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This article provides an overview of human genetics, discussing various traits, diseases, and inheritance patterns. It explores both simple dominant and recessive traits, as well as genetic diseases like cystic fibrosis, Tay-Sachs, and phenylketonuria. Additionally, it delves into the persistence of certain genes, using Huntington's disease as an example.
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Humans are not pea plants! • Although in all organisms genes control the production of proteins that show up on our phenotype, most human genetics cannot be explained by tall/short, pink/white, round/wrinkled. • There are a few human traits determine by a gene with two alleles, one recessive and one dominant.
Can you roll your tongue? • Tongue rolling is determined by a gene with two alleles, the dominant roller and the recessive non-roller. • If two rollers give birth to a non-roller, what is the genotype of each?
Set up the problem- ? R • R= roller • r=non roller • Both parents are rollers, so they must both have at least one R • The offspring shows the recessive trait, so it must be homozygous recessive= rr • R? x R? R ? So, each of the parents must carry the recessive allele. That means they are both heterozygous for tongue-rolling.
Here’s an interesting one…. • POLYDACTYLY-having 6 fingers on one or both hands or feet. • The dominant allele is six fingers, showing dominant doesn’t always mean “better” or “most common”. • What’s the chance a child will have polydactyly if both parents have 5 fingers?
Polydactyly is a dominant allele • You cannot pass along alleles you do not have. • If both parents have 5 fingers, they have no allele for 6 fingers, so they cannot pass on the six-fingered allele • 0% chance of 6 fingered children
Some human genetic diseases • Show simple recessive heredity, such as cystic fibrosis. • Cystic fibrosis results from a defective gene that produces a defective protein, accumulating thick mucus in lungs. • If a child is born with cystic fibrosis from parents without the disease, what are the chances his sister will have the disease?
Tay-Sachs and Phenylketonuria • Are also serious disorders. • Some of these defective genes have been located. • Since some genetic disorders run in certain ethnic groups, some people may choose to be tested for the defective gene before they have children.
Some human inheritance is simple dominant • Such as hitchhiker’s thumb. Does anyone in your family have that? • Huntington’s’- a fatal disease caused by a dominant gene, but the gene persists in our population. Why? • Symptoms don’t usually appear until after age 40.
