1. FUNDAMENTALS OF GENETICS
Modern Biology
Chapter 9
Pages

2. Fundamentals of Genetics
Objectives:
Describe how Mendel’s results can be explained by the scientific knowledge of genes and chromosomes.
Differentiate between a monohybrid cross and a dihybrid cross.
Predict & perform results of monohybrid and dihybrid crosses

3. Corkscrew tails can be traced back to one of the original American bulldogs used to develop the boston terrier breed.

4. SOOKIE

5. Do Now What is the genetic code? What molecule carries
What is genetics?
Genetic code - The genetic code is a set of instructions for transferring genetic data stored in the form of DNA or RNA into proteins. Proteins are integral to almost all of the biological processes that occur in living things. They are made up of amino acid sequences, and amino acids are produced based on the sequence of the genetic code.
DNA carries the genetic code – RNA translates it.
Genetics – field of biology dedicated to understanding how characteristics are transmitted from parents to offspring.

6. K – W - L What do you know about inheritance?
What do you want to know about inheritance?
What have you learned about inheritance?

7. Fundamentals of Genetics
All of your characteristics or traits are unique to you.
Parents may pass many of their own traits to their children, or offspring.
For example, the color of your hair, the size of your feet and the shape of your nose are some of
your traits.

8. Fundamentals of Genetics
The passing of these traits from parents to offspring is called heredity.
The study of heredity is called genetics.
Biologists who study
heredity are called
Geneticists.

9. Fundamentals of Genetics
Look at the photographs to the right.
What traits have these babies inherited from their parent?

10. Gregor Mendel The Father of Genetics
rpee Seeds and Plants Home> Vegetables > Peas > Pea, Easy Peasy
                                                
Gregor Mendel The Father of Genetics
Genetics was founded with the works of an Austrian Monk, scientists and mathematician Gregor Johann Mendel.
He experimented with garden pea plants.
One of the first people to study genetics was an Austrian monk and scientist, named Gregor Mendel. In the late 1800’s Mendel began studying the passing of traits from parents to offspring.
He, too wanted to know why certain patterns of traits showed up in living things.
Mendel knew nothing about chromosomes, genes, or DNA

11. Gregor Mendel
His task of tending the garden gave him time to observe the passing of traits from parent
pea plants to their offspring.
He became interested in why
certain patterns of
traits showed up
in living things.

12. Mendel began his experiments by collecting seeds from his pea plants, carefully recording the traits of each plant.
Seeds from tall plants usually produced tall plants but sometimes produced short plants.
Seeds from short plants only produced short plants.
…but, “WHY?”

13. Mendel’s Experiments
He studied 7 different characteristics in his pea plants, each with 2 contrasting traits.
CHARACTERISTIC-a distinguishing quality that an organism exhibits.
Ex: height, hair color, eye color, skin color.
TRAIT- specific hereditary options available for each characteristic.
Ex: tall height/short height, smooth/
blonde hair, brown/blue eyes,
Dark/light skin.

14. Inflated vs. Constricted
CHARACTERISTICS
TRAIT
1. Plant Height
Tall vs. Short
2. Seed Color
Yellow vs. Green
3. Seed Shape
Round vs. Wrinkled
4. Pod Color
Green vs. Yellow
5. Pod/Flower Location
Axial vs. Terminal
6. Pod Shape
Inflated vs. Constricted
7. Flower Color
Purple vs. White

15. Mendel’s Methods
He decided to grow plants that were purebred - having a trait that will always be passed to the next generation
The term strain denotes all plants that are pure for a trait.

16. Mendel Controlled Pollination
He produced 14 strains (one for each of the 14 traits he observed) by allowing the plants to self-pollinate for several generations
This became his Parent generation or his
“P1 Generation”
Mendel conducted his experiments with pea plants because they grow quickly and there are a lot of different kinds of pea plants.

