Chapter 15 Lecture Monday November 30 2015 8 10 AM Thomas Hunt Morgan Morgan first observed o Cross between red eyed and white eyed o Red eyed is wild type and dominant Punnett square o Little w for mutant eye colored gene The white eye mutant allele must be located on the X chromosome o Female is heterozygous so there are two types of eggs as well o All white eyed are male flies o F1 generation M herterozygous recessive o F1 generation F homozygous dominant o F2 generation all males are white eyed o F2 generation 1 homozygous dominant female 1 heterozygous dominant femail Each chromosome o Has hundreds or thousands of genes o Genes 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 Chromosomes o When 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 greenwrinkled homozygous recessive parent yyrr YyRr yyrr Parental type Yyrr yyRr Recombinant offspring Morgan Crossed Flies Vestigial underdeveloped wings Cross two true breeding parents o Hybrid heterozygous o Gray body color and normal wing shape o According to independent assortment the hybrid can produce o Hybrid will have equal chance to produce recognant However the offspring was counted from test cross o There is no 1 1 1 1 ratio o See more of parent type o Stick together rather than to be separated Genetic Recombination and Linkage Morgan determined that o Genes that are close together on the same chromosome are linked and do not assort independently o Unlinked 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 offspring Recombination frequency recombinants total offsprings x 100 Genetic Map An ordered list of the genetic loci among a particular chromosome o The distances between genes are expressed as map units centimorgans with one map unit equivalent to a 1 recombination frequency Many fruit fly genes o Were mapped initially using recombination frequencies o Calculate 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 C o 50 is the upper limit o Throw away the 50 o A 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 organisms o The X 0 system o The Z W system o The 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 DISEASES Some genetic diseases are autosomally inherited Genetic diseases that result from mutations on an autosome can be either autosomal dominant or autosomal recessive o Recessive more preserved o End up with more autosomal recessive in population Inheritance Patterns Autosomal recessive carrier parents o Half of girls as carrier half is healthy o Half of boys as carrier half is healthy o Disease pass on with equal chance with boys and girls Autosomal dominant parents are affected and unaffected o Half with disease o Half 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 gene o Sex linked genes are X linked o Father 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 to a All his sons b All of his children c Half of his daughters d All of his daughters e 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 fiber o Dystrophin 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 check o Cells are stained o Number of Barr body number of X chromosomes 1 X inactivation If a female is heterozygous for a particular gene located on the X chromosome o She 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 chromosomes o Results from the fertilization of gametes in which nondisjunction occurred o Common in cancers Euploidy cell have normal number of chromosomes o True number of chromosomes o In humans euploidy is 46 chromosomes Aneuploidy Scenarios If a zygote is trisomic n 1 o It 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 o It 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 chromosomes o Creates variation of sex chromosome number o Produces