Presentation on theme: "Mendel and the Gene Idea"— Presentation transcript:
1 Mendel and the Gene Idea CHAPTER 14Mendel and the Gene Idea
2 Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes.Mendel was able to describe a model of inheritance of traits, and his work represents an application of mathematical reasoning to a biological problem.However, most traits result from interactions of many genes and do not follow Mendelian patterns of inheritance (ex. hair color, eye color.)Understanding the genetic basis of specific phenotypes (physical outcomes due to proteins assembled) and their transmission in humans can raise social and ethical issues.
3 What is INHERITANCE?The study of how genesand traits are passed from generation to generation.
4 Genetic information provides for continuity of life and, in most cases, this information is passed from parent to offspring via DNA.Review meiosis w/ your partner. 1. What are the 3 sources of genetic variation for sexually reproducing organisms? 2. Why is it beneficial to be a “diploid” organism?
5 1) Crossing over makes recombinant chromosomes that are unique. Independent assortment makes new combinations of chromosomes (one of each kind) in the gametes by “shuffling” the pairs of chromosomes.Fertilization joins gametes from two separate gene lineages (hopefully) to make a diploid zygote with new gene pairs.2) Gene pairs = “back up copy” in case one gene is mutated/nonfunctional.
6 GREGOR MENDEL:The “father of genetics”Austrian MonkFirst to explain patterns ofinheritance.Analyzed sweet pea plantsover 12 years.
7 Figure 14.x2 Round and wrinkled peas Characteristic comesin 2 contrasting traits:Ex. PEA SHAPERoundWrinkledEx. FLOWER COLORPurpleWhite
8 Mendel’s Experiments: Parent Generation (P generation):Pure for one of two contrasting traitsResult of many generations of self-pollinationChose two plants pure for the two contrasting traits for the characteristic flower color & crossed them.purple X white
9 Mendel’s Experimental RESULTS: (F1) First Generation :Offspring of parent generationAll F1 plants looked like only one of the parents (that was the dominant trait)The recessive trait “disappeared”Hybrid offspring
10 Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
11 Mendel’s 2nd Experiment: Mendel then crossed two F1 plants (“Ewww incest!” jk)(F2) Second Filial Generation :The traits from both parents reappear in these offspringMendel found the ratio of expression to be 3:1(3 dominant:1 recessive)* note, not EXACTLY 3:1
12 IMPORTANT CONCLUSIONS: If a characteristic exists in two contrasting forms one is dominant, one is recessive.Factors controlling traits occur in pairs.The dominant factor prevents the recessive factor from being expressed.Recessive factors are only expressed when both factors in the pair are recessive.When pea plants reproduce, a factor pair is segregated (split) and each factor ends up in a separate gamete. Mendel’s law of segregation.
13 In modern terms:Mendel’s factors are called genes. Some genes are dominant, others recessive.Different forms of a single gene are called alleles.Genes occur in pairs, at the same position on two chromosomes.The gene position is called the locus.
14 The two chromosomes that contain the same genes are called: homologous. When solving inheritance problems, use capital letters to represent dominant genes. TWhen solving inheritance problems, use lowercase letters to represent recessive genes. tIf both alleles in a gene pair are the same, we say the pair is: homozygous (dominant or recessive) TT, ttIf both alleles in a gene pair are different, we say the pair is: heterozygous. TtA genotype is the combination of genes an individual possesses. (for one trait shown w/ pair of letters) TTA phenotype is the appearance of an individual as the genes are being expressed & proteins are being made or not made.
