6 Generations Parent generation = P Offspring of P generation = F1 Offspring of F1 generation = F2Cross a homozygous dominant Tall flowerwith a homozygous recessive short flower.Give the F1 genotype and phenotype percents.Tall = TT, short = tt
7 Genetics TerminologyPhenotype – the physical appearance of an organism. Determined by it’s alleles (maternal/paternal) “Photo”Genotype – the genetic makeup of an organism “Genes”The many different alleles that an organism can possess: BB, Bb or bb(Often use the 1st letter of the dominant trait)
8 Homozygous – an individual who has the same alleles for a trait. Ex. 2 genes for cystic fibrosis(CC = homozygous dominant or cc = homozygous recessive)Heterozygous – an individual who has different alleles for a trait. Ex. One gene for cystic fibrosis, one for normal (Cc)
9 Mendel’s crosses and results Statistics/RatiosConclusionsDominant/Recessive4 Principles Notesheet
10 A trait is controlled by factors (genes) that occur in pairs 1865 Paper Published by Gregor Mendel based on his research with garden peas1. Principle of Unit Characters:A trait is controlled by factors (genes) that occur in pairs
11 2. Principle of Dominance: One gene in a pair can mask or hide the expression of the other gene (dominant vs recessive) Dominant allele: When only ONE of the alleles affects the trait. (Use a CAPITAL letter) Recessive allele: the allele that is NOT expressed if there is a dominant allele present. (Use a small letter).
12 3. Principle of Segregation: A pair of genes (alleles) separate during the formation of sex cells (gametes)(Later learned that gametes are formed during meiosis…come together later to supply the alleles that form a trait)
13 4. Principle of Independent Assortment: The inheritance of one gene does not affect or depend on the inheritance of another gene *Mendel was looking at traits on different chromosomes….. *Modification: Linked genes are inherited together on a chromosome) **EXCEPTION: crossing over.
14 Inherited Traits in Humans Handout: DOMINANT vs RECESSIVEDark HairNonred hairDark SkinSkin PigmentBrown eyesNear or far sightedAstigmatismNormal Hearing
15 Cross …. Punnett Square. (TT x tt) Cross … Punnett Square* (TT x tt) *Represents ONE offspring- 4 possible genetic outcomes…Phenotype:%Ratio:Genotype:% Hom. Dom.% Het. Dom.% Hom. Rec.*HW: Key, Cross, Punnett, AnswerGenetics Online Practice ProblemsMore Online Genetics ProblemsHW:#1-5,7
16 Incomplete Dominance Neither gene dominates Blending of traits Notation: 2 different Capitol LettersExample: White Flowers x Red Flowers produce PINK flowersWW x RR = RWwhite red pink(HW #8-9)
17 Codominance BOTH genes are expressed Notation: 2 different Capitol LettersExample: “ROAN” cows/horsesWhite/Red hair dispersed evenly…looks pinkP176 L1 text… (HW #7)(HW #7)
18 Example of Codominance: ‘Pink’ Roan Horse RR= red WW =white RW= Roan (RR, R’R’,R’R)
19 Sex-linked inheritance (on X or Y) Sex-linked inheritance (on X or Y) *We will look at only X-linked traitsGenes on the X chromosomeUsually recessive; different chances male/femaleEx: Color-blindness, hemophiliaNOTATION:How males and females inherit:X Y = Normal vision maleXc Y = Color blind male*More in males-50/50X X = Normal vision femaleX Xc = Female color blind carrierXc Xc = Color blind female(or written with hashmarks X ’ X ’)
20 Sex-Linked Recessive males get their X from their mother fathers pass their X to daughters onlyfemales express the trait only if they get a copy from both parents.recessive in females; females can be ‘carriers’ALWAYS expressed in males if present; can NEVER be carriers of X-linked traitsSex-Linked Inheritance Problem Sets(#20-24)
