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1/20/15 What is genetics? DNA CRAPSHOOT l The study of heredity l l Mendel takes control Mendel l l He changed biology FOREVER. He used pea plants l l l l Ordinary pea plants are self pollinators; meaning the offspring will be identical to parent This is called true breeding Mendel’s mixes l He studied 7 traits l l He “neutered” the flower by cutting away the male parts; this prevented self pollination Then he dusted the neutered flower with pollen from another flower From generation to generation l Trait—specific characteristic, like height or color Hybrid— offspring of crosses between parents with different traits (a combo) Inheritance—receiving characteristics from parents Gene—sequence of DNA that codes for a protein, (characteristic). l The parent’s were called the P (parental) generation Each successive generation was labeled the F generation, like F1, F2, F3, etc. P F1 F2 1 1/20/15 Mendel’s Conclusion l Inheritance is determined by “factors” passed from one generation to the next l More Conclusions l Allele for short gene One gene exists in two contrasting forms l This factor is the gene! For example, there are two genes for the height trait: l l l 1. short gene 2. tall gene The different forms are called alleles Allele for tall gene Something peculiar Detective Mendel When Mendel bred a white and purple flower (P generation), the F1 generation was all purple l So what happened to the white trait? l l How did it appear? How do the alleles separate? l l Let’s assume: l l 1. Purple is the dominant allele 2. When the purple allele is present it masks the white allele Therefore, in order to see the white allele expressed, the purple allele can not be present l The alleles must be separated! Mendel produced a F2 generation by self pollinating the F1 to find out if the “missing trait” was truly gone. l The separation, (segregation) occurred during sex cell (gamete) formation. A gamete will carry only one type of allele l 2 1/20/15 Gene expression: which version of the trait will we see? When female and male gametes combine to form offspring, that offspring will get one allele from mom and one from dad l If just one gamete carries the dominant allele, purple, than the offspring will be purple l In order to see the recessive allele, BOTH gametes must carry the recessive allele l l l l l l l Probability; The Punnett Square l l T t How to? Dad’s Allelles Likelihood that a particular event will occur Past outcomes do not affect future outcomes Can use probability to predict genetic crosses Mom’s Allelles l Possible Allele Combo for Offspring Possible Allele Combo for Offspring Possible Allele Combo for Offspring Possible Allele Combo for Offspring t T t t t tall short T t t t tall short l l T Heterozygous tall male mated with a short female What’s the prediction? T t Genotypes Tt = 2/4 =1/2 = 50% tt = 2/4 =1/2 = 50% Phenotypes Tall = 2/4 =1/2 = 50% short = 2/4 =1/2 = 50% 1:1 l l Probability predicts average outcome, not precise numbers! The largest the number of offspring, the more likely the actual number will be close to the predicted number t t t Tt t Average 1:1 t Dominant alleles are written with a capital letter; Tall = T Recessive alleles for the same trait are written in lower case of the same letter for the dominant trait; short = t Organisms with two of the same allele are called homozygous l TT l tt Organisms with two different alleles are heterozygous l Tt Genotype—genetic makeup, designated by letters l TT, tt, or Tt Phenotype—physical characteristic, description, based on genotype l TT, Tt = Tall l tt = short t tt T t t Tt tt t Tt tt 1:1 or 50:50 Total = 100 Tall = 53 Short = 47 3 1/20/15 Monohybrid l l One pair of alleles being studied; one trait Example l l l l l l Phenotype ¾ = tall ¼ = short 3:1 t T TT Tt t Tt tt Heterozygous x heterozygous Dominant = tall = T Recessive = short = t Principle of Dominance l l l Some alleles are dominant and others recessive Organism that carry a dominant allele will always express that form Can only express the recessive allele when the dominant allele is not present Law of Independent Assortment l Mendel’s Principles l l T Trait = height One allele = tall One allele = short The cross l Genotype ¼ = TT 2/4 = Tt ¼ = tt 1:2:1 Alleles for different characteristics are distributed to gametes independently l Principle of Dominance Principle of Segregation Principle of Independent Assortment Law of Segregation l l l A parent has two alleles Offspring must have two alleles The alleles for a characteristic must be separated during the formation of egg and sperm so baby gets 1 allele from mom, 1 from dad to make the set complete Pedigree l Chart which shows the genetic relationships within a family Female Male Children Marriage Individual II-6 Carrier Does not express trait Expresses the trait *Note: Children go in order of birth. 