UMass Amherst BIOLOGY 283 - Genetics Study Guide Exam 2 (8 pages)

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Genetics Study Guide Exam 2



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Genetics Study Guide Exam 2

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8
School:
University of Massachusetts Amherst
Course:
Biology 283 - General Genetics
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Genetics Study Guide Exam 2 Chapter 4 Hemizygous XY Homozygous XX Y Chromosome Male specific genes are found on it lacks copies of genes found on the X chromosome Sex Linked genes are found on one of the two sex chromosomes not both X linked most likely to affect males Y linked Relatively few genes referred to as holandric genes transmitted only from father to son Pseudoautosomal inheritance refers to the very few genes found on both X and Y chromosomes X Linked Conditions Color Blindness deutan type Insensitivity to Green Light Color Blindness Protan type Insensitivity to Red Light Fabry s disease Deficiency in galactosidase A Heart and kidney defects early death G 6 PD deficiency Severe anemic reactions following intake of primarques in drugs and foods fava beans Hemophilia A Classic form of clotting deficiency Clotting factor VIII Hemophilia B Christmas diseases deficiency of clotting factor IX Hunter syndrome Mucopolysaccharide storage disease Short stature claw like fingers coarse facial features slow mental deterioration and deafness Ichthyosis Scaly dry skin on extremities Lesch Nyhan syndrome HPRT deficiency Motor and mental retardation self mutilation and early death Duchenne muscular dystrophy Progressive life shortening disorder Muscle degeneration and weakness mental retardation Lethal X Linked recessive disorders Only in males females can only be heterozygous carriers Ex Duchenne muscular dystrophy A man with Duchenne muscular dystrophy must have inherited it from his mother Bc he only has one X chromosome which he gets from mom he would only pass it to his daughters Sex influenced traits Traits where an allele is dominant in one sex but recessive in the opposite sex heterozygote phenomenon Sex influenced does not mean sex linked Sex influenced are autosomal Sex Limited inheritance Traits that only occur in one of the two sexes Genes are controlled by sex hormones or the sexual development pathway Ex In humans ovary development is limited to females Ex In birds males have more ornate plumage Male pattern baldness Allele B behaves dominant in males and recessive in females In BB genotype in females phenotype is less pronounced Homogametic Producing like chromosomes Zygotes with two x chromosomes Results in female offspring in humans Heterogametic Producing unlike chromosomes Zygotes with one X and one Y chromosome Results in male offspring in humans The presence of a Y chromosome determines maleness in humans Heterogametic Females ZZ ZW sex determination Females are heterogametic ZW sex Males are homogametic ZZ sex In chickens X and Y are not homologous Pseudoautosomal regions refer to the very few genes found on both Y Chromosome 50 genes and X chromosome 100 genes PARS Present on both ends of Y shares homology w regions on X synapse and recombine with X during meiosis MSY Male specific region of the Y Non Recombining region of Y SRY Sex determining region Y Located adjacent to PAR of the short arm of Y chromosomes Controls Male development TDF Testis determining factor At 6 8 weeks of development SRY gene becomes active in XY embryos Encodes protein that triggers testes formation PAR SRY MAY PAR Haplotype The set of alleles at two or more loci present in a particular chromosome Sex Chromosome Variation 75 go undiagnosed XXX Trisomy X Females Sometimes perfectly normal Sometimes sterile or mental retardation XXY Klinefelter syndrome Nondisjunction of X X Turner Syndrome Female Nondisjunction of X XYY Males are over 6ft tall Subnormal intelligence Personality disorders 1 1000 newborn boys Sex ratio Actual proportion of male to female offspring Primary sex ratio Reflects proportion of males to females conceived in population Secondary sex ratio Reflects proportion of each sex born It is speculated slightly more males are convinced because Y bearing sperm are more motile than X bearing sperm Although none of these hypotheses is strongly supported by experimental evidence Y bearing sperm have less mass than X bearing sperm and are presumably more motile Dosage Compensation Drosophila The level of expression of genes on the male X chromosome is increased two fold Humans One of the females X chromosomes is deactivated Barr Body Marsupials Females paternal X chromosome is deactivated Elegans Level of gene expression on both X s are decreased by 50 Susumu Ohno correctly proposed that the Barr body is a highly condensed X chromosome Mary Lyon proposed that dosage compensation in mammals occurs by theinactivation of a single X chromosome in females Xic X inactivation center Xist On Xic causes inactivation Tsix On Xic prevents inactivation It does not encode a protein It codes for a long RNA which coats the inactive X chromosome Other proteins will then bind and promote chromosomal compaction into a Barr body Sex determination in Drosophila Ratio of X chromosomes to number of haploid sets of autosomes Y does not determine sex 1 Female 1 x 5 Intersex 5 Male Ch 5 Alleles Alternative forms of a gene Mutation Ultimate source of alleles New phenotypes result from changes in functional activity of gene product Eliminating enzyme function Changing relative enzyme efficiency Changing overall enzyme function Wild type wt allele Occurs most frequently in nature and is usually but not always dominant Mutant is how we refer to the recessive one Gene interaction single phenotype is affected by more than one set of genes Loss of function mutations New phenotype results from change in activity Mutation causes loss of wildtype function Result generally in recessive mutations Gain of function mutations Mutation enhances function of wild type Quantity of gene product increases Result generally in dominant mutations Recessive Human diseases Disease Protein that is produced by normal gene Description Phenylketonuria Phenylalanine Hydroxylase Inability to metabolize phenylalanine Albinism Tyrosinase Lack of pigment in skin eyes and hair Tay Sachs disease Hexosaminidase A Defect in lipid metabolism Leads to paralysis blindness and early death Sandhoff disease Hexosaminidase B Defect in lipid metabolism Muscle weakess blindess and deterioration Cystic Fibrosis Chloride transporter Inability to regulate ion balance across epithelial cells Lung infections Lesch Nyhan syndrome Hypoxanathine guanine phosphoribosyl transferase Inability to metabolize purines which are bases found in DNA and RNA Self mutiation behavior poor motor skills mental impairments Heterozygotes and Homozygous Dominant expressive


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