1. Genetics
Chapter 11, 12, & 14

2. Gregor Mendel’s Peas Genetics is the scientific study of heredity.
Heredity is the passing on of traits from parents to offspring
Gregor Mendel
Nickname: Father of Genetics
worked with pea plants
work was important to the
understanding of heredity
Mendel carried out his work with ordinary garden peas.
self-pollinating: when sperm and egg come from same plant
inherit all of their characteristics from a single plant
cross-pollination: having pollen from one plant fertilize the egg of another plant
True-breeding: organisms that only have one version of each trait
Made by allowing the plants to self-pollinate for many generations

3. Gregor Mendel’s Peas Fertilization: when sperm and egg cells join
to make a new cell
Gene: a section of DNA that codes for a specific trait.
A trait is a specific characteristic that varies from one individual to another.

4. F1 generation: offspring of the P generation
parental generation, or P generation: organisms that you originally cross
F1 generation: offspring of the P generation
F2 generation: offspring of the F1 generation
Mendel then cross-pollinated two P generation plants that showed different forms for the same trait (ex: one produced white flowers and the other produced purple flowers).
The offspring from the cross are called the F1, or “first filial,” generation.
Filius is Latin for “son”
The offspring of crosses between parents with different traits are called hybrids.
The F1 hybrid plants all had the character of only one of the parents (ex: all the offspring only produced purple flowers)

5. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
What does the P stand for? Parental
What are the traits? Seed shape, seed color, seed coat color, pod shape
What are the alleles for seed shape? Round and wrinkled
What are the alleles for see color? Yellow and green
What are the alleles for seed coat color? Grey and white
What are the alleles for pod shape? Smooth and constricted
Why did only one version show in the offspring (F1 generation)? Because that allele is dominant.
What is the dominant allele for seed shape? Round

6. Rule of Inheritance
Each person has 2 copies of each gene, 1 from each parent.
Alleles: versions of a gene
determine your physical characteristics

7. Principle of Dominance
The principle of dominance states that some alleles are dominant and others are recessive.
Dominant, if present, always masks recessive
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.
An organism with a dominant allele for a trait will always exhibit that form of the trait.
An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present.

8. Dominant: allele physically seen or expressed if present; represented by a capital letter (A, B, T)
Recessive: only expressed if both alleles are recessive; represented by a lower case letter (a, b, t)
allele may be present but not physically seen if the dominant version is present

9. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.

10. Homozygous: organisms that have two identical alleles for a particular trait, true-breeding for that trait
Ex: TT (Tall), tt (short)
Heterozygous: organisms that have two different alleles, hybrids for that trait
Ex: Tt (Tall), Yy (Yellow Seed)

11. Genetics Terms
Homozygous Dominant: organisms that have both dominant alleles for a particular trait
Ex: TT (Tall), YY (Yellow Seed), WW (Widow’s Peak)
Homozygous Recessive: organisms that have both recessive alleles for a particular trait
Ex: tt (Short), yy (Green Seed), ww (Straight Line)

12. Genotype: genetic makeup
Ex: heterozygous, Tt
Phenotype: physical characteristics, determined by alleles/genotype
Ex: Tall

13. Genes and Dominance

14. The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).
Although these plants have different genotypes (TT and Tt), they have the same phenotype (tall). TT
Homozygous Tt
Heterozygous

15. P (tt: short) X P (TT: tall) = F1 (Tt: tall)
Mendel then cross-pollinated two P generation plants that showed different forms for the same trait (ex: one produced white flowers and the other produced purple flowers).
The offspring from the cross are called the F1, or “first filial,” generation.
Filius is Latin for “son”
The offspring of crosses between parents with different traits are called hybrids.
The F1 hybrid plants all had the character of only one of the parents (ex: all the offspring only produced purple flowers)

16. Law of Segregation
The Law of Segregation states that the two alleles responsible for a trait separate from each other when gametes, or sex cells, are formed (meiosis).
A gamete will receive one allele or the other.
Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

17. Applying the Law of Segregation

18. Mendel’s Original Cross P (tt: short) X P (TT: tall) = F1 (Tt: tall)
Mendel’s Second Cross (Two heterozygous plants)
F1 (Tt: tall) X F1 (Tt: tall)
= F2 (TT; Tt; tt; some tall some short)
Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation.
The traits controlled by recessive alleles reappeared in one fourth of the F2 plants.
Mendel assumed that a dominant allele had masked the corresponding recessive allele in the F1 generation.
The trait controlled by the recessive allele showed up in some of the F2 plants.
This indicated that at some point the allele for shortness had been separated, or segregated, from the allele for tallness.

