1. Mendelian Genetics 3
AIM: How do complex heredity patterns determine phenotype?
DO NOW: Complete Do Now assignment on today’s handout
HOMEWORK: Handout on Mendel’s Laws

2. I. Incomplete Dominance
Sometimes it’s not a matter of who “wins” like it is in dominant and recessive genes. Sometimes it’s more cooperative.
What are we doing when we do cooperative learning?
A. Incomplete dominance – neither allele is dominant, so there is a blending of traits, resulting in an intermediate phenotype
White (WW) PINK (??) RED (RR)

3. WW RR RW B. Snapdragon Flowers If you cross a
white ______ flower with a red ______ flower,
you get a pink ______ flower.
Is the pink flower purebred or hybrid? WW RR RW
W W R RW RW RW RW
*REMEMBER* Since neither one is dominant over the other, both are written with CAPITAL letters!

4. Codominance
What happened here?
Does it look like dominance?
Does it look like incomplete dominance?
A. Codominance – neither allele is dominant, so both alleles show up at the same time in the organism’s phenotype
B. This horse’s color is called roan, which is a codominant phenotype resulting from a cross between purebred white _____ and purebred red ____. The genotype for roan is _____. WW RR WR

5. Codominance example: Ms. Wolf’s pet mice
I had one black pet mouse, named Inky.
I had one white pet mouse, named Blinky.
Pretty soon, I had a 3rd pet mouse, named Moo-Cow.
________
Inky BB
________
Blinky WW
________
Moo-Cow BW
B B W BW BW BW BW

6. D. Codominance example: Sickle Cell Disease
Sickle Cell Disease results in crescent-shaped red blood cells. That means cells can get stuck in the bloodstream and make it very difficult to transport oxygen.
People that have two alleles for this disease usually die, so those that have it are usually heterozygous.
Normal cell allele = N
Sickle cell allele = S
What genotype would a person living with sickle cell disease have?

7. III. Multiple Alleles
So far, we’ve learned that genotypes can be either Y or y, A or a, E or e…
…but in reality, most genotypes are not formed from only 2 alleles – they are formed from multiple allele possibilities
A. Multiple Alleles – traits that are controlled by more than 2 allele types

8. Multiple allele example: Blood Types
1. Blood types have 3 forms of alleles. They are sometimes called AB Markers.
IA = Type A
IB = Type B
i = Type O (absence of AB markers)
Type O is recessive to type A and B,
but A and B are codominant
You can see that Type O can be used by every blood type.
Why do you think that is?

9. Which would you be more likely to find?
C. Multiple allele example: Rabbit fur color
Rabbit coat color depends on five genes! Some turn off color expression, some turn them on. The final result makes some rabbits very common and some very rare.
Which would you be more likely to find?

10. SUMMARY How do complex heredity patterns determine phenotype?
Complete the summary worksheet

11. XY XX IV. Sex-Linked Traits
What genotype makes an organism male? XX
What genotype makes an organism female?
Men only get one X chromosome. If there happens to be a recessive gene on the X, men don’t have a dominant gene that can cancel it out. They are going to express it.
Females have a far greater chance of having a dominant gene to hide the recessive one.
Sex-linked traits – traits carried by either the X or the Y chromosome

12. D. Sex-linked trait example: Color Blindness
Color blindness is a gene located on the
X-chromosome.
Who would be more likely to be affected by this gene? Men or women?

13. E. Sex-linked trait example: Hemophilia
1. Hemophilia – characterized by really slow clotting of the blood

14. V. Polygenic Traits
A. Most traits are the result of the action of many genes (One trait = many genes).
ex. Skin color and height depend upon the interaction of many independent genes.
Polygenic traits are controlled by two or more genes.
1. They show a wide range of phenotypes

15. Genes + Environment = Phenotype
VI. Environmental Influences on Heredity
Your genes are not the final answer!
There is so much that can be influenced by the environment, including nutrition, exercise, and where you live.
Genes + Environment = Phenotype
Ex. Diseases like diabetes or ulcers may be in a genetic code, but may never be seen in the phenotype if the person leads a healthy lifestyle.
Analyze the phrase, “Heredity loads the gun, but environment pulls the trigger”

16. SUMMARY How do complex heredity patterns determine phenotype?
Complete the summary worksheet