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Mendel and Meiosis

Mendel and Meiosis. Learning Goal: predict possible outcomes of various genetic combinations such as monohybrid crosses. Gregor Mendel. Heredity is the passing of characteristics from parents to offspring. Genetics is the study of heredity or how those traits are inherited.

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Mendel and Meiosis

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  1. Mendel and Meiosis Learning Goal: predict possible outcomes of various genetic combinations such as monohybrid crosses

  2. Gregor Mendel • Heredity is the passing of characteristics from parents to offspring. • Genetics is the study of heredity or how those traits are inherited. • Gregor Mendel was the first person to succeed in predicting how traits were inherited thus he became known as the Father of Genetics.

  3. Gregor Mendel • Gregor Mendel is best known for his study of pea plants. • He used pea plants because they have 2 distinct sex cells called gametes. • Mendel pollinated the flowers himself by transferring the male pollen to the stigma of the flower (pollination).

  4. Pollen

  5. Uniting of the male and female gametes is called fertilization.

  6. Mendel cross-pollinated pea plants in order to study the various traits: Dominant: the trait that was observed Recessive: the trait that disappeared.

  7. Genotypes and Phenotypes • Phenotype – the way that the organism looks and behaves. Pheno (physical) type (model) • Genotypes – the combination of alleles (genes) in the organism. Gen (birth) type (model)

  8. Genotypes and Phenotypes • Allele– the different forms of a gene ex: Blue eyes or Brown eyes • Alleles can be dominant or recessive • Dominant • The trait covers up (masks) the recessive trait • Symbol is a capital letter (T) • Recessive • The trait is masked by the dominant allele • Symbol is a lowercase letter (t)

  9. Genotypes and Phenotypes • Phenotype • Genotype Alleles

  10. t t t t T T T Genotypes and Phenotypes Alleles • Homozygous dominant: Homo (same) • Homozygous recessive: • Heterozygous: Hetero (different)

  11. Crossing traits • Hybrid: a cross between plants with different traits like tall and short. • Mendel’s first cross he called a monohybrid cross. (Mono means one) • Later Mendel began crossing plants with 2 traits. These crosses were called dihybrid crosses. • Testcross: Breeding an individual of unknown genotype to a homozygous recessive individual to reveal the unknown genotype

  12. Parent generation Parents Filial (son or daughter) generation Children 2nd Filial generation Grandchildren

  13. t T Mendel’s Laws of Inheritance • Law of segregation: the 2 alleles for each trait (on homologous chromosomes)will segregate (separate) with the formation of the gametes during meiosis.

  14. Mendel’s Laws of Inheritance • Law of independent assortment: Each trait (or gene) is inherited independently of the other traits. • In other words, all blondes do not have blue eyes.

  15. Punnett Squares • In 1905, Reginald Punnett, an English biologist, devised a shorthand way of predicting the outcomes of the various crosses. • These are called Punnett squares.

  16. Monohybrid crosses BB B: White b: Black gametes B B Bb Bb b bb Genotypes Phenotypes Bb Bb b Bb: 100% Bb 100% White

  17. Monohybrid crosses B: White b: Black gametes B b BB Bb Genotypes B Phenotypes BB: 25% Bb: 50% bb: 25% White: 75% (BB and Bb) black: 25% Bb bb b Genotypic ratio 1:2:1 Phenotypic ratio 3:1

  18. Monohybrid crosses Bb BB: White bb: Black gametes B b Genotypes Phenotypes b bb Bb BB: 0% Bb: 50% bb: 50% Genotypic ratio 0:1:1 50% White 50% Black Phenotypic ratio 1:1 bb Bb bb b

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