1. Genetics: Understanding Heredity
(How traits are passed from parent to offspring)

2. Dominant and Recessive Alleles
Alleles are the different versions of a gene.
Ex/ Gene = height in pea plants
One version (allele) codes for a tall stem
One version (allele) codes for a short stem
Dominant allele – version of the trait that always shows up if it is present
Recessive allele – version of the trait that only shows up if the dominant allele is not present

3. How do alleles control traits?
Organisms inherit one allele from each parent (two copies in total)
Symbols are used to represent alleles
Capital letters represent dominant alleles
Lower case letters represent recessive alleles
Ex/ Tall stem = T (dominant)
Short stem = t (recessive)

4. Homozygous: When an organism inherits two of the SAME alleles for a trait
Homozygous dominant = TT
Homozygous recessive = tt
Heterozygous: When an organism inherits two different alleles for a trait (Ex/ Tt)

5. If T = tall and t = short: TT = tall
Tt = tall (dominant covers recessive)
tt = short
The allele combination is called an organisms genotype (Ex/ Tt)
The physical expression of the trait is called the phenotype (Ex/ Tall)

6. Practice:
Determine if the following allele combinations are homozygous or heterozygous: HH Uu Xx PP dd Rr

7. What would be the phenotype for the following genotypes:
B = brown fur b = tan fur
BB =
Bb =
bb =

8. Come up with the symbols to represent the following trait:
Blue flowers are dominant to white flowers
Blue:
White:
Then, show the Genotype and Phenotype for:
Homozygous dominant:
Heterozygous:
Homozygous recessive: