I.
Punnett Squares-A diagram that predicts the expected outcome of a genetic cross
a. Steps for completing an Punnett square:
i. Determine the genotypes you need to cross.
ii. Put the female (♀) genotype on the top of the Punnett square
iii. Put the male (♂) down the side of the Punnett square
iv. Put the dominant allele (the capitol letter) first, if one is present.
v. Put the recessive allele (the lower case letter) second, if one is present
Example 1:
♀ A
a
♂
A
AA
Aa
a
Aa
aa
II.
Probability = the likelihood a particular event will occur
a. # of times the event occurs
# of trials
b. Previous events DO NOT affect future outcomes
c. The larger the number of trials the more accurate probability you will have. (Closer to actual
population probabilities)
III.
Ratios- Relationship between two characteristics.
a. Phenotypic ratios- The observable physical characteristics of an organism presented as a ratio
i. Dominant : Recessive ( 3:1 above)
b. Genotypic ratios- The alleles for a trait in a population presented as a ratio
i. Homozygous Dominant : Heterozygous : Homozygous Recessive
(1:2:1 above)