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Heredity – or What did Mendel do?

Heredity – or What did Mendel do?. Biology. Mendel’s main points:. Physical traits are determined by “factors” (genes) passed down by both parents. “Factors ” are passed down in predictable patterns from one generation to the next. Other points.

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Heredity – or What did Mendel do?

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  1. Heredity – or What did Mendel do? Biology

  2. Mendel’s main points: • Physical traits are determined by “factors” (genes) passed down by both parents. • “Factors” are passed down in predictable patterns from one generation to the next.

  3. Other points • Mendel grew pea plants to determine what “traits” were passed on to offspring. (chose 7 traits to study) • He did not know about genes.

  4. Mendel’s peas – flower color only

  5. Mendel’s Generations • Parent Generation – the original breeding plants (parents) • F1 Generation – the first “offspring” that resulted. (children) • F2 Generation – the “offspring” that result from mating 2 of the F1 Generation plants (grandchildren) Go back to picture

  6. Vocabulary • Traits – features that make up who you are (determined by your genes) • Phenotype – physical makeup (example – brown hair, pointy ears) • Genotype – genetic makeup (example – genes on chromosomes)

  7. Alleles • An alternative form of a gene located at a specific position on a specific chromosome. (photo next slide) • Organisms have 2 alleles for each trait: HH, Hh, or hh (each letter is an allele) • Your chromosomes occur in pairs (called homologous pairs)

  8. Alleles for one trait – flower color One allele comes from father, other allele comes from mother

  9. Mendel’sLaw of Segregation • Alleles for a trait separate when gametes form during meiosis. • Resulting gametes have only one allele for each trait.

  10. What this means…… • 1. A gene exists in more than one form – gene for flower color might be either white or purple. • 2. You inherit randomly a “form” of the gene from each parent – these “forms” are called alleles.

  11. What this means…… • 3. When you form sex cells, alleles separate and resulting eggs or sperm contain only 1 allele (your body cells have both alleles) • 4. If Alleles are different (purple vs. white), one is dominant, the other is recessive.

  12. Genotypes • Dominant versus Recessive alleles • Possibilities = Homozygous dominant, Heterozygous, Homozygous recessive • What are these?? Hh, hh, HH • Dominant trait “hides” recessive

  13. Practice • T = tall t = short • TT = • Tt = • tt = • Which is homozygous dominant? • Which is heterozygous? • What’s the other one called?

  14. Mendel’s Law of Independent Assortment • Allele pairs separate independently of each other during gamete formation. • Example – the gene for hair color is passed on to offspring independently from eye color. • Also – which alleles you get from each parent is random

  15. How chromosomes line up before division is random Tetrads – group of 4 chromosomes

  16. Inheritance • You inherited genes from both your father and your mother. • Meiosis – because of “crossing over”, each time your parents had a child, different traits were passed on. • Crossing over – results in variation.

  17. Crossing over

  18. Review • When you cross parents (P generation) you get a ____ generation. • What you physically look like is your _____. • Write an example of heterozygous. • Write an example of homozygous recessive. • Alternate forms of the same gene are called _______.

  19. Review • Your chromosomes occur in homologous pairs. Where did you get these? • Which of Mendel’s laws says that different alleles separate independently of each other during meiosis? • What’s Mendel’s other law called? • What causes variation among you and your siblings? stop

  20. How to determine traits of offspring • Punnett squares are used to find the “possible” traits an offspring can have. • Cross a father with a mother • Each resulting “box” = probability of an offspring having that trait (genotype and phenotype)

  21. Monohybrid Cross – Parents

  22. Monohybrid Cross

  23. Mendel’s peas (flower color) (PP) (pp) (All Pp) Phenotype: 3 purple, 1 white Genotype: 1 PP, 2 Pp, 1 pp

  24. Monohybrid crosses – Punnett squares * * *(Possible alleles to pass down)

  25. Practice Cross a homozygous male for pointy ears with a heterozygous female for pointy ears. (use letter “e”) Pointy ears are dominant over non-pointy ears. Phenotype ratio: Genotype ratio:

  26. Answer E E Genotype ratio: 2:2 or 50% EE, 50% Ee (2 = EE, 2 = Ee) But…reduce ratio to 1:1 EE EE E e Ee Ee Phenotype ratio: 4:0 pointy ears or 100%

  27. Make the following crosses • 1. HH X hh • 2. Aa X AA • 3. Ff X ff • 4. BB X Bb • 5. dd X dd • 6. Ee X ee • 7. Long haired male with a short haired female. Long is dominant over short. Male is heterozygous. Use “h’s”. • 8. Pointy earred male with pointy earred female. Pointy is dominant. Male is homozygous, female is heterozygous. Use “e’s”. stop

  28. Special situation – Incomplete Dominance • Heterozygous offspring show a “blending” of the parents phenotypes. • Example: red flower (RR) X white flower (rr) = pink flower (Rr)

  29. Incomplete Dominance (rr) (RR) (Rr)

  30. Codominance • Both alleles of the parents are expressed in the heterozygous offspring. • Example: Red cow (RR) X White cow (rr) = Red and white spotted cow (Rr)

  31. Codominance

  32. Multiple alleles • Trait is determined by genes with 3 or more alleles • Example: blood types. Type O = ii; recessive. Type A = IAIA or IAi Type B = IBIB or IBi Type AB = IAIB. A and B are codominant

  33. Linked genes • Genes that tend to be inherited together, because they are located close to each other on the chromosome. • A result of crossing over.

  34. Polygenic Traits • Traits that are a results of more than one gene. • Example of polygenic traits: skin color or eye color

  35. Polygenic traits

  36. Sex-linked traits • Female chromosomes = XX • Male chromosomes = XY • “Y” chromosome is shorter than “X” so cannot carry many traits. “X” chromosomes can carry more traits – are larger so can carry more genes.

  37. Sex-linked traits • Traits that are carried on the X or Y chromosomes. X-linked more common since has more room for genes. • If trait is recessive, male more likely to show it. (XY – Y cannot hide trait) • Examples: Hemophilia, colorblindness • XHXh XHXH XhXh XHY XhY

  38. Practice – sex-linked trait Use the letter “h”. Mother is a carrier for hemophilia. Father does not have hemophilia. Hemophilia is a recessive trait.

  39. Answer How do you know which is male vs. female? Name genotype and phenotype of each offspring?

  40. Another – sex-linked trait Use the letter “t”. Mother lacks a tail. Father has a tail. Tails are a dominant trait. stop

  41. Dihybrid Crosses AaBb *Parents (both Heterozygous for both traits). Different colors mean offpsring have different phenotypes. AaBb Phenotypic ratio: 9:3:3:1 Know this ratio for heterozygous parents

  42. How to set it up and read it… (GGbb) (ggBb)

  43. Answer - volunteer Phenotypic ratio:

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