1. Ch. 11
Mendelian Genetics

2. Important Vocab Genetics: the study of heredity
Fertilization: the joining of sperm and egg
Genes: chemical factors that determine traits (a specific characteristic)
Alleles: different forms of a gene
Ex: tall vs short, yellow vs green
Trait: a specific characteristic (color, size, shape, etc.)

3. More Important Vocab
True-breeding: individuals that will produce offspring identical to themselves if allowed to self-pollinate
TT, tt, RR, rr
Hybrid: individuals that will not produce offspring identical to themselves if allowed to self-pollinate
Tt, Rr, Ss

4. Principle of Dominance
States that some alleles are dominant and others are recessive
An organism that has a dominant allele for a particular trait will always show that trait
An organism with a recessive allele for a trait will exhibit that form only when the dominant allele is absent

5. Who is the Father of Genetics?
Gregor Mendel
What organism did he study?
Pea plants
Started with true-breeding plants
He crossed a true-breeding tall plant (TT) with a true-breeding short plant (tt)
Found that all offspring were tall
TT x tt = all tall
Why?
Principle of dominance

6. Probability and Genetics
Probability: the likelihood that a particular event will occur
Why do we look at probability when studying genetics?
All the traits you receive from your parents depends on chance!
What do we use to predict the outcome of a genetic cross between two individuals?
Punnett Squares

7. Probabilities Predict Averages
Probabilities predict the average outcome of a large number of individuals
You are more likely to get the predicted outcome with 500 individuals rather than 5 individuals.

8. (One factor crosses)
Monohybrid Crosses

9. Vocab for Punnett Squares
Homozygous: organisms that have two identical alleles for a particular trait
Aka – true-breeding
Heterozygous: organisms that have two different alleles for a particular trait
Aka – hybrid
Phenotype: physical characteristics
Yellow, green, tall, short
Genotype: genetic makeup
YY, Yy, yy, TT, Tt, tt

10. Let’s Practice the Vocab!
T= tall, t = short
Homozygous tall = TT
Heterozygous = Tt
Homozygous short = tt
Y = yellow, y = green
Homozygous yellow = YY
Heterozygous = Yy
Homozygous green = yy
Let’s try some monohybrid (single factor) crosses!

11. Practice with Punnetts!
Heterozygous tall x heterozygous tall
What are the genotypes?
Tt x Tt
Punnett Square
Phenotypic ratio?
Tall:short
3:1
Genotypic ratio?
TT:Tt:tt
1:2:1 T t T TT Tt t Tt tt

12. More Practice with Punnetts!
Homozygous tall x homozygous short
What are the genotypes?
TT x tt
Punnett Square
Phenotypic ratio?
Tall:short
4:0
Genotypic ratio?
TT:Tt:tt
0:4:0 T T t Tt Tt t Tt Tt

13. More Practice with Punnetts!
Heterozygous tall x short
What are the genotypes?
Tt x tt
Punnett Square
Phenotypic ratio?
Tall:short
2:2
Genotypic ratio?
TT:Tt:tt
0:2:2 T t t Tt tt t Tt tt

14. Your turn to try! T T T TT TT t Tt Tt
Homozygous tall x heterozygous tall
What are the genotypes?
TT x Tt
Punnett Square
Phenotypic ratio?
Tall:short
4:0
Genotypic ratio?
TT:Tt:tt
2:2:0 T T T TT TT t Tt Tt

15. (Two Factor crosses)
Dihybrid Crosses

16. Back to Mendel!
When looking at a single trait (i.e. height), the two alleles will separate from each other
The 2 T’s separate from each other
Now let’s look at 2 traits at the same time.
Mendel asked:
Does the segregation of one pair of alleles affect the segregation of another pair of alleles?
Tall vs short and yellow vs green
No, they will separate independently. What the alleles for height do will not affect what the color alleles do.

