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11-1 The Work of Mendel

11-1 The Work of Mendel. What does every living thing inherit from their parents? Genetics – the study of heredity Look around at your classmates and make a list of some of the traits that are inherited. What did Mendel already know…. Each flower produces pollen (sperm) and egg cells

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11-1 The Work of Mendel

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  1. 11-1 The Work of Mendel • What does every living thing inherit from their parents? • Genetics – the study of heredity Look around at your classmates and make a list of some of the traits that are inherited.

  2. What did Mendel already know… • Each flower produces pollen (sperm) and egg cells • Cross fertilization (sexual) – male and female cells join • Self-pollination (asexual) – pollen fertilizes eggs from same plant • Mendel’s pea plants were true-breeding • A tall plant with green seeds would produce a tall plant with green seeds

  3. Genes, Alleles and Dominance • Trait – specific characteristic • Mendel studied 7 different pea plant traits • What are some examples? Plant Height, Seed Shape, Pod Color

  4. Genes, Alleles and Dominance • Genes – the chemical factors that determine traits (the segment of DNA) ex. pea plant: height • Alleles – different forms of a gene from each parent ex. pea plants: tall and short (T or t)

  5. Principle of Dominance • Principle of dominance: some alleles are dominant and others arerecessive • Dominant allele – the trait is always shown • Capital letter (T = tall) • Recessive allele – the trait that will only show if there is no dominant allele • Lower case letter (t = short)

  6. Heterozygous – organisms that have 2 different alleles for the same trait • Hybrid for that trait • Ex: Tt • Homozygous – organisms that have 2 identical alleles for a particular trait • True-breeding for a particular trait • Ex: TT or tt

  7. Genes, Alleles and Dominance • Phenotype – physical characteristics • Ex: tall, short, yellow, green • Genotype – genetic make-up • Ex: TT, Tt, tt • Tall plants have the same phenotype (tall), but not the same genotype (TT or Tt) • Why are TT and Tt genotypes for tallness, but tt is not???

  8. 11-2 Probability and Punnett Squares Mendel realized…the principles of probability could be used to explain the results of genetic crosses.

  9. Genetics and Probability • Probability – the likelihood a particular event will occur. • Ex: probability of flipping a coin to heads = ½ or 50% • Probability of head 3 times in a row = ½ x ½ x ½ = 1/8 • The greater the number or trials, the closer to the expected ratio • Past outcomes do not affect future outcomes • Alleles segregate randomly (like a coin)

  10. Principle of Segregation • Segregation = separation • The alleles for tall vs. short separate during the formation of gametes – sex cells • Each gamete carries one allele for each gene

  11. The Two-factor Cross: F1 • 4 alleles (2 genes) at the same time • Provides the hybrid plants (F2 generation) • Crossed a homozygous RRYY (round yellow peas) with a homozygous rryy (wrinkled, green peas)

  12. 11.3 Beyond Dominant and Recessive Alleles • Genes can act in various ways • Dominant vs. Recessive – one allele completely masks another allele. • Incomplete Dominance • Definition : one allele is not completely dominant over another Ex: flowers – white x red flowers = pink flowers

  13. 11.3 Beyond Dominant and Recessive • Codominance • Definition: both alleles contribute to the phenotype of the organism Ex: chicken feather – black and white alleles = black and white feathers Colors don’t blend like incomplete dominance

  14. 11.3 Multiple Alleles • Definition: more than two alleles • (more than 2 alleles exist in a population not an individual) Blood Types Ex: rabbit’s coat color Ex: human’s blood type

  15. 11.3 Polygenic Traits • Definition: traits that are controlled by 2 or more genes Ex: fruit fly red eyes - 3 genes involved in making pigment • Diff. combo of genes produce different eye colors Ex: Human skin color – more than 4 different genes Human height – more than 50 genes

  16. 11.3 Genetics and the Environment • Genes provide a plan for development, but how the plan unfolds also depends on the environment: • Ex. Butterflies have different wing colors depending on when they hatch • Hydrangea flowers are different colors depending on soil pH.

  17. Mendel Questions Using tall and short pea plants and the letters T = dominant and t = recessive describe Mendel’s F1 generation and F2 generation. Provide the genotype and phenotype for each of four offspring from each generation. You do not need to use a punnett square.

  18. Meiosis

  19. Ttrr x ttRr

  20. ttRr x TtRr

  21. Questions • Genetics is the study of ________. • Alternate characteristics of an organism such as height, hair color, eye color, etc. are called _______. • Why did pea plants make such a good subject for Mendel to study? • What does “true breeding” mean?

  22. Considering the allele related to short and tall pea plants. • Plants of the P generation (tall) will produce only_____________ if not crossed with plants having other alleles. • Describe the phenotype (what we can see) of Mendel’s F1 Generation. • What was the genotype (use letters “T” and “t”) for Mendel’s F1 generation? • How did the F2 generation suggest that genes were simply segregated, not lost?

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