17. Mendel Controlled Pollination
Pollination-transfer of pollen from anther (male flower part) to stigma (female flower part)
Self–Pollination – occurs on same plant
Cross Pollination – occurs between different plants

18. Mendel’s Methods
Then, Mendel cross pollinated plants that had contrasting traits to see what the offspring would look like. (P1 X P1- i.e. pure tall x pure short)
Would the offspring (F1 Generation – offspring of P1) be tall, short, or medium ?
Cross-pollination happens when pollen from one plant is transferred to the reproductive structure of another plant. The parent plants will produce a new plant. Cross-pollination happens in nature all the time.
It can happen when an insect sits on a flower and pollen sticks to the insect.

19. Mendel’s Results
In his first crosses, Mendel found that only one of the two traits appeared in the offspring plants –
(F1 generation).
For example, when he crossbred tall pea plants with short pea plants, the offspring (F1) were always tall.
F1 – the first generation that result from cross between P1, P2.
These plants are called the parent generation or P1.
Their offspring are called first-generation plants, or F1. In Mendel's experiment, all of the first-generation plants were tall.

20. After his first crosses, Mendel took those offspring plants (F1) and crossed them.
In these second crosses, both traits showed up again in the F2 generation.
(F2 GENERATION-offspring of crosses between the F1 generation).
He observed that ¾ of the plants had the same trait as the F1 generation.

21. This happened with every set of traits that Mendel studied.
The same results happened in every experiment. One trait, like being tall, was always there in the first generation (F1).
The other trait, like being short, seemed to go away; only to reappear again in the second generation (F2).
This happened with every set of traits that Mendel studied.

22. EXAMPLES:
Plant Height Cross
Seed Color Cross
Seed Shape Cross
Parent
P1 x P1
Tall x Short
All Tall Plants
Tall x Tall
¾ Tall
¼ Short
Yellow x Green
All Yellow Plants
Yellow x Yellow
¾ Yellow
¼ Green
Round vs. Wrinkled
All Round Plants
Round X Round
¾ Round
¼ Wrinkled
First Generation
F1 x F1
Second Generation F2

23. He called these controls “factors”
Mendel hypothesized that something in the pea plants was controlling the characteristics that came through
He called these controls “factors”
(We now know that these factors are really traits controlled by Genes)

24. Because each characteristic had two forms, he said there must be a pair of “factors” controlling each trait.
Each pair consists of alternate forms (we now call alleles) of the same trait; one from mother and one from father.

25. MENDEL’S 3 CONCLUSIONS:
Based on his findings, Mendel formulated three laws or principles of heredity:
1. Principle of Dominant and Recessiveness
2. Principle of Segregation
3. Principle of Independent Assortment

26. Principle of Dominant & Recessiveness
Through crossing thousands of pea plants, he was able to conclude that that both of these factors (alleles) together controlled the expression of a trait.
Dominant traits were controlled by dominant alleles and recessive traits were controlled by
recessive alleles.
Genes are the different parts of the DNA that decide the genetic traits a person is going to have. Alleles are the different sequences on the DNA-they determine a single characteristic in an individual. Another important difference between the two is that alleles occur in pairs. They are also differentiated into recessive and dominant categories. Genes do not have any such differentiation.

27. Principle of Dominant & Recessiveness
DOMINANT-can mask or dominate the other ‘factor’ and is displayed most often.
RECESSIVE-the ‘factor’ that can be covered up; is displayed less often.
Ex: the ‘factor’ (allele) for tall is dominant over the ‘factor’ (allele) for short, so the short allele would be the recessive allele.

28. Principle of Dominant & Recessiveness
Letters are used to represent the alleles that carry the trait found on genes
If the gene that controls the trait is dominant, the letter is written in uppercase.
If the gene is recessive, the letter is written in lowercase.
i.e. T- represents a dominant trait for tallness; t – represents a recessive trait for lack of tallness, or shortness

29. T – dominant allele for tallness
t – recessive allele for lack of tallness or shortness.
W – dominant allele for round or smooth seeds
w – recessive allele for wrinkled seeds
P – dominant for flower color (purple)
p – recessive allele for white flower

30. Vocabulary Review
GENE- a segment of DNA that codes for a specific characteristic.
Ex: height
ALLELE-the different forms of a gene (Mendel’s “factor”)
Ex: allele for brown eyes is B/ allele for blue eyes is b
SO…if BB is a brown eyed person and bb is a blue eyed person, what color eyes does someone with Bb have?

