Notes 2-17-09 Genetics -ask extra credit questions online to get back some points -Genotype=complete set of genes, your DNA sequence Phenotype=observed traits, your hair, eye, skin color etc. -Your genotype partially determines your phenotype. Also influenced by environment. -Genes-DNA sequence that codes for a functional product. We have 23 pairs of chromosomes. The paired ones are called homologous chromosomes -The two copies of our genes are not always identical. Alleles are alternative versions of a gene that have slightly different DNA sequences. Slightly different versions of the same gene pair. -If alleles are identical, homozygous. If different, heterozygous. -Punnett squares show all possible patterns for 2 individuals with a known genotype -Gregor Mendel-Austrian Monk, studied inheritance in pea plants. Started the field of genetics with a paper published in 1865. Came up with two laws. Law of segregation, law of independent assortment. -Presence of dominant allele determines the phenotype. Dominant alleles code for functional proteins. Widows peak is a dominant allele, attached and unattached earlobes are another option. -Most recessive alleles are inconsequential. Some genes this is a very bad thing. Ex. Cystic fibrosis -Incomplete dominance. Straight curly or wavy hair. It lands in the middle. It can?t completely dominate one so it compromises. White and red flowers mix to form the incomplete pink flower -Co dominance- both alleles are expressed. Ex. Blood Type -Just because it is dominant does not mean it is the most frequent. -Most of our traits result from more than 1 gene. Called polygenic traits. Show a continuous range of variation. If shown a statistical graph of this, would form a bell curve. -Phenotuype is determined by the genotype and the environment. Both parts play a role in how you end up. Ex. Height is linked to nutrition. Shorter during periods of war. Breast cancer and cholesterol. Having the gene may increase your risk, but it doesn?t guarantee that you will have it. -Linked genes. Some genes tend to be inherited together, violating mendel?s law. They do this because they are on the same chromosome. One gene determines sex, if not turned on at the right time, you could have some real troubles. -X linked traits-Hemophilia and colorblindness. Males are xy, females xx. So if a male gets the recessive gene, he automatically has it. Makes it more common in males. -Most errors in chromosome # are fatal. Down syndrome, three copies of chromosome 21, trisomy 21. Alterations in # of sex chromosomes not fatal. Several options available, many involve slight mental retardation. These mutations are not very common, only 1 in several thousand births.
Want to see the other 2 page(s) in Lecture Notes Feb 17?JOIN TODAY FOR FREE!