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The Study of Inheritance

`. GENETICS. The Study of Inheritance. Gregor Mendel – The Father of Genetics. Austrian monk Published ideas in 1866 Worked with garden peas Determined basic genetics principles. Garden Peas. Self pollinating so Mendel didn ’ t have to worry about bees and wind, etc.

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The Study of Inheritance

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  1. ` GENETICS The Study of Inheritance

  2. Gregor Mendel – The Father of Genetics • Austrian monk • Published ideas in 1866 • Worked with garden peas • Determined basic genetics principles.

  3. Garden Peas • Self pollinating so Mendel didn’t have to worry about bees and wind, etc. • Traits are contrasting • Easily controlled • Can be eaten at end

  4. Mendelian Genetics Some terminology: parental strains (P1 or F0)-- originally crossed organisms F1 generation-- offspring of the F0 generation (parents) F2 generation-- offspring of F1 generation crossed to itself reciprocal cross-- switching the phenotype of the male and female parents dominant-- phenotype visible in the F1 generation -----a trait that masks another recessive-- trait which reappears in the F2 generation after self cross ---- a hidden trait

  5. Mendelian Genetics gene-- hereditary element that gets segregated allele-- particular form of a gene can a single gene have multiple alleles? homozygous-- organism carrying two copies of the same allele heterozygous- organism carrying different alleles of the same gene genotype-- genetic makeup of an organism (what alleles it contains) phenotype-- observable properties of an organism (characteristic)

  6. Traits studied by Mendel round wrinkled

  7. Crosses by Mendel: round wrinkled All round ¾ round ¼ wrinkled

  8. Round Wrinkled seeds

  9. Simple Steps for Solving Genetics Problems: Determine what the question is asking • Write a key with information given: Ex: KEY: TT = tongue roller Tt = tongue roller tt = nontongue roller Use letters given or make up your own – be sure to include all possible genotypes and the phenotypes they produce. Keep the key handy – I must be able to find it easily

  10. 2. Determine what the cross is: read carefully and figure out which two genotypes are being crossed: • Ex – if the problem states that a heterozygous man is married to a woman who can’t roll her tongue, the cross would be: Tt x tt • If the problem states that the P1 generation is one homozygous dominant crossed with a homozygous recessive, the cross would be: TT x tt

  11. 3.Draw a Punnett Square Write the cross _____ x _____ Ex:Tt x Tt Determine which gametes will be possible by each parent. The gametes of the individual on the left go down the side of the square, those of the parent on the right, go across the top of the square: NOW YOU CAN FIGURE OUT THE POSSIBLE TYPES OF OFFSPRING THEY MAY HAVE

  12. Move each gamete over or down and then make pairs of gametes to show what genes will be expected to be in the offspring.

  13. 4. Now you can show the genotypic and phenotypic ratios • First, do the genotypic ratio – GR • Count how many of the offspring will have each genotype • Ex –GR = 1TT:2Tt:1tt • Then do the phenotypic ratio – PR • Ex – PR = 3 tongue-rollers:1 nontongue roller

  14. Possible Questions Regarding a Cross: • Can they have a child who is a tongue roller? • Can they have a heterozygous tongue-rolling child? • Can they have a child who is a homozygous tongue roller?

  15. Other types of problems • You might be given the offspring and asked to determine the possible cross: • Ex – If two brown dogs had a litter of puppies that included 3 brown and 1 white, what are the most likely genotypes of their parents? • Write a key • Write the cross, leave genotypes blank • Write the kinds of offspring • Then figure out what the parents were Key: brown is dominant so use B = brown and b = white BB = brown ______ x _______ Bb = brown 3 brown 3 brown:1white ratio bb = white 1 white 3 B_ : 1 bb The bb got one b from the mother, the other from the father, so each parent must have a small b. Since both parents are brown, they must also have a B, making them both Bb

  16. Monohybrid and Dihybrid Crosses • The previous examples were monohybrid crosses. We were interested in one characteristic only. • In a dihybrid cross we will be following two characteristics at the same time.

  17. Garden pea example • We have two characteristics we’d like to follow, flower color and plant height. • Each characteristic is controlled by a pair of alleles, one dominant and the other recessive: • F – purple flowers, dominant • f – white flowers, recessive • T – tall plants, dominant • t – dwarf plants, recessive • Each gene is located on a different type of chromosome.

