Chapter 15 - LectureMonday, November 30, 20158:10 AM Thomas Hunt Morgan-Morgan first observedoCross between red-eyed and white eyedoRed eyed is wild type and dominant-Punnett squareoLittle w for mutant eye-colored gene-The white-eye mutant allele must be located on the X chromosomeoFemale is heterozygous so there are two types of eggs as welloAll white-eyed are male fliesoF1 generation - M-herterozygous recessiveoF1 generation - F-homozygous dominantoF2 generation - all males are white eyedoF2 generation - 1 homozygous dominant female/1 heterozygous dominant femail-Each chromosomeoHas hundreds or thousands of genesoGenes in a same chromosome are tend to be inherited together-Linked genes-Is it following Mendel's law of independent assortment - do not assort independently(Use dihybrid cross for 2nd law to determine)-Recombination of Unlinked Genes: Independent Assortment of ChromosomesoWhen Mendel followed the inheritance of two characters-He observed that some offspring have combinations of traits that do not match either parent in the P generation-Four different phenotypes 1:1:1:1 ratio-Gametes from yellow round heterozygous parent (YyRr) vs. gametes from green-wrinkled homozygous recessive parent (yyrr)YyRr yyrr Yyrr yyRrParental type Recombinant offspring Morgan Crossed Flies-Vestigial - underdeveloped wings-Cross two true-breeding parentsoHybrid, heterozygousoGray body color and normal wing shapeoAccording to independent assortment - the hybrid can produceoHybrid will have equal chance to produce - recognant-However, the offspring was counted from test crossoThere is no 1:1:1:1 ratiooSee more of parent typeoStick together rather than to be separated Genetic Recombination and Linkage-Morgan determined thatoGenes that are close together on the same chromosome are linked and do not assort independentlyoUnlinked genes are either on separate chromosome and assort independently-Body color and wing-shaped are not assorted independently-Parents in testcross (b+ vg+/b vg) x (b vg/b vg) Linked Genes-Exhibit recombination frequencies less than 50%-To calculate recomb, the greatest number to get is 50%-Between unlinked genes - Rf is 50%-Linked genes is under 50% -Never negative number-Never over 50%Test cross offspring = parental-type offspring/recombinant offspringRecombination frequency = recombinants/total offsprings x 100% Genetic Map-An ordered list of the genetic loci among a particular chromosomeoThe distances between genes are expressed as map units (centimorgans) with one map unit equivalent to a 1% recombination frequency-Many fruit fly genesoWere mapped initially using recombination frequenciesoCalculate distance between each Example:-The RF between genes A and B is 50% between genes B and C is 14%, between A and C is 39%. Draw the derived genetic map containing genes A, B, Co50 is the upper limitoThrow away the 50%oA and B 50 means AB are unlinked, either on different chromosomes Sex linked traits-Humans have 22 pairs of "autosomal chromosomes: and 1 pair of "sex chromosomes"-Females are XX, while males are XY-Genes that are found on the X chromosomes are called "sex-linked" genes-The Y chromosome carries no homologous copies of the genes on the X chromosomes-Human sex determining system Different systems of sex determination-Are found in other organismsoThe X-0 systemoThe Z-W systemoThe haplo-diploid system Simplicity of Human Y chromosome-Human Y chromosome contains 78 genes, which code for only 23 distinct proteins-Human X chromosome contains between 900 to 1200 genes-SRY (sex-determining region) - a sex-determining gene INHERITANT GENETIC DISEASESSome genetic diseases are autosomally inherited-Genetic diseases that result from mutations on an autosome can be either autosomal dominant or autosomal recessiveoRecessive - more preservedoEnd up with more autosomal recessive in population Inheritance Patterns-Autosomal recessive - carrier parentsoHalf of girls as carrier, half is healthyoHalf of boys as carrier, half is healthyoDisease pass on with equal chance with boys and girls-Autosomal dominant - parents are affected and unaffectedoHalf with diseaseoHalf are healthy Sex-Linked Genes-In addition to their role in determining sex of an organism, X and Y chromosomes have many other genes that are unrelated to sex-A gene on either sex chromosome is called a sex-linked geneoSex-linked genes are X-linkedoFather is not affected, mother carries the allele-Girls look healthy but half are carriers-Half of boys are normal, half are affected Q. A man who carries an X-linked allele will pass it on toa. All his sonsb. All of his childrenc. Half of his daughtersd. All of his daughterse. Half of his sons Color Blindness-Absence or unbalanced visual pigments (red, green, and blue light) in cone photoreceptors-X-linked recessive genetic Duchenne Muscular Dystrophy-Mutation in Dystrophin - a rod-shaped cytoplasmic protein and a vital part of a protein complex that connects the cytoskeleton of a muscle fiberoDystrophin - connector-X-linked recessive genetic disorder-Mainly in boys (1/3500) X inactivation in Female Mammals-Contains over a thousand functional genes-Women have twice as much-Barr body checkoCells are stainedoNumber of Barr body = number of X chromosomes - 1 X inactivation-If a female is heterozygous for a particular gene located on the X chromosomeoShe will be a mosaic for that character Abnormal Chromosome Number-Caused by nondisjunction-Abnormal chromosome structure is caused by crossing over -Aneuploidy - cell has abnormal number of chromosomesoResults from the fertilization of gametes in which nondisjunction occurredoCommon in cancers-Euploidy - cell have normal number of chromosomesoTrue number of chromosomesoIn humans, euploidy is 46 chromosomes Aneuploidy Scenarios-If a zygote is trisomic (n+1)oIt has three copies of a particular chromosome-Trisomy 21 (Down Syndrome)-XXX (Triple X Syndrome)-XXY (Klinefelter's Syndrome)-XYY (XYY Syndrome)-If a zygote is monosomic (n-1)oIt has only one copy of a particular chromosome-X0 - only one X chromosome instead of the usual two (XX) seen in a normal female (Turner's Syndrome) Down Syndrome-Usually the result of an extra chromosome 21, (Trisomy 21)-Three copies of chromosome 21-Normally the embryo does not survive due to natural abortion-1 in 700 babies born-Risk increases when mother is over 40 years old-Developmental and mental problems Aneuploidy of Sex Chromosomes-Nondisjunction of sex chromosomesoCreates variation of sex