Honors Biology Unit 5

Transcription

1 Honors Biology Unit 5 1

2 } Genome: Complete complement of an organism s DNA. Includes genes (control traits) and noncoding DNA organized in chromosomes. Genome > Chromosome > DNA > Genes 2

3 } Heredity way of transferring genetic information to offspring } Gene unit of heredity. 3

4 } Fusion of two gametes to produce a single zygote. } With exception of selffertilizing organisms (e.g. some plants), zygote has gametes from two different parents. 4

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6 } Total = 46 chromosomes (23 pairs) 44 autosomes + 2 sex chromosomes 6

7 1. Autosomes: Code for most genes in your body (not sex determining chromosomes) In humans chromosome #1-22

8 2. Sex Chromosomes: chromosomes that determine what gender you will be. #23 in humans: Females are: XX Males are XY

9 } Gametes: sperm/egg haploid (n) Haploid= Contains a single set of chromosomes (23) } Zygote: fertilized egg now diploid (2n) Diploid= Contains a two sets of chromosomes (23x2=46) } Somatic cell: any cell other than gametes All are diploid (2n) Meiosis KM 9

10 Meiosis KM 10

11 } Chromosomes exist in homologous pairs in diploid cells. } homologous pairs: chromosomes that code for the same genes but possibly have different alleles (get one from each parent) Exception: Sex chromosomes (X, Y). All autosomes are in homologous pairs. 11

12 Now each homologous chromosome has a sister chromatid Still considered diploid (2n) cell because still just two chromosomes (even though they now have a twin) Meiosis KM 12

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14 Meiosis KM 14

15 All are even numbers diploid (2n) sets of homologous chromosomes! Ploidy = number of copies of each chromosome. Diploidy 15

16 } Meiosis: cell division process by which the number of chromosomes per cell is cut in half } Why does it occur: Meiosis is used to produce the haploid(n) gametes (sperm and eggs) 16

17 } Meiosis reduces the number of chromosomes by half. } Daughter cells differ from parent, and each other. } Meiosis involves two divisions, Mitosis only one. 17

18 Meiosis KM 18

19 Meiosis KM 19

20 Meiosis 1: Separates homologous chromosomes 20

21 produces recombinant chromosomes, mixing the genes of the mother and father, recombining them. Occurs during Prophase 1 21

22 Meiosis KM 22

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24 Meiosis II: Separates Sister Chromatids 24

25 Meiosis KM 25

26 Meiosis KM 26

27 } During normal cell growth, mitosis produces daughter cells identical to parent cell (2n to 2n) } Meiosis results in genetic variation by: Shuffling of maternal and paternal chromosomes and crossing over. No daughter cells formed during meiosis are genetically identical to either mother or father During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring. 27

28 Meiosis KM 28

29 Number of combinations: 2 n e.g. if there are 2 chromosomes in haploid 2n = 4; n = 2 2 n = 2 2 = 4 possible combinations 29

30 e.g. 23 chromosomes in haploid 2n = 46; n = 23 2 n = 2 23 = ~ 8 million possible combinations! 30

31 At least 8 million combinations from Mom, and another 8 million from Dad >64 trillion combinations for a diploid zygote!!! Meiosis KM 31

32 Male gamete formation - Spermatogenesis } all 4 products of meiosis develop into sperm cells. They lose most of their cytoplasm, remodel their cell shape, and grow a long flagellum (tail).

33 Female gamete formation - Oogenesis } In females, most of the cytoplasm goes into 1 of the 4 meiotic products, which becomes the egg. } The other 3 meiotic cells are small polar bodies, which degenerate.

34 } 1. More genetic diversity: more potential for survival of species when environmental conditions change. Shuffling of genes in meiosis Crossing-over in meiosis Fertilization: combines genes from 2 separate individuals 34

35 } 2. DNA back-up and repair. Asexual organisms don't have back-up copies of genes, sexual organisms have 2 sets of chromosomes and one can act as a back-up if the other is damaged. (some organisms have more) Sexual mechanisms, especially recombination, are used to repair damaged DNA - the undamaged chromosome acts as a template and eventually both chromosomes end up with the correct gene. Meiosis KM 35

36 1. How does metaphase of mitosis differ from metaphase I of meiosis?" 2. What happens as homologous chromosomes pair up during prophase I of meiosis?" 3. What specific activities, involving DNA, occur during interphase prior to both mitosis and meiosis? " " 4. Compare mitosis and meiosis on the following points: "a. number of daughter cells produced. "b. the amount of DNA in the daughter v. parent cell "" "c. mechanism for introducing genetic variation." 5. What is a zygote and how is it formed? 36

37 6. Summarize the process of meiosis in 4 sentences or less (include the following in your summary)" 1. What is the main purpose of Meiosis?" 2. What does it start with and what does it end with (include males and females)" 3. Use and underline vocab words gamete, diploid, haploid, crossing over, eggs, sperm, homologous pairs, and sister chromatids" 37