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Biol 121 225 Freeman 286-289, 401-405, 316-318 Pedigree

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BIOL 121
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Biol 121 225 Freeman 286-289, 401-405, 316-318 Feb. 12, 10 Pedigree -to understand transmission of human traits, must analyze human crosses that already exist b/c making specific crosses will take too long (and ethical issues)! -a pedigree (like a family tree) records genetic relationships among the individuals in a family along with each person’s sex and phenotype with respect to the trait in question -pedigree may reveal whether trait is due to dominant or recessive allele; and whether it is on a sex chromosome or autosome Autosomal recessive traits -if a phenotype is due to an autosomal recessive allele, then 1) Individuals with the trait must be homozygous (recessive) 2) If parents of affected individual do not have the trait, they are both heterozygous Carrier -a carrier is a heterozygous individual who carries a recessive allele for an inherited disease – they transmit the allele even though they do not exhibit signs of the disease 3) When carriers mate, they produce offspring with the recessive phenotype 25% of the time Autosomal dominant trait -individuals with at least one allele for the trait must have the phenotype -unless new mutation occurs, any child with the trait must have a parent with the trait -e.g. Huntington’s disease Marker -a marker is a trait that appears in people that have a specific disease -e.g. in Huntington’s disease, people have many CAG repeats on chromosome 4 which is unstable for the protein -researchers found many CAG repeats in people with the disease and also found that affected individuals always have this trait – this means that this is the gene for the disease, which they named IT15 and the protein product huntingtin protein. Autosomal or sex-linked? -if a trait appears about equally often in males and females, then likely to be autosomal -if males much more likely to be affected, then probably X-linked -e.g. Haemophilia is due to an X-linked recessive allele
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