Exam 1 Genetics Final Exam Study Guide hybrid offspring of cross between parents that differ in one or more traits F1 progeny of cross 1st filial F2 progeny of cross between F1 s phenotype observable properties genotype genetic makeup usually one or few traits gene hereditary unit alleles various forms of a gene homozygous carrying same alleles of a gene heterozygous carrying different alleles of gene test cross cross of unknown to homozygous recessive Addition rule mutually exclusive events what is probability of rolling 4 OR 6 Cross Ww x Ww What is prob of round progeny Multiplication rule independent events probability of rolling 1 3 times in a row prob that first two offspring from Ww x Ww are round indicates wildtype uppercase indicates wildtype indicates mutant lowercase indicates mutant Gene names italicized protein names not Somatic cells most of body muscle brain skin mitosis type of cell division produces same ploidy as mother cell germ cells sperm and egg reproductive cells homologues pairs of chromosomes humans have 23 pairs or 46 chromosomes diploid 2n having 2 sets of similar chromosomes haploid 1n having only single set of similar chromosomes o precise process of nuclear division that ensures that each daughter receives a chromosome complement identical to the parent cell meiosis type of cell division produces half ploidy of mother cell produces germ cells o point is to reduce ploidy by half and reshuffle genetic material o produces gametes o each daughter cell receives one copy of each homologous chromosome o crossing over used to increase genetic diversity equal exchange of corresponding DNA segments between homologous chromosomes o 1st division 2n cell divides to give 2 1n cells o 2nd division each 1n cell divides to give total of four 1n cells o meiosis I prophase I leptotene chromosomes begin to condense zygotene also homologs begin to find one another and start pairing synapsis pairing of homologues pachytene synapsis complete tetrad or bivalent sometimes visible bivalent pair of synapsed chromosomes tetrad 4 chromatids in 2 chromosomes diplotene synapsed chromosomes begin to separate homologous remain together at chiasmata cytokinesis cell division Overview of mitosis chromosomes condense and align chromosomes divide longitudinally separated halves move to opposite poles cell usually divides as well as nucleus o o o o o Steps prophase chromosomes condense nucleoli disappear and nuclear envelope breaks down chromosomes and chromatids same metaphase mitotic spindle formed chromosomes attach to spindle at centromere chromosomes 1n chromatids 2n chromosomes align at metaphase plate dynamics anaphase centromeres divide sister chromatids separate and move to poles chromosomes 4n chromatids 4n telophase spindle disappears nuclear envelope forms nucleoli form chromosomes decondense typically cytoplasm divides chromosomes 2n chromatids 2n Exam 2 Linkage tendency of genes located on the same chromosome to segregate together Recombination exchange of material between dna molecules or chromosomes that generates new gene or allelic combination applies to linked genes Crossing over exchange of corresponding chromosome segments between homologs Locus location on a chromosome Cis vs trans refers to het for two linked genes o Cis coupling wm o Trans repulsion w m o W m w m neither cis nor trans Parental combination same combination of alleles found in parent s Nonparental combination different combination of alleles from parents i e chromosomes recombinants Perfect linkage complete segregation of combination of alleles from parent to offspring Independent assortment applies to unlinked genes Genetic map linear representation of gene arrangement on chromosome aka linkage or chromosome map Map unit unit of genetic distance map unit crossovers between genes map unit recombinants expressed as map units or centiMorgans cM Interference the occurance of a single crossover event makes the occurance of a 2nd single crossover event less likely Null hypothesis opposite of what we really want to test Degrees of freedom independent variables classes 1 Mitotic nondisjunction causes unusual tissues Twin spot to have mutations have to be in trans and both genes have to recombine Epigenetics heritable state of gene function not encoded within DNA sequence can be mediated by protein expression often mediated by DNA histone modification methylation can silence genes modification of histones may be activating or inhibiting for gene expression genomic imprinting copy of gene inherited from one parent is silenced Imprinted silent not imprinted expressed position effect variegation position of gene on chromosome affects its expression x chromosome inactivation in some animals one of the 2 x chromosomes is inactivated Transition replaces 1 pyrimidine with other or 1 purine with other Transversion replaces pyrimidine with purine or vice versa Silent mutation triplet encodes same amino acid Synonymous mutation same as silent Conservative mutation codon specifies biochemically similar amino acid Missense mutation codon specifies different amino acid Nonsense mutation codon specifies stop translation Frameshift nucleotide additions or deletions that change reading frame often introduce stop shortly downstream Coding strand sequence same as RNA besides U Loss of function mutant no gene function reduce or completely eliminate gene function Gain of function generally dominant gene product has new function Dominant negative mutant gene product interferes with wildtype product Oxidative damage reactive forms of oxygen consequence of aerobic metabolism and radiation Fragile x syndrome results from expansion of CGG in 5 UTR Induced mutations base analogs chemicals similar to bases incorporated into dna during replication cause mispairing Ex 5 bromouracil resembles thymine incorporated in place of T can base pair w G 2 aminopurine resembles adenine incorporated in place of A can base pair with C Specific mispairing some chemicals alter bases so that it can pair with incorrect partner Alkylating agents ethyl methanesulfonate EMS ethylates guanine O 6 ethyl guanine base pairs with T causes GC A T transitions Intercalators some chemicals insert themselves into DNA distortion affects fidelity of replication eg Acridine orange UV light causes DNA damage particularly pyrimidine dimer formation Ionizing radiation causes wide range of types of DNA damage radiation interacts with compounds in solution to produce