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Intro to Genetics

Intro to Genetics. p. 263 - 269. Sex Cells. Gametes = sex cells The male gamete is a sperm cell The female gamete is an egg cell Gametes are the only human cells that have 23 chromosomes Zygote = fertilized egg 23 from sperm + 23 from egg = 46 in zygote

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Intro to Genetics

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  1. Intro to Genetics p. 263 - 269

  2. Sex Cells • Gametes = sex cells • The male gamete is a sperm cell • The female gamete is an egg cell • Gametes are the only human cells that have 23 chromosomes • Zygote = fertilized egg • 23 from sperm + 23 from egg = 46 in zygote • The zygote then divides & divides & divides

  3. Traits • Genes- sequence of DNA that codes for a protein • Genes determine traits(characteristics that can be inherited) • Therefore, proteins determine traits

  4. Inheritance • A zygote inherits two genes for each trait – one from mom’s chromosome and one from dad’s chromosome mom dad

  5. D = dimples d = no dimples Alleles • Trait: dimples • Geneticists use letters to show which trait is inherited & • The different forms of a gene are called alleles • There can be more than two alleles per trait

  6. Dominant vs. Recessive • Dominant– the allele whose trait shows up in offspring • Represented by a capital letter, ie D • Recessive – the allele whose trait is masked in the offspring (by the dominant trait) • Represented by a lower-case letter, ie d

  7. Homozygous vs. Heterozygous • Zygotes can inherit a different combination of alleles • For example, for dimples a zygote can inherit the alleles • DD • Dd • dd Homozygous recessive Homozygous dominant Heterozygous Homozygous dominant Heterozygous Homozygous recessive

  8. Genotype vs. Phenotype • Genotype- genetic makeup (combination of alleles inherited) • DD, Dd, dd • Phenotype- physical expression of the inherited trait (characteristic) • Dimples, dimples, no dimples

  9. Trait: gender X and Y chromosomes have many alleles that determine sex. XX= female XY= male Sex Determination Punnett Square- helps geneticists determine the probabilities of which alleles (traits) will be passed on to offspring

  10. Mendel’s Peas • Trait: plant height • Complete dominance • T = tall allele • t = short allele Punnett Square – Cross between two heterozygous plants

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