HUMAN GENETICSHUMAN GENETICS

Humans are not pea plants!Humans are not pea plants!

• Although in all organisms genes control Although in all organisms genes control the production of proteins that show up the production of proteins that show up on our phenotype, most human on our phenotype, most human genetics cannot be explained by genetics cannot be explained by tall/short, pink/white, round/wrinkled.tall/short, pink/white, round/wrinkled.

•There are a few human traits There are a few human traits determine by a gene with two determine by a gene with two alleles, one recessive and one alleles, one recessive and one dominant.dominant.

Can you roll your tongue?Can you roll your tongue?

• Tongue rolling is determined by a Tongue rolling is determined by a gene with two alleles, the dominant gene with two alleles, the dominant rollerroller and the recessive and the recessive non-roller.non-roller.

• If two rollers give birth to a non-If two rollers give birth to a non-roller, what is the genotype of each?roller, what is the genotype of each?

Set up the problem-Set up the problem-

• R= rollerR= roller

• r=non rollerr=non roller

• Both parents are Both parents are rollers, so they must rollers, so they must both have at least one both have at least one RR

• The offspring shows the The offspring shows the recessive trait, so it recessive trait, so it must be homozygous must be homozygous recessive= rrrecessive= rr

• R? x R?R? x R?

RRRR R?R?

R?R? rr=non-rr=non-rollerroller

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….Here’s an interesting one….

• POLYDACTYLY-having 6 fingers on POLYDACTYLY-having 6 fingers on one or both hands or feet.one or both hands or feet.

• The dominant allele is six fingers, The dominant allele is six fingers, showing dominant doesn’t always showing dominant doesn’t always mean “better” or “most common”.mean “better” or “most common”.

• What’s the chance a child will have What’s the chance a child will have polydactyly if both parents have 5 polydactyly if both parents have 5 fingers?fingers?

Polydactyly is a dominant Polydactyly is a dominant alleleallele

• You cannot pass along alleles you do You cannot pass along alleles you do not have.not have.

• If both parents have 5 fingers, they If both parents have 5 fingers, they have no allele for 6 fingers, so they have no allele for 6 fingers, so they cannot pass on the six-fingered allelecannot pass on the six-fingered allele

• 0% chance of 6 fingered children0% chance of 6 fingered children

Some human genetic Some human genetic diseasesdiseases• Show simple recessive heredity, such Show simple recessive heredity, such

as cystic fibrosis.as cystic fibrosis.• Cystic fibrosis results from a defective Cystic fibrosis results from a defective

gene that produces a defective protein, gene that produces a defective protein, accumulating thick mucus in lungs.accumulating thick mucus in lungs.

• If a child is born with cystic fibrosis If a child is born with cystic fibrosis from parents without the disease, what from parents without the disease, what are the chances his sister will have the are the chances his sister will have the disease?disease?

Tay-Sachs and Tay-Sachs and Phenylketonuria Phenylketonuria

• Are also serious disorders.Are also serious disorders.

• Some of these defective genes have Some of these defective genes have been located.been located.

• Since some genetic disorders run in Since some genetic disorders run in certain ethnic groups, some people certain ethnic groups, some people may choose to be tested for the may choose to be tested for the defective gene before they have defective gene before they have children.children.

Some human inheritance Some human inheritance is simple dominantis simple dominant• Such as hitchhiker’s thumb. DoesSuch as hitchhiker’s thumb. Does anyone in your family have that?anyone in your family have that?

• Huntington’s’- a fatal disease caused Huntington’s’- a fatal disease caused by a dominant gene, but the gene by a dominant gene, but the gene persists in our population. Why?persists in our population. Why?

• Symptoms don’t usually appear until Symptoms don’t usually appear until after age 40.after age 40.

NEXT-when inheritance NEXT-when inheritance doesn’t follow simple rules-doesn’t follow simple rules-