PCB3062 General Genetics Final Exam Study Guide Fall 2014 Meiosis q 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 Meiosis I 1st division DNA is replicated during interphase Homologous chromosomes align Chromosome recombination crossing over occurs during prophase Homologous chromosomes are separated into different daughter cells Result two haploid daughter cells Meiosis II 2nd division NO DNA replication occurs before meiosis II Sister chromatids are separated into different daughter cells Result four haploid daughter cells 1 PCB3062 General Genetics Final Exam Study Guide Fall 2014 2 Structure visible during mitosis meiosis Chromosome A DNA molecule complexed with proteins and RNA to form a threadlike structure containing genetic information Sister Chromatids The two parallel parts of the chromosome a double structure joined at the centromere that are exact duplicates of each other Homologous Chromosomes Chromosomes that synapse or pair during meiosis are identical with respect to their genetic loci centromere placement Diploid 2n A condition in which each chromosome exists in pairs having 2 of each chromosome Haploid n When a cell or organism has one member of each pair of homologous chromosomes Equal to 1 2 the diploid number PCB3062 General Genetics Final Exam Study Guide Fall 2014 Crosses and Inheritance q Be able to do a dihybrid cross and crosses involving partial dominance codominance and X linkage Dihybrid Cross A cross that involves two pairs of contrasting traits Ex Pea plants having yellow seeds that are round are bred with pea plants having green seeds that are wrinkled Incomplete Partial Dominance When neither allele is dominant the phenotype of the heterozygote is intermediate Ex Flower color crossing red flowers with white flowers produces pink flowers 3 PCB3062 General Genetics Final Exam Study Guide Fall 2014 Codominance Condition in which the phenotypic effects of a gene s alleles are fully and simultaneously expressed in the heterozygote Both alleles expressed Phenotype of heterozygote is a combination of the two homozygotes Ex MN blood group Genotype LMLM LMLN LNLN Phenotype M MN N q Be able to analyze human pedigrees to determine whether a trait is inherited as an autosomal recessive autosomal dominant X linked recessive or X linked dominant Autosomal Recessive Inheritance For rare traits the pedigree usually involves mating between two unaffected heterozygotes and the production of one or more homozygous offspring The probability of an affected child from a mating of two heterozygotes is 25 Two affected individuals usually produce offspring all of whom are affected Males and females are at equal risk since the trait is autosomal In pedigrees involving rare traits consanguinity is often involved Autosomal Dominant Inheritance Every affected individual should have at least one affected parent An affected individual has a 50 chance of transmitting the trait Males and females should be affected with equal frequency Two affected individuals may have unaffected children 4 PCB3062 General Genetics Final Exam Study Guide Fall 2014 Sex Linked Traits Hemizygous males and homozygous females are affected Phenotypic expression is much more common in males than in females and in the case of rare alleles males are almost exclusively affected Affected males transmit the gene to all daughters but not to any sons Daughters of affected males will usually be heterozygous and therefore Sons of heterozygous females have a 50 chance of receiving the recessive unaffected gene X linked Dominant Inheritance X linked Recessive Inheritance q Know that the frequency of crossing over between genes recombination can be used to map the positions of genes on chromosomes and be able to make a genetic map from a three point cross Recombination frequency reflects the distance between two linked genes 5 PCB3062 General Genetics Final Exam Study Guide Fall 2014 Single Crossover Double Crossover Three Point Cross 1 Identify the parental types a Parental non recombinant types are most frequent 2 Identify the double crossover types a Double crossover types are least frequent 6 PCB3062 General Genetics Final Exam Study Guide Fall 2014 3 Determine which gene has moved to convert the parental types into the double crossover DCO types a This gene is in the middle 4 Identify which gene has moved to make each of the single crossover types 5 Add up the crossover frequencies to make the map a 1 map unit 1 crossing over 1 centimorgan cM Sex Chromosomes q 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 Sex Determining Region Y SRY The sex determining region of the Y chromosome found near the chromosome s pseudoautosomal boundary Critical gene that controls male sexual development Encodes a protein that causes the undifferentiated gonadal tissue of the embryo to form testes TDF Testis Determining Factor SRY expressed gonads develop into testis 7 PCB3062 General Genetics Final Exam Study Guide Fall 2014 o Cells in testis secrete Anti Mullerian Hormone prevents Mullerian ducts from developing into uterus ovaries Testosterone stimulates the formation of internal external male SRY NOT expressed gonads develop into ovaries structures Pseudoautosomal Region PAR A region on the Y chromosome that is also represented on the X chromosome Shares homology with regions on the X chromosome and synapse recombine The presence of this pairing region is critical to segregation of X Y with it during meiosis chromosomes during male gametogenesis Y Chromosome Carries far fewer genes than the X Y chromosome contains about two dozen active genes X Chromosome Carries thousands of genes 8 PCB3062 General Genetics Final Exam Study Guide Fall 2014 q Be able to provide an explanation for the existence of XX males and XY females XX males have a translocation from the Y to the X Includes SRY so they have the region even though they lack a Y chromosome XY females have a deletion of part of the Y The part where SRY should be is missing compensation is X inactivation occurs during the late blastula stage q Know what X inactivation is what the Barr body is and what dosage Random choice in each cell of which X is inactivated XIST X Inactive Specific
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