Codominant vs Incomplete Dominant- What’s the difference?

Beyond Dominant and Recessive

• Incomplete Dominance One allele is not completely dominant over

the other – something in the middle is expressed

Ex. Red and White Snapdragons Result can be heterozygous (Rr) or two

separate dominant alleles (RW) each resulting in a mixture of both alleles

Another way that incomplete dominance can be expressed

• Red= RR• White= WW

• RW= pink- each allele is equally expressed to result in a blended product

One way to express incomplete dominance

• RR (Red) X rr (White)= (Rr)Pink

• Rr- results in a blended result of PINK

Incomplete Dominance Practice

• In certain cats, tail length is determined by a gene that demonstrates incomplete dominance. The allele that causes a long tail (T) is not completely dominant over the allele that causes no tail (t). If a cat is heterozygous forthis trait (Tt), then the cat will have a short tail. What is the probability that the offspring will be manx cats (no tail) if a short – tailed cat is bred with a manx cat (no tail)?

•

Incomplete Dominance Practice

• Incomplete dominance is seen in snapdragons. The allele that causes red flowers (F) is not completely dominant over the allele that causes white flowers (f). When a plant is heterozygous for the trait of flower color (Ff), pink flowers result. Cross two pink snapdragons, and provide the genotype and phenotype of all offspring.

Beyond Dominant and Recessive

• Codominance Both alleles are expressed in the phenotype

Ex. Cow Hair Color RR – Red WW – White RW – Roan (Red & White)

Practice Codominance/Incomplete Dominance #1-4

Beyond Dominant and Recessive

• Multiple Alleles Genes have more then two alleles

Ex. Blood Type

Type A blood- AA or AO alleles

A is dominant to O

Type B blood- BB or BO alleles

B is dominant to O

Type AB- codominant- A and B alleles

A nor B is dominant so both are expressed on organisms RBC

Type O- recessive- OO alleles

Both alleles must be recessive in order to have type O.

More on blood types…..• The blood type determines what antibodies are

located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death.

• Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors"

• Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"

Co-dominance Practice

• In humans, blood types A and B are equally dominant (codominant). Both types are dominant to type O. A man with type AB blood marries a woman with type O blood. Give the genotypes and phenotypes of all possible offspring.

Co-dominance Practice

• If a man with blood type A, one of whose parents had blood type O, marries a woman with blood type O, what percentage of their offspring would have blood type OO?

Polygenic Traits

• Traits that are controlled by the interaction of several genes.

• Example: – Reddish brown eyes in varying degrees found

in fruit flies is controlled by 3 genes– Human skin color is controlled by 4 different

genes which result in a variety of skin color.

Sex-linked Genetics

Ex. Colorblindness

Sex Chromosomes- last pair (23rd) in a karyotype

MALE KARYOTYPE FEMALE KARYOTYPE

Sex Chromosomes- last pair (23rd) in a karyotype

• Male – XY and Females – XX• The 23rd pair of chromosomes will determine

the gender of an individual

• Very few genes are located on the Y chromosome……Most are located on the X

• Sex linked alleles will ALWAYS be tracked on the X chromosome ONLY when we conduct practice genetic problems

Sex-Linked Genes• Ex. Colorblindness is carried on the sex-

chromosomes

• It is a recessive trait – Xc

How many genes do females need to express the trait (colorblindness)?

2 Xc Xc

How many genes do males need to express the trait (colorblindness)?

1 XcY

Sex-Linked Punnett Square

• Let C = Normal Vision and c = Colorblind• Cross: Normal Male ( ) x Carrier Female ( )

Sex-Linked Punnett Square

• Let C = Normal Vision and c = Colorblind• X Y x X X = Normal Male x Carrier Female

X Y

X

X

C

C C c

C

C

c

1st put male genotype on the top of the table & female genotype on the left side

Sex-Linked Punnett Square

• C – Normal Vision and c - Colorblind• X Y x X X - Normal Male x Carrier Female

X Y

X

X

C

C C c

C

C

c

X X X Y

X X X Y

C C C

C c c

2nd, cross them

Sex-Linked Punnett Square

• C – Normal Vision and c - Colorblind

X Y x X X -Normal Male x Carrier Female

X Y

X

X

C

C C c

C

C

c

X X X Y

X X X Y

C C C

C c c

Offsprings:

1 Normal Female

1 Normal (Carrier) Female

1 Normal Male

1 Colorblind Male

3rd, list the sex and appearanceof each possible offspring

Sex-linked Practice

• Hemophilia is a disease caused by a gene found on the X chromosome. Therefore, it is referred to as a sex – linked disease. The recessive allele causes the disease. A normal man marries a woman that is heterozygous for the trait. Give the genotypes and phenotypes of all possible offspring. Will any of their children have the disease?

PRACTICE and HW

• Complete problems 1-3 on the sex linked genetic practice problems sheet NOW!

• Complete the remaining 3 Co-dominant and Incomplete dominant practice problems and Sex Linked practice problems # 4-8 from today’s class for HW