Day 27 Dominant and Recessive Alleles
Watch this video on Dominant Genetics. Pay special attention to vocabulary. Take good notes and write down questions you still have. This is a long and detailed video. You might have to take breaks, watch it 5 minutes at a time. You might also have to watch it more than once.
The genes you have are called your genotype
The genes that are expressed (shown) are your phenotype
When we write a genotype we use a capital letter for the dominant trait and a lowercase letter for the recessive trait. The letter chosen is usually the first letter of the dominant trait
-For example when talking about purple and white pea plants
-Purple is the dominant trait and white is recessive
-So the possible genotypes for flower color are:
PP= Homozygous dominant purple
pp= Homozygous recessive white
Pp= Heterozygous purple
A plant that is PP can only make P gametes
A plant that is pp can only make p gametes
-If you cross-fertilize the two the only possible offspring are Pp
If the heterozygous offspring (Pp) reproduce, their offspring can be any of the four possible combinations
PP, Pp, pP, pp
Punnett Squares
We can figure our the possible allele combinations of offspring by using a Punnett Square
Mendel then started testing other traits in the pea plants
Lets do some practice Punnett Squares using these traits!
What if we want to do a Punnett Square for more than one trait?
-We can do what is called a dihybrid cross. A cross between two traits
Extra resources
Intro to Genetics
http://www.khanacademy.org/science/biology/heredity-and-genetics/v/introduction-to-heredity
Punnett Squares
http://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun