1. TOPIC INHERITANCE

2. 3.4 – A – Inheritance & Alleles

3. IB BIO – 3.4
Gregor Mendel was an Austrian monk who is known as the father of genetics.
He noted that pea plants in his garden had characteristics that were sometime passed on to offspring. 3
Understandings
U1: Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
Key Terms
Gregor Mendel

4. IB BIO – 3.4
To study how pea plants pass on traits, he bred plants for that were pure for seven traits. Those traits included: 4
Understandings
U1: Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
Key Terms
Gregor Mendel

5. IB BIO – 3.4
Then, he crossed large numbers of plants with different characteristics to determine which traits would appear in offspring.
His observations allowed him to discover the principles of inheritance which are discussed in this topic.
*See the video at the end of this Topic for further explanation 5
Understandings
U1: Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
Key Terms
Gregor Mendel

6. IB BIO – 3.4
As discussed in Topic 3.3, meiosis results in haploid gametes, which only contain half the chromsomes and one allele of each gene. 6
Understandings
U2: Gametes are haploid so contain only one allele of each gene.
U3: The two alleles of each gene separate into different haploid daughter nuclei during meiosis.
A zygote results when two gametes fuse together. It is able to grow and develop into an adult organism.
Key Terms
Haploid / Diploid

7. IB BIO – 3.4
During gamete production, the two alleles for a gene segregate into different daugher nuclei. The overall combination of alleles in the resulting cells is random, promoting variation. 7
Understandings
U2: Gametes are haploid so contain only one allele of each gene.
U3: The two alleles of each gene separate into different haploid daughter nuclei during meiosis.
Key Terms

8. IB BIO – 3.4
When gametes fuse, the resulting diploid zygote has two alleles for every gene. These alleles may be the same or different.
Heterozygous – the two alleles for a gene are different
Homozygous – the two alleles for a gene are the same 8
Understandings
U4: Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.
Key Terms

9. IB BIO – 3.4
Practice 9
Understandings
U4: Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.
Determine whether the following are Heterozygous or Homozygous
Key Terms

10. IB BIO – 3.4
When discussing inherited traits, two important terms are used:
Genotype – the combination of alleles an organism has, typically shown using pairs of letters.
Phenotype – the observable physical characteristics 10
Understandings
U5: Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
Key Terms
Genotype
Phenotype

11. IB BIO – 3.4
Some alleles are able to mask the effects of others when they are present. These are called dominant alleles and are represented using upper case letters (A = purple).
Recessive alleles are those that are masked by dominant alleles. They are represented using lower case letters (a = white). 11
Understandings
U5: Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
Key Terms
Dominant Allele
Recessive Allele

12. Determine the phenotype in the following examples
IB BIO – 3.4
Practice 12
Understandings
U5: Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
Determine the phenotype in the following examples
Key Terms

13. IB BIO – 3.4
Co-dominance occurs when co-dominant alleles are present. These have joint effects and so are both seen in the phenotype. In the example here, red and white alleles mix to form a pink flower. 13
Understandings
U5: Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
Key Terms
Co-dominant Allele

14. VIDEOS TedEd – How Mendel’s Pea Plants Helped Us Understand Genetics
IB BIO – 3.4
TedEd – How Mendel’s Pea Plants Helped Us Understand Genetics
CrashCourse - Heredity 14
VIDEOS

15. IB BIO – 3.4
Outline Mendel’s use of peas in discovering principles of genetics.
Describe the segregation of alleles during meiosis.
Define the following: - Genotype - Phenotype - Heterozygous - Homozygous
Compare the effects of dominant and recessive alleles.
Describe co-dominance using an example. 15
REVIEW

16. 3.4 – B – Monohybrid Crosses

17. IB BIO – 3.4
Punnett grids are a tool that can be used to predict the outcomes of monohybrid crosses. These are crosses that involve the study of a single trait. 17
Skills
S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
Key Terms
Punnett Grid
Monohybrid Cross

18. IB BIO – 3.4 Using Punnett Grids18
Skills
S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
Determine the genotype of the parents and write them as a cross (i.e. Rr x Rr). _______ X _________
Write the genotypes of the parents on the top and left side of the Punnett grid. There should be one allele per box on each side.
Key Terms
Punnett Grid
Monohybrid Cross