31. Principle of Segregation
Each parent has two factors (copies of each trait) and they segregate, or separate into different sex cells (gametes)
Each gamete
gets only 1 factor (allele)
of each trait

33. Principle of Independent Assortment
Mendel also crossed plants that differed in 2 characteristics, such as flower height and flower color.
The data from these crosses showed that dominant traits do not always appear together
ttP?

34. Principle of Independent Assortment
The alleles for different genes on different chromosomes are not connected.
The alleles for different traits are distributed into gametes independently (randomly) from each other.

35. Principle of Independent Assortment
Blue-eyed blonde Nmachi, whose name means “Beauty of God” in the Nigerian couple’s homeland, has baffled genetics experts because neither Ben nor wife Angela have ANY mixed-race family history.
Pale genes skipping generations before cropping up again could have explained the baby’s appearance.

36. Mendel’s law of independent assortment is supported by the fact that chromosomes segregate independently to gametes during meiosis.

37. Gregor Mendel and his pea plants experiments (1857-1865)

38. Do Now Who is the father of genetics?
What type of organism did he work with?
What are dominant and recessive traits?

39. Vocabulary Review Chromosomes – made of DNA
Gene – segment of DNA that controls a specific hereditary trait.
Because chromosomes occur in pairs, genes occur in pairs
Allele - (Mendel’s “factor”) – contrasting form of a gene
Dominant allele – capital letter
Recessive allele – lowercase letter
Most of Mendel’s findings agree with what biologists now know about molecular genetics – the study of the structure nad function of chromososmes and genes.

40. AFTER MENDEL
Today, Geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses.
Why would geneticists want to predict the probable genetic make up and appearance of offspring resulting from specified crosses?

41. GENOTYPE & PHENOTYPE
GENOTYPE-the genetic makeup of an organism (the combination of alleles an organism inherits).
Use 2 letters together to represent genotype.
PHENOTYPE-the trait displayed based on the genotype.
Ex: BB – Brown eyes
bb – Blue eyes
Bb – Brown eyes

42. GENETIC CROSSES

43. Blue alleles b b
Phenotype
Genotype

44. GENOTYPE & PHENOTYPE
Organisms with different genotypes may have the same phenotype.
For example, a brown-eyed organism (BB) and a brown eyed organism (Bb) have different genotypes.
However, they have the same phenotype, which is brown eyes

45. Brown Alleles
Brown Alleles B b B B
One pair of chromosomes
for eye color
One pair of chromosomes
for eye color

46. AFTER MENDEL

47. GENOTYPE & PHENOTYPE
HOMOZYGOUS- organism has 2 of the same alleles for a trait.
Homozygous Dominant-has 2 dominant alleles; dominant trait is displayed
Ex: BB = Brown-eyed organism
Homozygous Recessive-has 2 recessive alleles; recessive trait is displayed
Ex: bb = blue-eyed
HETEROZYGOUS-organism has 1 dominant and 1 recessive allele; the dominant trait is displayed.
Ex: Bb = brown eyes

48. Blue alleles
Brown Allele
Blue Allele b b b B
Homozygous –
alleles are the same
Heterozygous –
alleles are different

49. Do Now What are Mendel’s Laws of Inheritance?
What is an allele? What is homozygous vs. heterozygous?
What is genotype vs. phenotype?

