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Published byVincent Golden Modified over 9 years ago
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Codominant vs Incomplete Dominant- What’s the difference?
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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
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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
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One way to express incomplete dominance RR (Red) X rr (White)= (Rr)Pink Rr- results in a blended result of PINK
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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)?
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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.
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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
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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.
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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"
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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.
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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?
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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.
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Sex-linked Genetics Ex. Colorblindness
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Sex Chromosomes- last pair (23 rd ) in a karyotype MALE KARYOTYPE FEMALE KARYOTYPE
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Sex Chromosomes- last pair (23 rd ) in a karyotype Male – XY and Females – XX The 23 rd 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
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Sex-Linked Genes Ex. Colorblindness is carried on the sex- chromosomes It is a recessive trait – X c How many genes do females need to express the trait (colorblindness)? 2 X c X c How many genes do males need to express the trait (colorblindness)? 1 X c Y
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Sex-Linked Punnett Square Let C = Normal Vision and c = Colorblind Cross: Normal Male ( ) x Carrier Female ( )
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Sex-Linked Punnett Square Let C = Normal Vision and c = Colorblind X Y x X X = Normal Male x Carrier Female X Y X C CCc C C c 1 st put male genotype on the top of the table & female genotype on the left side
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Sex-Linked Punnett Square C – Normal Vision and c - Colorblind X Y x X X - Normal Male x Carrier Female X Y X C CCc C C c X X X Y CCC Ccc 2nd, cross them
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Sex-Linked Punnett Square C – Normal Vision and c - Colorblind X Y x X X - Normal Male x Carrier Female X Y X C CCc C C c X X X Y CCC Ccc Offsprings: 1 Normal Female 1 Normal (Carrier) Female 1 Normal Male 1 Colorblind Male 3rd, list the sex and appearance of each possible offspring
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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?
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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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