19. IB BIO – 3.4 Using Punnett Grids19
Skills
S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
Use the genotypes on the outside of the grid to fill in the squares with completed genotypes.
Determine the number of each type of genotype and phenotype. This can be used to predict ratios of offspring.
Key Terms
Punnett Grid
Monohybrid Cross

20. https://d2gne97vdumgn3.cloudfront.net/api/file/iOA8caDKSK2Th0aVHRNg
IB BIO – 3.4
Punnett Grid Example 1 20
Skills
S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
A heterozygous yellow pea plant is crossed with a homozygous green pea plant. What percentage of offspring will be yellow?
Y = yellow (dominant) y = green (recessive)
Yy x yy
Genotype: % yy % Yy
Phenotype: % green % yellow
Key Terms
Punnett Grid
Monohybrid Cross

21. BB x Bb IB BIO – 3.4 Punnett Grid Example 221
Skills
S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
A heterozygous brown-eyed man reproduces with a homozygous brown-eyed woman. What portion of offspring will be blue-eyed?
B = brown (dominant) b = blue (recessive)
BB x Bb
Genotype: % Bb % BB
Phenotype: % brown % blue
Key Terms
Punnett Grid
Monohybrid Cross

22. IB BIO – 3.4
Human blood types are determined by the presence of proteins on the surface of red blood cells. The blood types of parents’ offspring can be predicted using monohybrid Punnett squares. 22
Applications
A1: Inheritance of ABO blood groups.
Key Terms
Blood Type

23. IB BIO – 3.4 Blood Type Genotypes23
There are four blood types in humans: A, B, AB and O. The genotype for each is shown in the table below. Each allele is represented as an I with a superscript or i (absence of protein).
Applications
A1: Inheritance of ABO blood groups.
Key Terms
Blood Type

24. Determining Blood Type – Example 1
IB BIO – 3.4
Determining Blood Type – Example 1 24
Punnett grids for blood types are used the same way as other monohybrid crosses. For example, this grid shows the results of crossing two AB individuals:
IAIB x IAIB
Applications
A1: Inheritance of ABO blood groups. IA IB
Key Terms
Blood Type

25. Determining Blood Type – Example 1
IB BIO – 3.4
Determining Blood Type – Example 1 25
Punnett grids for blood types are used the same way as other monohybrid crosses. For example, this grid shows the results of crossing two AB individuals:
IAIB x IAIB
Genotypes: % IAIB % IAIA % IBIB
Phenotypes: % AB % A % B
Applications
A1: Inheritance of ABO blood groups. IA IB
IAIA
IAIB
IBIB
Key Terms
Blood Type

26. Determining Blood Type – Example 2
IB BIO – 3.4
Determining Blood Type – Example 2 26
If a heterozygous Type A male mates with a heterozygous Type B female, what percentage of the offspring will have Type O blood?
IAi x IBi
Applications
A1: Inheritance of ABO blood groups. IB i IA
Key Terms
Blood Type

27. Determining Blood Type – Example 2
IB BIO – 3.4
Determining Blood Type – Example 2 27
If a heterozygous Type A male mates with a heterozygous Type B female, what percentage of the offspring will have Type O blood?
IAi x IBi
Genotypes: % IAIB % IAi % IBi % ii
Phenotypes: % AB % A % B % O
Applications
A1: Inheritance of ABO blood groups. IB i IA
IAIB
IAi
IBi ii
Key Terms
Blood Type

28. VIDEOS Learn Biology: How to Set Up a Punnett Square
IB BIO – 3.4
Learn Biology: How to Set Up a Punnett Square
SciShow: What are Blood Types
TedEd: Why Do Blood Types Matter 28
VIDEOS

29. IB BIO – 3.4
Outline the use of Punnett Squares in predicting the outcomes of monohybrid crosses.
If wrinkled pea plant (Ww) is crossed with a smooth pea plant (ww), what percentage of the offspring would be smooth.
If a Type O woman mated with a Type AB male, what percentage of their offspring would have: - Type O Blood? - Type AB Blood? - Type A Blood? 29
REVIEW

30. 3.4 – C –Diseases & Sex-Linkage

31. IB BIO – 3.4
Genetic diseases are disorders that are caused by errors in the genome. Most result from recessive alleles on the autosomal chromosomes (1-22), though some are the result of dominance.
Many diseases have been found in humans, but most are very rare. Improving genetic techniques are allowing scientistics to identify and study more. 31
Understandings
U6: Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some diseases are due to dominant or co-dominant alleles.
U8: Many genetic diseases have been identified in humans but most are very rare.