50. Probability
In order to understand genetics you need to have some basic concepts concerning probability.
Probability – the likelihood that a specific event will occur
Can be expressed as a decimal, percentage, ratio or fraction.
P= number of times an event is expected to happen
number of opportunities for an event to happen

51. Probability
If you flip a coin once, what is the probability that it will land on heads? P(Event)= 1 (Heads) 2 (Heads or Tails) P= 1 2 ; .5; or 50%; 1:2 If you flip a coin twice, what is the probability that it will land on heads twice? P = 1 (Heads) 4 (Heads, Tails; Tails, Heads; Tails, Tails; Heads, Heads) P = ??
Expected event – the one you are predicting or want to happen
Possible outcome – how many different outcomes there are. (total number of times the event happens or can happen)

52. Predicting the Results of Genetic Crosses
Remember, probability is the likelihood that a chance event will occur.
The value of studying genetics is in understanding how we can predict the likelihood of inheriting particular trait.
The expected frequency of a particular event when an experiment is repeated an infinite number of times is the probability of the event. For a single coin toss, the probability of a head on a single toss is ½.
Predicating the likelihood of a particular trait can help plant and animal breeders in developing varieties that have more desirable qualities. It can also help people explain and predict patterns of inheritance in family lines.
His technique employs what we now call a Punnett square. This is a simple graphical way of discovering all of the potential combinations of genotypes that can occur in children, given the genotypes of their parents. It also shows us the odds of each of the offspring genotypes occurring.

53. Predicting the Results of Genetic Crosses
MONOHYBRID CROSS – a genetic cross between 2 individuals involving 1 pair of contrasting traits.

54. Predicting the Results of Genetic Crosses
One of the easiest ways to calculate the mathematical probability of inheriting a
specific trait was
invented by an early 20th
century English geneticist,
Reginald Punnett .
You can show probability as a percent by using this formula:
Number of times an event occurs
x 100 = Probability %
Number of total possible events
For example the probability for heterozygous tall (Tt) is:
2 x 100 = 2 x 100 = 200 = 50 %
Remember:
200/4 is the same as 200 divided by 4.
1 divided by 4 is the same as ¼
The Punnett square also shows that there is a 25% chance (1/4 X 100) that the offspring will be homozygous tall (TT) or homozygous short (tt).

55. Predicting the Results of Genetic Crosses
His technique employs what we now call a Punnett square.
A Punnett square is a chart that shows possible gene combinations of offspring of two parents whose genotypes are known.

56. HOW TO DRAW A PUNNETT SQUARE
1. Write what each allele means.
2. Write the genotypes of the parents.
3. Draw a grid.
4. Put the alleles for one parent along the top; put the alleles for the other parent along the side.
5. Fill in the grid.

57. EXAMPLE 1:HOMOZYGOUS X HOMOZYGOUS
T= tall plant TALL X SHORT
t = short plant (TT x tt)
Genotype = 4 Tt
Phenotype = 4 tall plants
Probability = number of times an event(tall) is expected to happen
number of opportunities (total) for an event to happen
Probability Ratio : 4/4 Probability percent: 100% T T Tt Tt t Tt Tt Tt t

58. EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS
T= tall plant TALL X SHORT
t = short plant (Tt x tt)
Genotype = 2 Tt, 2 tt
Phenotype = 2 tall, 2 short
Probability = number of times an event(tall/short) is expected to happen
number of opportunities (total) for an event to happen
Probability: 2/4 tall plants; 50% tall plants; 2:4
2/4 short plants; 50% short plants; 2:4 T t Tt tt t Tt Tt tt t

59. EXAMPLE 2:HOMOZYGOUS X HETEROZYGOUS
T= tall plant TALL X TALL
t = short plant (TT x Tt)
Genotype = 2 TT, 2 Tt
Phenotype = 4 Tall
Probability = number of times an event(tall/short) is expected to happen
number of opportunities (total) for an event to happen
Probability: 4/4 tall plants; 100% tall plants; 4:4
0% short T T TT T TT Tt Tt Tt t

60. EXAMPLE 2:HETEROZYGOUS X HETEROZYGOUS
T= tall plant TALL X TALL
t = short plant (Tt x Tt)
Genotype = 1 TT, 2 Tt, 1 tt
Phenotype = 3 Tall, 1 short
Probability = number of times an event(tall/short) is expected to happen
number of opportunities (total) for an event to happen
Probability: ¾ tall plants; 75%; 3:4
¼ short plants; 25%; 1:4 T t TT T Tt Tt Tt tt t

61. TESTCROSS
TESTCROSS - Cross to determine genotype of parent with dominant phenotype.
Use to determine if the unknown is heterozygous or homozygous dominant genotype.
Ex: A plant with green seed pods could have a genotype of GG or Gg.
Cross the unknown parent with a homozygous recessive.