21 “X” linked Problem #20: or X Y x X’X’ Key: Cross: XR Y x XrXr AnswerWhite eyed fruit flies are the result of an X- linked recessive gene. Show the results from a cross between a red-eyed male and a white-eyed female Drosophila.Indicate the results of each sex separately for genotype and phenotype.*Phenotype:“Carrier Females” are considered “Unaffected/Normal”
22 Multiple AllelesThere are more than 2 alleles in the gene pool BUT an individual inherits only TWO (one allele from mom, and one from dad)When there are 4 or more possible phenotypes for a particular trait.Example: Blood Typing: Inherited A,B,OSix GENOTYPE possibilities ??= FOUR different bloodtypes: ??(#10-12)
23 Blood Typing 3 different possible alleles for the blood type gene: Co-dominant A or B, or recessive O4 possiblePhenotypes: Genotypes:Type A IAIA, IAIi (AA,AO)Type B IBIB, IBIi (BB,BO)Type AB IAIB (AB)Type O IiIi (OO)(#10-12)
24 Worksheet #11 Key Cross i i x IAIB AnswerWorksheet #11If a type O person marries a type AB person, what blood type could occur in their children? Remember, type O is recessive to both A and B(#10-12)
25 DiHybrid Cross: Independent Assortment The factors for different traits are sorted into the gametes independent of each other. S = Smooth pea Y = Yellow ColorDetermine all possible combinations of alleles in the gametes for each parent.(#13-19)
26 Dihybrid crosses Involves TWO traits Ex: tall/short, green/yellow 1. To set the Crosses: The FOIL Method:First Outer, First Inner, Last Inner, Last Outer2. Fill in, matching the traits back up againTypical Question: What is the Phenotypic Ratio?ie: Number that will be bothTall and Yellow, etcStart with the FIRST box and count (add up to 16)Marking boxes as you go, choose the NEXT Phenotype and add those that match, until all boxes accounted for; final ratio(#13-19)
29 Genetics Probability Mendelian Cross: PROBABILITY: Same set-up: what is the probability that the offspring will be homozygous recessive?Probability that an egg from the F1 (Pp) will receive a p allele = 1/2.Probability that a sperm from the F1 will receive a p allele = 1/2.The overall probability that two recessive alleles will unite, one from the egg and one from the sperm, simultaneously, at fertilization is: 1/2 X 1/2 = 1/4.Mendelian Cross:In Pea Plants, the flower color Purple is dominant to white.If two heterozygous plants are crossed, what % of the offspring will be white?Rules of Multiplication n and Addition 10.35
31 Pedigree ChartsPedigree charts follow a genetic mutation/disease through several generations of a family.You can determine what chance offspring has of having a disease based on family history and Punnett Square.The main diseases that are tracked this way are:Tay-sachsHuntingtonsColorblindnessHemophiliaCystic fibrosis
34 Pedigree: Dominant Inheritance 1 Pedigree: Dominant Inheritance 1.Every affected individual has at least one affected parent 3. Two affected MAY have unaffected children
35 Pedigree: recessive disorder 1 Pedigree: recessive disorder 1. An individual who is affected may have parents who are unaffected. 2. ALL children of 2 affected parents are affected
36 Sample Pedigree: Inheritance 1 Sample Pedigree: Inheritance 1.Dominant (has the trait, one parent has the trait) or recessive trait? If Dominant….Know the FIRST allele is a Large letter, so can fill that in…. If recessive, must be two small letters
37 Dominant or recessive trait? Autosomal Recessive (nn)*Back of Problems
38 Autosomal Dominant (D_) Dominant or recessive trait?
43 % RecombinationCalculating the frequency of crossing-over reveals the linear order of linked genes on a chromosome.Total Recombinant/Total # Offspring X 100= 11% where 1% recombination = 1 map unitSo the loci are 11 map units apart on the same chromosome (11 centimorgans)The closer two genes are to each other, the less likely crossing over will occur; genes are linked.
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