1. The study of how genes are passed from Generation to Generation!
Standard 3
Unit 7 Genetics
(Heredity)
Chapters pages:
The study of how genes are passed from Generation to Generation!

2. Probability Chapter 6.3 Pg. 177
Unit 7 Genetics
Probability
Chapter 6.3 Pg. 177

3. Heredity Patterns can be calculated using the rules of probability.
If 2 plants have certain characteristics and they are bred together, you can calculate the probability of the offspring having certain characteristics. There are 2 rules to help calculate these probabilities.

4. Probability The likelihood that an event will occur
Probability = # of one kind of possible outcome
total # of all possible outcomes
ADDITION RULE!
When the word or is used you add the odds.
So, 1/6 + 1/6 = 2/6
MULTIPLICATION RULE!
When the word and appears you multiply the odds.
So, 1/6 x 1/6 = 1/36

5. Probability What is the probability of rolling a 6 on a die?
1/6
What is the probability of rolling a 6 or a 5 on a dice cube?
1/6 + 1/6= 2/6
What is the probability of rolling a 6 and a 5
1/6 x 1/6= 1/36
Please do the practice problems on the worksheet HW#1

6. Probabilities Predict Averages
Probabilities predict the average outcome of a large number of events.
Probability cannot predict the precise outcome of an individual event.
In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.
Copyright Pearson Prentice Hall

7. Traits, Genes and Alleles chap 6.4 pgs 180-182
A trait is a specific characteristic that varies from one individual to another
Genes: the factors that determine traits
Alleles: alternate forms of a gene
Homozygous: Two of the SAME alleles (AA)
Heterozygous: Two different alleles (Aa)
Genome: all of an organism’s genetic material
Genotype: genetic makeup of a specific set of genes
Phenotype: The physical characteristics or traits

8. Dominant allele: Gene that is expressed AA BB Recessive allele: Gene that is not expressed aa bb

9. Mendelian Genetics Gregor Mendel (1822-84)
Father of Genetics
Austrian Monk, spent his life working with traits of Pea Plants
Traits passed in “factors” GENES! from Generation to Generation
Working during the same time period as Darwin
He didn’t know what a GENE was !!

10. Genes and Dominance
Mendel studied seven pea plant traits, each with two contrasting characters.
Each original pair of plants is the P (parental) generation.

11. The offspring are called the F1, or “first filial,” generation.
The offspring of crosses between parents with different traits are called hybrids

12. How do we look at gene combinations?
We use : Punnett Squares
The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square.
Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

13. 6 steps to solving a problem
Genetics problems require the same 6 steps!
Identify Dominant and Recessive Phenotypes T=Tall t=Short
Parent phenotype x parent phenotype tall x tall
Parent genotype x parent genotype Tt x Tt
Punnett Square
Genotypic ratio :2: TT:Tt:tt
Phenotypic ratio tall: 1 short

14. Copyright Pearson Prentice Hall
Punnett Squares
Lets try this Mono- (1) hybrid(mixture) cross
A capital letter represents the dominant allele for tall.
A lowercase letter represents the recessive allele for short.
In this example,
T = tall
t = short
The principles of probability can be used to predict the outcomes of genetic crosses. This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants.
Copyright Pearson Prentice Hall

15. Are the parent plants heterozygous or homozygous?
Homozygous organisms are TRUE-BREEDING
Heterozygous organisms are HYBRID
Are the parents True-breeding or Hybrids?

16. Copyright Pearson Prentice Hall
Punnett Squares
All of the tall plants have the same phenotype, or physical characteristics.
BUT..All of the tall plants do not have the same genotype, or genetic makeup.
One third of the tall plants are TT, while 2/3 of the tall plants are Tt.
The offspring are the
F1 generation
Copyright Pearson Prentice Hall

17. Copyright Pearson Prentice Hall
Punnett Squares
These F1 plants have different genotypes (TT and Tt), but they have the same phenotype (tall).
Lets find out what kind of plants we will get by crossing these!
Although these plants have different genotypes (TT and Tt), they have the same phenotype (tall). TT
Homozygous Tt
Heterozygous
Copyright Pearson Prentice Hall

18. Look back at the F1 plant that have the TALL Phenotype TT, Tt
How can you determine the genotype of these plants ? How can you tell the
Homozygous dominant TT from the
Heterozygous Tt

19. What do you do if you don’t know the genotype of the dominant parent?
Testcross!!!!

20. TEST CROSS
A test cross is used to determine the genotype of a dominant trait.
(A dominant trait can be either homozygous dominant or heterozygous.)
The unknown trait is crossed with the recessive trait.
If any offspring show the recessive trait, the dominant parent had to be heterozygous.

