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BSC 2011-03 Lecture 13 Spring 2006
Mendelian genetics – multiple traits
Summary of Mendel's theory = Mendel's Laws I. Law of unit factors
II. Law of segregation
III. Law of Dominance
IV. Law of independent assortment
Important differences from blending inheritance
Mendelian genetics can predict quantitative patterns
Probability theory : used to predict likelihood of a particular outcome of an event
1. The probability of a particular outcome of one event (e.g. heads in a coin toss):
When all outcomes equally likely, the probability that a given outcome will occur = #ways to obtain that outcome / total # possible outcomes.
Probability scales from 0 to 1
Sometimes outcomes are not equally likely :
- Rules for probability of more than one event or outcome
Outcomes of multiple events must be independent
Product rule ("and" rule)
Addition rule (“or” rule) :
These rules can be combined:
Using probability this way will work only as long as genes conform to the assumption of independence
Using probability to predict outcome of a dihybrid cross
Cross PpYy with PpYy
Some assumptions about inheritance that Mendel made:
- Each gene has 2 alleles (e.g. Purple, white)
- Alleles are either dominant or recessive
- Each gene (locus) affects only one trait
- Each trait is affected by only one locus
- The genotype determines the phenotype
- All genes assort independently
- All traits in diploid organisms are affected by 2 copies of a gene (chromosomes occur in homologous pairs)
You should now be working on the genetics problems. Very important to DO PROBLEMS. There is no substitute for experience (should be able to do 1-6 now)
The symbol for the gene is named after the unusual (mutant) phenotype Example: v for vestigial wings
The dominant allele (or “normal” phenotype, which is also called the “wild type”) is indicated with a “+” on the gene Example: v for vestigial wings, v+ for normal wings (or “wild type” wings).
