Genetics

Add to Favourites

Post to:

Description
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 F1 generation

Comments

Presentation Transcript

Genetics : Genetics The study of inherited characteristics Visit www.worldofteaching.com For 100’s of free powerpoints

Monohybrid inheritance : 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 F1 generation R R r r F1 phenotypes 100% plants producing round seeds F1 genotypes 100% heterozygotes Rr

Slide3 : F1 intercross Parents phenotype round seeds x round seeds genotype Rr Rr Gametes F2 generation R r r R Phenotype 75% plants producing round seeds 25% plants producing wrinkled seeds Genotype 25% RR 50% Rr 25% rr Ratio 3:1 Round seeds: wrinkled seeds

Slide4 : 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

Slide5 : 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?

BackcrossTo test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant : 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 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