32. IB BIO – 3.4
Cystic fibrosis is a genetic diseases that results from recessive allele on chromosome #7.
The allele produces Cl- ion channels that increases chloride levels in sweat and decreases levels in mucus.
This interferes with osmosis, which causes a buildup of thick mucus outside of the cell membranes. 32
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Cystic Fibrosis

33. IB BIO – 3.4 Sticky mucus builds up in the lungs, which causes:
Frequent infections
Trouble Breathing
The pancreatic duct is also blocked, which causes:
Trouble digesting food
Abnormal pancreas activity/function 33
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Cystic Fibrosis

34. IB BIO – 3.4 34
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Cystic Fibrosis

35. IB BIO – 3.4
Since cystic fibrosis is an autosomal recessive disease, Punnett grids can be used to determine how the trait will pass from parent to offspring.
Chances of inheriting the disease are not related to sex. 35
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Cystic Fibrosis

36. IB BIO – 3.4
Huntington’s disease (HD) is a genetic disease caused by a dominant allele on chromosome #4. Because the allele is dominant, any individual who has even one copy of it will be affected. 36
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Huntington’s Disease

37. IB BIO – 3.4
The HD allele causes degenerative changes in the brain, which typically starts between ages Eventually, affected individuals require nursing care and succumb to infectious diseases. 37
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Huntington’s Disease

38. IB BIO – 3.4
Punnett grids like the one here can be used to predict the likelihood of parents passing on Huntington’s disease. Like cystic fibrosis, inheritance of the condition is independent of sex. 38
Applications
A3: Inheritance of cystic fibrosis and Huntington’s disease.
Key Terms
Huntington’s Disease

39. IB BIO – 3.4
Other genetic diseases can be linked to sex, which means the associated alleles are located on the sex chromosomes (23).
As a result, the sex of offspring can determine the likelihood of inheriting these disease.
Two common examples include:
Red-Green Color Blindness
Hemophilia 39
Understandings
U7: Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.
Key Terms
Sex-linked

40. IB BIO – 3.4
Punnett grids can be used to determine the inheritance of sex- linked traits. The sex chromosomes of the parents are used instead of autosomal alleles (male = XX, female = XY). The general setup is shown here: 40
Understandings
U7: Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. X XX Y XY
Key Terms
Sex-linked

41. Red-Green Colour Blindness
IB BIO – 3.4
Red-green color blindness is a sex-linked condition caused by a recessive allele on the X chromosome.
Since males have only one X, they are more likely to be affected than women, who have two alleles for each X-linked gene. 41
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
Key Terms
Red-Green Colour Blindness

42. Red-Green Colour Blindness
IB BIO – 3.4
Those with the disease have mutated genes for red or green color receptors in the retina. As a result, they are unable to properly distinguish the two colors. 42
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
Key Terms
Red-Green Colour Blindness

43. XBXb XBY XbXb XbY Xb Y XB XBXb x XbY IB BIO – 3.4
Sex-Linked Inheritance Example 1 43
If a male with color blindness mates with a carrier female, what percentation of their sons will have the trait?
B = normal b = color blind
XBXb x XbY
Sons: % XBY (normal) % XbY (color blind) Daughters: % XBXb (carrier) % XbXb (color blind)
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance. Xb Y XB
XBXb
XBY
XbXb
XbY
Key Terms
Red-Green Colour Blindness

44. IB BIO – 3.4
Hemophilia is another genetic disease caused by a recessive allele on the X-chromosome. The disease prevents the ability to form Factor VIII, which is vital for blood clotting. It is life-threatening. 44
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
Key Terms
Hemophilia