4 1/20/15 Pedigree of Queen Victoria and her descendants tracing the gene for Hemophilia Advancing past simple Mendelian Genetics l l Incomplete dominance Codominance l Multiple alleles l Polygenic traits l Sex-linked traits l Incomplete dominance l l Neither gene is dominant; Both contribute to the phenotype When a genotype is heterozygous, there is a blending Codominance l l l The dominant does not mask the recessive Both alleles are displayed in the phenotype Example: B l l B = Black W = White W W Multiple alleles B BW BW BW BW Multiple Alleles: Blood Types A gene that has more than two allele Does not mean an individual can have more than two alleles! l Only means that more than two versions of the gene (allele) exist in the population l l 5 1/20/15 Personality Traits By Blood Type Type O: Compatibility by Blood Groups: Type O's are outgoing, and very social. They are initiators, although they don't always finish what they start. and popular, they love to be AB the center of attention and A isCreative most compatible with A and appear very self confident. Type A: B is most compatible with B and AB While outwardly calm, they have such high standards (perfectionists) that they tend to be balls of nerves on the inside. Type A's are the most artistic of the blood groups. They can AB is mosttrustworthy, compatible AB, B, A and O be shy, are conscientious, and with sensitive. Type B: is most compatible with andand ABcontinue it until Goal oriented andOstrong minded, type B's will startO, a task completed, and completed well. Type B's are the individualists of the blood group categories and find their own way in life. Type AB: Type AB's are the split personalities of the blood groups. They can be both outgoing and shy, confident and timid. While responsible, too much responsibility will cause a problem. They are trustworthy and like to help others. Polygenic traits l l Traits controlled by two or more genes Show a wide range of phenotypes Sex-linked traits l Practice l l l l Cross an AB dad with an O Mom Who can Dad donate donate to? AB Who can Mom donate to? O, A, B, AB What blood type do the potential offspring have? IAi = type A ; 50 % IBi IA IB i IAi IBi i IAi IBi = type B ; 50% • Can two blood type B parents have a blood type O child? Show the punnet square. • Can a type O Dad and a Type B mom have a type A child? Show your work. AaBbCc X AaBbCc (each square shows the number of dark skin alleles in the genotype) Gametes ABC ABc AbC Abc aBC aBc abC abc ABC 6 AABBCC 5 AABBCc 5 AABbCC 4 AABbCc 5 AaBBCC 4 AaBBCc 4 AaBbCC 3 AaBbCc ABc 5 AABBCc 4 AABBcc 4 AABbCc 3 AABbcc 4 AaBBCc 3 AaBBcc 3 AaBbCc 2 AaBbcc AbC 5 AABbCC 4 AABbCc 4 AAbbCC 3 AAbbCc 4 AaBbCC 3 AaBbCc 3 AabbCC 2 AabbCc Abc 4 AABbCc 3 AABbcc 3 AAbbCc 2 AAbbcc 3 AaBbCc 2 AaBbcc 2 AabbCc 1 Aabbcc aBC 5 AaBBCC 4 AaBBCc 4 AaBbCC 3 AaBbCc 4 aaBBCC 3 aaBBCc 3 aaBbCC 2 aaBbCc aBc 4 AaBBCc 3 AaBBcc 3 AaBbCc 2 AaBbcc 3 aaBBCc 2 aaBBcc 2 aaBbCc 1 aaBbcc abC 4 AaBbCC 3 AaBbCc 3 AabbCC 2 AabbCc 3 aaBbCC 2 aaBbCc 2 aabbCC 1 aabbCc abc 3 AaBbCc 2 AaBbcc 2 AabbCc 1 Aabbcc 2 aaBbCc 1 aaBbcc 1 aabbCc 0 aabbcc Red/Green Color Blindness When the gene is found only on the X chromosome and not the Y Do you see the faint brown circle? Do you see a 15 or a 17? 