2 The Work of Gregor Mendel A. Genetics is the scientific study of heredity.Every living thing has a set of characteristics inherited from its parent or parents!
3 B. Gregor Mendel What: Who & Where: Austrian monk, “Father of Genetics”, born 1822What:His work was important to theunderstanding of heredity. Incharge of monastery’s garden;studied traits of pea plants
4 C. So Why Peas? Pea plant flowers are closed Self-fertilizing True-breedingHave 7 easily visible traits called phenotypes
9 If these hybrids self-pollinate.. The Next GenerationIf these hybrids self-pollinate..The hidden trait returns!F1 generation: Tt x Tt Result?
10 What happened to Recessive Allele? Plants with different genotypes(TT and Tt)can have the same phenotype (“tall”).
11 Genotype: genetic makeup of organism Phenotype: physical characteristics of an organismGenotypePhenotypeC cT TP p
12 D. Principle of Dominance Definition:some alleles are dominant and others are recessive. The dominant gene shows up in the phenotype when present.Example: Smooth peas Swrinkled peas s
13 E. Principle of Segregation During sex cell formation, alleles separates from each otherEach gamete has one allele for each trait
14 Each trait is controlled by a gene that is in two contrasting forms The different forms of a gene are called alleles.
15 Homozygous: two identical alleles Example: TT or tt or SS or ssHeterozygous: two different allelesfor the same traitExample: Tt or Ss
16 II. Probability and Punnett Squares Why used?Punnett squares used to predict and compare genetic variations that will result from a crossThe Rules:Dominant traits arethe 1st letter andCAPITALRecessive are the 2ndletter and lowercase
17 B. Practice T T t T t T t t T t T t Tall= T short= t 1) If a homozygous tall person was crossed with a homozygous short person, what are probably offspring?TTTall= Tshort= ttTtTttTtTt
18 Punnett Square T t T T T T t 1 TT: 2 Tt: 1 tt T t t t t 2) Cross two heterozygous tall parents.Tall= Tshort= tTtWhat is thegenotype ratio?TTTTt1 TT: 2 Tt: 1 ttWhat is thephenotype ratio?Ttttt3 Tall: 1 short
19 Punnett Square 3) The long-eared allele (L) is dominant to the short-eared allele (l). Cross ahomozygous long ear with ahomozygous short-ear.Cross the F1 generation and give the F2 results.
20 III. Independent Assortment Mendel discovered that genes for different traits segregate independently during gamete formationEx. Wrinkled/Smooth and Yellow/Green peas
21 Here is a heterozygous tall, heterozygous purple plant: B. Dihybrid Cross:two traits being crossed at the same timeHere is a heterozygous tall, heterozygous purple plant:T t P p
22 TP Tp tP tp F O I L First Outer Inner Last How can we figure out the alleles present in the gametes?F O I LFirst Outer Inner LastUsing F.O.I.L., list the possible gametes:TP Tp tP tp
23 Tall and Purple are dominant to short and white. Example: Cross two heterozygous tall,heterozygous purple pea plants.T t P p x T t P pThere are four possible gametes each parent can make..
33 1. Example of Codominant Problem Red feathers are codominant to white feathers in chickens.CR= redCW= whiteCross a homozygous Red with a homozygous white feathered chicken.CRCRGENOTYPE:100%CWCRCWCRCWCRCWPHENOTYPE:100%Red and white mixed feathersCWCRCWCRCW
34 C. Multiple Alleles One trait, many allele options! But remember: an individual cannot inherit more than two actual alleles, even if more than two possible alleles exist.Example: Blood typeA, B, AB, O!
35 Blood Type Problem I IA IA IB IA IB IA i i Cross a homozygous Type A with a heterozygous Type B. What are the possible phenotypes of offspring?IAIAIBIAIBPhenotypes:50% Type AB50% Type AIAii
36 Blood Type Problem II i IA IB IA IB IB i IA i i i i Cross a heterozygous Type A man with a heterozygous Type B woman. Is it possible for them to have an O child?iIAPhenotypes:25% Type AB25% Type A25% Type B25% Type OIBIAIBIBiIAiiii
37 Blood Type Problem III Rh- Rh+ Rh- Rh+ Rh- Rh- Rh- Rh+ Rh- Rh- Rh- Rh- Cross a heterozygous Rh+ man with a Rh- woman. What are the possible phenotypes of offspring?Rh-Rh+Phenotypes:50% Type +50% Type -Rh-Rh+Rh-Rh-Rh-Rh+Rh-Rh-Rh-Rh-
38 Rabbits have 4 basic colors (alleles!) brownchinchilla or greyIt is recessive to brown.himalayan or white with black tips.It is recessive to both brown and chinchilla.albinoIt is recessive to all.
40 D. Polygenic Traits Traits produced by many genes with many alleles Most human traits are polygenicMost variety of expressionThere are 3 genes that contribute to skin color.. And many alleles for each gene!