62. T ? T t Tt T t ? t t Tt T t ? t Tt T= tall plant TALL X SHORT
EXAMPLE 2: ? ? X HOMOZYGOUS
T= tall plant TALL X SHORT
t = short plant (T? x tt)
If Phenotype = 4 Tall
Genotype of Unknown = TT T ? T Tt t
T t
? t Tt Tt
T t
? t t

63. T ? t t Tt ? t t t t Tt ? t t t Tt T= tall plant TALL X SHORT
EXAMPLE 2: ? ? X HOMOZYGOUS
T= tall plant TALL X SHORT
t = short plant (T? x tt)
If Phenotype = 3 Tall, 1 short
Genotype of Unknown = Tt T ? t Tt t
? t
t t Tt Tt
? t
t t t

65. More Complex Patterns of Heredity
The way genes control traits can be complex and interact in different ways.

66. All of these crosses we just did were examples of COMPLETE DOMINANCE.
COMPLETE DOMINANCE-one allele is totally dominant over the other allele.
EXAMPLE: PP and Pp = purple flower plants

67. Incomplete Dominance
When one gene for a certain trait is not completely dominant over the other gene, a blending effect occurs.
INCOMPLETE DOMINANCE is a type of inheritance in which one allele (dominant) for a specific trait is not completely dominant over the other (recessive) allele. This results in a combined phenotype (expressed physical trait).

68. Incomplete Dominance EXAMPLE: Four o’clocks (flowers)
RR = red rr = white Rr = pink
RED (RR) X WHITE (rr)
Genotype = 4Rr
Phenotype = 4 pink R R r
R r
R r r
R r
R r

69. Incomplete Dominance EXAMPLE: Four o’clocks (flowers)
RR = red rr = white Rr = pink
PINK (Rr) X PINK (Rr)
Genotype = 1 RR;2Rr;1rr
Phenotype = 1 red, 2 pink, 1 white R r R
R R
R r r
r r
R r

70. Codominance
Another pattern of heredity can occur when two dominant genes are present for a certain trait.
This pattern of heredity is called co-dominance (both variations of the gene appearing at the same time).
Neither allele is dominant or recessive, nor do they blend.
In the phenomenon of co-dominance, both dominant and recessive alleles lack their dominant and recessive relationships and both have capability to express themselves phenotypically

71. Codominance EXAMPLE: roan horse: RR – red coat color
R’R’ – white coat color
RR’ – roan coat – both red and white hairs
Genotype = 4 RR’
Phenotype = 4 Roan R R R’
R R’
R R’ R’
R R’
R R’

72. Codominance & Multiple Alleles
Many traits are controlled by one gene that has more than two possible variations.
These traits are controlled by multiple alleles.
Human blood groups are controlled by multiple alleles.

73. Codominance & Multiple Alleles
There are 3 alleles for the gene that determines blood type. A, B, O
(Remember: You have just 2 of the 3 in your genotype - 1 from mom & 1 from dad).
With three alleles,
we have a higher number of
possible combinations in
creating a genotype.
There are 6 different
genotypes and four different
phenotypes blood type.

74. IA IA IB IB Genotype = 4 IAIB Phenotype = 4 Blood Type AB
Blood Type A (IAIA) X Blood Type B (IBIB)
Genotype = 4 IAIB
Phenotype = 4 Blood Type AB IA IA IB
IAIB
IAIB IB
IAIB
IAIB

75. Possible Blood Type Combinations

76. FYI The A and B alleles are equally dominant.
A child who inherits and A allele from one parent and a B allele from the other parent will have type AB blood.
What type of dominance is this?
co-dominance
The O allele is recessive to both A and B alleles. A child who inherits an A allele from one parent and an O allele from the other parent will have a genotype of AO and a phenotype of Type A blood.
A child who inherits on O allele from one parent
and an O allele from the other will have:
Genotype?
Phenotype?

