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Download Sexual Reproduction Homologous Chromosomes have different
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Sexual Reproduction 3 steps to reproduction – Meiosis – Gametes produced – Fertilization (two gametes join) All three steps help to create genetic variation in offspring Homologous Chromosomes have different traits Allele Cell – variation of a gene has two of each chromosome – one from mom & one from dad Paternal and maternal chromosomes carry different alleles Meiosis: Two Divisions Two nuclear divisions – Meiosis I & Meiosis II DNA is NOT duplicated between meiosis I and II END RESULT: Four haploid cells are formed 1 Meiosis Meiosis I Meiosis II Prophase I Prophase II Metaphase I Metaphase II Anaphase I Anaphase II Telophase I Telophase II Meiosis I Meiosis II 2 Crossing Over/Recombination PROPHASE I •Chromosomes link with homologue while in sister chromatid stage •Homologues trade segments Crossing Over With genetic recombination, each chromosome has maternal and parental sections Creates genetic variation Random Alignment – Independent Assortment When chromatids pair with homologues and line up during metaphase I they do so randomly So genes from mom and dad can go to either pole leading to a blend of genes from mom and dad in gamete 3 Fertilization Male and female gametes join Two haploid cells make a diploid cell Mom provides the cellular components (e.g. mitochondria) The two gametes that join is random Genetic Variation Comes from: Genetic recombination during prophase I Random alignment at metaphase I Random combination of gametes at fertilization 4 Results of Mitosis and Meiosis Mitosis – Two diploid cells produced – Each identical to parent Meiosis – Four haploid cells produced – Differ from parent and one another What are the key differences between male and female gamete production? 5 Asexual Reproduction Single parent produces offspring – Fission – Vegetative reproduction – Regeneration All offspring are genetically the same (clones) Dominance It’s not just dominant and recessive Complete dominance dominance Incomplete – Heterozygote phenotype is in between – like the blending theory Codominance – Heterozygote (two different alleles) are both expressed 6 Continuous Variation A more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait 7 Genetics & Environment A phenotype results from the interaction of the genotype with the environment Environmental factors may control the expression or inhibition of a gene Potentilla Category Genetics & IQ scores Predicted Correlation Bouchard (1997) Actual Median Correlation # of studies Identical twins reared together 1.0 0.85 34 Identical twins reared apart 1.0 0.75 5 Fraternal twins reared together 0.5 0.58 41 Siblings reared together Parents and offspring 0.5 0.45 69 0.5 0.39 32 Parents and adoptive offspring 0.0 0.18 6 8 Garter Snakes Arnold. A. (1980) % of snakes Newborn eating patterns 80 70 60 50 40 30 20 10 0 Inland Coastal 0 1 2 3 4 5 6 7 8 9 10 # slug chunks eaten 9