1. Types of Dominance

2. Complete Dominance
Genetic crosses that result in the dominant phenotype being shown due to a dominant gene being present.
Ex: Tallness is dominant. Crossing a homozygous dominant pea plant (TT) with a homozygous recessive pea plant (tt) results in F1 offspring all having a dominant gene (Tt)
These problems use the same letter (T)
T T Tt Tt t Tt Tt

3. Incomplete Dominance
When some alleles are neither dominant nor recessive.
One allele is not “stronger” than the other.
Phenotypes are blended together.
Uses TWO letters
Crossing a red flower (RR) with a white flower (WW) creates pink flowers (RW).
R R RW RW W RW RW

4. Co-dominance When both of the phenotypes are visibly seen.
Phenotypes do NOT blend, they are both seen.
Uses TWO letters
Ex: In a breed of chickens, the allele for black feathers is co-dominant with the allele for white feathers.
Black (BB) father and White (WW) mother produced Black AND white (speckled) baby chicks
B B BW BW W BW BW

5. Example 1
In mice, the two most common colors seen are brown (BB) and white (WW). How would you cross a brown mouse with a white mouse to get a cream-colored mouse?
What type of dominance is this?
What is the probability of getting a cream colored mouse from this cross?

6. Example 2
In certain breeds of salmon, there are fish with the “A” allele for scales (Aa) and without scales (aa). When you cross the two breeds, some fish end up with scales, some don’t.
What type of dominance?
What’s the probability of getting a fish with scales?

7. Example 3 What type of dominance is this?
You have identified a new species of grasshopper that come in two different colors: ones with red stripes (RR) and ones with yellow stripes (YY). When you cross them you get a grasshoppers with red and yellow stripes.
What type of dominance is this?
What will the offspring look like?

8. Complete a Punnett Square for this cross
Example 4
A species of chicken’s color is determined by CODOMINANT genes. A Heterozygous (BW) chicken is crossed with a Homozygous (BB) chicken:
Complete a Punnett Square for this cross
What color is the Heterozygous (BW) parent chicken?
What color is the Homozygous (BB) chicken?
What is the probability that a black chick will be born?
What is the probability that a white chick will be born?
What is the probability that a black AND white chick will be born?
What is the probability that a GREY chick will be born?
What is the genotypic ratio for this cross?
What is the phenotypic ratio for this cross?

9. Complete a Punnett Square for this cross
Example 5
A species of flower’s color is determined by INCOMPLETELY DOMINANT genes. R is for Red and W is for White. A Heterozygous (RW) flower is crossed with a Homozygous (RR) flower:
Complete a Punnett Square for this cross
What color is the Heterozygous parent flower?
What color is the Homozygous (RR) parent flower?
What is the probability that a Red flower will be made?
What is the probability that a White flower will be made?
What is the probability that a Red AND White flower will be made?
What is the probability that a PINK flower will be made?
What is the genotypic ratio for this cross?
What is the phenotypic ratio for this cross?

10. Complex Inheritance Polygenic Traits Multiple Alleles Sex-Linked Genes

11. Multiple Alleles
A gene (characteristic) with more than two alleles is said to have multiple alleles.
Ex: coat color in rabbits, blood types.
Most characteristics we’ve dealt with so far have two alleles (R and r). Multiple Alleles have more than two (ex: A, B, O in blood types).
***There can be multiple alleles for a certain trait, but each individual STILL ONLY HAS 2  ONE FROM MOM, ONE FROM DAD.****

12. Polygenic Traits
A trait that is controlled by two or more genes (each with two alleles)
Ex: AaBbCc
Polygenic inheritance usually shows up as a range of variation such has height, skin color or eye color.

13. Human Blood Types

14. Human Blood Types A B AB O There are 4 different blood phenotypes
3 alleles are in the pool instead of just two (A, B, O)
You still only get ONE from Mom and ONE from Dad.

15. Genotypes for blood type
ALLELE
CODES FOR IA
Type A Blood IB
Type B Blood i
Type O Blood
Type O is the recessive blood type, which is why it gets a lowercase (i).

16. Genotypes & Phenotypes of Blood
IAIA
Type A - Homozygous
IAi
Type A - Heterozygous
IAIB
Type AB - Heterozygous
IBIB
Type B - Homozygous
IBi
Type B - Heterozygous ii
Type O – Homozygous recessive

17. Example Problem: IB i IAIB IAi IA
Dad is homozygous for Type A blood. Mom is heterozygous for Type B blood. Do a Punnett Square to find out the offspring.
What are the new genotypes? Phenotypes?
IAIB Type AB
IAi Type A
IAIB Type AB
IB i
IAIB
IAi IA

18. Blood Donors & Receivers

19. Sex Linked Traits

20. Sex – Linked Genes
We each have two sex chromosomes (one donated from mom, one donated from dad.
Females: X X
Males: X Y
Genes on the first X chromosome are shared traits between the sexes, and is inherited from your mother.
Genes on the Y chromosome contain very few instructions (primarily just for male development).

21. Sex-Linked Disorders Colorblindness Hemophilia
Two of the most common sex-linked disorders are
Colorblindness
Hemophilia
The genes that cause these disorders is located on the X chromosome (usually passed from mother to son)
This makes it very rare for a colorblind father to pass the gene onto his son.

22. Sex-linked Genotypes Genotype Codes for: XRXR XRXr XrXr XRY XrY
Female – Homozygous – Dominant
XRXr
Female –Heterozygous – Dominant
XrXr
Female – Homozygous – Recessive
XRY
Male – Dominant
XrY
Male – Recessive

23. Example Problem: Xr Y XRXr XRY XrXr XrY XR Xr
Colorblindness is an X-linked recessive disorder. Show a cross between a heterozygous mother and a father who is colorblind.
What are the new genotypes? Phenotypes?
XRXr – (F) Not Colorblind
XRY – (M) Not Colorblind
XrXr – (F) Colorblind
XrY – (M) Colorblind
Xr Y
XRXr
XRY
XrXr
XrY XR Xr