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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
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