Genetics Background Information Understanding of genetics began with the domestication of plants and animals agriculture Benefits Ex corn which is genetically modified is in most foods The Green Revolution applied agricultural knowledge and technology to under privileged parts of the world increased production decreased death rates Forensics Experimentation with model organisms Ex PAX6 gene is mutation in the eye studied in other species with same gene and findings are applied to humans Gene therapy can add or remove genes in the genome Ex Leber s congenital amaurosis LCA therapy can restore vision Personalized medicine genetic counseling and genome sequences available to anyone who can afford it Drawbacks Eugenics forced sterilization mandated by the government similar to selective breeding extremely unethical Chromosomes and Transmission Genetics Mitosis Transmission problem 1 cell needs to create 10 trillion cells via development so the process must be extremely accurate errors can lead to cell death or disease disorders failure of sister chromatids to separate during Non disjunction anaphase somies Unregulated cell division cancer Solution mitosis is highly regulated to insure genome integrity during growth and development 3 main checkpoints G1 S G2 M Spindle Meiosis Divided into phase I and phase II Meiosis I o Separation of homologous chromosomes o Crossing over may occur o Reduces chromosome number Meiosis II mitosis o Separation of sister chromatids Prophase metaphase anaphase telophase and cytokinesis 1 diploid cell 4 haploid cells Creates gametes 4 sperm cells but only 1 useable egg cell Each gamete has 1 copy of each chromosome Produce genetic variation via fertilization crossing over and independent assortment helps species adapt to changing harmful environments and to avoid dangerous mutations Number of chromosomes number of centromeres Homologous chromosomes same gene information on each but actual alleles are different depending on the genetic code one chromosome in pair comes from each parent Chromatid DNA molecule 2 sister chromatids make up a chromosome held together by cohesion Morphology shapes of chromosomes vary in the human genome Metacentric Submetacentric Acrocentric Telocentric 3 principles of meiosis 1 Segregation of homologs o Homologous chromosomes separate into separate cells during meiosis I anaphase I 2 Independent assortment of non homologs o Occurs during metaphase I o Homologous pairs act independently of one another o Equal probability of homologous pairs aligning and separating into different combinations in different cells o 2X different combinations of chromosomes X number of sets of chromosomes Basic terminology 3 Crossing over between non sister chromatids o Occurs during prophase I o Non sister chromatids in homologous pair exchange pieces of o Chiasmata DNA chromosomes that forms during crossing over visual crossing over physical breaking of the o Forms recombinant gametes o External factors such as radiation can cause knicks in the chromosomes which eventually break hereditary factor responsible for a characteristic phenotype Gene exists on a chromosome o Locus o Allele location of a gene on a chromosome in the genome form variant of a gene different alleles reflect different phenotypes each organism has 2 alleles for each gene represented by letter combination GG gg or Gg 2 identical alleles at the same locus in a Homozygous homologous pair GG or gg homologous pair Gg Heterozygous 2 different alleles at the same locus in a Relationship between alleles phenotype is determined by dominant allele o Dominant regardless of existence of recessive allele R is present r Types of Dominance o Recessive another allele on the same gene one allele is dominant or is recessive to no visible effect on phenotype when dominant allele o Complete dominance the other dominant allele masks recessive allele one allele is completely dominant over DD and Dd D phenotype o Incomplete dominance intermediate phenotype both alleles are expressed to form Dd Red white pink time o Co dominance both alleles are expressed fully at the same Dd Blood type antigens AB A B O Dominance series ranks alleles based on dominance o Multiple alleles allelic series many different possible alleles for a gene but each individual still only has 2 alleles 1 from each parent Ex ABO blood group o Relationship between different alleles is all relative so the same allele can be dominant or recessive based on what it is being compared to o C cch ch ca cch is dominant to ch but recessive to C number of individuals with the genotype allele that also variation of phenotype between individuals degree to Penetrance show the expected phenotype 0 100 which a character is expressed Expressivity o Ex polydactyly neurofibromatosis o Factors that influence expressivity Epistasis interaction between 2 genes loci in genomic network one gene masks another gene Dominant epistasis Ex baldness and hair traits have the same locus may have black hair but baldness masks hair color phenotype Ideal ratio 9 3 3 1 A B A bb aaB aabb 12 3 1 1 dominant allele at 1 loci masks expression of alleles at another loci 9 3 4 2 recessive alleles at 1 loci masks expression of alleles at another loci alleles at either loci are capable of suppressing a phenotype Duplicate recessive epistasis Recessive epistasis 9 7 2 recessive Sex influenced characteristics autosomal genes may have same genotype but may express different phenotypes based on other factors zero penetrance in 1 sex hormones Environmental factors Ex Himalayan rabbits in colder environments has mutation in allele that makes a protein temperature sensitive and thus extremities are black while rabbits in warmer environments are all white Predicting outcomes analysis is helpful in predicting genotypes and their frequencies Monohybrid crosses examining 1 gene at 1 locus o Example frequency of R 0 5 and frequency of r 0 5 RR 0 5 x 0 5 0 25 Rr 0 5 x 0 5 0 5 x 0 5 0 5 rr 0 5 x 0 5 0 25 Dihybrid multilocus crosses examining 2 different genes on different loci assumes no crossing over Ry rY ry o Must consider all possible combinations and outcomes RrYy RY o 4 different gamete types per parent 4 x 4 16 o Make a punnett square for each gene to find probability of allele combination and then multiply those together o Example RrYy x RrYy P RR 0 5 x 0 5 0 25 P YY 0 5 x 0 5 0 25 P RRYY P RR and YY 0 25 x 0 25 1 16 o Example AABbDdEeGg x AaBbDdEeGg P AABBddEegg P AA x P BB x P