  18. F f T t x F f T t list gametes from one parent here list gametes from other parent here

  19. F f T t x F f T t F T F t f T f t F T F t f T f t

  20. F f T t x F f T t F T F t f T f t F T F F T T genotype of diploid offspring F t f T f t

  21. F f T t x F f T t F T F t f T f t F T F F T T F F T t F f T T F f T t F t F F T t F F t t F f T t F f t t f T F f T T F f T t f f T T f f T t F f T t F f t t f f T t f f t t f t

  22. F f T t x F f T t Genotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t

  23. F f T t x F f T t F T F t f T f t F T F F T T F F T t F f T T F f T t F t F F T t F F t t F f T t F f t t f T F f T T F f T t f f T T f f T t F f T t F f t t f f T t f f t t f t

  24. F f T t x F f T t Genotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t 1/16 f f T T 2/16 f f T t 1/16 f f t t

  25. F f T t x F f T t F T F t f T f t F T F F T T F F T t F f T T F f T t F t F F T t F F t t F f T t F f t t f T F f T T F f T t f f T T f f T t F f T t F f t t f f T t f f t t f t

  26. F f T t x F f T t Phenotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t 1/16 f f T T 2/16 f f T t 1/16 f f t t 9/16 Purple flowers and Tall plants

  27. F f T t x F f T t Phenotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t 1/16 f f T T 2/16 f f T t 1/16 f f t t 3/16 Purple flowers and dwarf plants

  28. F f T t x F f T t Phenotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t 1/16 f f T T 2/16 f f T t 1/16 f f t t 3/16 white flowers and Tall plants

  29. F f T t x F f T t Phenotypes 1/16 F F T T 2/16 F F T t 1/16 F F t t 2/16 F f T T 4/16 F f T t 2/16 F f t t 1/16 f f T T 2/16 f f T t 1/16 f f t t 1/16 white flowers and dwarf plants

  30. Non-Mendelian Genetics • Codominance – two alleles and are both dominant; both express themselves, in an unchanged fashion, whenever present • Multiple Alleles – more than two alleles are present for a gene

  31. Incomplete dominance • Neither allele is dominant and when hybrid (heterozygous/both alleles present), the phenotype is mixed.

  32. Incomplete dominance Heterozygotes Intermediate in phenotype

  33. Incomplete Dominance • Red, pink and white flower color in snapdragons • R – red flowers, incomplete dominant • W– white flowers, incomplete dominant • Mate a red flowered plant with a white and all the offspring have pink flowers, • RW • What would you get from a cross of two pink flowered plants?

  34. Solving Incomplete Dominance Problems • Since neither gene is dominant, use two different capital letters in your key: Ex: Key RR = red Cross = RW x RW RW = pink WW = white GR = PR =

  35. Codominance • In codominance, both traits are dominant at the same time. • Example: A roan cow has both red and white hairs at the same time • Genotypes: RR=red cow WW=white cow RW= roan cow(some red hairs, some white hairs)

  36. Sex-Linked traits :gene is found on X-chromosome, not the Y • Genes for colorblindness and hemophilia are common in humans • Females have two genes for this trait • Males have only one gene – so they have no chance to be a carrier

  37. Are you colorblind?Can you see the shapes?

  38. Sex-linked Traits – hemophilia pedigree in royal families of Europe Current royalty in England Russian family before revolution

  39. Pedigree analysis

  40. Sex-Linked Traits – the gene for that trait is on the X-chromosome, not on the Y-chromosome • Ex: in humans, both colorblindness and hemophilia are sex-linked • Key for colorblindness: XBXB = normal visioned female XBXb = normal visioned female XbXb = colorblind female XBY = normal visioned male XbY = colorblind male

  41. Punnett Square for colorblindness: Cross = XBXB x XbY

  42. Would you expect any of their children to be colorblind? • What happens when the carrier daughters grow up and marry men who have normal vision? • Do that cross at your seats….Can they have colorblind children? Colorblind daughters? Colorblind sons?

  43. Multiple Alleles • Some traits are controlled by more than two alleles that can be inherited. Each person only inherits two of those alleles – one from each parent. • This is the case with human blood types: • There are 3 alleles in the population: • IA allele • IB allele • i allele – recessive to the other alleles Incompletely dominant to each other

  44. A Blood test will show which type you are:

  45. ABO Blood type crosses: • The key is complicated: • IAIA or IAi = type A • IBIB or IBi = type B • IAIB = type AB • ii = type O • How could we simplify this key?

  46. Polygenic Traits • Traits that are controlled by more than one pair of alleles • For example, human skin color is controlled by several pairs of alleles. • Let capital letters represent alleles that produce lots of pigment and lower case letters produce less pigment. • Assume we have three pairs of alleles.

  47. AaBbCC AABbCc aaBBCc aaBbCc AaBBCc AaBbCc AabbCc AaBbCC AabbCC AaBbcc AaBBCC AABBcc AaBBcc aabbCC aabbCc AABbCC AAbbCC AAbbCc aaBBcc aaBbcc AABBCC AABBBc aaBBCC AABbcc AAbbcc Aabbcc aabbcc 6 5 4 3 2 1 0 Increasing number of alleles for dark skin If we mate two individuals both with the genotypes AaBbCc, 27 different genotypes are possible with 7 different phenotypes.

  48. Fetal diagnosis

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