42 More examples:HeightWeightIntelligenceEye color
43 V. Sex DeterminationIn humans, the X and Y chromosomes control the sex of offspring.Outcome is always 50% chance of a male, and 50% chance of a female
44 Sex-linked traits XR XR Xr y Traits controlled by genes on the sex chromosomes are called sex-linked.Alleles for sex-linked traits are written as superscripts on the X chromosomes only.Example: Red eyes in fruit flies found in femalesMales tend to have white eyes, which is recessive.XRXRXry
45 X and Y sex chromosomes are non-homologous Any allele on the X chromosome will NOT be masked by a matching allele on the Y chromosome.
46 Why are sex-linked disorders more common in males than in females? Males have just one X chromosome containing an allele. So all X-linked alleles are automatically expressed in males, even if they are recessive.
47 C. Examples of Sex-Linked Color blindnessDuchenne Muscular DystrophyHemophilia
48 Frank and Awilda at Breakfast Frank: Are you sure you want to wear that new shirt to work today? A green and red shirt like that would be better for Christmas, not for St. Patrick's Day.Awilda: Oh no! Not again! I hate being color blind! I really thought this shirt was just different shades of green. Where's the red?At Dinner That NightAwilda: We should try to find a way to make sure we only have sons, no daughters. I don't want to have any daughters who might be color blind and have so many problems like I do. Color blindness wouldn't matter so much for a boy.
49 Frank: Remember, the doctor said that, since I'm not color blind, none of our daughters would be color blind, only our sons.Awilda: That doesn't make any sense. Our daughters should be color blind like me and our sons should be normal like you.Frank: No, the doctor said the gene for color blindness is on the X chromosome, so only our sons will inherit your colorblindness.Awilda: I don't agree. Girls have more X chromosomes than boys, so girls should be more likely to be color blind.
50 Help Frank to explain to Awilda why the doctor was right by answering the following questions. 1. What are the genotypes of Awilda and Frank? (Since the allele for color blindness is recessive and located on the X chromosome, use the symbol Xc for an X chromosome with the allele for color blindness and XC for an X chromosome with the normal allele.)Awilda: Frank:Xc XcXC y
51 X X X XC Xc XC Xc Xc y Xc y y C = normal vision c = colorblind 2. Draw the Punnett square for this couple and their children. In this Punnett Square, circle each daughter and use arrows to indicate any colorblind offspring.ccXXCXXC XcXC XcXc yXc yyC = normal visionc = colorblind
52 3. Write an explanation to help Awilda understand why their daughters will not be colorblind like their mother. 4. Explain why their sons will be colorblind even though their father has normal vision. 5. Explain why having two X chromosomes decreases a person’s risk of color blindness, instead of increasing their risk, as Awilda fears.
53 Practice ProblemsHemophilia is an X-linked recessive disease. Cross a heterozygous female with a normal male.Duchenne Muscular Dystrophy is an X-linked recessive disease. Cross a heterozygous female with a normal male.
55 D. Sex-Limited TraitsA few traits are not caused by genes on the X or the Y chromosome but still occur in only one sex of animalsExamplesAntlers in deer- only bucks have antlersMilk yield in bovines is a trait expressedby only cows (females)Eggs in chickens
56 E. Sex-InfluencedSome traits are sex-influenced because of genes that interact with a substance (like hormones) that is not produced equally in males and femalesExample: early pattern baldness
57 Baldness Sample Problem Baldness is a dominant trait. Heterozygous men are bald, BUT heterozygous women have all hair.Cross a Heterozygous woman with a normal hair male. Bb x bbGenotype - PhenotypeIf all girls?If all boys?BbB bbb bbB bb b
59 Down Syndrome Symptoms: learning difficulties, mental retardation, a characteristic facial appearance, and poor muscle toneDetection/Frequency?1 in 1000 live born infantsMode of Inheritance/ChromosomeChromosome 21, nondisjunctionTreatmentPhysical therapy for muscle weakness, heart is checked regularly for problems, educational therapyPrognosisMay have shortened life span
61 Marfan Syndrome Symptoms: Myopia, retinal detachment, bone overgrowth and loose joints, may have long thin arms and legs, bent chest inwards or outwardsDetection/Frequency?occurring 1 in 10,000 to 20,000 individualsMode of Inheritance/ChromosomeAutosomal dominant, Chromosome 15TreatmentSurgery to correct skeletal problems, sight issues fixed with glasses, must avoid contact sports
87 Phenylketonuria (PKU) Symptoms:causes increase of phenylalanine in blood - results in mental retardation, heart problems, small head size (microcephaly) and developmental delayDetection/Frequency?1 in 10,000 to 1 in 15,000 newborn babiesMode of Inheritance/ChromosomeTreatmentLimiting dietary intake of phenylalaninePrognosis
95 11.5 Linkage & Gene Maps Thomas Hunt Morgan, 1910 Research fruit fliesFound 50+ Drosophilia genesMany of them “linked” togetherAll the genes from one group were inherited togetherChromosomes assort independently, not the genes
97 How did Mendel miss this linkage? By pure luck, the 6 genes he looked at were on different chromosomesGene MapsCrossing-over sometimes separates genes on the same chromosomes onto homologous chromosomes.Occasionally separate and exchange linked genes and produce new combinations
98 The farther apart two genes are, the more likely they are to be separated by a crossover in meiosis. Alfred Sturtevant created a gene map showing the locations of each known gene on one of the Drosophila chromosomes