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Published byRoy Pitts Modified over 9 years ago
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Asexual vs. Sexual Reproduction Asexual: -single individual is sole parent and passes ALL genes to offspring -offspring are genetically identical to parent’s -results in a clone…rarely a genetic difference will occur as a result of a mutation which can lead to cancer
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Sexual Reproduction -two parents give rise to offspring -each person passes on half of its genes to its offspring -offspring have a unique combination of genes inherited from both parents -results in greater genetic variation; offspring vary genetically from their siblings and parents
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Meiosis creates genetic variation -Recall mitosis produces two daughter cells genetically identical to parent and to each other. Meiosis will produce FOUR daughter cells genetically different from parent and each other.
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Sexual Reproduction Varies in Meiosis By… -Independent assortment- random alignment and each chromosome orients independently of other pairs -Random Fertilization- An egg cell is 1 of 8 million possibilities and a sperm cell is also 1 of 8 million possibilities…thus, a zygote can have 1 of 64 trillion different combinations -Crossing Over- (we’ll get to this at the end)
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Crossing Over
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Crossing Over Cont… -occurs when homologous portions of two nonsister chromosomes trade places -produces chromosomes that contain genes from both parents -in humans, average of 2-3 crossovers per chromosome pair
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Intro Sex Cell Division: Meiosis Meiosis is cell division of sex cells to form egg and sperm
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Meiosis vocabulary 1. Meiosis - a two stage cell division in which the chromosome number is halved. It forms four different gametes (sex cells) Meiosis I and Meiosis II 2. Gamete - the reproductive cell (egg or sperm)
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Meiosis vocabulary cont. 3. Haploid – “half” (as in when the human cell has only 23 single chromosomes (gamete cells) (n=23) 4.Diploid – “two” (as in when the human cell has 23 pairs of chromosomes (2n =46) 5.“homologous” chromosomes- same size, centromere pairing, and staining pattern
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Vocab Cont… 6. somatic cell- any cell other than sperm or egg 7. autosome- a chromosome (recall: threadlike structure in eukaryote made of DNA + protein) that is NOT a sex chromosome 8. zygote- diploid cell that results from union of two haploid gametes
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Meiosis Steps 1. Pre-Meiosis - Interphase 2. Meiosis I - Prophase I - Metaphase I - Anaphase I - Telophase I 3. Meiosis II - Prophase II - Metaphase II - Anaphase II - Telophase II 4. Post-Meiosis - Cytokinesis
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Why is Meiosis important? All gametes must be haploid (n = 23 chromosomes) Egg (n=23) + Sperm (n=23) offspring (2n=46) normal
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Pre-Meiosis: Interphase 46 chromosomes ----> 92 chromosomes diploid 1. copy Chromosomes 2. copy centriole
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No Interphase between Meiosis I and Meiosis II
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Chromosome Vocab SYNAPSIS
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Chiasma
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In males, cytokinesis makes four equal cells that develop heads and tails = sperm Cytokinesis In females, cytokinesis is unequal; one cell gets most of the cytoplasm to become the mature egg, while the other three (called polar bodies) are not involved.
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Cytokinesis In Males, cytokinesis makes four equal cells that develop heads and tails = sperm In females, cytokinesis is unequal; one cell gets most of the cytoplasm to become the mature egg, the other three (polar bodies) usually die
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Variety of Sexual Life Cycles -in animals, gametes are the only haploid cells -in fungi, the organism in normally haploid and the only diploid stage is the zygote (meiosis follows immediately) -plants (and some algae)- called “alternation of generations”… (see following diagram)
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Ch 14 WarmUp 1. What is the difference between an allele and a gene? 2. Briefly define the following terms: a. homozygous b. heterozygous c. phenotype d. Genotype 3. What is the difference between pleiotrophy and epistasis? 4. Describe the following disorders: Cystic Fibrosis, Tay- Sachs, Sickle Cell Anemia, Achondroplasia, and Huntington’s disease.
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