1. Complete Incomplete Codominance Multiple Alleles Sex-linked Traits
Forms of dominance
Complete
Incomplete
Codominance
Multiple Alleles
Sex-linked Traits

2. Complete dominance Mendel’s garden peas showed complete dominance Tt
Example: TT x tt = 100% Tt
tall short tall
T T Tt
tall t t

3. Want more practice?

4. Incomplete dominance
The dominant allele does not completely cover up the expression of the recessive allele
The phenotype of the offspring appears as a blend of the two
For example:
snapdragons
red x white = pink

5. Incomplete dominance
RR x rr
Red white R R Rr
Pink
pink r r

6. Codominance Two alleles are both dominant
If inherited together, both will be expressed

7. Codominance
Black x White
BB WW B B BW
Blue roan W W

8. Multiple Alleles Sometimes there is more than two forms of a trait!
Example human blood typeshttp://nobelprize.org/medicine/educational/landsteiner/index.html

9. Ex: Blood type problems
What are their possible blood types if a heterozygous type A man and a heterozygous type B woman have children?
IAi x IBi IA i
IAIB
IBi
IAi ii
25 % chance for
AB, A, B, or O IB i

10. Blood types and paternity
Blood type can only exclude a person from being the possible father of a child
Ex: a man accused of fathering a child has type O blood and the child has type AB
ii x _____ i i
The man can only pass on recessives!
He could not possibly have
fathered this
child

11. Sex-linked traits
Traits that are controlled by genes inherited only on the X sex chromosome

12. Red-Green colorblindness

13. XH Xh XH Y Hemophilia XH XH Normal XH Xh carrier XH Y normal Xh Y
a hemophilia carrier and a normal man want to know the probability of having children affected by hemophilia
Genotype
Phenotype for blood clotting
XH XH
XH Y
Normal female
Normal male
XH Xh
Female who is a carrier, she has normal blood clotting
Xh Y
Male who inherited the recessive allele located on the X sex chromosome will not produce the blood clotting factor XH Xh
XH XH
Normal
XH Xh
carrier
XH Y
normal
Xh Y
hemophilia XH Y

14. Polygenic Inheritance
occurs when more than one gene controls a single trait
these are sometimes called quantitative traits because the number of dominant to recessive alleles creates a wide range of observable phenotypes
Example: human height, skin color, eye color

15. Melananin Production in skin and eyes

16. Human Height