Genetics and the Work of Gregor Mendel

Gregor Mendel Modern genetics began in the mid-1800’s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas Used experimental design Used mathematical analysis Collected and counted peas Scientific method

Where are genes located? On chromosomes! Remember chromosomes are made up of DNA located inside of the nucleus Every individual receives one copy of each gene from both parents

Mendel’s Work Bred pea plants Cross-pollinated Raised seed and then observed traits Allowed offspring to self-pollinate and observed next generation.

Mendel collected data for 7 traits

Generations… P1= parent generation F1= first generation after the parent generation F2 = second generation after the F1 generation (F1 hybrid is a term used in genetics and selective breeding. F1 stands for Filial 1, the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types.)

Mendel’s Peas in a “nutshell” P1 = TT (homozygous tall) x tt (homozygous short) Results= 100% Tt heterozygous tall plants (F1 generation) F2= Tt x Tt (he crossed two offspring from the F1 generation) Results= 25% TT, 50% Tt, 25% tt (F2 generation)

Law of Segregation When Mendel performed cross-pollination between a true-breeding yellow pod plant and a true-breeding green pod plant, he noticed that all of the resulting offspring, F1 generation, were green. He then allowed all of the green F1 plants to self-pollinate. He referred to these offspring as the F2 generation. Mendel noticed a 3:1 ratio in pod color. About 3/4 of the F2 plants had green pods and about 1/4 had yellow pods. From these experiments Mendel formulated what is now known as Mendel's law of segregation.

Law of Segregation Mendel's law of segregation states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. t T Sperm The resulting union would be Tt. Egg

Law of Segregation – four main ideas… There are alternative forms for genes. For each characteristic or trait organisms inherit two alternative forms of that gene, one from each parent. These alternative forms of a gene are called alleles. (such as T = tall, t= short) When gametes (sex cells) are produced, allele pairs separate or segregate leaving them with a single allele for each trait. When the two alleles of a pair are different, one is dominant and the other is recessive.

Law of Segregation From Mendel's law of segregation we see that the alleles for a trait separate when gametes are formed (through a type of cell division called meiosis). These allele pairs are then randomly united at fertilization. Traits come in these combinations: Homozygous= both letters are the SAME (TT, tt) Heterozygous = there is both a capital and lower case letter in the pair (Tt)

Genotype vs. phenotype Difference between how an organism “looks” and its genes Phenotype – what the organism looks like Genotype – genetic makeup of the organism Explain cross using Mendel’s idea of ….Dominant and recessive ….Phenotype and genotype

What did Mendel’s Findings mean? Some traits mask others Purple & white flowers are separate traits that do not blend Purple x white ≠ light purple Dominant allele – LAW OF DOMINANCE Functional protein that masks another gene Affects the characteristic Recessive allele Not noticable effect Allele makes a non-functioning protein

Warm UP Cross a homozygous white flower with heterozygous white flower. What is the probability of getting a purple flower?

Making Crosses Pp Alleles are represented as letters flower color alleles P (dominant) or p (recessive) True breeding purple flowers = PP True breeding white flowers = pp PP x pp Pp

Mendel’s system is just TOO easy! Peas are genetically simple Most traits are controlled by a single gene Each gene only has 2 versions 1 completely dominant 1 recessive

Many genes, one trait Polygenic inheritance Additive effects of many genes Humans Skin color Height Weight Eye color Intelligence behaviors

Independent Assortment When more than one gene passes from generation to generation, each gene separates independently of the other Produces two factor crosses Yellow round peas x Green wrinkled peas RRYY x rryy

Human Skin Color AaBbCc x AaBbCc Can produce a wide range of shades Most children = intermediate skin color Some can be very light, some can be very dark

Human Skin Color

Two Factor cross = dyhibrid cross

Coat color in other animals                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Coat color in other animals Two genes: E, e and B, b Color = E; no color = e How dark the color is: B = black, b= brown

Incomplete dominance Hybrids have an “in-between” appearance RR = red flowers rr = white flowers Rr = pink flowers Make 50 % less color

Incomplete dominance

Codominance Equal dominance Human blood ABO blood groups 3 versions A, B, i A & B alleles are codominant Both A & B alleles are dominant over the i allele The genes code for different sugars on the surface of red blood cells “Name tag” of the red blood cell

A type A female would like to have a child with a Type B male A type A female would like to have a child with a Type B male. The type A female’s genotype is IAi. The type B male is IBIB. What are the possible genotypes and phenotypes for their child? What if the parents are Type O and Type AB? What are the possible genotypes and phenotypes for their child?

Many genes, one trait Polygenic inheritance Additive effects of many genes Humans Skin color Height Weight Eye color Intelligence behaviors

Independent Assortment When more than one gene passes from generation to generation, each gene separates independently of the other Produces two factor crosses Yellow round peas x Green wrinkled peas RRYY x rryy

Human Skin Color AaBbCc x AaBbCc Can produce a wide range of shades Most children = intermediate skin color Some can be very light, some can be very dark

Human Skin Color

Two Factor cross = dyhibrid cross

Coat color in other animals                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Coat color in other animals Two genes: E, e and B, b Color = E; no color = e How dark the color is: B = black, b= brown

Environmental Effect Phenotype is controlled by both the environment and genes altering the pH of the soil = Blue flowers appear when the soil has an acidic pH of 5.5 or lower

Coat color in Arctic animals is influenced by the environment.