Presentation on theme: "BIOL 160 Genetics Terms Gene = a section of DNA (on a chromosome) that codes for a specific trait Alleles = alternate forms of a gene Where are the alleles."— Presentation transcript:
1BIOL 160Genetics TermsGene = a section of DNA (on a chromosome) that codes for a specific traitAlleles = alternate forms of a geneWhere are the alleles of a gene located?How many alleles can a person inherit for any one trait?How many alleles are there in a population for a particular trait such as hair color?
2Genetic terms, continued… BIOL 160Genetic terms, continued…Dominant allele =Homozygous dominant =Heterozygous =Homozygous recessive = aaRecessive trait is expressedGenotype = particular alleles a person carries: AaBBccDdPhenotype = an individual’s observable traits (hair color, eye color, height,….
7True-breeding plants (homo-zygous) BIOL 160True-breeding plants (homo-zygous)Fig 9.6bAll plants had purple flowers, all heterozygous
8Monohybrid cross: Pp x Pp BIOL 160Monohybrid cross:Pp x PpPunnett square predicts a phenotypic ratio of 3:1 for the F2 Generation
9Mendel’s Principle of Segregation BIOL 160Mendel’s Principle of SegregationFormation of gametes from a pre-gamete cellGenotype of Pre-gamete cell:meiosisGenotype of Gametes:AaAa
10The Chromosomal Basis of Mendel’s Principle of Segregation: BIOL 160The Chromosomal Basis of Mendel’s Principle of Segregation:
11Pea shape gene Round allele (R) Wrinkled allele (r) Seed color gene BIOL 160Pea shape geneRound allele (R)Wrinkled allele (r)Seed color geneYellow allele (Y)Green allele (y)NucleusMendel’s Second question: how do 2 pairs of genes (on different chromosomes) assort into gametes?–
14Mendel’s principle of independent assortment BIOL 160Mendel’s principle of independent assortment=
15R r r R y Y y Y r R r R Y y y Y RY ry Ry rY (figure not in book) BIOL 160(figure not in book)RrrRyYyYrRrRYyyYRYryRyrY
16Laws of Probability—application to inheritance BIOL 160Laws of Probability—application to inheritanceThe results of one trial of a chance event do not affect the results of later trials of that same chance eventE.g. Tossing of a coin, gender of children, etc.
17Laws of Probability—application to inheritance BIOL 160Laws of Probability—application to inheritanceThe Multiplication Rule:What are the chances of a couple having 4 girls?E.g. What are the chances of a couple having a boy with the following characteristics:Brown hair (3/4), Non-tongue roller (1/4), Blue eyes (1/4), Attached earlobes (1/4)
18How to Solve Genetics Problems BIOL 160How to Solve Genetics ProblemsSample Problem: Mom and dad are heterozygous for tongue rolling where tongue rolling is dominant to non-rolling. What is the chance that the couple will produce a child that is a non-roller?
19Select a letter to represent the gene involved: BIOL 160Use the following steps as a general guide to solve this and other problems:Select a letter to represent the gene involved:Write the genotypes of the parents.Determine all possible gametes for each parent.
20BIOL 1604. Make a Punnett square to represent all possible gamete combinations between the two parents and determine the genotypes of the offspring.5. Use the genotypes found in the Punnett Square to determine the possible phenotypes of the offspring to answer the question.
21Types of genetics problems: Monohybrid Cross BIOL 160Types of genetics problems: Monohybrid CrossSample problem: A true breeding black mouse was crossed with a true breeding brown mouse to produce the F1 generation, below. The F1 generation was then inbred to produce an F2 generation.a.) Which allele is dominant? How do you know?b.) Determine the genotypes and phenotypes for all 3 generationsc.) Predict the genotypic and phenotypic ratios for the F2
23Monohybrid Cross Sample Problem #2 BIOL 160Monohybrid Cross Sample Problem #2A mouse with black fur was crossed with a mouse with brown fur to produce the F1 generation, below. The F1 generation was then inbred to produce the F2 generation. Dominance is the same as in sample problem #2.a.) Determine the genotypes and phenotypes for all 3 generationsb.) Predict the genotypic and phenotypic ratios for the F2.
25Monohybrid Cross Sample Problem #3 BIOL 160Monohybrid Cross Sample Problem #3A couple, Jack and Jill, is concerned about having a child with cystic fibrosis. Although both of Jack’s and both of Jill’s parents are healthy and show no signs of cystic fibrosis, both Jack and Jill each had a sister die of the disease. The couple went to a clinic to be genetically tested for cystic fibrosis and were each found to be heterozygous for cystic fibrosis. What are the chances of Jack and Jill having a….a.) phenotypically healthy child?b.) child that is homozygous dominant? Heterozygous? Homozygous recessive?c.) girl with cystic fibrosis? Boy with cystic fibrosis?
