beyond mendel 11.3 into the genetic frontier. genes can be inherited based on various patterns...
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Beyond Mendel 11.3Into the Genetic Frontier
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Genes can be inherited based on various patterns
• Mendel’s Dominance vs. Recessive
• Incomplete dominance
• Co-dominance
• Multiple alleles
• Polygenic genes
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Incomplete Dominance• In this pattern neither allele is considered recessive
• Heterozygous conditions produce a blend of the two traits creating a third phenotype.
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Co-dominance• In this pattern much like
incomplete dominance, neither allele is considered recessive
• In a heterozygous condition where each type of allele is present the phenotype displays both traits from each allele
• There are 3 possible phenotypes
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Multiple alleles
• In this pattern there is more than just two alleles (3 or more)
• Combinations of other patterns
• Ex. Some alleles behave in a dominant/recessive fashion while other alleles display a co-dominant or incomplete dominant relationship
• This can lead to multiple phenotypes
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There are 4 Human Blood Types
A, B, AB & O = 4 phenotypesBlood type is controlled by one
gene, with 3 different alleles – A, B and O
The 3 alleles can be combined to produce 6 different genotypes
AA BBAO BOAB OO
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Inheritance of Blood TypeIs a mix of complete dominance and
codominance - AA & AO produce type A blood - BB & BO produce type B blood - AB produces type AB blood - OO produces type O blood
From this we can infer that both A & B alleles are dominant to the O allele
The A allele is codominant with the B allele
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Determining Possible Outcomes
How would a person who is homozygous for B blood be notated?
- IB IB
How would a person who is
heterozygous for B blood be
notated?
- IB i
Notating Blood Type IA = A allele IB = B allele i = O allele
Example a person who heterozygous for A blood = IA iAnd a person with O blood = i i
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What exactly is blood type?Each blood type is the result of a specific
combination of proteins found on the blood cells called antigens and proteins found in the blood plasma called antibodies
- type A blood = A antigens & B antibodies - type B blood = B antigens & A antibodies - type AB blood = both A & B antigens & no
antibodies - type O blood = no antigens & both A & B
antibodies
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Why is Blood Typing Important?
If a person is given blood with antigens that their blood plasma contains antibodies for, the antibodies will attach to the blood causing it to clump
- this clumping is called agglutination
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BloodGroup(Phenotype) O
GenotypesAntibodiesPresent inBlood
Red Blood CellsReactions When Blood from Groups Below IsMixed with Antibodies from Groups at Left
A B AB
O
A
B
AB
ii
IAIB
IBIB
orIBi
IAIA
or IAi
Carbohydrate A
Carbohydrate B
Anti-A
Anti-B
Anti-AAnti-B
—
Figure 9.20
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Polygenic traits
Some traits which have many possible
phenotypes are controlled by more than one gene.
- the interactions of these genes allows for the large numbers of phenotypes.
- human examples: Hair, eye and skin color
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The Inheritance of Eye Color Only partially understood. at least 3 different genes with 2
alleles each are responsible for eye color.
– bey 1 bey 2 and geyThese genes code for the
formation of the pigment melaninThe function of only 2 of the 3
genes is currently understood
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The Inheritance of Eye Color as it is Currently Understood
Known as the 2 gene modelOne gene known as bey 2 has 2 alleles B
for brown eyes and b for blue eyesThe other gene known as gey has 2
alleles G codes for green eyes and g for blue eyes
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The 2 Gene Model
- B is dominant to all other alleles- BBGG,BBGg,BBgg,BbGG BbGg,Bbgg = Brown eyes
- G is dominant to b bbGG , bbGg = Green eyes
- bbgg only = blue eyes
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Genes and the Environment
◦ The characteristics of any organism are not determined solely by the genes that organism inherits.
◦ Genes provide a plan for development, but how that plan unfolds also depends on the environment.
◦ The phenotype of an organism is only partly determined by its genotype.
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Environment Can Influence Gene Expression
example: Siamese cats
- Siamese coloring is a partial albinism. Most of the cat is white
-Black fur is only expressed in areas where the temperature is lower than the rest of the body
- if black hair is shaved and the area kept warm then the hair that grows back will be white
- if white hair is shaved and the area is cooled, then the hair will grow back black
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In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales.
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In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. What happens when you breed 2 pink dragons?