1. Genetics and the Work of Gregor Mendel

2. 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

3. 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

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

5. Mendel collected data for 7 traits

6. 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.)

8. 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)

9. 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.

10. 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

11. 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.

12. 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)

13. 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

14. 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

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

16. 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

17. 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

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

19. 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

20. 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

21. Human Skin Color

22. Two Factor cross = dyhibrid cross

23. 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

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

26. Incomplete dominance

27. 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

29. 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?

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

31. 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

32. 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

33. Human Skin Color

34. Two Factor cross = dyhibrid cross

35. 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

37. 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

38. Coat color in Arctic animals is influenced by the environment.