27Types of Genetics Problems: Dihybrid Cross BIOL 160Dihybrid Cross Sample Problem #1: True breeding parental pea plants were crossed to produce the F1 generation, below. The F1 generation was inbred to produce an F2 generation.a.) Which alleles are dominant? How do you know?b.) Determine the genotypes and phenotypes for all 3 generationsP: Long & purple flowered pea plant x Short & white flowered pea plantF1: All Long & Purple Flowered pea plantsF2: Long & Purple : 3 Long & White : 3 Short & Purple : 1 Short & White
28Genotype ratio for F2: 1/16 = YYRR 2/16 = YYRr 2/16 = YyRR 4/16 = YyRr BIOL 160Genotype ratio for F2:1/16 = YYRR2/16 = YYRr2/16 = YyRR4/16 = YyRr1/16 = YYrr2/16 = Yyrr1/16 = yyRR2/16 = yyRr1/16 = yyrr
29BIOL 160ExampleFrom the crosses below, what are the chances of producing an organism with alldominant phenotypes?recessive phenotypes?homozygous dominant genotypes?AaBb x AaBbAaBbCc x AaBbCcAaBBCc x aabbcc
30How to use the probability method BIOL 160How to use the probability methodTreat the problem as if it consisted of several monohybrid crossesDetermine the gametes for each of these monohybrid crossesMake a Punnett square for each of the monohybrid crossesUse the information from each Punnett square and the “multiplication rule” to solve the problem
31Non-Mendelian Inheritance BIOL 160Non-Mendelian InheritanceSometimes there are more than 2 alleles in a population
321. Codominance Both alleles expressed together as heterozygotes BIOL 1601. CodominanceBoth alleles expressed together as heterozygotes
33Codominance: Blood Types BIOL 160Codominance: Blood TypesBlood Type(Phenotype)Surface Molecule on R.B.C.Possible GenotypesAIAIA or IAiBIBIB or IBiABIAIBOiiAllelesIA = Allele for Type AIB = Allele for Type Bi = Allele for Type OWhat do these alleles code for? Different carbohydrate “markers” on the RBCs
34Blood Types: Sample Problem #1 BIOL 160Blood Types: Sample Problem #1A couple has the type A and Type B, respectively. Is it possible for them to have a child with the following blood types?Type OType AType BType AB
35Blood Types: Sample Problem #2 BIOL 160Blood Types: Sample Problem #2A couple has the type A and Type AB, respectively. Is it possible for them to have a child with the following blood types? If so, what is the genotype of each parent?Type OType AType BType AB
36Rhesus Factor—a RBC surface molecule BIOL 160Rhesus Factor—a RBC surface moleculeRh factor is inherited independently from the ABO systemRh positive people:Rh Negative people:AllelesR = Rh factor is presentr = no Rh factor presentPhenotypePossible GenotypesRh +(Rh positive)Rh-(Rh negative)
37Blood Types: Sample Problem #3 BIOL 160Blood Types: Sample Problem #3A couple has the type A+ (heterozygous) and Type AB+, respectively. What are the chances of the couple having a child with the following phenotypes? Both parents are heterozygous for the rhesus factor.Type O b. Type O-c. Type A+ d. Type A-e. Type B+ f. Type B-g. Type AB+ h. Type AB-
382. Incomplete dominance One allele isn’t fully dominant over the other BIOL 1602. Incomplete dominanceOne allele isn’t fully dominant over the other
403. Continuous variation in a population BIOL 1603. Continuous variation in a populationIndividuals in a population show a range of small differences in a certain traitEx.Causes:1.2. Multiple environmental factors affect gene expression.
422. Environmental influence on gene expression: Ex. BIOL 1602. Environmental influence on gene expression:Ex.
43Human Genetics Three types of disorders: Autosomal recessive – BIOL 160Human GeneticsThree types of disorders:Autosomal recessive –Autosomal dominant :AA – embryo diesAa – is afflictedaa – normal individualEx. DwarfismVary rare
443. Sex-linked recessive inheritance BIOL 1603. Sex-linked recessive inheritanceRecessive on X-chromosomee.g.Males usually get the disorder more than females – why?Son cannot inherit a recessive allele from his father but a daughter can. Why?
45Human Sex Chromosomes Sex chromosomes in humans Female Genotype = BIOL 160Human Sex ChromosomesSex chromosomes in humansFemale Genotype =Male Genotype =Sex-linked Alleles are carried on the X-chromosomeY-chromosomeSRY gene on Y chromosome stimulates gonads to differentiate into male sex organs.SRY = Sex-determining Region, Y-chromosome
46Gender Determination in Humans BIOL 160ParentsFemaleMaleGender Determination in HumansChromosomessegregate inmeiosisSpermOffspringEggsTwodaughtersTwosons
47BIOL 160Sample ProblemMary’s paternal and maternal grandfathers are both colorblind. There is no evidence of colorblindness in either grandmother’s family histories, and Mary’s father is not colorblinda. What is Mary’s genotype? Phenotype?b. What are the chances that Mary’s brother is colorblind?