16 The Punnett Square Used to solve inheritance problems Predicts the possible gene combinations inherited by the offspringFor example, a monohybrid cross: involves one character/trait.ex. Heterozygous X Heterozygous (on board)
17 Figure 14.8 Segregation of alleles and fertilization as chance events POSSIBLE GENE COMBINATIONS FOR OFFSPRING ARE A RESULT OF 3 CHANCE EVENTS:Segregation of alleles into eggsSegregation of alleles into spermFertilization of WHICH egg by WHICH sperm
18 Figure 14.4 Mendel’s law of segregation (Layer 2)
19 -> offspring phenotype If all dominant -> PP Figure A testcrossA test-cross: used to determine the genotype of an individual with a dominant phenotype…Not sure if they areHomo dom: PPOrHetero: Ppcross the individual in question with an individual with a recessive phenotype____ X homo rec-> offspring phenotypeIf all dominant -> PPIf ½ recessive -> Pp
20 For another example, a DIHYBRID cross: a two character/trait cross, with two gene pairs.ex. AaBb X AaBb(see board)
21 Attractive, Boring X Attractive, Boring Man WomanBoth are Heterozygous for both genes…AaBb X AaBbWhat gametes can each make?What are their chances of having:Attractive Boring kids? List the genotypes possible. #/16Attractive Exciting kids? List the genotypes possible. #/16Unattractive Boring kids? List the genotypes possible. #/16Unattractive Exciting kids? List the genotypes… #/16
22 Mendel’s Law of Independent Assortment states when the two gene pairs are located on non-homologous chromosomes they segregate independently of each other. Results = 4 possible gamete combinations. (use FOIL) first: AB outer: Ab inner: aB last: ab
23 Attractive, Boring X Attractive, Boring Man WomanBoth are Heterozygous for both genes…AaBb X AaBbWhat gametes can each make? AB, Ab, aB, abWhat are their chances of having:Attractive Boring kids? List the genotypes possible. #/16AABB, AaBB, AaBb, AABbAttractive Exciting kids? List the genotypes possible. #/16Aabb, AAbbUnattractive Boring kids? List the genotypes possible. #/16aaBB, aaBbUnattractive Exciting kids? List the genotypes… #/16aabb
26 AaBb X AaBb AABB AABb AaBB AaBb AAbb Aabb aaBB aaBb aabb AB aB ab Ab
27 AaBb X AaBb AABB AABb AaBB AaBb AAbb Aabb aaBB aaBb aabb AB aB ab Ab
28 Phenotype Ratio of dihybrid cross 9:3:3:19/16 Attractive, Boring3/16 Attractive, Exciting3/16 Unattractive, Boring1/16 Unattractive, Exciting
29 Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross
30 Now, it can’t be that easy & boring can it? No it can’t.
31 1)Incomplete Dominance: Both alleles are the same strength Heterozygous individuals…express BOTH alleles, The resulting phenotype is a mix (blend) of the two.3 phenotypes possible.For example: Carnation flower colorThe alleles are also written differently:AA’ or CR CWCRCR CR CW CWCW
32 2) Codominant Genes:In a heterozygous individual both alleles affect the phenotype in separate distinguishable ways.For example: Roan Horses have red (or black) and white hairsAnother example: A, B, and AB blood groups in humans.
33 3) Multiple Alleles: When more than 2 forms of the gene exist For example: Human Blood Types (ABO blood groups)Blood cells have a carbohydrate marker that is found on the surface of red blood cells.These markers are called: A substance or B substance.They are recognized by antibodies present in the blood serum of individuals for foreign carbohydrate markers.There are two types of RBC antibody: Anti-A & Anti-BThe genes for creating these antibodies are determined by the genes for creating the A or B substance.
