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Genetics of Inheritance

Genetics of Inheritance. History. Gregor Mendel was a monk who did experiments on garden peas in the 1860s. Peas have many varieties and strict control over mating is possible. Mendel. Example: Mendel bred round peas and wrinkled peas. The first generation had only round peas.

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Genetics of Inheritance

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  1. Genetics of Inheritance

  2. History Gregor Mendel was a monk who did experiments on garden peas in the 1860s. Peas have many varieties and strict control over mating is possible.

  3. Mendel Example: Mendel bred round peas and wrinkled peas. The first generation had only round peas. When the first generation round peas were self-fertilized, the second generation had one wrinkled pea plant for every three round pea plants…. Why???

  4. Mendel Each gene has 2 alleles (forms of the gene). An allele can be dominant (designated by a capital letter), or recessive (designated by a lower-case letter). The combination of alleles is called the genotype.

  5. Pea Genotypes Let R = dominant round pea allele Let r = recessive wrinkled pea allele Possible genotypes for pea plants: RR Rr rr Terms: RR = homozygous (ie. “the same”) dominant Rr = heterozygous (ie. “different”) rr = homozygous recessive

  6. Pea Phenotypes The expression of the genotype in the organism is called the phenotype. Resulting phenotypes: RR (round peas) Rr (round peas) Why? The dominant round allele masks the recessive wrinkled allele rr (wrinkled peas)

  7. A Closer Look… One parent had the genotype RR. What alleles can it donate to its haploid sex cells? Only the R allele The other parent had the genotype rr. What alleles can it donate? Only the r allele After fertilization, ALL offspring will therefore have the combination of R and r, resulting in Rr (round peas).

  8. A Closer Look… When these first generation (a.k.a F1 generation) peas are making gametes, which alleles could be present for each parent? R r

  9. R r Possible alleles for each gamete R r A Closer Look… What are the possible genotypes for the F2 generation? (draw a matrix chart… a.k.a a Punnett Square)

  10. R r R r A Closer Look… Fill in the possible genotypes in the square. RR Rr Rr rr

  11. R r R r The answer is… Genotypic Ratios: ¼ will be RR 2/4 or ½ will be Rr ¼ will be rr RR Rr Rr rr

  12. R r R r The answer is… Phenotypic Ratios: ¾ will be Round ¼ will be Wrinkled RR Rr Rr rr

  13. Terms: RR = homozygous (ie. “the same”) dominant Rr = heterozygous (ie. “different”) rr = homozygous recessive The mystery is solved!

  14. An example: Example: A heterozygous purple-flowered pea plant (Pp) is crossed with a homozygous recessive white-flowered pea plant (pp). a) What are the expected genotypic ratios? b) What are the expected phenotypic ratios? (hint: start with the possible alleles for the gametes, then make the Punnett Square)

  15. Dihybrid Crosses:

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