1. Patterns of Inheritance
Phenotype is affected by many different factors!

2. 1. Incomplete Dominance Blending of traits
Neither allele is completely dominant or recessive

3. Incomplete Dominance Example: snapdragons (flower)
red (RR) x white (rr)
RR = red flower
rr = white flower
Rr = Pink

4. Co-dominance Both traits are present at the same time Example #1:
Red flower + white flower = a flower that with both colors
(such as white with red edges, etc.)
Example #2: Blood types

5. Polygenic Traits “Many Genes” Traits produced by 2 or more genes
Example: Human skin color is a result of 4 genes that react to produce a continuous range of colors
Example: Human eye color is a result of at least 3 genes
Scientists hypothesize that additional genes code for variations in color, pattern, and changes over time

6. Environmental Impacts on Phenotype
Phenotype is more than just gene expression
Example: Sea turtles
Eggs that mature in warmer sand = females
Eggs that mature in cooler sand = males

7. Sex Linked Traits
A trait determined by a gene or genes carried on the X chromosome but not on the Y chromosome
Example: Color Blindness, hemophilia, etc.

8. *If a son inherits an X chromosome with the hemophilia gene, the trait will be expressed and he will have the disorder. If a daughter inherits the mutated X chromosome, her normal X chromosome will compensate for the abnormal chromosome and the disease will not be expressed.

10. Mendel’s Laws

11. 1. Law of Dominance
When the dominant allele is present, it will mask the recessive trait

12. Example of Dominance R = red flower r = white flower
Problem: Cross homozygous
dominant with homozygous recessive
___ ___ x ___ ___
What are the results?
Phenotype:
____ % red, ____ %white
Genotype:
____ % homozygous or heterozygous

13. 2. Law of Segregation & Recombination
A parent randomly passes on only one allele for each trait to each offspring.
Just because your parents have certain traits, doesn’t mean you are guaranteed to have the same traits

14. Example of Segregation
Problem: Cross two offspring from the 1st filial generation (both are heterozygous) ___ ___ x ___ ___ Results? Phenotype: _____% red, ____% white Phenotypic ratio: ___ red : ___ white Genotype: ___% homozygous dominant ___% homozygous recessive ___% heterozygous

15. 3. Law of Independent Assortment
The genes for different traits are inherited independently of each other.
Ex. Seed color and flower color have no relation.

16. Example of Independent Assortment
Requires the use of a dihybrid Cross:
Dihybrid Cross – Examines the inheritance of 2 different traits
The genes are on separate chromosomes, so the traits themselves are unrelated
*Handout

17. RrYy vs. RrYy (Seed Shape vs. Texture)
R=round, r=wrinkled, Y=yellow, y=green
The 4 allele combinations possible in each gamete are used to label each axis

18. Phenotypes & Genotypes
Round/Yellow:
9/16
Round/Green:
3/16
Wrinkled/Yellow:
Wrinkled/Green:
1/16
Ratio - 9:3:3:1