Bio102: Introduction to Cell Biology and Genetics



Bio102: Introduction to Cell Biology and Genetics

Mendelian Genetics and Extensions

Key Terms:

|incomplete dominance |antigen |pleiotropy |

|codominance |multiple alleles |polygenic inheritance |

|loss-of-function |testcross | |

Key Questions:

• How are incomplete dominance and co-dominance different?

• We said an individual can have only two alleles of any gene (the same or different). How, then, can there be multiple alleles for something like blood type?

• What does your book mean by the statement that our evaluation of dominance depends on the level at which we choose to observe a genetic phenomenon? Give a specific example.

• What ratio of F2 phenotypes would we expect to see for a gene that shows incomplete dominance? How about a gene that shows codominance? How would we distinguish between these two possibilities?

• Blood typing can be used to determine whether a particular man could be the father of a particular child. Why can't it be used to determine if a particular man is the father of the child?

• In the snapdragon example, the book uses the symbols CR and CW for the alleles. Why not just use R and W?

Lecture Outline:

Suggestions for working problems:

Determine dominance

Assign symbols. One letter = one gene. Upper case = dominant

Each individual needs two alleles for each gene

Decide what gametes can be made. One allele of each

Put gametes together to get offspring

Determine phenotypes and ratios

Incomplete Dominance

heterozygote has a phenotype that is between the homozygotes

Codominance

heterozygote has a phenotype that involves both homozygote’s phenotypes

Both can still be explained by regular Mendelian genetics! Assigning phenotypes is different

Multiple alleles

ABO blood types in humans

Pleiotropy and polygenic inheritance

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