Chapter2BiologicalandEnvironmentalFoundations.docVIP

Biological and Environmental Foundations Genetic Foundations chromosomes: rodlike structures that store and transmit genetic information. 23 matching pairs, 1 from our mother and one from our father Genetic code DNA - a long double-stranded molecule consists of pairs of chemical substances called bases, joined together between the 2 strands. The sequence of bases provides genetic instructions. a gene is a segment of DNA along the length of the chromosome. Genes send instructions for making proteins DNA can reproduce itself through a process called mitosis Sex cells a gamete contains 23 chromosomes meiosis: the chromosomes pair up and exchange segments so that genes form one are replaced by genes from another. males can sire offspring any time after sexual maturity females are born with all the ova they will ever have Male or female? the 23rd pair of chromosomes are sex chromosomes. The other 22 pairs are called autosomes. In females, the 23rd pair is called XX in males, it is XY. In males, X-bearing sperm and Y-bearing sperm In females, all gametes have an X chromosome Multiple Births: Dizygotic twins Monozygotic twins Patterns of Genetic Inheritance: homozygous versus heterozygous Dominant –recessive inheritance E.g., hair colour (dark is dominant, blond is recessive) Many diseases and disabilities are also the product of recessive genes phenylketonuria (PKU) Cystic fibrosis Sickle cell anemia Tay-Sachs disease only rarely are serious diseases due to dominant genes. An exception: Huntington disease - degeneration of the CNS beginning after the age of 35 codominance: a pattern of inheritance in which both genes influence the person’s characteristics. x-linked inheritance: when a harmful gene is carried on the x chromosome. Males are more likely to be affected because they only have one x chromosome. E.g. hemophilia besides x-linked disorders, many sex differences reveal the male to be at a disadvantage more males are miscarried more childhood deaths