Objectives for Cumulative Part of the Final Exam Genetics Fall 2012 Meiosis Know what happens in meiosis how chromosomes are separated in the two divisions when crossing over occurs Know what homologous chromosomes are what haploid and diploid chromosome and chromatid mean Be able to state how many chromosomes chromatids and pairs of chromosomes are present at different stages of meiosis Most organisms are diploid have two copies of each chromosome 2n Homologous chromosomes carry the same genes but may have different alleles A B C on one and a b c on the other Some organisms are haploid fungi some algae protozoan s 1n Meiosis is the formation of gametes sex cells One diploid cell divides twice and forms 4 haploid cells Each daughter cell gets one chromatid from each pair of homologous chromosomes This leads to half the number of chromosomes as the parent There are two stages of mitosis I and II In meiosis I homologous chromosomes are separated into different daughter cells Chromosome recombination crossing over occurs and exchanges bits of DNA and forms tetrads prophase I In meiosis II the sister chromatids are separated into different daughter cells This second division follows the same steps as mitosis would except the daughter cells would now have half the amount of DNA as the parent hence gametes Crosses and inheritance Be able to do a dihybrid cross and crosses involving partial dominance codominance and X linkage Partial dominance crossing of red and white flowers yields pink Codominance both alleles are expressed Phenotype of the heterozygote is a combination of the two homozygotes Crossing of red and white flowers yields flowers that have petals that are both red and white Blood types are a good example of codominance Know that the frequency of crossing over between genes recombination can be used to map the positions of genes on chromosomes Be able to make a genetic map from a three point cross Step 1 identify the progeny with parental phenotypes single and double crossover phenotypes Double crossovers have the lowest numbers parental non recombinant types are the most frequent Step 2 compare the double crosses least frequent with the parentals to see which gene is in the center chromosome that is flipped Sex chromosomes Know the XY sex determination mechanism the differences in the genetic makeup of the X and Y chromosomes know the name of the gene that determines sex and where it is located on the Y The X chromosome carries thousands of genes whereas the Y chromosome carries very few it s smaller than the X The Y chromosome is the one that determines sex TDF is testis determining factor which is coded for by the STY gene located on the Y chromosome The SRY gene is located near the pseudoautosomal region PAR When SRY is expressed the gonads develop into testes When it s not expressed the gonads develop into ovaries In this way the SRY represses female development testis secrete anti Mullerian hormone that blocks development into uterus ovaries and stimulates the formation of internal and external male structures via testosterone Be able to provide an explanation for the existence of XX males and XY females The existence of xx males and xy females is due to translocations on the genes as well as TDF and SRY XY females had a portion of a chromosome that was missing deletion of part of the Y the SRY because SRY was missing they became females instead of developing into males In XX males part of their Y picks up the missing SRY from the Y chromosome and adds it to the X chromosome that it has Know what X inactivation is what the Barr body is and what dosage compensation is Because females have two x chromosomes and males only have one expression of genes on the X is unbalanced Dosage compensation takes care of this by the development of Barr body s and inactivating one x chromosome in each cell in females during early development Chromosome mutations Know the genetic makeup of individuals with Down syndrome Turner syndrome and Klinefelter syndrome and know the general phenotype of these syndromes Individuals with Down syndrome have 21 chromosomes Turner syndrome 45 chromosomes X Short stature webbed neck shield chest underdeveloped breast and widely spaced nipples rudimentary ovaries sterile Klinefelter syndrome 47 chromosomes XXY Tall stature poor beard growth minor breast development female pubic hair pattern testicular atrophy sterile Be able to correctly use the terms aneuploidy monosomy trisomy and polyploidy Aneuploidy changes in chromosome number due to mistakes in mitosis or meiosis Monosomy one copy of a chromosome Trisomy three copies of one chromosome Polyploidy multiple copies of chromosome sets triploid tetraploid etc Know what translocations are why they can cause miscarriages and know the example of familial Down syndrome A translocation is a chromosomal mutation associated with the reciprocal or nonreciprocal transfer of a chromosomal segment from one chromosome to another Familial Down syndrome is a human translocation because of the translocation carrier 14 21 The resulting progeny are Normal 46 chromosome monosomy lethal 45 trisomy down 21 translocation carrier 45 Bacterial genetics Know that bacteria are haploid and have a circular chromosome Bacteria have no nucleus are haploid have no mitosis or meiosis and have circular chromosome DNA with circular plasmids Know the three mechanisms by which bacteria share DNA and be able to describe them conjugation transformation transduction In order for conjugation recombination to occur the cells must be in contact with one another Conjugation is also unidirectional If Strain A has an F factor plasmid F and is a donor and is crossed with stain B F recipient strain B will pick up that plasmid F x F One strand of the F factor is nicked by an endonuclease This strand moves across the conjugation tube As the strand proceeds complementary DNA synthesis occurs on both strands both the one moving across the tube and the one that has unwound in order to allow part of it to move across tube Movement across the tube is then completed as well as DNA synthesis and ligase closes the circles Genetic recombination can also occur through transformation by the uptake of free DNA Free DNA binds to a component bacterium and enters The DNA strands separate one strand degrades and the other transforms and forms a heteroduplex with the bacterial chromosome Transduction is the sharing of DNA my means of viruses A bacteriophage
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