17. Principle of Independent Assortment
States that genes for different traits can segregate independently during the formation of gametes.
Gametes: sex cells
What are the two types of gametes?
Sperm
Egg

18. Dihybrid Crosses Let’s look at two factors: seed shape and color
Round (R) vs wrinkled (r) seed shape
Yellow (Y) vs green (y) seed color
Homozygous round and yellow = RRYY
Wrinkled and green = rryy
Heterozygous for both traits = RrYy

19. Dihybrid Crosses RRYY rryy RY ry RY ry RY ry ry RY
Let’s cross 2 truebreeding plants: Round yellow x wrinkled green
Step 1: What are the genotypes?
RRYY
rryy
Step 2: What are the possible gamete combinations?
RRYY
rryy RY ry RY ry RY ry ry RY

20. Dyhybrid Crosses Step 3: Draw out the Punnett Square RY ry RrYy RrYy

21. Dyhybrid Crosses Step 4: Figure out the Phenotypic ratio
Round yellow: round green: wrinkled yellow: wrinkled green
16:0:0:0

22. Now you try!
Cross two individuals that are heterozygous for both traits.
Round vs wrinkled
Yellow vs green
What are the genotypes?
RrYy
What are the gametes?
RrYy = RY, Ry, rY, ry

23. RrYy x RrYy 9: 3: 3: 1 RY Ry rY ry RRYY RRYy RrYY RrYy RRYy RRyy RrYy
Phenotypic ratio:
Round/yellow : round/green : wrinkled/yellow : wrinkled green
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy 9: 3: 3: 1

24. Other types of Dominance
Incomplete Dominance
Codominance

25. Incomplete Dominance
Case in which one allele is not completely dominant over another
Heterozygote phenotype is somewhere between the two homozygote phenotypes
Example: Snapdragons
Red (R) and white (r)
RR = red and rr = white
What about Rr?
These are pink!

26. Let’s Practice! R R r Rr Rr r Rr Rr Red snapdragon x white snapdragon
Genotypes?
RR x rr
Punnett Square
Ratios:
Phenotypic
Red: pink: white
0:4:0
Genotypic
RR: Rr: rr R R r Rr Rr r Rr Rr

27. Now It’s Your Turn: R r R RR Rr r Rr rr Pink x Pink Genotypes?
Rr x Rr
Punnett Square
Ratios:
Phenotypic
Red: pink: white
1:2:1
Genotypic
RR: Rr: rr R r R RR Rr r Rr rr

28. Codominance
Situation in which both alleles contribute to the phenotype
Heterozygote is usually spotted or speckled compared to the solid colored homozygotes
Example: Chickens
B = black, W = White
BB = black chicken
WW = white chicken
BW = black and white speckled chicken

29. Let’s Practice! B B W BW BW W BW BW Black chicken x White Chicken
Genotypes?
BB x WW
Punnett Square
Ratios:
Phenotypic
Black: speckled: white
0:4:0
Genotypic
BB: BW: WW B B W BW BW W BW BW

30. Your Turn! B W B BB BW W BW WW Speckled chicken x speckled chicken
Genotypes?
BW x BW
Punnett Square
Ratios:
Phenotypic
Black: speckled: white
1:2:1
Genotypic
BB: BW: WW B W B BB BW W BW WW

31. Bloodtyping is Codominant!
Types A and B are both dominant to O
Bloodtype A B AB O
Genotype
Antigens
Antibodies
Will take blood from:
Can’t take blood from:
IAIA or IAi
IBIB or IBi
IAIB ii A B
A and B
None B A
None
A and B
A or O
B or O
AB, A, B, O O
---
B or AB
A or AB
A, B, AB
Antigen: substance that triggers an immune response
Antibody: protein that helps destroy pathogens

32. Meiosis

33. Chromosomes
Genes are located on chromosomes which are found in the nucleus.
Mendel’s principles of genetics requires 2 things:
Each organism must inherit a single copy of every gene from each parent.
When an organism produces its own gametes, those two sets (copies) of genes must be separated from each other so that each gamete contains just one set of genes.

