1. Genetics
The study of heredity

2. Genetics
Genetics is the scientific study of heredity - how traits are passed from generation to generation.
The characteristics that are inherited are called traits.

3. Genes Humans have 23 homologous pairs of chromosomes.
On each chromosomes, there are sections called genes that code for traits.

4. Genes

5. Alleles An allele is a distinct form of a gene.
Every person has 2 alleles for a gene  1 from the father and 1 from the mother

6. Alleles
Letters of the alphabet are used to represent an allele of interest.
Every person has two copies of an allele, so they will have two letters. T P A Y R

7. Alleles
Dominant alleles are symbolized with a capital letter. Dominant alleles will mask a recessive alleles in cases of simple dominance/recessiveness.
Recessive alleles are symbolized with lower case letters. A a

8. Homozygous Alleles AA aa
If an organism has two like copies of an allele, it is homozygous (homo = same).
If the two alleles are dominant, the organism is homozygous dominant.
If the two alleles are recessive, the organism is homozygous recessive. AA aa

9. Heterozygous Alleles Aa
If an organism has two different copies of an allele, it is heterozygous (hetero = different). Aa

10. Genotype and Phenotype
The letters an organism has represent the organism’s genotype - what alleles the organism has.
As a result of the alleles present, a trait is expressed. The phenotype is the expressed trait.

11. Genotype and Phenotype
Example: In a plant species, there are two alleles for flower color: R and r.
R is dominant, and codes for red flowers
r is recessive and codes for white flowers

12. Genotype and Phenotype
The genotype is the combination of alleles: either RR, Rr, or rr.
The phenotype is what is expressed: either red or white flowers.

13. Genotype and Phenotype
RR -
Homozygous dominant
Red flowers
Rr -
Heterozygous dominant
rr -
Homozygous recessive
White flowers
In cases of simple dominance, an organism must have two copies of the recessive alleles to express the recessive trait.

14. Purebreds and Hybrids
Purebred - an organism that receives the same genetic traits from both of its parents
Hybrid - an organism that receives different forms of a genetic trait (different alleles) from each parent

15. Contributions of Gregor Mendel
Mendel’s Laws
Contributions of Gregor Mendel

16. Law of Dominance
The dominant alleles is expressed and may mask a recessive allele. The recessive form of a trait is only shown in a homozygous recessive organism.
Ex. R is allele for round, r is allele for square.
RR - round
Rr - round
rr - square

17. Parent: Dd Parent: dd D d d d Gametes Gametes Law of Segregation
Gene pairs separate when gametes are formed.
Parent: Dd
Parent: dd D d d d
Gametes
Gametes

18. Law of Independent Assortment
Genes segregate randomly and independently. This means that if there are 2 or more traits, every combination of those traits is possible.
AbC
Abc
abC
abc
AabbCc

19. Probability and Punnett Squares
Predicting the genotypes and phenotypes of offspring

20. Probability
Probability - the likelihood that a particular event will occur (what are the odds?)
What is the probability that a single coin flip comes up heads?
50% or 1/2

21. Probability
True or False? The past outcomes of coin flips greatly affects the outcomes of future coin flips.
False.
There’s still a 50% chance of heads and 50% chance of tails!

22. Probability
The way in which alleles separate is random, like a coin flip. (Mendel’s Law of Segregation)
From a mother who is heterozygous for an allele, there is a 50% chance she passes on the dominant allele and a 50% chance she passes on the recessive allele.

23. Punnett Squares
Punnett squares show probabilities for genotypes and phenotypes of offspring of two parent organisms.
Example:
In Mendel’s pea plants, the plants had either purple (P) or white (p) flowers.

24. Punnett Squares Step 1. Make the grid.
If there is 1 trait, it is a 2x2 grid.
If there are 2 traits, it is a 4x4 grid.
Because we are only looking at 1 trait (flower color), a 2x2 grid is needed.

25. Punnett Squares Pp
Step 2: Determine the parents’ genotypes and possible gametes.
Example: a heterozygous pea plant and a homozygous dominant pea plant. P p P PP P

26. Punnett Squares Pp
Step 3: Fill in the squares by combining what is on top of the column and to the left of the row. P p P PP Pp PP PP Pp P

27. Punnett Squares Pp
Step 4: Use the Punnett square to determine probabilities and ratios. P p P PP Pp PP PP Pp P

29. Punnett Squares
What is the probability of an offspring plant having purple flowers?
100%
What is the probability of an offpsring plant being heterozygous?
2/4 = 1/2 = 50% PP Pp PP Pp

30. Punnett Squares
If there are 2 traits, the Punnett square will be a 4x4 grid.
Example: Cross a pea plant that is heterozygous for both flower color and seed shape with a plant that has white flowers and is heterozygous for seed shape
P - purple; p - white
R - round, r - wrinkled

31. Punnett Squares PpRr ppRr PR, Pr, pR, pr pR, pr, pR, pr
Cross a pea plant that is heterozygous for both flower color and seed shape with a plant that has white flowers and is heterozygous for seed shape
PpRr
ppRr
PR, Pr, pR, pr
pR, pr, pR, pr

32. Punnett Squares
ppRr pR pR pr pr PR Pr
PpRr pR pr

33. Punnett Squares
ppRr pR pR pr pr
PpRR
PpRr
ppRR
ppRr PR Pr
PpRr pR pr

34. Punnett Squares ppRr pR pR pr pr PR Pr PpRr pR pr PpRR PpRr Pprr ppRR

35. Punnett Squares pR pR pr pr PR Pr pR pr PpRR PpRr Pprr ppRR ppRr pprr
2 / 16 = 1 / 8 or
12.5% Pr pR pr
What is the probability of an offspring having white flowers and wrinkled seeds?

