1. 11-16-09 Notes
--page 160: principles of probability--
Mendelian inheritance reflects the rules of probability
-Rule of Multiplication – the probability of two independent events
occurring together is the product of their independent probability
-Rule of addition – the probability of two events that can happen in two
different ways is the sum of the probabilities of the two events
Extending Mendelian genetics
The relationship between genotype and phenotype is rarely simple
-Complete dominance
-Incomplete dominance
-One trait is not fully dominant over the other
-Codominance
-Two different alleles = two phenotypes. Ex. blood grouping
-Multiple alleles
-Epistasis
-One gene influences how another gene works.
Ex. C – make colour
B – black b – brown
No C gene, no colour made, regardless of which
colour allele is present.
-Polygenic inheritance
Pedigrees
-These are diagrams of “family trees”
-Each level is a generation, horizontal lines re “marriage” lines and vertical
lines are “descendent” lines.
First generation [grandparents]
2nd generation [parents, aunts and
uncles]
3rd generation [brothers, sisters
linked, cousins unlinked].
Sex Linked Traits

2. -Humans have 22 pairs of “autosomal chromosomes” and 1 pair of “sex
chromosomes
-Male – XY Female -XX