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Genetics

Genetics. The study of inherited characteristics. Monohybrid inheritance. Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotype round seeds x wrinkled seeds genotype RR rr Gametes

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Genetics

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  1. Genetics The study of inherited characteristics

  2. Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotyperound seeds x wrinkled seeds genotype RRrr Gametes F1 generation R R r r F1 phenotypes 100% plants producing round seeds F1 genotypes 100% heterozygotes Rr

  3. F1 intercross • Parents phenotyperound seeds x round seeds genotype RrRr • Gametes • F2 generation R r R r Phenotype 75% plants producing round seeds 25% plants producing wrinkled seeds Genotype25% RR 50% Rr 25% rr Ratio 3:1 Round seeds: wrinkled seeds

  4. Does the observed ratio match the theoretical ratio? • The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled • Mendel’s observed ratio was 2.96:1 • The discrepancy is due to statistical error • The observed ratio is very rarely the same as the expected ratio • The larger the sample the more nearly the results approximate to the theoretical ratio • Statistical tests such as the chi-squared test can be used to test the closeness of fit of the observed and theoretical ratios

  5. What if the parents are not homozygous? • The use of the term F1 generation is limited to the offspring of two homozygous parents • The use of the term F2 is limited to the offspring of intercrossing the F1 generation • In all other cases the terms offspring (1) and offspring (2) should be used • The complete set of headings will be: Parents phenotypes Parents genotypes Gametes Offspring (1) genotypes Offspring (1) phenotypes Gametes Offspring (2) phenotypes Offspring (2) genotypes

  6. If plant is homozygous dominant RR Parents phenotype round x wrinkled genotype RR rr gametes Offspring If plant is heterozygous Rr Parents phenotype round x wrinkled genotype Rr rr gametes Offspring BackcrossTo test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant R r r r R R r r Offspring phenotype 100% round Genotype 100% Rr Offspring phenotype 50% round 50% wrinkled genotype 50% Rr 50% rr

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