copyright cmassengale Mendelian Genetics 5/21/2018 Mendel’s Laws copyright cmassengale

Results of Monohybrid Crosses Mendelian Genetics 5/21/2018 Results of Monohybrid Crosses 1. Inheritable factors or genes are responsible for all heritable characteristics 2. Phenotype is based on Genotype 3. Each trait is based on two genes, one from the mother and the other from the father. 4. True-breeding individuals are homozygous ( both alleles) are the same. copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds) copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Law of Dominance copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale

Applying the Law of Segregation Mendelian Genetics 5/21/2018 Applying the Law of Segregation copyright cmassengale

Law of Independent Assortment Mendelian Genetics 5/21/2018 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses. copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes) copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Question: How many gametes will be produced for the following allele arrangements? Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtQq copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Dihybrid Cross RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Test Cross A mating between an individual of unknown genotype and a homozygous recessive individual. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bC b___ bc copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Test Cross Possible results: bC b___ bc bbCc C bC b___ bc bbCc bbcc or c copyright cmassengale

Summary of Mendel’s laws Mendelian Genetics 5/21/2018 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Incomplete Dominance F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower r R copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Incomplete Dominance r R r All Rr = pink (heterozygous pink) produces the F1 generation Rr copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Incomplete Dominance copyright cmassengale

Codominance When both alleles contribute to the phenotype of an organism Ex. Speckled Chickens

copyright cmassengale Mendelian Genetics 5/21/2018 Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type 1. type A = IAIA or IAi 2. type B = IBIB or IBi 3. type AB = IAIB 4. type O = ii copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Codominance Problem Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IB IA i IAIB IBi 1/2 = IAIB 1/2 = IBi copyright cmassengale

Another Codominance Problem Mendelian Genetics 5/21/2018 Another Codominance Problem Example: male Type O (ii) x female type AB (IAIB) i IA IB IAi IBi 1/2 = IAi 1/2 = IBi copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (IAIB) copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale

Human Blood Types Phenotype Genotype A B AB O IAIA or IAi IBIB or IBi IAIB ii

Question A man is suing his wife on grounds of infidelity. The man claims that the child is blood type O and therefore must be fathered by someone else. Can he use this evidence in court if he and his wife both have heterozygous B genotypes? Show the cross of the two parents

Know that : Human hair is inherited by incomplete dominance. Human hair may be curly (CC) or straight (cc). The heterozygous genotype (Cc) produces wavy hair. Show a cross between two parents with wavy hair

Curly Hair

Early geneticists reported that curly hair was dominant and strait hair was recessive. More recent scientists believe that more than one gene may be involved.

Polygenic Traits Traits controlled by two or more genes Ex.) eye color, skin color

copyright cmassengale Mendelian Genetics 5/21/2018 Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes XX chromosome - female Xy chromosome - male fruit fly eye color copyright cmassengale

Sex-linked Trait Problem Mendelian Genetics Sex-linked Trait Problem 5/21/2018 Example: Eye color in fruit flies (red-eyes male) x (white-eyes female) XRY x XrXr Remember: the Y chromosome in males does not carry traits. RR = red eyes Rr = red eyes rr = white eyes XY = male XX = female XR Xr Y copyright cmassengale

Sex-linked Trait Solution: Mendelian Genetics 5/21/2018 Sex-linked Trait Solution: XR Xr Y 50% red eyes female 50% white eyes male XR Xr Xr Y copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Female Carriers copyright cmassengale

Genetic Practice Problems Breed the P1 generation Mendelian Genetics 5/21/2018 Genetic Practice Problems Breed the P1 generation tall (TT) x dwarf (tt) pea plants t T copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Solution: tall (TT) vs. dwarf (tt) pea plants T t All Tt = tall (heterozygous tall) produces the F1 generation Tt copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Breed the F1 generation tall (Tt) vs. tall (Tt) pea plants T t T t copyright cmassengale

copyright cmassengale Mendelian Genetics 5/21/2018 Solution: tall (Tt) x tall (Tt) pea plants T t produces the F2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype TT Tt tt copyright cmassengale

Genetics and the Environment The characteristics of any organism, is not only determined by the genes it inherits Characteristics are determined by interactions between genes and the environment Ex. genes may affect a plants height but the same characteristic is influenced by climate, soil conditions and availability of water.

END