19. Mendel's F2 Generation F1 Generation F2 Generation P Generation Tall
When Mendel allowed the F1 plants to reproduce by self-pollination, the traits controlled by recessive alleles reappeared in about one fourth of the F2 plants in each cross.
Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation.
The traits controlled by recessive alleles reappeared in one fourth of the F2 plants.
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short

20. Segregation Alleles separate during gamete formation.
During gamete formation, alleles segregate from each other so that each gamete carries only a single copy of each gene. Each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness. The alleles are paired up again when gametes fuse during fertilization. The TT and Tt allele combinations produce tall pea plants; tt is the only allele combination that produces a short pea plant.
Each F1 plant produces two types of gametes—those with the allele for tallness, and those with the allele for shortness.

21. Heterozygous Segregation
What is the probability that the parent will give the offspring the dominant allele?
50%
Organisms that are heterozygous for a trait have a 50% chance of passing on either the dominate or recessive allele to their offspring
Parent Aa A a
50% Chance
50% Chance

22. Genetics and Probability
The likelihood that a particular event will occur is called probability.
The principles of probability can be used to predict the outcomes of genetic crosses.

23. Probabilities Predict Averages
Probabilities predict the average outcome of a large number of events.
Probability cannot predict the precise outcome of an individual event.
Just because it was predicted to happen does NOT mean it will happen
In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

24. Punnett Squares

25. Punnett Squares
Punnett square: diagram used to predict and compare the gene combinations that might result from a genetic cross

27. Types of Genetic Crosses
Monohybrid cross - cross involving a single trait e.g. flower color
Dihybrid cross - cross involving two traits e.g. flower color & plant height

28. Monohybrid Crosses

29. t t Tt Tt T T Tt Tt P1 Monohybrid Cross Trait: Plant Height
Alleles: T – Tall t – short
Cross: Tall plant x Short plant
TT x tt
Genotype: Tt
Phenotype: Tall
Genotypic Ratio: All alike
Phenotypic Ratio: All alike t t Tt Tt T T Tt Tt

30. P1 Monohybrid Cross Review
Homozygous dominant x Homozygous recessive
Offspring all Heterozygous (hybrids)
Offspring called F1 generation
Genotypic ratio is ALL ALIKE
Phenotypic ratio is ALL ALIKE
4 tall plants

31. T t TT Tt T t Tt tt F1 Monohybrid Cross Trait: Plant Height
Alleles: T – Tall t – short
Cross: Tall plant x Tall plant
Tt x Tt
Genotype: TT, Tt, tt
Phenotype: Tall & short
G.Ratio: 1:2:1
P.Ratio: 3:1 T t TT Tt T t Tt tt

32. F1 Monohybrid Cross Review
Heterozygous x heterozygous
Offspring: 25% Homozygous dominant TT 50% Heterozygous Tt 25% Homozygous Recessive tt
Offspring called F2 generation
Genotypic ratio is 1:2:1
Phenotypic Ratio is 3:1
3 tall plants to 1 short plan

33. Independent Assortment
The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.
Just because you get the tall allele doesn’t mean you’ll get the purple flower allele
Today we know that it is the chromosomes that segregate independently.
Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

34. Independent Assortment
To determine if the segregation of one trait affects the segregation of another trait, Mendel performed a two-factor cross.
Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy).

35. All of the F1 offspring produced round yellow peas (RrYy).
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.

36. 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

37. In Mendel’s experiment, the F2 generation produced the following:
some seeds that were round and yellow
some seeds that were wrinkled and green
some seeds that were round and green
some seeds that were wrinkled and yellow
The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment.
These genes do not influence each other's inheritance. (example: just because you have blue eyes does not mean you will inherit blonde hair too)

38. Dihybrid Cross: Gamete Formation
Traits: Seed shape & Seed color
Alleles: R round r wrinkled Y yellow y green
FOIL!!!!!!!!!
RrYy x RrYy
RY Ry rY ry
RY Ry rY ry
All possible gamete combinations

39. Two Factor Cross: RrYy x RrYy
The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation.
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.

40. Two Factor Cross RRYY x rryy
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.

41. FOIL!!!!!! Dihybrid Cross TtRr x TtRr
Traits: Plant height & Seed shape
Alleles:
T tall & t short
R round & r wrinkled
FOIL!!!!!!
TtRr x TtRr
TR Tr tR tr
TR Tr tR tr
All possible gamete combinations

42. Dihybrid Cross TR Tr tR tr TR Tr tR tr

43. Dihybrid Cross TR Tr tR tr Tall/Round: 9 Tall/wrinkled: 3
short/Round: 3
short/wrinkled: 1
9:3:3:1 phenotypic ratio TR Tr tR tr
TTRR
TTRr
TtRR
TtRr
TTRr
TTrr
TtRr
Ttrr
TtRR
TtRr
ttRR
ttRr
TtRr
Ttrr
ttRr
ttrr

44. A Summary of Mendel's Principles
Genes are passed from parents to their offspring. (Rule of Inheritance)
If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive (Law of Dominance).

