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Monohybrid & Dihybrid Crosses

Monohybrid & Dihybrid Crosses. Probability and Genetics!. Why did Mendel use Pea Plants?. - easy to control pollination. Pistil (female) produces ovules. Stamens (male) produce pollen. Pea Flower. - seven distinct, inherited traits. Seed shape. Seed color. Pod shape. Pod color.

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Monohybrid & Dihybrid Crosses

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  1. Monohybrid & Dihybrid Crosses Probability and Genetics!

  2. Why did Mendel use Pea Plants?

  3. - easy to control pollination Pistil(female)producesovules Stamens(male)producepollen Pea Flower

  4. - seven distinct, inherited traits Seed shape Seed color Pod shape Pod color Flower color Flower location Plant size

  5. P1 F1

  6. F1 F2

  7. Cross Fertilization of Parents Pollen Cross-Fertilize Pollen P P PurebredPurple-floweredParent PurebredWhite-floweredParent F1 All Purple-floweredOffspring

  8. Self-fertilization of F1 F1 Self-Fertilize 75% Purple25% White F2 F2 F2 F2

  9. Punnett squares • The probability the next generation will exhibit a certain trait can be shown with a Punnett square. T T • The genotype of the mother is shown on the top of the square (TT) • The genotype of the father is shown on the side of the square (tt) • The various combinations of genes (genotypes) are shown in the squares. All of these offspring will be (T) tall and carry the recessive (t) short allele. t t Tt Tt Tt Tt

  10. Monohybrid Cross(crosses that examine the inheritance of only ONE specific trait) T t Genotypic Ratio: TT :Tt : tt 0 : 2 : 2 Phenotypic Ratio: Tall : Short 2 : 2 t t Tt tt Tt tt • What happens if you cross a tall (heterozygous) plant (Tt) with a short plant (tt)?

  11. Punnett squares 3 possible genotypes: DD, Dd, dd Genotypic Ratio: DD : Dd : dd 1 :2 : 1 2 possible phenotypes: Not deaf or Deaf Phenotypic Ratio: Not Deaf : Deaf 3 : 1 Dd D d DD Dd Dd dd • If deafness in dogs are recessive (dd), show what offspring could result from two dogs that are heterozygous (Dd)

  12. Test Cross • Farmer Dan breeds guinea pigs. • There is a gene in guinea pigs for teeth length. Teeth can either be normal (T) or bucked (t). • Farmer Dan buys what he thinks is a normal TT guinea pig. How can he be sure it is “pure” (TT) and not a heterozygote (Tt)?

  13. Test Cross: Breed the unknown genotype with a homozygous recessive. A heterozygous guinea pig will result in a 2:2 or 1:1 ratio of normal to buck-teethed offspring. A homozygous dominant guinea pig will result in offspring that all have normal teeth.

  14. Dihybrid Cross(crosses that examine the inheritance of only TWO different traits) • Mendel also studied dihybrid crosses. • He crossed a plant with yellowroundpeas with a plant withgreenwrinkledpeas.

  15. Mendel and Dihybrid Crosses • Mendel began his experiments with purebred (homozygous) parent plants. RRYY x rryy • Remember each trait has 2 genes due to getting half your genes from mom and half from dad. • How many gamete options do you have for RRYY?? RY • How many gamete options do you have for rryy? ry • These are the gametes from the “P” (parent) generation.

  16. Mendel and Dihybrid Crosses “P” generation:RRYY x rryy RRYY rryy

  17. Mendel and Dihybrid Crosses What is the genotypic ratio? 16 RrYy:0 anything else Phenotypic ratio? 16 Round Yellow: 0 anything else

  18. Mendel and Dihybrid Crosses He then crossed two “F1” organisms: RrYyx RrYy RrYy RrYy

  19. Mendel and Dihybrid Crosses What is the genotypic ratio for the F2 generation? 1 RRYY:2 RRYy: 1 RRyy: 2 RrYY: 4 RrYy: 1 rrYY: 2 Rryy: 2 rrYy: 1rryy

  20. Mendel and Dihybrid Crosses Phenotypic ratio for the F2 generation? 9:16 Round Yellow, 3:16 Round Green, 3:16 Wrinkled Yellow, 1:16 Wrinkled Green

  21. Mendel and Dihybrid Crosses 9:16 yellow and round, 3:16 green and round, 3:16 wrinkled and yellow, 1:16 wrinkled and green.

  22. Mendel and Dihybrid Crosses • Mendel continued to find this approximately 9:3:3:1 phenotypic ratio in the F2 generation, regardless of what 2 different traits he chose.

  23. Mendel and Dihybrid Crosses • This is due to his Law of Independent Assortment. • Each allele pair separate independently from other allele pairs during meiosis (gamete formation)… • different traits are inherited separately.

  24. Dihybrid Cross Practice • Suppose you are studying the color and texture of kernels on a corn cob. • Kernels can be either purple (R) or yellow (r). • They can also be smooth (T) or wrinkled (t). • Predict the phenotypic and genotypic outcome of crossing a dihybrid (heterozygous) purple smooth with a yellow wrinkled. • Don’t forget to answer the questions on the bottom of your note template.

  25. Answer: phenotypic and genotypic outcome of crossing a dihybrid (heterozygous for both) purple smooth with a yellow wrinkled 4:16 Purple Smooth, 4:16 Purple Wrinkled, 4:16 Yellow Smooth, 4:16 Yellow Wrinkled Cross: RrYyx rryy RrYy rryy

  26. Parent generation (AABB x aabb) are purebred for both traits because they are homozygous for both traits. • Possible gametes AaBb -> AB, Ab, aB, ab • Genotype: AAbb -> Phenotype: Purple, short

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