3.4 & 10.2 Inheritance Topics 3 & 10 Genetics. 1 – Understanding Genes Read & Consider Understandings 3.4.1-3.4.4 & 10.2.1-10.2.4 How many alleles of.

3.4 & 10.2 Inheritance Topics 3 & 10 Genetics 1 Understanding Genes Read & Consider Understandings & How many alleles of each gene does offspring receive? Where do the alleles come from? Key Terms Genotype the alleles (genes) Phenotype the characteristics of an organism Dominant allele the allele that will be expressed Recessive allele expressed if inherited from both parents Codominant allele alleles that will both have an equal effect on phenotype Locus the particular location of a gene on a chromosome Homozygous identical alleles were inherited from both parents Heterozygous different alleles were inherited from each parent Carrier an individual that has a recessive allele for some trait but is not expressing it, though it could be passed on. Test cross testing a suspected heterozygote by crossing it with a known homozygous recessive. Allele Source The two alleles for each gene separate into different gametes during meiosis. Gametes are haploid and contain only one allele for each gene they contribute. Things to remember Fertilization is a random process with each allele from one parent having an equal chance of fertilizing any other gamete of the other parent. One allele for the offspring comes from each parent. One allele will be dominant over the alternative factor. Allele Loci The genes carried on a particular chromosome are called a linkage group. Chromosomes of a linkage group will tend to be inherited together, barring crossing over of an allele. Unlinked genes segregate independently during meiosis Mendels Study Gregor Mendel discovered the principles of inheritance by carefully observing and recording hundreds of crosses between pea plants. Polygenic Traits All of Mendels observed traits were controlled by one gene so had discrete variation. Polygenic traits are controlled by multiple genes, so have continuous outcomes when observing phenotype. 2 Punnett Squares & Pedigrees Read & Consider Understandings Describe dominant and recessive allele behavior. Monohybrid Cross T = tall; t = dwarf Parent 1: genotype Tt; phenotype Tall Parent 2: genotype Tt; phenotype Tall Tt T t Genotypes Genotype Ratios Phenotype Phenotype Ratios Dihybrid Cross Dihybrid cross the simultaneous inheritance of two pairs of contrasting characteristics, each characteristic is inherited independently. Example: pea plants R = round; r = wrinkled Y = yellow; y = green Parent 1 = RRYY; Parent 2 = rryy RY ryRrYy ryRrYy ryRrYy ryRrYy Generation #2 Phenotypes Phenotype ratio Genotypes RYRyrYry RY Ry rY ry Co-Dominance Both alleles are expressed equally and simultaneously. represented by one capital letter to represent the gene locus and additional letters, as superscripts, to represent the co- dominant alleles F R F R = red; F W F W = white; F R F W = pink FRFR FWFW FRFR FWFW Genotypes Genotype Ratios Phenotype Phenotype Ratios Multiple Alleles Multiple alleles most genes have more than two trait possibilities. One capital letter represents the gene. Individual alleles are represented by letters as superscripts. Multiple alleles & Co-dominance Human blood belongs to one of four groups: A, B, AB, or O. Parent 1 = heterozygous A (I A I i ) Parent 2 = heterozygous B (I B I i ) Phenotype O A B AB Genotype I i I A I A or I A I i I B I B or I B I i I A I B IAIA IiIi IBIB IiIi Genotypes Genotype Ratios Phenotype Phenotype Ratios Sex Chromosomes XX X Y Genotypes Genotype Ratios Phenotype Phenotype Ratios Sex Linkage Sex linkage is a special case of linkage occurring when a gene is located on a sex chromosome (usually X) and is therefore inherited with the sex of the individual. Most are carried on the X chromosome. Sex-Linked Disease X B = normal vision; X b = color blind X H = normal clotting; X h = hemophilia Color BlindnessHemophilia Female X B X B = normal X B X b = carrier X b X b = severely colorblind X H X H = normal X H X h = carrier X h X h = hemophiliac (fatal) MaleY B Y = normal X b Y = color blind X H Y = normal X h Y = hemophiliac Create Punnett grids to determine the genotype / phenotype frequencies for a female carrier and a normal male. Repeat this for each disease. Predict the genotypic and phenotypic ratios of offspring crosses of the above patterns. Complete the practice worksheet of genetic crosses. Autosomal Genetic Disease Most often a recessive trait that impacts a single gene allele. There are more than 6000 known diseases caused by single gene mutations and pass throughout families. Cystic Fibrosis (Recessive) Huntingtons Disease (Dominant) Pedigree Chart Circles are female, squares are males Filled in shapes indicate that the individual is affected by the condition Empty shapes indicates that the individual has an unaffected phenotype Mating is indicated by a horizontal line from male to female Offspring branch vertically from the mating parents. For the following pedigree, affected individuals are homozygous for a recessive allele. Deduce the genotypes of all individuals in the pedigree. Dominant = D; Recessive = d Crossing Over Crossing over is a process by which a section of DNA is exchanged between homologous pair through the formation of chiasmata. Linked Genes G = normal body color; g = ebony body color S = straight wings; s = curled wings Parent 1:gs gs Parent 2:GS gs g s G S g s Recombinants Using the example from there are also some recombination possibilities: Gs GS These may be made as additions to the table or considered separately as they are possibilities that may occur for linked genes during meiosis. Normal body; curled wings Ebony body; straight wings, respectively. Polygenic Inheritance Discontinuous variation Polygenes Polygenic inheritance Continuous Variation Parent 1: AaBbParent 2: AaBb R = red; r = white Parent 1: RrRrRrParent 2: RrRrRr ABAbaBab ABAABBAABbAaBBAaBb AbAABbAAbbAaBbAabb aBAaBBAaBbaaBBaaBb abAaBbAabbaaBbaabb Polygenic Outcomes - 3 - Significance Read & Consider Understandings & What could cause observed genotypes to differ greatly from the expected outcome? Mutation Rates Mutations are spontaneous permanent changes to base sequences that can occur at any time in an organism. Some environmental factors increase the number and frequency of mutation. Chi-Square Test See totals for the following crosses from your notes. Use the following observed outcomes to determine if there is a significant difference from what is expected. Monohybrid Cross Tall: 180, Dwarf: 50 Dihybrid Cross round/yellow: 213, round/green:78, wrinkled/yellow: 70, wrinkled/green: 39 Linked Gene normal body/curled wings: 61, ebony body/straight wings 49 NOTE: parent 1 = normal body/straight wind, parent 2 = ebony body/curled wings Works Cited Diaz, Hortensia Jimenez. "How Mendel's Pea Plants Helped Us Understand Genetics." YouTube. TED-Ed, 12 Mar Web. 15 Aug "Drosophilab - A Free Genetics Simulator." Drosophilab. N.p., n.d. Web. 17 Aug Walpole, Brenda. Biology Guide - First Assessment International Baccalaureate Diploma Program. N.p., Dec Web. Dec "What Are Dominant and Recessive Alleles?" Your Genome. N.p., n.d. Web. 15 Aug