unit: mendelian genetics. for example: ◦ some alleles are neither dominant nor recessive. ◦ in...
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Unit: Mendelian Genetics
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For example:
◦Some alleles are neither dominant nor recessive.
◦In most organisms, the majority of genes have more than two alleles.
◦Many important traits are controlled by more than one gene.
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Incomplete dominance - acondition in which offspringdisplay an intermediate traitbetween two parents.
Example: The F1 generation
produced by a cross between many red-flowered (RR) and white-flowered (WW) plants consists of pink-colored flowers (RW)
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Codominance- a phenomenon in whichtwo dominant alleles are expressed at thesame time.
Example #1 Speckled Chickens: In certain varieties of chicken, the allele for black feathers (B) is codominant with the allele for white feathers (W).
◦Heterozygous chickens have a color described as “erminette,” (BW) speckled with black and white feathers.
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If two erminettechickens werecrossed, what is the probability that:
a. They would have a black chick?
b. They would have a white chick?
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In horses and cattle, red coloration (R) and white coloration (W) are codominant. Individuals with each allele are roan (RW)
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Take two minutes to summarize whatyou have learned by stating thesimilarities & differences that existbetween traits that exhibit codominanceand traits that exhibit incompletedominance.
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Multiple alleles- a term used todescribe a genewith more than twoalleles.
Example: ABO bloodgroups in humans.
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Alleles: IA IB
and i
• A person only has two of these three alleles though! There are 4 possible blood types.
Dominance IA and IB are bothdominant over i, butneither is dominant over the other (A=B)
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Type A blood Type B blood IA IA IB IB IA i IB i
Type AB blood Type O blood IA IB ii
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Answer: If the wrong blood type is used in a transfusion, antibodies in the recipients blood couldattack the new blood received and make the person very ill.
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Why are they called that?
Since there are no antigens on thesurface of Type O their blood cells, there is
norisk of the antibodies in the recipients bloodattacking the new blood received from atransfusion.
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Why are they called that?
Since people with AB blood have noantibodies for A or B, they can safely receiveany type of blood in a transfusion.
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Polygenic Traits: Traits that are controlled bytwo or more genes.
Examples: human skin color, eye color, height
◦The genes that code for the trait may be scattered along the same chromosome, or located on different chromosomes.
◦Polygenic traits often show a wide range of phenotypes.
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Take two minutes to summarize what you havelearned regarding the similarities & differences
that exist between traits that have multiplealleles and traits that are referred to as
polygenic.
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◦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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◦Western white butterflies that hatch in the summer have different color patterns on their wings than those hatching in the spring.
◦Scientific studies show that butterflies hatching in springtime had greater levels of pigment in their wings than those hatching in the summer.
◦In other words, the environment in which the butterflies develop influences the expression of their genes for wing coloration.
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◦In order to fly effectively, the body temperature of the Western white butterfly needs to be 28–40°C.
◦Since it is cooler in the spring, more pigmentation allows a butterfly to reach the warm body temperature faster.
◦Similarly, in the hot summer months, less pigmentation prevents the butterflies from overheating.
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Take two minutes to summarize what you have
learned regarding the role the environment has
in gene expression.