Unit 6 : Meiosis & Sexual Reproduction

Transcription

1 Unit 6 : Meiosis & Sexual Reproduction

2 Cell division / Asexual reproduction Mitosis produce cells with same information identical daughter cells exact copies clones same number of chromosomes same genetic information Aaaargh! I m seeing double!

3 Asexual reproduction Single-celled eukaryotes yeast Paramecium Amoeba Simple multicellular eukaryotes Hydra budding What are the disadvantages of asexual reproduction? What are the advantages?

4 Review : Mitosis aka identical cells!

5 How about the rest of us? What if a complex multicellular organism (like us) wants to reproduce? joining of egg + sperm Do we make egg & sperm by mitosis? What if we did, then egg sperm zygote No! Doesn t work!

6 diploid = 2 copies 2n Human female karyotype 46 chromosomes 23 pairs XX

7 diploid = 2 copies 2n Human male karyotype 46 chromosomes 23 pairs XY

8 How do we make sperm & eggs? Must reduce 46 chromosomes 23 must half the number of chromosomes haploid 23 egg meiosis zygote fertilization sperm gametes

9 Meiosis makes sperm & eggs 46 chromosomes to 23 chromosomes half the number of chromosomes meiosis egg diploid sperm haploid

10 Practice: Compared to human cells resulting from mitotic cell division, human cells resulting from meiotic cell division would have twice as many chromosomes the same number of chromosomes one-half the number of chromosomes one-quarter as many chromosomes

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12 Paired chromosomes Homologous chromosomes both chromosomes of a pair carry matching genes control same inherited characters homologous = same information diploid 2n 2n = 4 eye color (brown?) eye color (blue?) homologous chromosomes double stranded homologous chromosomes

13 Meiosis 1 overview 1st division of meiosis double stranded Divide 1 Copy DNA Line Up 1 4 chromosomes diploid 2n prophase 1 metaphase 1 gamete telophase 1 2 chromosomes haploid 1n

14 Bye Bye 2 Meiosis 2 overview telophase 2 telophase 1 Line Up 2 2nd division of meiosis looks like mitosis metaphase chromosomes haploid 1n gametes

15 Meiosis = reduction division Meiosis special cell division in sexually reproducing organisms reduce number of chromosomes 2n 1n diploid haploid half makes gametes sperm, eggs

16 Meiosis & mitosis Meiosis to make gametes sperm & egg Mitosis to make copies of cells growth repair development

17 Sexual reproduction lifecycle 2 copies diploid 2n 1 copy haploid 1n fertilization We re mixing things up here! A good thing? meiosis 1 copy haploid 1n

18 Putting it all together meiosis fertilization mitosis + development gametes meiosis 46 egg sperm fertilization zygote mitosis mitosis & development

19 The value of meiosis 1 Consistency over time meiosis keeps chromosome number same from generation to generation Mom from Mom Dad offspring from Dad

20 The value of meiosis 2 Change over time meiosis introduces genetic variation gametes of offspring do not have same genes as gametes from parents new combinations of traits We re mixing things up here! from Dad variation from Mom offspring new gametes made by offspring

21 Practice: The great variety of possible gene combinations in a sexually reproducing species is due in part to the 1. sorting of genes as a result of gene replication 2. pairing of genes as a result of mitosis 3. pairing of genes as a result of differentiation 4. sorting of genes as a result of meiosis

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23 How does this explain: family resemblance & differences! Why are the kids so similar to the parents but not exact?

24 What are the advantages of asexual reproduction? What are the DISadvantages of asexual reproduction? Any Questions?? What are the advantages of sexual reproduction? What are the DISadvantages of sexual reproduction?