34. Chromosomes
Homologous chromosomes: term used to refer to chromosomes that each have a corresponding chromosome from the parent of the opposite sex
A cell that contains both sets of homologous chromosomes is said to be diploid (meaning 2 sets)
Having 2 complete sets of chromosomes agrees with Mendel’s idea that the adult organism contains 2 copies of each gene
A cell that contains only 1 set of chromosomes is called haploid – i.e. gametes

35. Chromosomes
Humans:
How many chromosomes does each of your typical body cells have?
46 (diploid)
How many chromosomes does each of your gametes have?
23 (haploid – one set of chromosomes)

36. Meiosis
Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Divided into 2 major steps:
Meiosis I
Meiosis II

37. Meiosis I
Prophase I
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad (made of 4 chromatids)
Homologous chromosomes then exchange portions of there chromatids during crossing-over
Results in the exchange of alleles between homologous chromosomes and produces new combinations of alleles

38. Meiosis I Metaphase I Anaphase I Telophase I and Cytokinesis
Spindle fibers attach to the chromosomes
Chromosomes line up across middle of cell at metaphase plate
Anaphase I
Fibers pull homologous chromosomes towards opposite ends of cell
Telophase I and Cytokinesis
Nuclear membranes reform
Cell separates into 2 haploid daughter cells

40. Meiosis II Prophase II Metaphase II
The 2 cells created by Meiosis I now enter into a second meiotic division
At this point, each cell’s chromosomes contains 2 sister chromatids (same genes, but different alleles  one may have “A” while the other may have “a”)
Metaphase II
Chromosomes line up at metaphase plate
Spindle attaches to centromeres

41. Meiosis II Anaphase II Telophase II and Cytokinesis
Sister chromatids separate and move towards opposite ends of cell
Telophase II and Cytokinesis
Nuclear membrane reforms
Cytoplasm divides
Result: 4 genetically different haploid gametes

43. Mitosis vs Meiosis Mitosis produces 2 identical diploid daughter cells
Meiosis produces 4 genetically different haploid gametes

44. Sex-linked Traits
Human Heredity

45. Human Heredity
Karyotype: a picture of chromosomes arranged in homologous pairs

46. Karyotypes Human karyotypes show 46 chromosomes
23 chromosomes came from the sperm (father)
23 came from the egg (mother)
Chromosome pairs #1-22 are called autosomes.
These determine all sorts of traits – eye color, hair color, height, shapes of features

47. Sex Chromosomes
Chromosome pair #23 are called sex chromosomes because they determine a person’s sex
Females have 2 X’s = XX
Males have 1 X and 1 Y = XY
All human egg cells carry 1 X.
Only ½ of human sperm cells carry an X, whereas the other ½ carry a Y
Results in a 50/50 chance of having either a girl or boy.
Who determines the sex of the baby? Why?

48. Sex-linked Genes
Sex-linked genes are genes located on the X chromosome.
Most sex-linked traits are recessive.
Males are more likely to show sex-linked traits.
This is because males have only 1 X – if this X is “bad”, the sex-linked trait will be expressed.
Females have 2 Xs – both Xs have to be “bad” in order for the trait to be expressed.
Examples: Colorblindness, Hemophilia, muscular dystrophy

49. Sex-linked Traits
In order to figure out the chance of getting a sex-linked trait, we follow the same procedure as we did for single-factor traits.
However, we have to add sex chromosomes (X and Y) into the equation.
Let’s use colorblindness as an example.

50. Colorblindness - Genotypes
Males have 2 possible genotypes:
Normal Male = XY
Colorblind male = XcY
Females have 3 possible genotypes:
Normal female (not a carrier) = XX
Normal female (carrier) = XcX
This means she doesn’t show the trait, but can pass it on to her offspring
Colorblind female = XcXc

51. Colorblindness with Punnetts
Normal male x colorblind female
What are the genotypes?
XY x XcXc
Punnett Square
What is the chance they will have a colorblind son?
50%
What is the chance they will have a colorblind daughter? 0% X Y Xc
XcX
XcY Xc
XcX
XcY