77. Predicting the Probability of a Dihybrid Crosses
Cross between individuals studying one trait is Monohybrid Cross
Cross between individuals studying two traits is Dihybrid Cross

78. Predicting the Probability of a Dihybrid Crosses
A DIHYBRID CROSS is more complicated than monohybrid because there are more possible combinations.
MONOHYBRID CROSS = 2 traits/4 possible offspring
DIHYBRID CROSS = 4 Traits/ 16 possible offspring

79. Predicting the Probability of a Dihybrid Crosses
Example: AA or Aa = purple; aa = white BB or Bb = tall; bb = short
AaBb x AaBb (Purple Flower, Short Plant x Purple Flower, Short Plant)

80. FYI
One really important thing that Mendel noticed from this type of cross was that traits (like flower color, height) are inherited independently - not together as a unit.
This is type of cross helped Mendel develop the Law of Independent Assortment.
REMEMBER - Law of Independent Assortment - Genes for various traits assort into gametes independently (due to homolouges lining up randomly at the metaphase plate.)

81. Dihybrid Cross Example:
Homozygous x Homozygous
Tall, Round Plant (TT RR) X Tall, Round Plant (TT RR)
First, we need to determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.
TTRR
TR, TR, TR, TR
TR, TR, TR, TR

82. Dihybrid Cross Example:
Homozygous x Homozygous
Tall, Round Plant (TT RR) X Tall, Round Plant (TT RR)
GENOTYPE: 16 TTRR
PHENOTYPE: 16 Tall, Round Plants
TR TR TR TR TR
TTRR
TTRR
TTRR
TTRR TR
TTRR
TTRR
TTRR
TTRR TR
TTRR
TTRR
TTRR
TTRR TR
TTRR
TTRR
TTRR
TTRR

83. Dihybrid Cross Example:
Heterozygous x Homozygous
LET’S TRY IT !!
Cross Tall, Round Plant (TtRr) X Short, Wrinkled Plant (ttrr)
Determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.
TtRr
ttrr
TR, Tr, tR, tr
tr tr tr tr

84. Dihybrid Cross Example:
Heterozygous x Homozygous
LET’S TRY IT !! Cross Tall, Round Plant (TtRr) X Short, Wrinkled Plant (ttrr)
GENOTYPE: 4TtRr, 4 Ttrr, 4 ttRr, 4 ttrr
tr tr tr tr
PHENOTYPE:
4 Tall, Round
4 Tall, Wrinkled
4 Short, Round
4 Short, Wrinkled
TtRr
TtRr
TtRr TR
TtRr Tr
Ttrr
Ttrr
Ttrr
Ttrr tR
ttRr
ttRr
ttRr
ttRr tr
ttrr
ttrr
ttrr
ttrr

85. Dihybrid Cross Example:
Heterozygous x Heterozygous
Cross Tall, Round Plant (TtRr) X Tall, Round Plant (TtRr)
Determine what alleles each parent could possibly give - all possible combinations of the alleles from each trait.
TtRr
TR, Tr, tR, tr
TR Tr tR tr

86. Dihybrid Cross Example:
Heterozygous x Heterozygous
Tall, Round Plant (Tt Rr) X Tall, Round Plant (Tt Rr)
GENOTYPE: 1 TTRR, 2TTRr, 2TtRR, 4TtRr,
1 TTrr, 2 Ttrr, 1ttRR, 2ttRr, 1 ttrr
TR Tr tR tr
TTRR
TtRR
TtRr TR
TTRr
PHENOTYPE:
9 tall, round
3 tall, wrinkled
3 short, round
1 short, wrinkled
Phenotypic
Ratio= 9:3:3:1 Tr
TTRr
TTrr
TtRr
Ttrr tR
TtRR
TtRr
ttRr
ttRR tr
ttrr
TtRr
Ttrr
ttRr