1. Heredity
Patterns of Inheritance

2. Patterns of Inheritance
Not all genes show simple patterns of dominant & recessive alleles
Majority of genes have more than 2 alleles
Many important traits controlled by more than 1 gene

3. Patterns of Inheritance
Some alleles are neither dominant nor recessive
Many traits are controlled by multiple alleles or multiple genes
Go beyond Mendel’s principle of dominance

4. Patterns of Inheritance
Incomplete dominance -
Condition in which 1 allele is not completely dominant over another
heterozygotes have their own phenotype
Phenotype expressed is somewhere between dominant and recessive

5. Patterns of Inheritance incomplete dominance
Cross between red-flowered (RR) and white-flowered (rr) plants produced:
F1 generation: pink-colored flowers (Rr)

6. Patterns of Inheritance
2) Codominance
Occurs when both alleles for a gene expressed completely
Both alleles in the heterozygotes are contributing to the phenotype

8. Codominance F1 HB HW HBHW
Crossing a purebred chestnut brown horse with a purebred white horse: HBHB x HWHW
A roan horse occurs F1 HB HW
HBHW

9. Codominance: Human Blood
Three alleles in the human race control blood type
IA, IB, i
These alleles code for certain antigens that will be present on RBC surface
Antigen: A certain carb/protein found on a cell’s membrane, elicits an immune response
3 alleles code for 4 blood types…

10. Codominance: Human Blood

11. Codominance: ABO blood types

12. Codominance: ABO blood types

13. Codominance: ABO blood types

14. Codominance: ABO blood types

15. Codominance: ABO blood types

16. Patterns of Inheritance
3) Multiple Alleles
Many genes have more than 2 alleles
Does NOT mean individual can have more than 2 alleles
More than 2 possible alleles exist in population

17. Patterns of Inheritance multiple alleles
Example: Color in rabbits
Rabbits coat color determined by single gene
has at least 4 different alleles
4 known alleles display pattern of simple dominance that can produce 4 possible coat colors
Figure 11-12, p.273 in text

18. Patterns of Inheritance
4)Polygenic Traits
“having many genes”
Traits controlled by 2 or more genes
Often show a great variety of phenotypes
Examples: skin color, eye color, and hair color