21. Dihybrid Crosses…they are twice as chap 6.5 pg 186 much fun!!!
Two Traits example: seed color and shape!
Created by Mendel to test Laws of Independent Assortment and Segregation

22. Cross 2 plants that are heterozygous for the 2 traits (seed shape & pod color)
Sample #1: Pea Plants
R = round seeds r = wrinkled seeds
Y= yellow pods y = green pods
Identity Dominant and Recessive
Parent phenotypes
Parent genotypes
1,3 1,4 2,3 2,4
Punnet square
Possible Phenotypes
Phenotypic ratio

23. R r Y y if this is one parent what alleles 1 2 3 4 can he contribute?
If you are looking at two genes at the same time, how do you figure out the possible combinations?
Look at the positions to determine combos
R r Y y if this is one parent what alleles can he contribute?
1&3 1&4 2& &4
RG Rg rG rg

24. Try this!
You have a round (R) and yellow (Y) pea plant and cross it with a wrinkled (r) and green (y) plant. Both are homozygous, one dominant and the other recessive
Please label and do this cross on your notes
What are the phenotypes for the offspring?
What are the genotypes for the offspring?

25. Independent Assortment
The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y).
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.
Copyright Pearson Prentice Hall

26. Now lets take two of these offspring and cross them.
Parent phenotype(F1 generation)
Parent genotype(F1 generation)
RrYy
Determine the alleles that each parent can give: 1&3 1&4 2&3 2&4
Please do the cross and generate the F2 generation

27. Independent Assortment
The Two-Factor Cross: F2 
Mendel crossed the heterozygous F1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F2 generation.
RrYy × RrYy
Copyright Pearson Prentice Hall

28. Independent Assortment
The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation.
Represents:
Independent Assortment
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.
Copyright Pearson Prentice Hall

29. Independent Assortment
The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment.
Genes that segregate independently do not influence each other's inheritance.
Copyright Pearson Prentice Hall

30. Independent Assortment
The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.
Inindependent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.
Copyright Pearson Prentice Hall

31. Mendel’s Data revealed 3 patterns, LAWS
1. Law of Dominance: traits can have 2 alleles
(one dominant “A” & one recessive “a”)
Dominant allele:-
- overpowers or covers up the recessive
- Fully expresses the protein
- Represented by Capital letter A, B EX: Brown eyes
Recessive allele:
- is masked by the other allele
- little or no protein is expressed
- is represented by lower case letter a,b EX: Blue eyes

32. Mendell’s Laws 2. Law of segregation :
Organisms inherit 2 copies of each gene, one from each parent.
Organisms donate only one copy of each gene, thus the 2 copies of each gene segregate or separate during meiosis

33. Mendel’s Laws 3. Law of Independent Assortment
The presence of one trait does not affect the presence of another, genes for different traits segregate independently of each other during gamete formation.
(this is seen in a two factor cross, dihybrid cross)
This helps account for many genetic variations observed in plants, animals and other organisms.

34. Incomplete Dominance RED Flower x WHITE Flower ---> PINK Flower
A cross between organisms with two different phenotypes produces offspring with a third phenotype
RED Flower x WHITE Flower ---> PINK Flower
(Flower Color in 4 O'clock’s or Snapdragons)
RR = red
ww = white
Rw = pink

35. Problem: Incomplete Dominance
Show the cross between a red and a white flower.
R R
PHENOTYPES: w
0:4:0
Red/Pink/white Rw
0:4:0
RR-Rr-rr
GENOTYPES:

36. Problem: Incomplete Dominance
Show the cross between a red and a white flower.
R w
PHENOTYPES: R w
1:2:1
Red/Pink/white Rw RR Rr
1:2:1
RR-Rw-ww
GENOTYPES:

37. Practice Problem
A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles.
What are the genotypes of the parent blahblah birds in the original cross?
What is/are the genotypes of the silver offspring?
What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

38. Co-dominance and Multiple Alleles
And other kookie crosses!

39. Codominance ININ = normal cells INIS = both ISIS = sickle cells sick
meaning of the prefix "co-" is "together
The heterozygous condition, both alleles are dominant and expressed equally
“I” Represents the Blood Cells
Alleles are both represented by Capital Letters
Sickle Cell Anemia in Humans
N= Normal S: Sickle Cells
ININ = normal cells
INIS = both
ISIS = sickle cells
sick

40. Problem: Codominance
Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick.
IS IS
- carrier (2); sick (2)
- ratio 0:2:2
PHENOTYPES: IN IS
INIS
INIS
- INIS (2) ISIS (2)
- ratio 0:2:2
GENOTYPES:
ISIS
ISIS

41. Multiple Alleles There are more than two alleles for a trait
Blood type in humans
Blood Types
Type A, Type B, Type AB, Type O
Blood Alleles
A, B,O

42. Rules for Blood Type A and B are codominant
IAIA = Type A
IBIB = Type B
IAIB = Type AB
A and B are dominant over O
IAi = type A
IBi = type B
i i = type O