34 Antigens on surface of RBC Write the possible genotypes for the blood types A, B, AB and OBlood TypeGenotypeAntigens on surface of RBCPlasma AntibodiesDonateReceiveABABO
35 A IA IA IAi B IB IB IBi AB IA IB O ii What are the actual antigens (surface molecules) found on the RBCs?Blood TypeGenotypeAntigensPlasma AntibodiesDonateReceiveAIA IAIAiBIB IBIBiABIA IBOii
36 A IA IA IAi B IB IB IBi AB IA IB O ii What kinds of antibodies does Blood Type A make? Who can he/sheDonate blood to? Receive it from?Blood TypeGenotypeAntigens on surfacePlasma AntibodiesDonateReceiveAIA IAIAiSubstance ABIB IBIBiSubstance BABIA IBSubstanceA and BOiinone
37 Substance on surface of RBC Fill in the rest… check your work. Which kind are you? Which kindWhich is called the “universal donor”? The “universal recipient?”Blood TypeGenotypeSubstance on surface of RBCPlasma AntibodiesDonateReceiveAIA IAIAiSubstance AAnti-BType A& AB& OBIB IBIBiSubstance BABIA IBOiinone
38 A IA IA IAi Anti-B Type A & AB & O B IB IB IBi Anti-A Type B AB IA IB Type AB is the universal recipient, Type O is the universal donor.Blood TypeGenotypeantigensPlasma AntibodiesDonateReceiveAIA IAIAiSubstance AAnti-BType A& AB& OBIB IBIBiSubstance BAnti-AType BABIA IBnoneTYPEA, B, AB & OOiiAll blood typesType O
39 Figure 14.10 Multiple alleles for the ABO blood groups
41 Remember, the IA & IB alleles are CODOMINANT. With human blood type, another marker called the Rh factor is denoted as + or -.So, type O -, is the worst to be in terms of getting a blood transfusion… but is the best donor.“universal donor”
42 Pleiotropy: One gene influences many traits. (i.e. disease genes)PKU (phenylketonuria). Mutation in a single gene that codes for an enzyme results in: mental retardation, reduced hair, and skin pigmentation.Enzyme phenylalanine hydroxylase converts the amino acid phenylalanine to tyrosine.Absence of the enzyme causes phenylalanine to accumulate in toxic levels.
43 Figure 14.15 Pleiotropic effects of the sickle-cell allele in a homozygote
44 2) Epistasis: When two genes control the expression of a single trait 2) Epistasis: When two genes control the expression of a single trait. One gene pair interferes with the expression of the other.Common for expression of pigmentFor example: Fur color in mice.Gene 1 = Fur color (B = Black fur, b = brown fur)Gene 2 = Depositing pigment in the hair(C = deposits color, c = deposits no color (albino))What is the phenotypic ratio that results from the cross a Black haired mouse, heterozygous both gene pairs and a Brown Haired mouse- heterozygous for gene 2?
46 3) Polygenic inheritance: When one phenotype is under the control of multiple gene pairs For example: Human Skin ColorAlleles are… Dark and lightAt least… three genes control the color of your skinThe phenotype is a result of… the cumulative effects of the dominant genesHuman skin color exists… as a gradient
47 Figure 14.12 A simplified model for polygenic inheritance of skin color
51 "temperature sensitive" or ts mutants Conditional mutants that grow at a low temperature but not at a high temperature are are called "temperature sensitive" or ts mutants.Conditional mutants are not necessarily associated with lethality.The dark ear tips, nose and feet of a Siamese cat are the phenotype of a temperature sensitive mutation in the c locus (determining fur color).The enzyme encoded is not functional at higher temperatures, but is functional at lower temperatures, such as the extremities of the cat.Hence the fur on these parts of the Siamese cat’s body is pigmented.
53 PEDIGREE PROJECT (Complete over Thanksgiving) 3 generationsExamples of TRUE mendelian traits (show dominance)WET EARWAX vs. dry earwax (recessive)PIGMENT vs. AlbinismRecessive: magenta urine after eating beats
54 PedigreeAn analysis of the results of mating that have already occurred- especially when studying a species with a long generation time.As much information as possible is collected about a family’s history for a particular trait.Information is assembled into a family tree describing the interrelationships across the generations.Helps us understand the past and predict the future.
55 For those traits exhibiting dominant gene action: affected individuals have at least one affected parentthe phenotype generally appears every generationtwo unaffected parents only have unaffected offspringAnd for those traits exhibiting recessive gene action:unaffected parents can have affected offspringaffected progeny are both male and female
56 Figure 14.16 Large families provide excellent case studies of human genetics
57 Figure 14.17 Testing a fetus for genetic disorders