3Let me tell a storyOnce upon a time* there was a monk who enjoyed gardening. He wondered why some plants were tall while others were short. He also wondered why some peas were green and others were yellow. So he started experimenting in his garden….*1857
5Basic terms Character- an inherited feature w/multiple variations Trait- each variantTrue breeding- create all offspring with the same traitsHybridization- mating/crossing of 2 true-breeding individuals
9Mendel’s 4 Hypotheses1. alternate versions of genes (alleles) account for variations in inherited characters
10Mendel’s 4 Hypotheses2. for each character, an organism inherits two alleles, one from each parent.3. If the two alleles differ, then the dominant allele is fully expressed in the organisms appearance, the recessive allele has no noticable effect on the organism’s appearance.
11Mendel’s 4 Hypotheses4. two alleles for each character segregate during gamete productionLAW OF SEGREGATION
12Old Vocab reminder Homozygous Heterozygous Phenotype Genotype Testcross- homozygous recessive + dominant trait (unk if it is homo or hetero)
14Dihybrid crosses Remember law of independent assortment Every possible combinationWhat ratio of results is always produced with a dihybrid cross when homo. Dominant + homo recessive are used?__________________
16Practice Punnett Squares Using the human traits discussed in class, we will make up scenarios and use punnett squares to solve the problems.
17Using Math to skip punnett squares Know your genotypesPpYyRr x PpyyrrP= purple, p= white flowersY=yellow, y=green seedsR=round, r=wrinkled seeds2. Know the question: the probability of having 2 recessive traits3. List all genotypes that would match this resultppyyRr, ppYyrr, Ppyyrr, PPyyrr, ppyyrr
18Probability lesson 2 traits- purple or white flowers Chance the sperm will have purple allele = ½Chance the sperm will have the white allele = ½Same for ovum (egg)For genotype pp½ x ½ = ¼ probability that this genotype will form
19When things aren’t so simple Mendel used all traits that were simple dominant or recessive, this is not that common in complex organisms
20INCOMPLETE DOMINANCE: Heterozygous organisms have a phenotype between that of the parents.
21Common Misinterpretation Dominant means “able to overpower”Dominant does NOT mean good OR more commonPolydactyly is dominant over 5 digits/appendage. 1/400 in US born with itSome types of dwarfism also dominant over average height.
22Codominance- human blood groups 3 groups based on presence of proteinsProteins called M and NHomozygous is M or NHeterozygous is MN (both present)
32Informal Research Rubric Results will be presented and discussed in class and collected ___________ You DO NOT need to write a formal essay for this .Name of Inherited Disorder _______________Direct Known Cause of Disorder _____________Prevalence of Disorder ____________How is the disorder passed on to other individuals? _____What does the disorder to do the human body? _________Is there any treatment to help those affected by the disorder?________Any particularly interesting facts you want to share? ____
33Inherited Disorders Cystic fibrosis 1/25 caucasians is a carrier Normal allele makes a membrane protein that functions in movement of chloride ionsDefective or absent in people with cystic fibrosisMucus builds up in lungs, digestive tractMore bacterial infections
35Untreated- fatal by age 5 Treated- live into the 20’s, some longer
36Tay Sachs diseaseDysfunctional enzyme fails to break down lipids in the brainInfant seizures, blindness, loss of motor and mental skillsUnusually high number in pop. Ashkenazic Jews whose ancestors are from central europe1/3600 in that pop, 100x more than other populations
38Sickle cell anemia 1/400 african americans Substitution of 1 amino acid in hemoglobinCodominance- carriers have the sickle cell trait- get the symptoms when blood oxygen is low for a long timeCauses resistance to malaria
39DOMINANT inherited diseases ACHONDROPLASIA-1/10,000 peopleMost people arehomozygous recessive
40HUNTINGTON’S DISEASE Degenerative disease of nervous system No phenotype noticable until ages 35-45Fatal, not reversiblePassed on because people have children before they know they have the disorder
49PKU and Newborn screening Phenylkenonuria- 1/10,000 -1/15,000 births in U.S.Inability to break down amino acid phenylalanineToo much of it can build up and result in mental retardationSolution- diet low in phenylalanine
51CHAPTER 15 Chromosomal Basis of Inheritance In 1900 scientists doing research on plants discovered that Mendel had recorded the same discoveries about inheritance 35 years earlier.LESSON OF THE DAY- DO YOUR RESEARCH FIRST!!!!!
