Genetics
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Transcript of Genetics
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Genetics
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Incomplete Dominance• Where neither the dominant or recessive allele
is truly dominant over the other, both are dominant
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Incomplete Dominance
• The heterozygote will “blend” the two traits into an intermediate third trait
• RED Flower x WHITE Flower ---> PINK Flower
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Incomplete Dominance
• Because neither allele is dominant over the other, we use a large base letter indicating the character and a capital superscript showing trait CR CR for red flower
CW CW for white flowerOne allele from each parent is passed on. A
cross would produce CR CW which is pink phenotype.
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• It’s important to know when you’re dealing with incomplete dominance*notice that the offspring is showing 3rd phenotype*notice that the trait in offspring is a blending of parental traits
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Codominance
• Similar to incomplete dominance because it too creates a 3rd phenotype, different from parents.
• Parental traits don’t blend, instead the two traits appear together in a hybrid
red and white --> red & white spotted
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• Here’s an example of a codominant flower showing both parental pink and white traits.
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X
ROAN COW
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Human Blood Types• Antigen- molecules that can trigger an immune response
• A carries A antigen • B carries B antigen• AB has both antigens• O carries neither antigenRh Factor; Rh+ carry this antigen, while Rh-
individuals don’t.• In transfusions, a new antigen cannot be
introduced into the body of recipient
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How common is your blood type?
46.1%
38.8%
11.1%
3.9%
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• Who can give you blood?
• People with TYPE O blood are called Universal Donors, because they can give blood to any blood type.
• People with TYPE AB blood are called Universal Recipients, because they can receive any blood type.
• Rh + Can receive + or -
• Rh - Can only receive -
Universal Recipient
Universal Donor
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Polygenic Inheritance• When multiple genes affect a single
character, variation • Height, weight, eye color, skin color• Suppose ABC were 3 “TALL” alleles and abc
were 3 “short” alleles• Someone with genotype AABBCC would be
very tall, while someone with genotype AaBBCC would be slightly less tall
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AB Ab aB ab
AB AABB AABb AaBB AaBb
Ab AABb AAbb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb
AB: Dark Red plantsab: white plants
Wide RANGE of phenotypes
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Environment Influence on Phenotype
• Sometimes an organisms phenotype depends on their environment regardless of genotype
• For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity
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An enzyme responsible for dark fur is only active at cooler temperatures like cat’s extremities
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Gene Linkage
• Genes on separate chromosomes assort and separate independently from each other
• Genes located on SAME chromosome and close together (close gene-loci) tend to be inherited together. * Genetic linkage
• If genes are far apart, but on the same chromosome, crossing over could separate them
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Sex-Linked Genes• Any gene located on an sex chromosome
is a sex-linked gene• In humans, most of these are on the X
chromosome (much bigger than Y)
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Hemophilia: X-linked genetic RECESSIVE disorder
h H h
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Mother is a carrier
h h HH H
hHH
H
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FATHER IS A CARRIER
h HH
h H H
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Red-green color blindness• X-linked color blind allele is recessive• Heterozygous females have normal vision• Males who get recessive allele in their only
X chromosome are affected.
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• X-linked recessive disorders are more common in men than women
• Women need 2 recessive alleles on each of her X chromosomes to be affected
• Men only need 1 recessive allele on his only X chromosome to be affected