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Genetics

Genetics. Mendel’s Laws of Heredity. Genetics. Main Concepts… a. Sexual reproduction involves the random distribution of genes . b. We have thousands of genes. c. Genes determine your traits . d. Genes line up on your chromosomes .

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Genetics

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  1. Genetics Mendel’s Laws of Heredity

  2. Genetics Main Concepts… a. Sexual reproduction involves the random distribution of genes. b. We have thousandsof genes. c. Genes determine your traits. d. Genes line up on your chromosomes. e. Chromosomes are in the nucleusof the cell. f. Chromosomes duplicateand dividein cell division. g. Chromosomes are typically in pairs. h. A diploidcell has complete set of chromosomes.

  3. Frog: 13 pairs Genetics Dog: 39 pairs Pea: 7 pairs Chimpanzee: 24 pairs Apple: 17 pairs

  4. Heredity • HEREDITY – the passing of characteristics from parents to offspring • Characteristics that are inherited are called TRAITS

  5. Gregor Mendel • Gregor Mendel was an Austrian monk and was the first person to successfully study GENETICS, the branch of biology that studies heredity

  6. Pea Plants • Mendel chose to study the garden pea plant: • The male gamete is pollenand fuses with the female gamete in a process called FERTILIZATION • Fertilized egg = zygote • The transfer of male pollen to the female reproductive organ is called POLLINATION

  7. Pea Plant (con’t) • Pea plants can reproduce by SELF-POLLINATION because each plant has both male and female gametes • Mendel performed a process called CROSS-POLLINATION by dusting pollen from one plant to any other plant of his choosing. This allowed him to control which plants mate with which plants

  8. Research • Mendel was a careful researcher: • He studied only one TRAITat a time (e.g. Height) and analyzed the data mathematically • Mendel used TRUE BREEDING plants for his crosses. This means the plants have the same traits for many generations (e.g. all purple flowers) • Pure bred

  9. Experiment • When Mendel crossed two different ALLELESfor a trait he called this a HYBRID • When Mendel only crossed onetrait at a time he called this a MONOHYBRID CROSS

  10. Monohybrid Cross (Height) • All pea plants are either tall (6ft) or short (2ft) • The 1stGeneration: • Mendel cross-pollinated a true breeding tall pea plant with a true breeding short pea plant. The offspring were all tall pea plants • P1  Tall x short = All tall plants

  11. Monohybrid Cross (Height) • The 2nd Generation: • Mendel allowed the tall offspring to self-pollinate. • F1 Tall x Tall = 75% Tall/25% Short • 3:1 ratio of tall

  12. Mendel’s Experiments Review Short pea plants X Tall pea plants Q: What did he get? A: All Tall pea plants!!!! Then, Tall X Tall pea plants Q: What did he get? A: 787 Tall pea plants & 277 short pea plants 3:1 Ratio = 75% tall : 25% short

  13. Generations • The original (true breeding) parents are known as the P1 generation • P = “parent” • The offspring of the P1 generation are known as the F1 generation • F = “filial” (son or daughter) • Crossing two F1 plants creates the F2 generation

  14. Conclusions from Mendel’s Experiments • Factors = Genes 2. Law of Dominance: in any pair of genes, one may hidethe appearance of the other. • Dominant: expressed • Recessive: masked, hidden, not expressed 3. Law of Segregation: During Meiosis chromosomes separate, and genes separate also. 4. Law of Independent Assortment: the pairs of genes (and chromosomes) separate randomly!

  15. Rule of Dominance • Mendel also concluded that one allele is DOMINANT and one is RECESSIVE • The dominant allele is the one that shows up in the F1 generation (Tall) • Capital letter  T • The recessive allele is the trait that is hidden in the F1 generation (Short) • Lowercase letter  t • Capital letter is always written before the lowercase letter tT Tt

  16. Dominant/Recessive Traits • A dominant trait (tall) is the result of either TT or Tt • TT = tall • Tt = tall • A recessive trait (short) can ONLY be the result of tt • tt = short • The dominant allele always overrides the recessive allele, therefore, dominant traits are more common than recessive traits