36. Punnett Squares pR pR pr pr PR Pr pR pr PpRR PpRr Pprr ppRR ppRr pprr
6 / 16 = 3 / 8 or
37.5% Pr pR pr
What is the probability of an offspring having purple flowers and round seeds?

37. Punnett Squares PpRR PpRr Pprr ppRR ppRr pprr
Write the probable genotypic ratio.
2 PpRR : 4 PpRr : 2 Pprr : 2 ppRR : 4 ppRr : 2 pprr
1 PpRR : 2 PpRr : 1 Pprr : 1 ppRR : 2 ppRr : 1 pprr

38. Intermediate Inheritance
Beyond Simple Dominance

39. Intermediate Inheritance
There are 3 types of intermediate inheritance, genetic patterns that don’t follow the simple dominant-recessive rules.
Incomplete dominance
Codominance
Multiple alleles

40. Incomplete Dominance
Incomplete dominance - neither allele is completely dominant over the other
The heterozygous form is a “blended” form of the two alleles.

41. Incomplete Dominance
Example: In snapdragon flowers, there is an allele that codes for red (r), and allele that codes for white (w).
rr - red
ww - white
rw - pink

42. Incomplete Dominance r w rr rw r r
Ex. Cross a red and a pink snapdragon. r w rr rw r r

43. Incomplete Dominance
Sometimes two like capital letters are used, but one gets a prime sign (‘).
Ex: Human hair
Curly hair HH
Straight hair H’H’
Wavy hair HH’

44. Codominance
Codominance - both alleles are dominant and get expressed equally
In the heterozygous has some of each phenotype, but they are not blended.

45. Codominance
Example - in a type of cattle, red hair (R) and white hair (W) are codominant.
RR - red
WW - white
RW - roan
Some red, some white, but not pink!

46. Codominance
Ex. Cross a red parent and a white parent. R R RW W W

47. Multiple Alleles
Multiple alleles - there are more than 2 alleles for a trait.
Ex. Fur color - gray, black, striped
Ex. Human blood types

48. Sex-linked, sex-limited, and sex-influenced traits
Sex Linkage
Sex-linked, sex-limited,
and sex-influenced traits

49. Human Chromosomes
Humans have 23 homologous pairs of chromosomes, for a total of 46.
22 pairs are called autosomes , which are all of the non-sex chromosomes
The 23rd pair is the sex chromosomes - X and Y.

50. Sex Chromosomes X and Y Females - XX All eggs have an X Males - XY
Sperm have either an X or Y

51. Sex-Linked Traits
Traits controlled by genes on the sex chromosomes are sex-linked traits.
Examples of sex-linked traits: hemophilia, color blindness, male pattern baldness
Most are “attached” to the X chromosome.
Therefore, females have 2 copies of these alleles and males only have one

52. Example - Hemophilia Hemophilia - a blood clotting disorder
Hemophilia is X-linked.
XH = normal
Xh = hemophilia
Y is still just a Y

53. Example - Hemophilia Females could be:
XHXH - don’t have hemophilia, not a carrier
XHXh - don’t have hemophilia, is a carrier
XhXh - have hemophilia

54. Example - Hemophilia Males can be: XHY - does not have hemophilia
XhY - has hemophilia
Males cannot be carriers - they either have it or they don’t!

55. Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh
Draw a Punnett square for cross between a carrier female and an unaffected male.
Female: XHXh Male: XHY XH Y
XHXH
XHY
XHXh
XhY XH Xh

56. Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh
What is the percent chance that a child of theirs will have the disorder?
25% XH Y
XHXH
XHY
XHXh
XhY XH Xh

57. Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh
What is the percent chance that a child of theirs will have the disorder?
25% XH Y
XHXH
XHY
XHXh
XhY XH Xh

58. Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh
What is the percent chance that a a son would have the disorder?
50% XH Y
XHXH
XHY
XHXh
XhY XH Xh

59. Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh
What is the percent chance that a daughter would be a carrier?
50% XH Y
XHXH
XHY
XHXh
XhY XH Xh

60. Example - Colorblindness
Color blindness is also X-linked.
X = normal
Xc = colorblind

61. Example - Colorblindness
Cross a colorblind male and a carrier female. Xc Y
XXc XY
XcXc
XcY X Xc

62. Sex-limited traits
Sex-limited traits are only expressed in the presence of sex hormones, or are only observed in one sex or the other.
Ex. Beard growth

63. Sex-influenced traits
Sex-influenced traits are expressed in both sexes, but they are expressed differently.
Ex. Baldness is dominant in men, recessive in women

64. Pedigrees

65. Pedigrees Males Females Affected - shaded Unaffected - not shaded
Carrier - half shaded

67. Pedigrees
A pedigree is a diagram showing family history and tracing a genetic trait.