1. Hereditary Factors in Development: Genes

2. Genetic Transmission
Two types
Gene pairs
Polygenic transmission

3. 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

4. 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

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

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

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

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

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

10. 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

11. 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

12. 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

13. 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

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