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

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
Studied pea plants
Started with true-breeding plants
True-breeding tall plant (TT) x true-breeding short plant (tt)
All offspring were tall
Why?
Principle of dominance

6. Probability and Genetics
Probability: the likelihood that a particular event will occur
Why study probability with genetics?
All the traits you receive from your parents depends on chance!
What do we use to predict the outcome of a genetic crosses?
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. Chromosomes and Meiosis

9. Chromosomes Contains genes Found in the nucleus in eukaryotes
Found in the cytoplasm in prokaryotes
Mendel states:
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.

10. Chromosomes
Homologous chromosomes: 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)
A cell that contains only 1 set of chromosomes is called haploid – i.e. gametes

11. 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)

12. 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 =

13. 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

14. 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

16. 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

17. 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

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

20. (One factor crosses)
Monohybrid Crosses

21. Vocab for Punnett Squares
Homozygous: two identical alleles for a particular trait
Aka – true-breeding
Heterozygous: 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

22. Let’s Practice the Vocab!
T= tall, t = short
Homozygous tall =
Heterozygous =
Homozygous short =
Y = yellow, y = green
Homozygous yellow =
Homozygous green = TT Tt tt YY Yy yy

23. Ratios for Normal Monohybrid Crosses
Phenotypic ratio
Compares the # of individuals that show the dominant trait to the # of individuals that show the recessive trait
Tall:short, Yellow:green
Genotypic ratio
Compares the # of homozygous dominant individuals to the # of heterozygous individuals to the # of homozygous recessive individuals
TT:Tt:tt , YY:Yy:yy

24. 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

25. 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

26. 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

27. 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

28. (Two Factor crosses)
Dihybrid Crosses

29. Back to Mendel!
Mendel asked: Does the segregation of one pair of alleles affect the segregation of another pair of alleles?
No, they will separate independently.
Example:
What the alleles for height do will not affect what the color alleles do.

30. 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

31. 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 =
Wrinkled and green =
Heterozygous for both traits =
RRYY
rryy
RrYy

32. 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: Genotypes
RRYY
rryy
Step 2: Gamete
combinations 
RRYY
rryy RY ry RY ry RY ry ry RY

33. Dihybrid Crosses R Y RY r y ry
Another way to figure out the gamete combinations
Parent: RRYY Parent: rryy R Y RY r y ry

34. Dihybrid Crosses Step 3: Punnett Square (RRYY x rryy) RY ry RrYy RrYy

35. Dihybrid Crosses Step 4: Phenotypic ratio
Round yellow: round green: wrinkled yellow: wrinkled green
16:0:0:0

36. Now you try! R r Y RY rY y Ry ry
Cross two individuals that are heterozygous round and yellow
What are the genotypes?
RrYy
What are the gametes?
RrYy = RY, Ry, rY, ry R r Y RY rY y Ry ry

37. 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

38. Other types of Dominance
Incomplete Dominance
Codominance

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

40. 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

41. 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

42. 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

43. 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

44. 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

45. Bloodtyping is Codominant!
Types A and B are both dominant to O
Bloodtype A B AB O
Genotype
Antigens
Will take blood from:
Can’t take blood from:
IAIA or IAi
IBIB or IBi
IAIB ii A B
A and B
None
A or O
B or O
AB, A, B, O O
B or AB
A or AB
---
A, B, AB

46. Bloodtyping with Punnetts
Homozygous A x Homozygous B
Genotypes?
IAIA X IBIB
Punnett Square
Probabilities
A = 0%
B = 0%
AB = 100%
O = 0% IA IA IB
IAIB
IAIB IB
IAIB
IAIB

47. Bloodtyping with Punnetts
AB x O
Genotypes?
IAIB X ii
Punnett Square
Probabilities
A = 50%
B = 50%
AB = 0%
O = 0% IA IB i
IAi
IBi i
IAi
IBi

48. Your Turn! IA i IB IAIB IBi i IAi ii Heterozygous A x Heterozygous B
Genotypes?
IAi X IBi
Punnett Square
Probabilities
A = 25%
B = 25%
AB = 25%
O = 25% IA i IB
IAIB
IBi i
IAi ii

49. Sex-linked Traits
Human Heredity

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

51. Karyotypes Human karyotypes show 46 chromosomes
23 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

52. How do Genetic Disorders Occur?
Non-disjunction
Occurs during Meiosis I
Homologous chromosomes fail to separate during Anaphase I
Result = gametes have wrong number of chromosomes
One ends up with an extra, while the other will have one less

53. Sex Chromosomes Chromosome pair #23 is called the sex chromosomes
Females = XX
Males = 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.

54. 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

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

56. 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

57. Colorblindness with Punnetts
Colorblind male x normal female
What are the genotypes?
XcY x XX
Punnett Square
What is the chance they will have a colorblind child? 0%
If they have a daughter, what
chance she will be a carrier?
100% Xc Y X
XcX XY X
XcX XY