Sperm & Eggs & Variation..OH MY!

Transcription

1 Sperm & Eggs & Variation..OH MY! 1

2 What if a new individual was formed through mitosis? 2

3 allele amniocentesis asexual reproduction autosome binary fission chorionic villi sampling crossing over diploid exon fertilization gamete genome haploid homologues intron karyotype nondisjunction placenta reduction division sexual reproduction zygote 3

4 Genome: Complete complement of an organism s DNA. includes genes (control traits) and non-coding DNA organized in chromosomes 4

5 Eukaryotic DNA is organized in chromosomes genes have specific places on chromosomes exon: portion of a gene that is translated into protein (more in unit 8) intron: non-coding segment of DNA, often found within an exon; removed before transcription 5

6 Heredity way of transferring genetic information to offspring Chromosome theory of heredity: chromosomes carry genes Gene unit of heredity 6

7 Asexual splitting budding parthenogenesis (egg develops w/o fertilization) occurs naturally in some invertebrate animal species (e.g., water fleas, aphids, nematodes, some bees, some scorpion species, and parasitic wasps) and a few vertebrates (e.g., some fish, amphibians, reptiles, and very rarely birds) 7

8 Fusion of two gametes to produce a single zygote. Introduces greater genetic variation, allows genetic recombination. With exception of self-fertilizing organisms (e.g. some plants), zygote has gametes from two different parents. 8

9 Karyotype: ordered display of an individual s chromosomes collection of chromosomes from mitotic cells staining can reveal visible band patterns, gross anomalies Make a Karyotype 9

10 Obtain some cells from the individual Culture them in a test tube with nutrients Treat cells w/chemical that stops them exactly midway through cell division (chromosomes are coiled thickly and more visible than usual) Cells are placed on a microscope slide and a stain is added that binds to the chromosomes, making them visible Chromosomes are arranged by size and shape and displayed on a monitor or in a photograph 10

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14 Chromosomes exist in homologous pairs in diploid (2n) cells. One chromosome of each homologous pair comes from the mother (called a maternal chromosome) and one comes from the father (paternal chromsosome). Homologous chromosomes are similiar but not identical. Each carries the same genes in the same order, but the alleles (alternative form of a gene) for each trait may not be the same. Exception: sex chromosomes (X, Y) 14

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16 23 chromosomes donated by each parent (total = 46 or 23 pairs). Gametes (sperm/ova): contain 22 autosomes and 1 sex chromosome haploid (haploid number n = 23 in humans) Fertilization results in zygote with 2 sets of chromosomes - now diploid (2n). Most cells in the body produced by mitosis. Only gametes are produced by meiosis. 16

17 All are even numbers diploid (2n) sets of homologous chromosomes. 17

18 Meiosis reduces the number of chromosomes by half. Daughter cells differ from parent, and each other. Meiosis involves two divisions, Mitosis only one. Meiosis I involves: synapsis homologous chromosomes pair up chiasmata form (crossing over of non-sister chromatids) metaphase I: homologous pairs line up at metaphase plate anaphase I: sister chromatids do NOT separate overall, separation of homologous pairs of chromosomes, rather than sister chromatids of individual chromosome 18

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23 Prophase 1 each chromosome duplicates and remains closely associated (sister chromatids) crossing-over can occur during the latter part of this stage Metaphase 1 homologous chromosomes align at the equatorial plate 23

24 Anaphase 1 homologous pairs separate with sister chromatids remaining together Telophase 1 two daughter cells are formed with each daughter containing only one chromosome of the homologous pair 24

25 Second division of meiosis: Gamete formation Prophase 2 DNA does not replicate Metaphase 2 chromosomes align at the equatorial plate 25

26 Anaphase 2 centromeres divide sister chromatids migrate separately to each pole Telophase 2 cell division is complete 4 haploid daughter cells 26

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29 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 29

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31 Number of combinations: 2 n e.g. 2 chromosomes in haploid 2n = 4; n = 2 2 n = 2 2 = 4 possible combinations 31

32 e.g. 23 chromosomes in haploid 2n = 46; n = 23 2 n = 2 23 = ~ 8 million possible combinations! 32

33 Chiasmata sites of crossing over, occur in synapsis. Exchange of genetic material between non-sister chromatids. Crossing over produces recombinant chromosomes. 33

34 Females don t have a Y chromosome in any of their cells, yet they are able to develop and live normal, healthy lives. For this reason, we know that nothing on the Y chromosome is absolutely necessary. 34

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36 At least 8 million combinations from Mom, and another 8 million from Dad >64 trillion combinations for a diploid zygote!!! 36

37 Life cycle = sequence of stages in organisms reproductive history; conception to reproduction Somatic cells = any cell other than gametes, most of the cells in the body Gametes produced by meiosis 37

38 Generalized animal life cycle 38

39 Unequal distribution of chromosomes during meiosis Resulting gametes zero or two copies of a chromosome instead of a single copy 39

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42 Large amounts of energy required to find a mate and do the mating: specialized structures and behavior required Intimate contact provides route for infection by parasites (AIDS, syphillis, etc.) Genetic costs: in sex, we pass on only half of genes to offspring. Males are an expensive luxury - in most species they contribute little to rearing offspring. 42

43 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 43

44 In what cellular processes is mitosis involved? In what cellular processes is meiosis involved? In what type of cells does mitosis occur? In what type of cells does meiosis occur? How many times does DNA replicate in mitosis? How many times does DNA replicate in meiosis? How many cellular divisions occur in mitosis? How many cellular divisions occur in meiosis? 44

45 How many daughter cells are formed by mitosis? How many daughter cells are formed by meiosis? What is the chromosome number in daughter cells formed by mitosis from diploid parent cells? What is the chromosome number in daughter cells formed by meiosis from diploid parent cells? In mitosis, are daughter cells identical to or different from parent cells? In meiosis, are daughter cells identical or different from parent cells? In mitosis, when do synapsis and crossing over occur? In meiosis, when do synapsis and crossing over occur? 45

46 cchs.churchill.k12.nv.us/marshk/notes/meio sis.ppt Genetic Science Learning Center, University of Utah, place/labbench/lab3/concepts2.html 46