43. The blood types differ due to the molecules that are present on the outside of RBC

44. Problem: Multiple Alleles
Show the cross between a mother who has type O blood and a father who has type AB blood.
i i
GENOTYPES:
- AO (2) BO (2)
- ratio 1:1 IA IB
IAi
IBi
PHENOTYPES:
- type A (2); type B (2)
- ratio 1:1

45. Problem: Multiple Alleles
Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood.
IA i
PHENOTYPES: IB i
IAIB ii
IBi
IAi
Type AB IAIB
type B IBi
type A IAi
type O ii
ratio 1:1:1:1

46. Genetic linkage Chapter 6.6 page 189-191
Independent assortment creates a lot of variation.
Crossing over in Meiosis also creates variation
Genes located close together on the same chromosome tend to be inherited together.
This is termed linkage

48. Sex-linked Traits
A trait that is determined by a gene found only on a sex chromosome
Females, are XX and have two alleles for genes that are on the X chromosome
Males, who are XY, only have one allele
For recessive traits, women that are heterozygous are said to be carriers

49. Red-Green Color Blindness
recessive genetic disorder
a condition that impairs a persons ability to distinguish between shades of red and green.
Does not otherwise effect vision
16x more prevalent in men, rarely seen in women.

50. What do you see?

51. X- Linked Genetics C=Normal Vision
Studies by T.H. Morgan in Fruit Flies
1,098 human X-linked genes
Colorblind
Hemophilia
C=Normal Vision
c= Colorblind
Y chromosome doesn’t carry an allele XC Xc
XC Xc
XcXc Y
XCY
XcY

52. Cross and a women with normal vision and a man that is colorblindXC Y Xc
XcY
XCY
XCXc
XC Xc
2 Carrier Females
1 Normal Male
1 Colorblind Male

53. Polygenic Traits
Traits determined by the combined effect of more than one pair of genes
EX: human height
Combined size of all of the body parts from head to foot determines the height of an individual
Different parts, are made by different genes

54. Sex Limited Only expressed in the presence of sex hormones
Female: estrogen
Male: testosterone
Only expressed in one of the sexes.
Beard growth in Men
Breast milk in Women

55. Sex influenced Traits Expressed in both sexes
Expressed differently based on the sex (gender).
Baldness
Traits are influenced by their environment
In the presence of testosterone, the allele is dominant, but in the presence of estrogen the allele becomes recessive.
Therefore a woman can only be bald if she has two recessive genes for Baldness.

56. Environment Influences Traits
Height in humans
Prenatal health
Diet
Illness
Gender of Alligators and Rabbit fur color
Enzymes that create differences are only produced at certain temperatures

57. Tracking Traits in Families
Pedigrees
A “family tree” drawn with standard genetic symbols, used to study human heredity

58. Females are represented with a circle
Males are represented with a square

59. Mating is represented with a line connecting a square and circle

60. Children are represented with another connecting line

61. Children are put in order of birth from left to right

62. Connecting Pedigree Symbols
Examples of connected symbols:
Fraternal twins
Identical twins

63. Affected or Not? Disorder Normal Normal Disorder
Un-shaded means they are not affected with the disorder
Completely Shaded means they have the disorder
Disorder
Normal
Normal
Disorder

64. What about the carriers?
In pedigrees, we use people with the disorder or trait to figure out who carriers the gene and who is normal for traits. aa AA Aa

65. Recognizing patterns in pedigrees
Recessive or Dominant Trait?
If dominant, every affected individual will have a parent with the disorder
If recessive, an affected individual can have normal parents
Recessive
Dominant
For those traits exhibiting dominant gene action:
affected individuals have at least one affected parent
the phenotype generally appears every generation
two unaffected parents only have unaffected offspring
The following is the pedigree of a trait controlled by dominant gene action.
And for those traits exhibiting recessive gene action:
unaffected parents can have affected offspring
affected progeny are both male and female
The following is the pedigree of a trait controlled by recessive gene action.

66. Sex-linked or Autosomal?
Autosomal= seen equally in males and females
Sex-linked = usually only seen in males
If it is sex-linked remember to use the X’s and that they Y can have an allele.
Sex-Linked
Autosomal
For those traits exhibiting dominant gene action:
affected individuals have at least one affected parent
the phenotype generally appears every generation
two unaffected parents only have unaffected offspring
The following is the pedigree of a trait controlled by dominant gene action.
And for those traits exhibiting recessive gene action:
unaffected parents can have affected offspring
affected progeny are both male and female
The following is the pedigree of a trait controlled by recessive gene action.

67. Dominant or Recessive?
Autosomal or Sex Linked?
Fill in the Genotypes

68. Dominant or Recessive?
Autosomal or Sex Linked?
Fill in the Genotypes