Final Exam Study Guide for Genetics Meiosis Know what happens in meiosis how chromosomes are separated in the two divisions when crossing over occurs o Meiosis Produces four haploid daughter cells which each contain one chromatid from each pair of homologous chromosomes Used mainly for formation of gametes sperm egg cells In Meiosis I the paired homologous chromosomes may undergo recombination and they are separated into 2 different daughter cells In Meiosis II the sister chromatids are separated into 2 different daughter cells 4 haploid cells o Pairing of homologous chromosomes in meiosis I is essential to ensure a large amount of variation exists because when homologous chromosomes are paired sometimes the DNA is crossed over or exchanged from one chromosome to the other Crossing Over between homologous chromosomes by breakage and reunion The exchange of chromosomal material Crossing over occurs at the Synaptonemal Complex Know what homologous chromosomes are what haploid and diploid chromosome and chromatid mean o Homologous Chromosomes but may have different alleles Chromosomes that carry the same genes o Diploid Sex Chromosomes are homologous chromosomes with an exception because they do not carry the same genes A condition in which each chromosome exists in pairs having two of each chromosome 2n A cell or organism having one member of each pair of homologous chromosomes gametic chromosome number n o Haploid o If a diploid organism has 10 chromosomes 2n 10 how many pairs of homologous chromosomes does it have 5 o If a diploid organism has 10 chromosomes 2n 10 how many DNA molecules are present in G1 phase of the cell cycle and how many in G2 10 20 chromosome A DNA molecule containing the organism s genome One of the longitudinal subunits of a replicated o Chromosome o Chromatid Crosses and Inheritance Be able to do a dihybrid cross and crosses involving partial dominance codominance and X linkage o Codominant express a combination of the two Both alleles are expressed therefore heterozygotes ABO Blood Group Mom AA Dad BB so Child AB Ex Coat color in mammals human hemoglobin types cystic fibrosis MN blood group etc o Incomplete Dominance Partial Dominance Neither allele is dominant therefore heterozygotes express an intermediate phenotype If R red and r white then Rr pink Half of the phenotype is expressed because half of the enzyme o X Linked Inheritance chromosome their inheritance is linked When two genes are located on the same Ex Red green color blindness hemophilia muscular is made dystrophy etc o Sex Influenced Genes are on autosomes but they are expressed differently in males and in females differential expressions are due to hormone differences Specific phenotype is observed only in one sex o Sex Limited 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 o Autosomes Chromosomes other than sex chromosomes 22 out of the 23 pairs of chromosomes o Dominant o Sex Chromosomes A chromosome involved in sex determination only 1 out of the 23 pairs of chromosomes dominant allele codes for functional protein usually the recessive allele doesn t code for functional protein One allele is expressed over the other one usually the One allele is hidden unless homozygous for that allele o Recessive o Pedigrees https campus fsu edu bbcswebdav pid 7652491 dt content rid 44121069 2 courses PCB3063 0001 fa15 pedigrees pdf Link to Dr Bates help with pedigrees file under sample exams 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 o Recombination combinations on chromosomes crossing over The process that leads to the formation of new allele o Due to recombination linkage is usually less than 100 As the distance between two genes increases the probability of recombination occurring increases and the linkage decreases o During recombination the most frequent gametes are parental noncrossover gametes and the least frequent are the recombinant crossover gametes o Two point cross 2 linked genes and three point cross 3 linked genes uually between 1 het female and 1 homo recessive male Non crossover gametes NCO most frequent Double crossover gametes DCO least frequent Single crossover gametes SCO frequent o Steps to identify and construct a genetic map 1 Identify the progeny with parental phenotypes NCO SCO 2 Determine the gene order the gene in the middle the gene that was moved to convert NCO to DCO 3 Calculate the recombination frequencies for each crossover and DCO type 4 Prepare a map using the recombination frequencies 1 recombination 1 mu Note Distance between end gene and middle gene SCO for that end gene DCO o If asked to find the number of DCO that should have been observed multiple the two distances converted from to numerical and then multiply by the sample size Distance between a and b 1 5 or mu Distance between b and c 18 5 or mu 0 015 0 185 1000 2 775 3 expected DCO Sample size 1000 o Note Recombination frequencies can never exceed 50 Genes on the same chromosome that are more than 50 map units apart undergo recombination so frequently that they assort independently they are inherited as if they were on different chromosomes Therefore if the frequency of recombination is 100 then only 50 of the gametes will be recombinant crossover 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 sex that produces gametes containing unlike o Heterogametic Sex sex chromosomes o Homogametic Sex with respect to sex chromosome content The sex that produces gametes that do not differ o 2 sets of undifferentiated gonads the Wolffian and the Mullerian ducts exist in each embryo Wolffian ducts differentiate into other organs of the male Mullerian ducts differentiate into structures of the female reproductive system reproductive system o Sex Determining Region Y SRY sexual development codes for testis determining factor TDF which differentiates embryonic gonadal tissue into testes A critical gene that controls male Located near the top of the p arm o Pseudoautosomal Region PAR chromosome that is also represented on the X chromosome male specific region of the Y MSY Located at the ends of the p and the q arms A
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