Mendelian Genetics Notes2

Mendelian Genetics Notes2 - 4.26.2007 Square male Circle...

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4.26.2007 Square male Circle female Shaded symbol is affected with condition Open symbol is unaffected individual (phenotypic statement to say affected vs. unaffected) Two lines is a marriage or mating between two individuals of the same family (inbreeding, consanguineous) First thing to consider is whether the gene is located on an autosome or a sex chromosome o Sex chromosome: shows remarked/convincing gender bias Affected individuals will be far more of one gender than other (true for X or Y linked) o Autosomal: no convincing gender bias Second: consider if it generally looks dominant, or generally looks recessive o Is it caused by a recessive or dominant allele o Recessive traits, affected individuals are homozygous and have to get one recessive allele from mom and dad who probably were heterozygous and didn’t have the condition You see affected offspring coming from unaffected parents o Dominant: most affected individuals are heterozygous rather than homozygous One affected allele is enough to cause the phenotype Probably inherited it from one parent or the other parent, the parent expressed the phenotype as well Dominant: individual will have at least one affected parent Example 1: aa Aa Aa Aa AA AA Aa Aa Aa (because she had a relative that had the disease, so most likely she is the a) aa Make some assumptions because you assume those coming not from the family and are unaffected are homozygous dominant Example 2: Conclude it is autosomal and dominant because you have two affected parents giving birth to an unaffected offspring, if it were recessive then both individuals would have to be homozygous and give the condition to ALL OF the offspring and BREED TRUE, but this is not the case How could two affected have an unaffected? Both parents are heterozygous Example 3:
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Assume autosomal Assume dominant, because you would have to have affected offspring with BOTH parents unaffected Don’t have to know this but… o Autosomal dominance in humans happens in: Huntingtons Disease, Marfan’s syndrome (overgrown longbones, weakness in tissues), Achondroplasia (dwarfism), etc. Example 4:
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Mendelian Genetics Notes2 - 4.26.2007 Square male Circle...

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