45. In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed. (Law of Segregation)
The alleles for different genes usually segregate independently of one another. (Principle of Independent Assortment)

46. Human Traits Pedigree Charts
shows the relationships within a family and follows how a particular trait is passed down

47. Human Traits A square represents A circle represents
a male.
A circle represents
a female.
A vertical line and a bracket connect the parents to their children.
A horizontal line connecting a male and a female represents a marriage.
A circle or square that is not shaded indicates that a person does not express the trait.
A shaded circle or square indicates that a person expresses the trait.
This drawing shows what the symbols in a pedigree represent.
Active Art:
PHSchool.com
Cpb-4141

48. Sometimes there can be a half-shaded circle or square
Half-shaded = heterozygous
Carrier = has one allele for the trait but does not show the trait (heterozygous)

49. Pedigree checklist
1. Is the trait dominant or recessive? 2. Fill in the genotypes of the recessive individuals. 3. Give the dominant individuals 1 dominant letter. 4. Look at the parents and/or kids of the dominant people to figure out their other letter.

50. The following is a pedigree chart showing the inheritance of a rare lung disease in a family.
Individuals who are homozygous dominant (AA) do not have the disease.
Individuals who are
heterozygous (Aa) do not have the disease but are said to be carries of the disease.
Individuals who are homozygous recessive (aa) have the lung disease.
What are the genotypes of the lettered individuals? aa Aa Aa
AA or Aa

51. Human Chromosomes
Karyotype: A picture of a full set of an organisms chromosomes arranged in pairs
Cell biologists analyze chromosomes by looking at karyotypes.
Cells are photographed during mitosis. Scientists then cut out the chromosomes from the photographs and group them together in pairs.

52. Human Chromosomes
sex chromosomes: a pair of human chromosomes that determine gender
Females = XX
Males = XY
Autosomes, or autosomal chromosomes: remaining chromosomes that do not determine gender

53. Pre-Sorted:

54. Post-Sorted:
It’s A Boy!

55. Mutations
12-4 Mutations

56. Mutations are changes in the genetic material.
Mutations that produce changes in a single gene are known as gene mutations.
Mutations that produce changes in whole chromosomes are known as chromosomal mutations.

57. Chromosomal Mutations
involve changes in the number or structure of chromosomes
include deletions, duplications, inversions, and translocations

58. Deletions involve the loss of all or part of a chromosome.
Chromosomal mutations involve changes in whole chromosomes.

59. Duplications produce extra copies of parts of a chromosome.
Chromosomal mutations involve changes in whole chromosomes.
Movie: Duplication

60. Inversions reverse the direction of parts of chromosomes.
Chromosomal mutations involve changes in whole chromosomes.

61. Translocations occurs when part of one chromosome breaks off and attaches to another.
Chromosomal mutations involve changes in whole chromosomes.
Movie: Translocation and inversion

62. Chromosomal Disorders
Nondisjunction
chromosomes fail to separate
can cause a person to have more than 2 or less than 2 of a chromosome
Meiosis I:
Nondisjunction
Nondisjunction causes gametes to have abnormal numbers of chromosomes. The result of nondisjunction may be a chromosome disorder such as Down syndrome.
Movie: Nondisjunction
Meiosis II

63. Chromosomal Disorders
Down Syndrome Karyotype
Down syndrome involves three copies of chromosome 21.
This karyotype is from a person with Down syndrome. Down syndrome causes mental retardation and various physical problems. People with Down syndrome can, however, lead active, happy lives. Photo credit: ©Dr. Dennis Kunkel/CNRI/Phototake

64. Sex chromosomes abnormalities
Human development more tolerant of wrong numbers in sex chromosome
But produces a variety of distinct syndromes in humans
XXY = Klinefelter’s syndrome male
XXX = Trisomy X female
XYY = Jacob’s syndrome male
XO = Turner syndrome female

65. Klinefelter’s syndrome
XXY male
one in every 2000 live births
have male sex organs, but are sterile
feminine characteristics
some breast development
lack of facial hair
tall
normal intelligence

66. Jacob’s syndrome male XYY Males 1 in 1000 live male births
extra Y chromosome
slightly taller than average
more active
normal intelligence, slight learning disabilities
delayed emotional maturity
normal sexual development

67. Trisomy X XXX 1 in every 2000 live births produces healthy females
Why?
Barr bodies
all but one X chromosome is inactivated
How many Barr bodies would you expect?

68. Turner syndrome Monosomy X or X0 1 in every 5000 births
varied degree of effects
webbed neck
short stature
sterile
How many Barr bodies would you expect?