HUMAN GENETICS

Humans are not pea plants! 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. 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. 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. 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? If two rollers give birth to a non-roller, what is the genotype of each?

Set up the problem- R= roller R= roller r=non roller r=non roller Both parents are rollers, so they must both have at least one R 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 The offspring shows the recessive trait, so it must be homozygous recessive= rr R? x R? R? x R? RRR? R? rr=non- roller 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. 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”. 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? 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. 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 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 0% chance of 6 fingered children

Some human genetic diseases Show simple recessive heredity, such as cystic fibrosis. 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. 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? 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. Are also serious disorders. Some of these defective genes have been located. 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. 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 Such as hitchhiker’s thumb. Does anyone in your family have that? anyone in your family have that? Huntington’s’- a fatal disease caused by a dominant gene, but the gene persists in our population. Why? 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. Symptoms don’t usually appear until after age 40.

NEXT-when inheritance doesn’t follow simple rules-