANAPHASE II
Centromeres divide, the two chromatids separate and move to opposite poles

19. TELOPHASE II Both daughter cells divide Four haploid cells form
Nuclear membranes form

23. COMPARING MITOSIS AND MEIOSIS
*Occurs in production of:
gametes in animals
spores in plants
some simple organisms
*Occurs in:
growth
asexual reproduction
*Homologous chromosomes not paired up
*No exchange in homologous chromosomes
*Homologous chromosomes paired up
*Exchange in homologous chromosomes
*Involves two cell divisions
*Involves one cell division
*Results in daughter cell receiving the same # of chromosomes as parent cell
Mitosis maintains chromosome number
*Results in each daughter cell receiving half the number of chromosomes as the parent cell
Meiosis reduces the chromosome number to one-half

25. SEXUAL REPRODUCTION IN SIMPLE ANIMALS
Conjugation
No distinctly different sexes but there are biochemical and chromosomal differences called (+) and (-)
A bridge forms and there is an exchange of nuclear material
Introduces variation into the species
Examples are: bacteria, spirogyra, paramecium

26. SEXUAL REPRODUCTION IN ANIMALS
Reproductive systems
Gonads – special organs that produce gametes
Male = testes produce sperm
Females = ovaries produce ova (eggs)

27. HERMAPHRODITISM An organism that has both testes and ovaries
Mostly slow moving animals (earthworms, snails, hydras)
Rarely self-fertilize
Usually exchange sperm into sperm receptacle of its partner
Both animals have fertilized eggs

28. MEIOSIS IN FEMALES AND MALES
GAMETOGENESIS
MEIOSIS IN FEMALES AND MALES
OOGENESIS: formation of eggs

29. OOGENESIS: formation of eggs

30. GAMETOGENESIS MEIOSIS IN FEMALES AND MALES
SPERMATOGENESIS: formation of sperm

31. SPERMATOGENESIS: formation of sperm

32. GAMETOGENESIS OOGENOSIS SPERMATOGENESIS Production of eggs
Only one ovum (mature egg)
Continual production of sperm
Meiotic divisions
Meiotic division
Meiotic process results in only
Meiosis process results in
Ova are
Sperm are
stops at birth
through out life
continual
develops per month
unequal
equal
one mature ovum (egg)
four mature sperm
haploid cells
haploid cells
♦ Round shape
♦ Head, middle, flagellum
♦ Non-motile
♦ Motile
♦ May have food stored as yolk
♦ Mitochondria for energy
♦ Larger than sperm
♦ Microscopic

33. Female ova are undeveloped until the female reaches sexual maturity
Female ova are undeveloped until the female reaches sexual maturity. Then only one ovum/month develops.
Sperm structure
Head
Nucleus
DNA material
Enzymes for penetrating the egg
Middle
Mitochondria for energy to swim to the egg
Flagellum
For motility

34. FERTILIZATION AND ZYGOTE FORMATION
Haploid (egg) cell + haploid (sperm) cell = diploid cell or zygote
Enzymes from the head of the sperm penetrate the egg cell
Only the nucleus of the sperm enters (DNA)
All cytoplasm is from the egg (female)
Fertilization membrane forms immediately to stop other sperm from entering the egg

35. TWO TYPES OF FERTILIZATION
External fertilization
Internal fertilization

36. External Fertilization – outside the females’ body (fish)
Need a water medium for sperm to swim in
Very hazardous – many are released
Spawning – female releases eggs and then male swims over the area immediately and releases sperm
Amplexus – male embraces female and eggs and sperm are released at the same time

37. Internal fertilization – sperm released into the female body (land animals, sharks and lobsters)
Fewer eggs needed because they are well protected
Greater numbers of sperm
Timing must be right
Some animals can store sperm for later use (bees and bats)
Reproductive adaptations controlled by hormones
singing
color display
feathers displayed

38. PARENTOGENESIS
Development of an unfertilized egg into an adult animal (bees, wasps, aphids, ants)
bees
- unfertilized eggs become male drones (workers)
- fertilized eggs become female workers or queens