I. Mendelian Genetics Unit IV: Genetics A. Gregor Mendel: Austrian monk who studied inheritance patterns in pea plants. “The Father of Genetics”

1. Terms added to Mendel’s conclusions in retrospect. He did not know the molecular side to genetics. Genes – Alleles – the factors that determine traits different forms of a gene A. Introduction:

2. Probability and Genetics a) Punnett Squares: used to predict the potential outcomes of genetic crosses. *Letters represent alleles: Uppercase = dominant Lowercase = recessive b) Important terms: Heterozygous: a “hybrid” genotype with different alleles for a gene. Ex. Tt Phenotype: displayed characteristics Genotype: genetic makeup Homozygous: a genotype with identical alleles for a particular gene. Ex. TT or tt

B. Mendel’s pea plants were “true-breeding” – reproduced by self- pollination. 1. He studied 7 different traits, each with 2 contrasting forms. Ex. 1) tall vs. short plants 2) green vs. yellow peas

Experiment #1: Mendel forced cross pollination between plants with contrasting traits. 1)P generation = 2)F 1 generation = Results: All offspring in the F 1 generation displayed only one of the contrasting traits. The characteristics did not blend. Original plants (parental) First generation offspring (first filial)

Parental cross: TT x tt TT t tTt Segregation of alleles into gametes (meiosis) Tt Recombination of alleles in offspring (fertilization) Probable Outcomes for F 1 Generation: Phenotype: 100% tall Genotype: 100% heterozygous dominant “hybrid” Nice.

Experiment #2: Mendel let the F 1 generation self-pollinate to produce F 2. Did the other traits disappear? Results: ¼ of the F 2 plants had the trait that had disappeared in the F 1 generation.

F 1 Generation cross: Tt x Tt T T t t TTTt ttTt Probable Outcomes for F 2 Generation: Phenotype: 75% tall; 25% short Genotype: 25% homozygous dominant 50% heterozygous dominant 25% homozygous recessive Ratio 1:2:1

Mendel’s Conclusions: 1.Biological inheritance is determined by factors passed from one generation to the next 2. Some “factors” are dominant and others are recessive *Dominant “factors” mask recessive ones

3. Mendel’s Experiment #3: Mendel performed a two factor cross to produce F 1 hybids a) RRYY x rryy  RrYy (round, yellow peas) (wrinkled, green peas) (round, yellow peas) R= round r = wrinkled Y= yellow y = green b)Dihybrid Cross: Mendel then crossed the F 1 generation to produce an F 2 He knew that the F1 genotype was RrYy Would the dominant alleles RY stay together? RrYy x RrYy

9:3:3:1

Mendel concluded that… *alleles for shape segregated independently from alleles for seed color. * Genes for shape and genes for color do not influence each other’s inheritance. I’ll have the peas and carrots. Hold the carrots.

*Test Cross Determining the unknown genotype of an organism by breeding it with a homozygous recessive organism. Example: Dominant PhenotypeRecessive Phenotypex PP or Pp ???pp (known) P = purple p = white If the unknown is PP then all offspring are hybrid purple If it’s Pp, then 50% purple, 50% white PP p p Pp Pp p p pp

E. Thomas Morgan * Studied inheritance in fruit flies 1) Gene Linkage Morgan noticed that many traits were almost always inherited together. Concluded that chromosomes, not genes, segregated independently during meiosis (1915). Linked Genes are located on the same chromosome and tend to be inherited together. *exception: crossing over I love fruit… OMG! Me too! I love fruit flies. and I love flies.

Independent Assortment Metaphase I Metaphase II: Gametes: 1/4 AB1/4 ab1/4 Ab1/4 aB AAAA AAAA AAAA BB BB BB BB BBBB aaaa aaaa aaaa bbbb bbbb bbbb OR

Gene Linkage

Crossover Frequency ABCD Crossing over will disrupt linkage between A and B more often than C and D

F. Beyond Dominant and Recessive Genes 1)Incomplete Dominance: one allele is not completely dominant over the other. Ex. Four o’clock plants- when a homozygous red flower is crossed with a homozygous white flower, the hybrid offspring are pink. What tiiiiime is it?!?! It’s 4 O’clock motha… CENSORED! Awwwww Yeah

2) Codominance: both alleles contribute to the phenotype. Ex. 1: Human Blood Type: When the alleles for type A blood and type B blood are combined, the offspring will have type AB blood. Ex. 2: Roan Cattle Coat

CRCR CRCR CWCW CWCW CRCWCRCW CRCWCRCW CRCWCRCW CRCWCRCW roan coat C R C W = roan coat C R C R X C W C W

CRCR CWCW CRCR CWCW CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW Red Red:White: Roan Roan: 25% 25% 50% C R C W X C R C W

3) Multiple Alleles: there are more than 2 alleles for a gene in a population’s gene pool. Ex. Human Blood Type: there are 3 alleles for human blood type: I A, I B, and i. *I A and I B, codominant to each other but dominant to i.

4) Polygenic Traits: certain phenotypes are controlled by several different genes. Ex. Human skin color & eye color: at least 3 genes are involved in each (per person).