6 1/20/15 Sex-linked traits Practice Y linked- Holandric traits 100% Daughters = Normal 100% Sons = Color Blind XC Xc Xc Cross a Normal vision father with a color blind mother. Normal Y Color Blind XCXc XcY Normal Color Blind XCXc XcY Ear hair distribution… you jealous ladies? Dihybrid l l The cross 2 pairs of alleles are studies; 2 traits Example l l l l l l Color Seed appearance One allele = yellow One allele = green One allele = round One allele = wrinkled Color Yellow = dominant = Y Green = recessive = y l Round = dominant = R l Wrinkled = recessive = r l Heterozygous x heterozygous l l YyRr x YyRr Seed appearance The Punnett Square YR YyRr x YyRr ? ? ? YR Yr ? YR ? yR yR ? yr yr ? Yr ? YR Yr YYRR YYRr yR yr YyRR YyRr Yr YYRr YYrr YyRr Yyrr yR YyRR YyRr yyRR yyRr yr YyRr Yyrr yyRr yyrr 7 1/20/15 Key Dominant = yellow = Y Recessive = green = y Dominant = round = R Recessive = wrinkled = r AYS ALWKE A MA !!!! Y KE YR YR yellow round yR yr yellow round yellow round yellow round YYRR YYRr YyRR yellow round yellow wrinkled yellow round Yr YYRr yellow round yR YyRR yellow round yr YyRr Thomas Hunt Morgan Yr YYrr yellow round YyRr yellow wrinkled Yyrr YyRr yellow wrinkled YyRr Yyrr green round green round yyRR green round yyRr yyRr green wrinkled yyrr l Genotype 1/16 = YYRR 2/16 = 1/8 = YYRr 2/16 = 1/8 = YyRR 4/16 = ¼ = YyRr 1/16 = YYrr 2/16 = 1/8 = Yyrr 1/16 = yyRR 2/16 = 1/8 = yyRr 1/16 = yyrr l l Applied Mendel’s principles to the fruit fly, Drosophila melanogaster Found them applicable! Discovered sex-linked traits Phenotype 9/16 = yellow round 3/16 = yellow wrinkled 3/16 = green round 1/16 = green wrinkled 1: 3 : 3 : 1 Nature vs Nurture Chromosome number Genes provide the plan l Environment also play role in the outcome l l l l The body cells of an organism has a unique number of chromosomes l Human = 46 l Donkey = 62 l Potato = 48 l Dog = 78 Half of those chromosomes come from mom, the other have come from dad The pair are considered Mitosis: Identical daughter cells homologous chromosomes Meiosis: Cells are halved. Meiosis l l Note that almost all chromosomes come in homologous pairs. l The parents carry two complete sets of genes When gametes are formed, the set of two must be separated so that the offspring will only receive one set from one parent and one from another (making a new but complete set) The number of chromosomes is cut in half by separating homologous chromosomes 8 1/20/15 Mitosis vs Meiosis: The Visual Diploid vs. Haploid l l Meiosis: To get from dip to hap A cell that contains both pairs of homologous chromosomes (body cell) is diploid l 2N l Humans 2N =46 A cell that contains only 1 of the homologous chromosome (gamete) is called haploid l N l Humans N = 23 Meiosis I l l l Prophase I l l l During interphase, each chromosome duplicates Each chromosome pairs with its corresponding homologous chromosome l THIS IS THE KEY TO UNDERSTANDING MEIOSIS! The four chromatids are called a tetrad Prophase I: The Visual Nuclear membrane breaks down Each chromosome pairs with its corresponding homologous chromosome (forms tetrad) First opportunity for variation!!!! l As homologous chromosomes pair up to form tetrads, portions of chromatids are exchanged—crossing over Tetrad; Homologous Chromosomes 9 1/20/15 Metaphase I Metaphase I: The visual Chromosome line up in the middle Spindle fibers attach to the chromosome l Second opportunity for genetic variation!!!! l l l Random alignment of homologous chromosomes will determine which new cell gets what— independent assortment Homologous Chromosomes Line Up Anaphase I l l l Telophase I & Cytokinesis Fibers pull the homologous chromosomes apart toward opposite end of the cell Tetrad now eliminated Only sister chromatids remain l l Nuclear membrane form The cell separates into two cells l l Tetrad (4 chromatids) These new cells are different from the diploid cell that entered into meiosis I AND these new cells are different from each other 2 Chromatids Telophase I & Cytokinesis: The Visual Meiosis II l l Two new cells enter a second round of meiotic division Chromosome replication does not occur What we started with 2 new cells different from the cell at start AND different from each other 10 1/20/15 Telophase & Cytokinesis l l Evidence of Crossing over l 4 new cells produces All four cells are haploid Called gametes 1 2 l l l Prophase II: Meiosis I results in two unique daughter cells Metaphase II: Chromosomes line up in middle Anaphase II: Sister chromatids are separated and moved to 34 opposite end of cell 1 12 12 3 1 34 4 Meiosis vs Mitosis Meiosis results in 4 genetically different haploid cells l Mitosis results in 2 identical diploid cells l 2 2 3 1 1 all blue 1 red/blue 1 red/blue 2 all blue 1 blue/red/blue 5 6 3 blue 3 red 3 1 2 Before crossing over 3 1 red/blue/red 2 red 1 blue/red 1 all red 1 red/blue 1 2 3 Girl vs Boy l In a girl, the cell divisions are uneven l l l Large = egg 3 small = polar bodies All 4 haploids of boy gametes (sperm) are equal and functional 11