Co-dominance:In genetics, an instance in which two different but equally powerful genes produce a phenotype in which both genes are expressed.Carrier: In genetics, individuals who possesses a recessive gene associated with a disease and who, although they do not have the disease, can transmit the gene for it to offspring.Sex-linked gene: An attribute determined by a gene that appears on one of the two types of sex chromosomes, usually the X chromosome;ex. Hemophilia, Fragile X Poly-genetic characteristics: Traits affected by several genes and environmental factors at once; ex. intelligence, height, weight, etc. Single-gene [pair inheritance]: The genetic mechanism through which a characteristic is influenced by only one pair of genes, one gene fromthe mother and its partner from the father.Chromosomal abnormalities: Conditions in which a child has too few, too many, or incomplete chromosomes because of errors in the formation of sperm or ova.Turner syndrome (X0)Klinefelter’s syndrome (XXY)Fragile X Know about Huntington’s (p. 73), sickle cell anemia (p. 72), PKU, muscular dystrophy, hemophillia (p. 70), Down’s (p. 70) Turner’s & Klinefelter’s (p. 71), etc.
Huntington’s is a dominant single gene defect that affects the nervous system. Sickle cell is recessive sex-linked PKU is recessive and affects the body’s ability to break down phenylalanine, leading to build up that interferes with cognitive development; a diet low in phenylalanine can prevent symptoms. Know percent of genetic relatedness among parent/child, sibs, grandparents, etc. (lecture). Child to parent – 50%Sibling – 50%Grandchild to grandparent – 25%Identical twin – 100%Fraternal twins – 50%What exactly did the Human Genome Project map (p. 66)? The Human Genome Project mapped the sequence of the chemical units that make up the strands of DNA in a full set of 46 human chromosomes (Weiss, 2003).Know Gotlieb’s Epigenetic Theory (lecture, also Ch. 3, p. 86). Genes do not dictate development; rather, they interact with each other, leading to epigenetic effects where cell expression is turned on or off according to the enviroments’ interaction with the given genes. Define epigenetics. Epigenetics:Ways in which the environment influences or alters the expression of genes. Know the two mechanisms discussed in class: histone acetylation and DNA methylation (lecture & p. 86). Histone acetylation adds an acetyl tail to a clump of proteins (genes) that make it unwindand easier to read – turning it ON. DNA methylation does the opposite, by adding a methyl group to the cytosine base, it represses transcription and turns it OFF. See also fetal programming on p. 100.