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Genetics The study of inherited characteristics. Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled.

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Presentation on theme: "Genetics The study of inherited characteristics. Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled."— Presentation transcript:

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) Parentsphenotype round seeds x wrinkled seeds genotypeRR rr Gametes F1 generation RRrr F1 phenotypes100% plants producing round seeds F1 genotypes100% heterozygotes Rr

3 F1 intercross Parents phenotype round seeds x round seeds genotype Rr Rr Gametes F2 generation RrrR Phenotype75% plants producing round seeds 25% plants producing wrinkled seeds Genotype25% RR 50% Rr 25% rr Ratio3:1 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 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 What if the parents are not homozygous?

6 Backcross To test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant 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 RRrr Rrrr phenotype 100% round Genotype 100% Rr Offspring phenotype 50% round 50% wrinkled genotype 50% Rr 50% rr

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