Meiosis and Sexual Reproduction

1. Meiosis and Sexual Reproduction

2. Asexual Reproduction sexual A = not • A form of reproduction that: • Is non-sexual (only single parent is needed) • produces geneticallyidentical clones of the parent • (exact copy of the original )

3. Asexual Reproduction Characteristics: • Rapid • Effective • Allows rapid spread of an organism (ex. bacterial growth) • Since the offspring are identical, there is no mechanism for introducing . diversity

4. Escherichia coli Paramecium caudatum Forms of Asexual Reproduction • Prokaryotes undergo _____ _____ • Hydra reproduce by ________ • Planaria reproduce by ____________ • Several plants reproduce through _________ ___________ • Most of these organisms can reproduce sexually as well. binary fission budding fragmentation vegetative reproduction.

5. Why do organisms have sex when… • It’s costly to the organism (energetically) • It’s time-consuming • There are far fewer offspring Sexual reproduction increases diversity by producing new genetic combinations. Genetic diversity allow populations to adapt to ever- changing environments

6. Sexual Reproduction + = • Gametes for fertilization usually come from separate parents • Female produces an _____ (Oogenesis) • Male produces _______ (Spermatogenesis) • Both gametes are haploid, with a single set of _____________. • The new individual is called a ______, with two sets of chromosomes (______). • Once the zygote begins to divide, it is called an _______. egg sperm chromosomes zygote diploid embryo

7. Sexual Reproduction Consists of meiosis and fertilization • Meiosis: Formation of four ______ reproductive cells (gametes) from a single ______ cell of the parent. • In humans, meiosis only occurs in the ________ • Spermatogenesis: In the ______(in males) • Oogenesis: In the _______ (in females) • Fertilization: Combination of haploid gametes from two different parents to produce a diploid individual haploid diploid gonads testes ovaries

8. Chromosomes vary from species to species one • Prokaryotes generally have only ___ major chromosome • Consisting of a single circle of DNA • Turkeys have 82! • Giant redwoods have 22! • A tropical fish has the same number of chromosomes as humans, which is ____ 46

9. Chromosome Characteristics • Diploid set for humans: 2n = 46 chromosomes • n= 23 chromosomes (haploid set) • Two types: • Autosomes (chromosomes 1 – 22) • Sex Chromosomes (chromosome 23) 2 2

10. Chromosome Characteristics • Autosomes • Homologous chromosomes (w/ matching pairs) • Humans have 22 pairs • Sex chromosomes • Humans have 1 pair • Female-sex chromosomes are homologous (XX) • Male-sex chromosomes are non-homologous (XY)

11. What can Chromosomes tell us? Scientists can organize chromosomes in a cell into a _________ karyotype • In a karyotype, chromosomes are arranged in order of size, banding pattern, and centromere position: • Let’s see if we can arrange a karyotype together: http://learn.genetics.utah.edu/content/begin/traits/karyotype/

12. What sex will this person’s offspring be if he passes on this set? What can this father pass on to the next generation? female male

13. MeiosisReduction/Division Begins after Interphase, when ______ replicates. DNA • Reduction: • Process takes a ______ cell with two sets of chromosomes and reducesit to a _________ cell with one set of chromosomes • Division • The cytoplasmic division of one cell into _____ cells. diploid four haploid

14. Meiosis:Reduction/Division Two divisions: Meiosis I & Meiosis II

15. Like Mitosis: Nuclear membrane disappears Spindles form Chromatin condenses into chromatids Prophase I • Unlike Mitosis: • Homologous chromosomes group with other homologous chromosomes to form a “tetrad” • A “chiasma” occurs at the point where the chromosomes cross over, detach, and exchange segments of the chromosome

16. Homologous chromosomes line up at the metaphase plate. Microtubules (spindles) attach to the kinetochore of centromere Metaphase I

17. Anaphase I • Homologous chromosomes separate. • Sister chromatids remain attached.

18. Telophase I • Two daughter cells are formed with each one containing only one chromosome of the homologous pair. • The daughter cells are now haploid.

19. Meiosis II:Gamete formation Prophase II: • DNA does not replicate. • Prophase II is just like mitotic prophase.

20. Metaphase II: • All of the chromosomes line up at the metaphase plate.

21. Anaphase II: • Centromeres divide • Sister chromatids migrate separately to each pole.

22. TelophaseII / Cytokinesis: • Chromosomes revert to chromatin. • Nuclei reform. • Cytoplasm cleaves • Four haploid daughter cells are obtained

23. Summary of Meiosis(video)

24. What is the difference between mitosis and meiosis? (flash) Based on the image alone, fill in the Venn Diagram comparing and contrasting mitosis from meiosis. Then watch the flash video with your class, and add information to your graphic organizer.