2 Rules of ProbabilityAddition Rule- probability that any one of two or more mutually exclusive events will occur is calculated by adding the individual probabilities.Example- the chance of getting heads or tails on a coin tossheads- ½ tails – ½ ½ +1/2 = 1
3 Rules of ProbabilityMultiplication- probability that two or more independent events will occur together Ex- What is the chance that two coins tossed together will both land heads up? probability of 1 head- ½ probability of 2 heads ½ x ½ = 1/4
4 Probability Problems Chance of rolling a three on a die? 1/6 Chance of getting any other number other than three? 5/6Chance of rolling a 1 and then a 2 and then 4?1/6 x 1/6 x 1/6 = 1/216Parents are PP and pp- chance that offspring will be Pp? 1 x 1 = 1Parents are PpYy x Ppyy chance that offspring will be ppYy? Pp= ½ x ½ Yy= ½ x 1 total=1/8
5 Incomplete dominanceHeterozygote shows an intermediate, blended phenotypeexample:RR = red flowersrr = white flowersRr = pink flowersmake 50% less colorRRWWRWRRRWWW
6 Incomplete dominance P F1 100% 1:2:1 F2 X true-breeding red flowers white flowers100%100% pink flowersF1generation(hybrids)self-pollinate25%whiteF2generationred1:2:150%pink
7 CodominanceThere are two or more alleles that are dominant in a phenotype.Both alleles are expressed in heterozygous condition.Ex: Red – RR, white – WW, red and white - RW
8 Multiple Alleles 2 alleles affect the phenotype equally & separately not blended phenotypehuman ABO blood groups3 allelesIA, IB, iIA & IB alleles are co-dominantglycoprotein antigens on RBCIAIB = both antigens are producedi allele recessive to both
9 Polygenic inheritance Some phenotypes determined by additive effects of 2 or more genes on a single characteristicphenotypes on a continuumhuman traitsskin colorheightweightintelligencebehaviors
10 Sex linked traits 1910 | 1933 Genes are on sex chromosomes as opposed to autosomal chromosomesfirst discovered by T.H. Morgan at Columbia U.Drosophila breedinggood genetic subjectprolific2 week generations4 pairs of chromosomesXX=female, XY=male
11 Hemophilia XHXh XHY Hh x HH XH XHXh XH Y Xh XHXH XHXH XHY XHY XH Xh XH sex-linked recessiveHemophiliaXHXhXHYHh x HHXHXHXhXHYmale / spermXhXHXHXHXHXHYXHYXHXhfemale / eggsXHXHYXHXhXHXhXhYXhYYcarrierdisease
12 Pedigree AnalysisUsed to predict inheritance based on past phenotypes
14 Autosomal Dominant Inheritance-Huntington Disease Generations are not skipped
15 Human disorders The family pedigree Recessive disorders: •Cystic fibrosis •Tay-Sachs •Sickle-cellDominant disorders:-Huntington’s
16 Practice QuestionSickle cell anemia is caused by the mutation of a single base pair in the gene for hemoglobin. This mutation results in hemoglobin molecules that form long chains in low-oxygen settings and stretch the blood cells into their characteristic sickled shape. What would the result be if a different base pair in the sickle cell hemoglobin gene were to become mutated?A. The effects of sickle cell would be increasedB. The effects of sickle cell would be reducedC. The new mutation would increase resistance to malariaD. It is impossible to predict what the effect would be without knowing more about the mutation
17 Practice ProblemIn the cross AaBBcc x aaBbCc, what is the probability of an offspring that is aaBbcc?A 1/2B 1/4C 1/8D 1/16
18 Practice ProblemWhat type of inheritance pattern is illustrated above?
19 Genetics of Sex X Y X XX XY X XX XY In humans & other mammals, there are 2 sex chromosomes: X & Y2 X chromosomesdevelop as a female: XXgene redundancy, like autosomal chromosomesan X & Y chromosomedevelop as a male: XYno redundancyXYXXXXYXXXXY50% female : 50% male
20 Discovery of sex linkage true-breedingred-eye femaletrue-breedingwhite-eye maleXPHuh! Sex matters?!100%red eye offspringF1generation(hybrids)100%red-eye female50% red-eye male50% white eye maleF2generation
21 Genes on sex chromosomes Y chromosomefew genes other than SRYsex-determining regionmaster regulator for malenessturns on genes for production of male hormonesX chromosometraits other than sex determinationmutations: (all are recessive)hemophiliaDuchenne muscular dystrophycolor-blindnessDuchenne muscular dystrophy affects one in 3,500 males born in the United States.Affected individuals rarely live past their early 20s.This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.The disease is characterized by a progressive weakening of the muscles and loss of coordination.
22 X-inactivation Female mammals inherit 2 X chromosomes XH XHXh Xh one X becomes inactivated during embryonic developmentcondenses into compact object = Barr bodywhich X becomes Barr body is randompatchwork trait = “mosaic”patches of blackXHXHXhXhtricolor cats can only be femalepatches of orange
23 Sex Linked Traits Usually found on the X chromosome Only if she is homozygous recessive, will she exhibit the traitExpressed more with males since they have only one X
24 Sex Linked diseases in humans Duchenne muscular dystrophyHemophiliaColorblindness
26 Linked GenesAre physically close to each other and get inherited together even with crossing overThe greater the distance between the genes, the greater the chance of separation during crossing over
27 Map UnitsMorgan and Sturtevant developed the genetic map that shows a list of ordered loci on a chromosomeThe distance between the genes is called a map unitA recombinant frequency of 1% = 1 map unit
28 ExampleIf the black body gene (b) is 17% or 17 map units from the vestigal wing gene (vg) and the cinnabar eye gene (cn) is 9.75% or 9.75 map units from the b gene, what are the order of the genes on the chromosome?
29 Cytogenic MapsLocates genes with respect to chromosomal features as stained bands
36 XYY- Jacob’s Syndrome Tall, thin, larger build More prone to acne Increased testosterone levels
37 Genomic ImprintingSome traits vary depending on which parent passes it onThe section of DNA has a methyl group (-CH3) added onCertain cancers can be stimulated this wayFragile X syndrome can come from father
38 Mitochondrial Defects These defects originate in the mitochondrial DNA. Some examples are:Some forms of DiabetesSome forms of DeafnessMultiple sclerosisSome forms of epilepsy
39 Environmental effects Phenotype is controlled by both environment & genesHuman skin color is influenced by both genetics & environmental conditionsCoat color in arctic fox influenced by heat sensitive allelesThe relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debatea single tree has leaves that vary in size, shape & color, depending on exposure to wind & sunfor humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence testseven identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiencesColor of Hydrangea flowers is influenced by soil pH
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