Mendelian Genetics Regular Biology Waggy

The Father of Genetics… Gregor Mendel, 1850 Austrian monk who was in charge of the monestary garden He noticed that each generation of pea plants looked like the parent generation, but with some differences

He collected pea seeds from each crop & carefully recorded the plants characteristics He called these characteristics: traits He began by testing for individual traits like height or flower color

For instance, he crossed a plant with white flowers with a plant with purple flowers These is the parental generation (P1) He found that in the first offspring generation, all the plants had purple flowers This generation is called the filial generation (F1) When one trait hides another the stronger trait is called: dominant The hidden trait is called the recessive trait

When he crossed two flowers from the F1 generation, the white flowers reappeared at a ratio of 3 purple to 1 white (3 : 1) This final generation is called F2 Mendel concluded that the paired factors separate during the formation of gametes And that each parent plant contributed one of the genes to the offspring He called this the Law of Segregation

Next, he crossed two traits He found that the dominant traits did not always appear together This means that not only do the paired genes separate during meiosis but they also rearrange He called this the Law of Independent Assortment

Modern Genetics Mendels work was unfortunately lost It was rediscovered in 1900 Barbara McClintock picked up where Mendel left off She worked with corn plants & discovered that genes did not have to stay in the same place on the chromosome

This added to the variability of the offspring This is called jumping genes or transposons

Genetic Crosses Genotype: an organisms genetic makeup (represented by a letter) Phenotype: an organisms physical appearance (represented by a word) Purple flower is represented by P (purple=phenotype & P=genotype) White flower is represented by p (white=phenotype & p = genotype) PP = ________ Pp = ________ pp = ________

Homozygous vs. Heterozygous When BOTH alleles are the SAME it is a homozygous trait (PP, pp) When the alleles are DIFFERENT it is a heterozygous trait (Pp)

Probability Probability is the likelihood that a specific event will occur It can be expressed as a decimal, percentage, fraction or ratio Use this simple formula: # of times an event is expected to occur total number of times could happen

In Mendel’s experiments, the dominant yellow seed color appeared 6,022 times The recessive green seed color appeared 2,001 times Calculate the probability of the seed being green: 2,001 = .25 (or 1/4 or 1:4 or 25% ) 8,023

Calculate the probability of the seed being yellow: 6,022 = .75 (or 75%, 3/4, 3:4) 8,023 Practice!

Monohybrid Cross A cross between two organisms that tracks only ONE trait is a monohybrid cross Scientists use Punnett squares to track these traits P=purple p =white p p P P

100% What is the probability that the offsprings genotype will be Tt? 4 = 1 (100%, 4/4, 4 4:4) T T t t

50% What is the probability that the offspring will be homozygous? 2 = .5 (50%, 2:4, 4 1/2) B b b b

-genotypes of the parents? -phenotypes of the parents? What are the -genotypes of the parents? -phenotypes of the parents? -probability of homoygous offspring? -probability of heterozygous offspring? -the phenotypes of the offspring? A a A a