1. Sexual Reproduction

2. Asexual Reproduction Problems
only one parent
offspring are genetically
identical = clones
lack of genetic variation
threatens species survival

3. Comparison of Asexual vs Sexual Reproduction
one parent
offspring clones
use mitosis
good for large #
of offspring
produces somatic
cells
Sexual
two parents
offspring unique
use meiosis
good for genetic
variation
produces sex cells

4. Sexual Reproduction Occurs in sex organs or gonads TESTES in 
in Seminiferous Tubules
Ovary in 
in Follicle

5. Sex Organs in Plants  

6. Produces sex cells called gametes in animals

7. or sex cells called spores in plants.

8. Chromosomes in eukaryotes homologous chromosomes
are grouped in pairs
called
homologues or
homologous chromosomes

9. Homologous Chromosomes
Blue eyes
Blue eyes
…chromosomes that carry the same kind of information at the same locus
Red hair
Blonde hair
Freckles
No Freckles

10. Diploid vs Haploid Diploid – 2n chromosomes in homologous pairs
1 of each pair from  and 1 of each pair from
Haploid – n
chromosomes
single, no pairs
chromosome from either  or parent

11. Meiosis

12. Meiosis… occurs only in sex cells carries out 2 divisions
produces 4 cells
cells produced have ½ normal #
of chromosomes
cells are genetically unique

13. Two Divisions… Meiosis I – reduces chromosome #
produces 2 haploid cells
Meiosis II –
divides the 2 cells into 4 cells

14. Overview of Meiosis

15. Meiosis I

16. 2 significant events occur
During Prophase I…
Synapsis – the pairing of
homologous chromosomes
Crossing Over – the exchange
of genetic material between
two nonsister chromatids

18. All 4 chromatids are now different.
Crossing Over is 1st major cause of
GENETIC VARIATION

19. Metaphase – chromosomes line up
in pairs
Anaphase – centromeres do
not divide; pulled to poles

20. 2nd major cause of genetic variation occurs…
During anaphase, the
2nd major cause of genetic variation occurs…
INDEPENDENT
ASSORTMENT OF
CHROMOSOMES

21. At the end of telophase I
we have 2 haploid cells.
Each cell has 1 of each chromosome pair, but each chromosome still has 2 sister chromatids – double DNA.

22. Meiosis I is followed by a Interkinesis is just like
resting stage called
INTERKINESIS
Interkinesis is just like
Interphase except
there is no S stage…
no replication of DNA

23. All events in Meiosis II
are just like Mitosis.

24. Note that centromeres
divide in Anaphase II.

26. Meiosis vs Mitosis Mitosis… Meiosis… 4 haploid cells 2 diploid cells
2 divisions
sex cells only
genetic variation
interkinesis
crossing over
independent assortment
Mitosis…
2 diploid cells
1 division
somatic cells
clones

27. Reproduction in Humans

29. Overview of Meiosis I

30. Note that… Meiosis I produces two “same size” cells in spermatogenesis
Meiosis I produces two different size cells in oogenesis
- one is small and called a
POLAR BODY

31. Oogenesis Fertilization triggers Meiosis II 1 ovum + 3 polar bodies
Cells are unequal size

32. Spermatogenesis
4 = sized sperm produced

33. Spermatogenesis Oogenesis Begins at puberty Continues thru life
Continuous process
4 = sized cells
Daily production
Oogenesis
Begins at puberty
Ends at menopause
Fertilization required
to trigger Meiosis II
4 unequal sized cells
Monthly production