52Chromosomal Theory of Inheritance The genes Mendel studied have specific loci on chromosomesChromosomes independently assort and segregate during meiosis
53The first experimental Mutant in Thomas Morgan’s experiments
54Drosophila melanogaster Fruit flyHarmlessBreed quickly and in large numbers3 pairs autosomes, 1 pair sex chromosomesWild type has red eyes, the “normal” phenotype
57Sex Linked TraitsWhite eyes in flies had to be on the X chromosome
58Morgan’s Evidence P- Male white eye mutant, Female wild type F1- 100% red eye flies, male or femaleWhite must be recessiveF2- 100% females red eyes,50% males white eyes50% males red eyesEye color trait must be on X chromosome
62Genetic Recombination Production of offspring with new combinations of traitsParental types- offspring that have the same phenotype as parentsRecombinants- offspring with different phenotypes as parents
63YyRr x yyrr Y- yellow R-round y-green r- wrinkled Complete the punnett square to see what the seeds of the next generation will look like.How many are recombinants? How many are the parental types?
64Correct Results 50% recombinants Therefore 50% frequency of recombinationAny 2 genes on different chromosomes have this recomb. frequency
65Linked genes can become recombinant in crossing over
66Genetic mapsAlfred Sturdevant calculated where genes were based on recombinant frequenciesCloser together = smaller frequency of recomb.Called Linkage Maps
671 map unit= 1% recombination frequency Aka centimorganGenes on 1 chromosome with 50% r.f. or higher are equivilent to being on different chromosomes.
68Cytological mapsShow actual location of genes on chromosome based on visible traits
69Mapping Human Genes: HGP I have a more updated human gene map in the classroom…but still several years old.
70Sex ChromosomesX and Y rarely cross over and do not match but count as homologous chromosomesGene SRY discovered 1990w/o SRY gonads form into ovariesSRY is a trigger causing many other genes to operate
71Not all organisms use the XY system, but they have variations in sex chromosomes to identify genders.
72Sex Linked Traits-aka X linked traits On X chromosome resulting is distinct patterns of expression in Males vs. females
73Trends in Sex Linked traits If the trait is sex linked and recessive you will see it more in males because they only have 1 x chromosomeLess common in females because they can inherit the dominant allele and hide the recessive trait
74Human Sex Linked Traits Color blindnessHemophiliaDuchenne muscular dystrophy
76X InactivationFemales have 2 X chromosomes, but one condenses and becomes a Barr BodyMost genes on barr body are never activatedAt the time of X inactivation each cell present randomly “assigns” one X to become the barr body.Therefore not all cells show the same phenotype
78How is X inactivated? Methyl group (CH3) attached to cytosine in DNA Only one X has XIST gene (X inactive specific transcript)Causes the DNA to be covered in RNAStarts the inactivationStill don’t know it all though
79Chromosome errorsNondisjunction- tetrads/chromatids fail to separate in Meiosis I or IIAneuploidy- abnormal # chromo.Trisomic- 3 copies of a chromo.Monosomic- only 1 copy of a chromo.Polyploidy- more than 2 complete chromo. Sets (common in plants)
82Specific Cases Down Syndrome- trisomy 21 Klinefelter Syndrome- XXY Turner Syndrome- XOCri du Chat- deletion in chromosome 5, but normal 46 chromo.Chronic Myelogenous Leukemia- part of #22 switched with part of #9
83More complicationsSometimes the phenotype depends on which parent provided the allele
84Prader Willi and Angelman syndromes Both caused by deletion of a specific section of #15Prader-Willi- deletion from fatherMental retardation, obesity, short stature, small hands and feetAngelman- deletion from motherSpontaneous uncontrollable laughter, jerky movements, motor skills problems, mental disabilitiesa
85Genomic imprinting Allele on one chromosome is silenced Caused by methylation, same as X inactivation
86Fragile X Syndrome Piece of the X chromosome is dangling on 1/1500 males, 1/2500 femalesThe most common genetic cause of mental retardationMore commonly inherited from mom
87Passing On Mitochondrial DNA Does not follow mendelian rulesPassed on from motherRare human disorders caused by thisMitochondrial myopathy- weakness, intolerance of exercise, muscle deteriorationMay contribute to alzheimers disease
88Clearly, we could spend more time on genetics Clearly, we could spend more time on genetics! But, I have MUCH more to cover in the world of biology this year!This is a summary of what the college boards states is on the AP exam.