Chapter 11: Genetics

When told to, put the PTC paper on your tongue PTC, or phenylthiourea, is an organic compound having the unusual property of either tasting very bitter, or being virtually tasteless, depending on the genetic makeup of the taster.tasting bitter genetic The ability to taste PTC is a dominant genetic trait.dominant T = Taster t = non-taster If you can taste, you are either TT or Tt. Those who can not taste are tt About 70% of people can taste PTC, varying from a low of 58% for Aborginal people of Australia to 98% for Native Americans

Ever wonder why people resemble their parents &/or siblings? How do farmers select the best plants or animals for breeding purposes? How’d you like that PTC paper? Why did some people in your class taste it and others didn’t?

Genetics Studies the transmission of traits or characteristics from 1 generation to the next

Gregor Mendel (1822 – 1884) The Father of Genetics Central European monk discovered the basic underlying principles of heredity. Work completed “Experiments on Plant Hybridization” in 1865Experiments on Plant Hybridization His work did not get recognized until 1900

He used pea plants and selectively crossed them over many generations Saw that certain traits show up in offspring plants without any blending of parent characteristics. X

Why peas? 1.Easy to grow in a short time 2. Ability to get pure breeds 3. Naturally self-pollinate (vs. cross-pollinate) 4. Isolated 7 different traits White or purple flower color Axial or terminal flower position Long or short stems Round or wrinkled seeds Yellow or green seeds Inflated or constricted pods Yellow or green pods

Mendel's work 1.Removed the stamen (male parts) to prevent self- pollination 2. Used the stamen from a tall plant and pollinated only flowers from other tall plants 3. Observed generations for 2 years to be certain of purebreds Tall XTallShort X Short Yielded all Talls Yielded all shorts Crossed plants with contrasting traits Tall X ShortShort X Tall

P = Parental generation F 1 = 1st Filial generation (offspring) F 2 = 2nd Filial generation (next set of offspring off the F1)

P 1 : Pure Tall X Pure Short T = Tall stems t = short stems TTXtt F 1 : Tall (Tt) Only one trait showed P 2 : F 1 Tall X F 1 Tall Tt Tt F 2 :3 Tall1 Short TT Tt Tt tt The “lost” trait reappears!

To get these results for the F 2, do FOIL – (firsts, outers, inners, lasts) *******Always got 75% Tall and 25% short or 3:1 whenever this type of cross occurred.

Mendel’s 4 conclusions (hypotheses) from his experiments 1. Concept of Unit Characters: The inheritance of each trait is determined by “units” or “factors” that are passed on. We now know these “units” as GENES These “units” occur in pairs. One from each parent

2.Law of Dominance: – One factor “masks” the appearance of another factor. It prevents it from showing Dominant – trait that must show if present (TT or Tt) Recessive – trait that will only show if in the pure form (tt) Hybrid – Contains a dominant & a recessive trait (Tt) Allele – alternate genes for a given trait (Tall or short)

3. Law of Segregation For any trait, pairs of alleles are separated in forming the gametes. Only 1 gene (allele) from the pair goes into the gamete during meiosis.

4. Law of Independent Assortment Different pairs of alleles are passed to offspring independent of each other. B = Brown b = White S = Short tail s = Long tail

More genetic vocabulary to learn Genotype: Shows actual genetic makeup. (Use symbols for genes) TT or Pure dominant or homozygous dominant Tt or Hybrid or heterozygous tt or Pure recessive or homozygous recessive Homozygous vs Heterozygous: Pure vs Hybrid (mixed)

Phenotype: Tells appearance (describes the trait) Tall (if TT or Tt) Short (if tt) NO HYBRIDS HERE!! Describes what you look like For Eye color, Blue, Green or Brown For Hair color, Red, Blond or Brown

Punnett Squares Shows possible gene pairing & probability of each pairing. Checkerboard method Foiling There are 2 kinds of sperm &/or 2 kinds of eggs depending on the genes that they carry. T T genes of 1 parent Tt genes of 1 parent tttt Phenotype ratio : 100% tall Genotype ratio : 100% Tt (hybrid)

Possible crosses Do the crosses (Punnett Sqs) & determine the : Phenotype and Genotype ratios Trait: T = Tall stem length t = short stem length 1. TT x TT 2. TT x Tt 3. TT x tt 4. Tt x Tt 5. Tt x tt 6. tt x tt

Probability Likelihood of an event occurring Shown by Punnett Square Shows how often a gene pairing may occur. **Need large numbers to get accurate predictions** Coin Toss Lab: Flip one coin 10x. Keep track of the # of Heads and Tails you get. 50:50 chance of getting heads or tail if you toss one coin

What happens when you toss two coins? If you toss 2 coins 100 times, you should get: 25 Heads/Heads 50 Heads/Tails 25 Tails/Tails As the # of trials increases, the ratios predicted by the laws of probability get closer Actual outcomes get closer to calculated predictions

Group Heads/Heads Heads/TailsTails/Tails Class Total/100

So you are a right handed person. How do you know if you are pure or a hybrid for the right handed trait? Could you ever have a lefty child? Test Cross: Method used to find out if something (or someone) is pure dominant or a hybrid for a given trait. Cross them with a pure recessive for that trait. If the results come up with a recessive individual, then the parent was a hybrid

In Guinea pigs: B = Black coat b = white coat Cross a BB guinea pig with a pure recessive (bb) Cross a Bb guinea pig with a pure recessive (bb) BB x bb Bb x bb

Monohybrid crosses: Cross two hybrids. Bb x Bb Always get a 3:1 phenotypic ratio!!!

What are your chances of having a blue eyed, blond haired child if one of your parents is brown haired and eyed and the other is a blond with blue eyes?

Dihybrid crosses Crossing two hybrids, that are hybrid for two different traits T = Tall stemY = Yellow seed t = short stem y = green seed TtYy x TtYy Dihybrid cross Phenotype ratio for a dihybrid is always: – 9:3:3:1 = (3:1)(3:1) 9 – Tall Yellow 3 – Tall green 3 – Short yellow 1 – Short green Trihybrid would be: 27:9:9:3:9:3:3:1 (3:1)(3:1)(3:1)