BIO 105 1st Edition Lecture 9 Genetics and Genetic Disorders Lecture Outline I II III IV V VI Know why Gregor Mendel is significant Be able to differentiate between alleles Know the characterisitcs of Mendel s laws Know the types of Dominance Relationships Be able to read a Punnet square Know the different types of genetic disorders and their characteristics Gregor Mendel Father of genetics researched pea plants because of variation Alleles different molecular forms of a gene Ex green brown and blue eye color variations of a gene Dominant allele masks a recessive allele that is paired with it must be Recessive at BOTH alleles or dominant not expressed for Recessive allele to show Phenotype physical appearance determined by genes Brown eye color Genotype genetic makeup determined by genes BrBr BrBl BrGr Allele Combinationns Capital Letters Dominant Trait Lower Case Recessive Trait Homozygous having two identical alleles at a locus Ex AA or aa Brown eyes vs Brown eyes Heterozygous having two different alleles at a locus Ex Aa Brown eyes vs Green eyes Homologous Chromosomes Are identical in length size shape and gene sequence like chromosome 21 from mom and chromosome 21 from dad make up your homologous pair of chromosome 21 KNOW HOW TO READ A PUNNET SQUARE Mendel s Laws 1 Mendel s Theory of Segregation o An Individual inherits a unit of information allele about a trait from each parent carried on the 23 pairs or 46 chromosomes o During gamete formation meiosis the alleles segregate from each other in metaphase so they up in different gametes 2 Mendel s Law of Independent Assortment o Mendel concluded that the two units for the first trait were to be assorted into gametes sperm and eggs independently of the two units for the other trait o Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis mean each of the 46 chromosomes moves to a gamete independent of the other 45 chromosomes Dominance Relationships 1 Complete dominance pea plants most common 2 Incomplete dominance snapdragons 3 Codominance blood groups Incomplete Dominance Heterozygotes show a distinctly different phenotype not seen in homozygotes Co dominance ABO Blood Type If either allele is present of the dominant alleles BOTH are expressed o O universal donor ii o AB universal acceptor AB Epistasis Interaction between gene pairs for one phenotype another phenotype must exist Before Black or Brown color can be laid down in hair the color CC or Cc genes must be present Black BB or Bb is dominant to brown bb if the color gene CC or Cc is NOT present cc there will be NO color fur will be white Pleiotropy Alleles at a single locus may have effects on two or more traits allele my impact several organs or traits o Marfan syndrome impacts connective tissue organs joints etc o Cystic fibrosis allele gene cause impact on lungs kidneys sweat etc multiple sites impacted from on gene Composition of Y Chromosome Fewer than two dozen genes identified on Y chromosome carries only 330 genes One is the master gene for male sex determination SRY gene sex determining region of Y Autosomal Recessive Inheritance Patterns Most common genetic transmission type Autosomal Dominant Inheritance Trait typically appears in every generation Most homozygous combinations lethal aborted or die before birth Heterozygotes show disease example Huntington s disease problem disease shows in 30s after many have reproduced already