Objectives for the Final Exam Genetics Fall 2015 Meiosis lecture 1 2 Know what happens in meiosis how chromosomes are separated in the two divisions o Meiosis formation of gametes sex cells 1 diploid cells divides twice and forms No DNA replication before meiosis II Each daughter cell gets 1 chromatid from each pair of homologous when crossing over occurs 4 haploid cells chromosomes o Two divisions Meiosis I homologous pairs are separated into diff daughter cells Chromosome recombination crossing over occurs in prophase 1 It s the crossing over of chromatids that holds them together Each daughter cell gets 2 chromatids from each pair of homologous chromosomes Meiosis II sister chromatids are separated into 4 diff daughter cells Each daughter cell gets 1 chromatid from each pair of homologous chromosomes Know what homologous chromosomes are what haploid and diploid chromosome and chromatid mean o Chromosome they carry genes and consist of a single DNA double helix bound by histone proteins a chromosome o Chromatid duplicate pairs are sister and are connected by a centromere to create Before replication there is only 1 chromatid chromosome and after replication there are two chromatids so 2 DNA double helixes 2 chromatids are part of one chromosome chromosome 1 has two pairs o Diploid 2n most organisms o Haploid n fungi algae and protozoa o Homologous chromosome carry the same genes but may have diff alleles Sex chromosomes are homologous but do not carry the same genes Crosses and inheritance lecture 3 4 7 Be able to do a dihybrid cross and crosses involving partial dominance codominance and X linkage o Dihybrid 9 3 3 1 ratio both parents were heterozygous for 2 diff traits Recessive traits get lower case letters When a 1 1 ratio the recessive trait gets the lower case letters o Partial dominance or incomplete neither allele is dominant Amount of product depends on the amount of enzyme made Phenotype of heterozygote is intermediate ex flower color o Incomplete dominance normal function allele cannot make enough protein product to do the job o Codominance both alleles are present LMLN MN phenotype ABO blood types o X linkage when 1 genes are located on the same gene their inheritance is linked All genes on the X chromosome for males are expressed 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 If parents do not have the trait but a child has it recessive The parents must be heterozygous o If both parents have the trait and children have it dominant Parents must be heterozygous o Fathers pass trait to daughters and mothers pass trait onto sons dominant x linked 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 lecture 11 o Recombination always occurs during tetrad stage o Recombination is reciprocal o Recombination underestimates the distance between genes due to double crossovers The further apart the greater the underestimate o Independent assortment 4 types of gametes made There are 2 genes on 2 diff homologous pairs of chromosomes Each makes up 25 of the total o Complete linkage 2 types of gametes made There is linkage between genes on single pair of homologs no exchange Each makes up 50 of the total o Linkage with recombination 4 types of gametes Linkage between 2 genes on a single pair of homologs exchange occurs Non crossover most frequent Crossover gamete But 4 outcomes but not equal frequencies o Chromatids that do not cross over are called parental or non recombinant o Chromatids that do cross over are called recombinant o The further apart 2 genes are the more likely crossing over will occur o For mapping One parent must be heterozygous and the other must be homozygous recessive The parent producing the crossover gametes must be hetero At all loci Out of the single crossover gametes the gene that is more further away in the mapping is the more frequent of the two single crossovers 1 map unit 1 crossing over 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 o Y chromosome determines sex o TDF testis determining factor o SRY genes codes for TDF which determines sex on Y chromosome This is the case for XY females and XX males Located on Y chromosome underneath the PAR gene Expressed then develop testis If not expressed then develop into ovaries Be able to provide an explanation for the existence of XX males and XY females o XXY Klinefelter syndrome in males o X Turner syndrome in women o XX males have a translocation from the Y to the X o XY females have a deletion of part of the Y No uterus testis present in abdominal cavity Has vagina but sterile Can t respond to testosterone Know what X inactivation is what the Barr body is and what dosage compensation is o One of the X chromosomes in females is inactivated to balance the male sex chromosome since they only have 1 X o Called Lyon Hypothesis o Barr Body the inactivated X dark spot near nuclear membrane Inaccurate X turned off o Random at which X is inactivated o The genetic dosage is now balanced between males and females o Barr Bodies determination N 1 where N total of X chromosomes present Ex Super female XXX has 2 Barr Bodies Only 1 X activated o X activation begins at XIC on X chromosome o The gene responsible for this is XIST o When gene turns on X shuts down o The inactive X chromosome has higher levels of cytosine methylation than does the active X chromosome Chromosome mutations Know the genetic makeup of individuals with Down syndrome Turner syndrome and Klinefelter syndrome and know the general phenotype of these syndromes o Down syndrome Genotype trisomy of chromosome 21 Phenotype fold in each eye flat face round head short protruding furrowed tongue short broad hands and physical and mental development are retarded Related to maternal age the older a female is giving birth the more likely the child will have down syndrome around age 35 o Turner syndrome in females Genotype X Phenotype short stature webbed neck shield chest underdeveloped breast and spaced out nipples and rudimentary ovaries o Klinefelter syndrome in males Genotype XXY Phenotype poor beard growth tall stature minor breast development female pubic
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