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Understanding Gametes, Inheritance, and Traits: The Basics of Genetics

This section covers key concepts of genetics, focusing on gametes, inheritance, and traits. Gametes, the sex cells (sperm in males and eggs in females), contain 23 chromosomes each, leading to the formation of a zygote with 46 chromosomes upon fertilization. Genes, defined as DNA sequences coding for proteins, determine traits inherited from both parents. Discussions on alleles, dominant vs. recessive traits, and genotype vs. phenotype clarify genetic inheritance. Methods like Punnett squares help predict allele combinations in offspring.

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Understanding Gametes, Inheritance, and Traits: The Basics of Genetics

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Presentation Transcript

  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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