Patterns of Heredity
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Transcript of Patterns of Heredity
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Patterns of Heredity
Incomplete Dominance, Codominance and Sex-linked
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Figure 14.2 Mendel tracked heritable characters for three generations
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Genetics Vocabulary• Incomplete Dominance - a form of
intermediate inheritance in which one allele for a specific trait is not completely dominant over the other. If the trait is incomplete it will be stated in the problem.
(Some people, like incomplete dominance, use superscripts or subscripts w/ diff letters)
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Figure 14.9 Incomplete dominance in snapdragon color
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Genetics Vocabulary• Codominance - A condition in which
both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other. If the trait is codominant it will be stated in the problem. (When crossing codominant traits, use different capital letters) RR RW WW
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Autosomes vs. Sex-chromosomes
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Sex-linked traits• Most human traits are inherited by passing
autosomes – non-sex chromosomes– (just like peas)
• Sex-linked traits = inherited by passing sex-chromosomes.– Many human diseases including:
• Hemophilia & Color blindness
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Designating Sex-Linked Traits
XA = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only)
* X-linked traits are only on the X chromosome
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Genotype Phenotype
XA XA Normal female
XA Xa Normal female, also called a carrier
Xa Xa Female with trait
XA Y Normal male
Xa Y Male with trait
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• X-linked traits may also skip generations
• Males are affected more often than females because they only have one X chromosome
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Sample problem
• Hemophilia is an X-linked disorder. If an affected father and a carrier mother have a boy, what is the probability that boy will have hemophilia?
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What is the probability that boy will have hemophilia?
Mother’s Genes
Xa XXa
Y
XaXa XaX
XaY XY
Fa
the
r’s
Gen
es
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Autosomal Dominant diseases
• Individuals have the trait if they have the dominant allele.– Ex: familial
hypercholesterolemia– Huntington’s disease– Dwarfism– Neurofibromatosis– Colon cancer– Kidney disease– Etc.