1. WHEN HEREDITY FOLLOWS DIFFERENT RULES
Chapter 12.2

2. When Heredity Follows Different Rules
Dominant (T) vs recessive (t) is called “simple heredity”
There is a more “complex” pattern to some things, and that’s what we’ll study today

3. Objectives
Distinguish between alleles for “incomplete dominance” and “codominance”
Explain the patterns of “multiple allelic” and “polygenic inheritance”
Analyze the pattern of “sex-linked” inheritance
Summarize how internal/external environmental factors affect gene expression

4. COMPLEX PATTERNS OF INHERITANCE
Incomplete Dominance
Phenotype of the heterozygous offspring is the intermediate between those of the two homozygous parents (What?)
Example is when red plants cross pollinate with white plants and you get a pink plant
APPEARANCE OF A 3RD PHENOTYPE!!!
F1 = 4:0 , F2 = 1:2:1

6. Codominance: Expression of Both Alleles
Codominant Alleles:
cause the phenotypes of BOTH homozygous parents to be produced in heterozygous offspring
Best example to relate this to is when a red cow breeds with a white cow, you get “ROAN CATTLE” (red-white combination cow)
“Co”w = “Co”dominant

8. Multiple Phenotypes from Multiple Alleles
traits controlled by more than 2 alleles
it is very common for traits to be controlled by more than 2 alleles (ex: TTt)
Multiple alleles are mostly found to control BLOOD TYPE!!!!

9. Sex Determination Autosomes: Sex chromosomes:
22 pairs of homologous chromosomes (pairs 1-22)
Sex chromosomes:
23rd pair (is different in males and females)
Chromosomes are either X or Y
Males are XY
Females are XX (homologous)

10. Sex Linked Inheritance
Sex-linked traits:
Traits controlled by genes on the sex chromosomes
Alleles for sex-linked traits are written as superscripts on the X and Y chromosomes
Do not put alleles on a Y chromosome
Therefore, a recessive alleles on a X chromosome will override the whatever would be on a Y

11. Sex Linked Inheritance

12. Polygenic Inheritance
Inheritance pattern of a trait that is controlled by 2 or more genes
Skin Color is a good example
Alleles look like AABBCC x aabbcc = AaBbCc

14. ENVIRONMENTAL INFLUENCES
External Factors
Temperature
Nutrition
Light
Chemicals
Infectious agents
Ex: Arctic Fox in Fig on page 321

15. ENVIRONMENTAL INFLUENCES
Internal Factors:
Hormones
Male-pattern baldness is different in males and females
Dominant in males, recessive in females
Feather color in peacocks is different in males and females
Age