  17. AA aa Purple is present (White is hidden) Aa AA Aa Aa aa Purple is dominant White is recessive

  18. Alleles • Mendel concluded that each organism must have two factors that control each of its traits • We now know that traits are controlled by GENES and are located on chromosomes. • Genes exist in alternative forms called ALLELES • Gene  plant height • Alleles  tall or short • Alleles  dominant or recessive

  19. Alleles • Alleles are located in exactly the same position on homologouschromosomes • In a diploid organism, there are twoalleles for a given gene • One from mother; one from father • A plant might have: • 2 copies of the tall allele (TT) • 2 copies of the short allele (tt) • 1 tall and 1 short allele (Tt)

  20. ♂ ♀

  21. Law of Segregation • The Law of Segregation – every individual has two alleles for each gene and each gamete receives one of these alleles

  22. Law of Segregation Each gamete only gets one allele Each offspring has one allele from each parent

  23. The Law of Independent Assortment • The Law of Independent Assortment – genes for different traits are inherited independently of each other • Height does not affect flower color; they are independent of each other • Independent assortment results in increased genetic diversity because of the shuffling of individual genes

  24. Law of Independent Assortment

  25. Genotype vs. Phenotype EX. Green pea pod, pink flower, tall stems EX. GG, Gg, gg • PHENOTYPE: physical appearance; what it looks like. • GENOTYPE: genetic make-up; combination of genes. • Represented by 2 letters. • 3 possible genotypes.

  26. Homozygous vs. Heterozygous • Homozygous – two alleles are the SAME • Homozygous dominant  TT • Homozygous recessive  tt • True breeding (pure bred) • Heterozygous – two alleles are DIFFERENT • Tt • Hybrids

  27. Traits due to 1 gene • Dominant • Free earlobe • Left handedness • Tongue rolling • Left arm on top • Left thumb on top • Recessive • Cleft chin • Dimples • Attached earlobe • Second toe longer • Widow’s peak • Double jointedness

  28. Human Genetics Cleft Chin Dimples

  29. Widow’s Peak

  30. Free and Attached Ear lobes

  31. Second toe is longer than big toe

  32. Tongue rolling

  33. Punnett Squares • Reginald Punnett devised an easy system to predict genotypic outcomes of a cross called a PUNNETT SQUARE • Parents gametes are combined in every possible combination • Monohybrid cross – one gene (height) • Dihybrid cross – two genes (height and color)

  34. Monohybrid Cross Father’s Gametes (sperm) Mother’s Gametes (egg) Possible Offspring #1 Possible Offspring #2 Possible Offspring #3 Possible Offspring #4

  35. Setting up the Punnett square T = tall t = short T T T T x t t t t (Tall) (Short) Mom Dad

  36. Solving the Punnett Square T T x T = tall t = short t t (Tall) (Short) Mom Dad t t t t t t T T T Tall Tall (Heterozygous) (Heterozygous) T T T Tall Tall (Heterozygous) (Heterozygous)

  37. Setting up the Punnett square T T t t x T T t t (Tall) (Tall)

  38. Solving the Punnett Square T t x T t (Tall) (Tall) T T T t t t T T T Tall Tall (Heterozygous) (Homozygous) t t t Tall Short (Heterozygous) (Homozygous)

  39. Fractions, Percent, Ratios • Offspring outcomes can be expressed as: • Fractions – ¼ or ¾ • Percent – 25% or 50% or 75% • Ratio – 3:1 or 1:2:1

  40. Test Cross • A TEST CROSS is a cross of an individual of unknown genotype with an individual with a known genotype • Test crosses use homozygous recessive individuals because the phenotype always indicates the genotype (short = tt) • Example: • Tall pea plant: genotype unknown (TT or Tt) • Short pea plant: known genotype (tt) • Cross the tall plant with the homozygous recessive and look at the offspring • If the offspring are all tall then the unknown genotype is TT • If the offspring are 50% tall and 50% the unknown genotype is Tt

  41. Test Cross P1 Tall Plant (TT or Tt?) Short Plant (tt) F1… TT Tt OR

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