Hereditary Factors in Development: Genes

Genetic Transmission Two types Gene pairs Polygenic transmission

Gene Pairs Two matching genes occur at the same location on the matching chromosome pairs One gene from the mother and one from the father Different forms of the genes are referred to as alleles. Same allele in the same location (locus) -homozygous for that gene pair Different alleles at that locus - heterozygous

Dominant - Recessive Relationships In many (but not all) heterozygous pairs, only one gene affects the characteristic - only that gene is expressed It is said to dominate over the other gene -- it is dominant and the other gene is recessive

Example from Eye Color Mother B b Mother B Father b BB Bb Bb bb

How to get green eyes when neither parent has them Mother B G Mother B Father b BB Bg Bb Gb

Recessive conditions, only one carrier parent Mother D D Mother D Father r DD DD Dr Dr

Recessive conditions, two carrier parents Mother D r Mother D Father r DD Dr Dr rr

Some Recessive Conditions Tay-Sachs Disease Sickle-cell Anemia Phenylketonuria (PKU) Cystic Fibrosis

Tay-Sachs Most common in people of Ashkenazi Jewish origins, and some other groups Babies born normal, but by 3-6 months, neurons in CNS are being destroyed Undergo seizures, paralysis, blindness, deafness, mental retardation, and eventually early death

Tay-Sachs treatment No treatment for juvenile Tay-Sachs Three forms of prevention Each involves first testing both parents to see if they are carriers, then Prenatal diagnosis, followed by elective abortion In vitro fertilization, discard affected embryos and implant healthy embryos Not reproducing; either choosing to have no children, or choosing not to marry another carrier

Phenylketonuria (PKU) Lack an enzyme that metabolizes phenylalanine, a component of animal protein (including milk) Without this enzyme, phenylalanine is converted to phenylpyruvic acid, which destroys neurons So, the normal child becomes profoundly mentally retarded simply by eating animal protein, including breast milk

PKU treatment Today, once a young baby has drunk milk, there is a blood test for the presence of phenylalanine If positive, they have to have a special diet for life

End of genes Move on to final “biology” lecture on behavior genetics