45. IB BIO – 3.4
Individuals with this disorder typically have a life expectancy of about 10 years if left untreated. Treatment involves infusing Factor VIII isolated from donor blood sources. 45
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
Key Terms
Hemophilia

46. Sex-Linked Inheritance Example 2
IB BIO – 3.4
Sex-Linked Inheritance Example 2 46
If a female with a hemophilia mates with a normal male, what percentage of their daughters will have the trait?
H = normal h = hemophilia
XhXh x XHY
Sons: % XhY (hemophiliac) Daughters: % XHXh (carrier) % XhXh (hemophiliac)
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance. XH Y Xh
XHXh
XhY
Key Terms
Hemophilia

47. Sex-Linked Inheritance Example 3
IB BIO – 3.4
Sex-Linked Inheritance Example 3 47
If a famale carrier for hemophilia mates with an affected male, what percentage of their daughters will have the trait?
H = normal h = hemophilia
XHXh x XhY
Sons: % XHY (normal) % XhY (hemophiliac) Daughters: % XHXh (carrier) % XhXh (hemophiliac)
Applications
A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance. Xh Y XH
XHXh
XHY
XhXh
XhY
Key Terms
Hemophilia

48. REVIEW Define genetic disease.
IB BIO – 3.4
Define genetic disease.
Outline the inheritance of Huntington’s disease and cystic fibrosis.
Define sex-linked disease.
Compare autosomal and sex-linked traits.
Outline the inheritance of hemophilia and red-green colorblindness. 48
REVIEW

49. 3.4 – D – Pedigrees

50. IB BIO – 3.4
Pedigrees are charts that show the passing of traits through a family. The typical conventions for constructing them are: 50
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
= male = affected male I, II, III = generation
= female = affected female = mating
Key Terms
Pedigree

51. IB BIO – 3.4
Patterns observed in pedigrees can be used to determine the type of disease/trait that is being studied. The typical possibilities are: Autosomal recessive - Autosomal dominant X-linked recessive - X-linked dominant 51
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Autosomal Recessive
Traits can skip generations and appear later
Males and females are affected equally
Key Terms
Pedigree

52. IB BIO – 3.4 Autosomal Recessive52
Determine the genotypes of as many members in this pedigree as possible. The genotypes of some members cannot be determined.
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases. aa
Aa or AA Aa
Key Terms
Pedigree

53. IB BIO – 3.4 Autosomal Dominant53
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Traits do not normally skip generations
Unaffected members are homozygous recessive
Traits affect males and females equally Aa aa
Key Terms
Pedigree

54. IB BIO – 3.4 XbXb XBY XbY XBXb X-linked Recessive54
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Traits tend to affect males more than females
Unaffected males have the normal X allele
XbXb
XBY
XbY
XBXb
Key Terms
Pedigree

55. IB BIO – 3.4 XBXb XbY XBY XbXb XbY X-linked Dominant55
Skills
S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Traits affect all individuals that have the dominant allele
Homozygous affected females pass trait on to all offpsring
XBXb
XbY
XBY
XbXb
XbY
Key Terms
Pedigree

56. IB BIO – 3.4
Determine the type of characteristic and the genotypes in the following pedigree: 56
REVIEW
Autosomal Dominant

57. IB BIO – 3.4
Determine the type of characteristic and the genotypes in the following pedigree: 57
REVIEW
X-linked Dominant

58. 3.4 – E – Genetic Mutations

59. IB BIO – 3.4
As discussed in Topic 3.1, mutations are changes in DNA that can result in new alleles. The rate of mutation can be affected by two types of factors: radiation & mutagenic chemicals. 59
Understandings
U9: Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
Key Terms

60. IB BIO – 3.4
Radiation increases the rate of mutation by adding enough energy to cause chemical changes in DNA molecules. This includes ultraviolet radiation, X-rays and radioactive materials. 60
Understandings
U9: Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
Key Terms
Radiation

61. IB BIO – 3.4
Mutagenic chemicals are those that cause chemical changes to the DNA sequence.
Where as radiation is energy, mutagenic chemicals are made of matter.
Such chemicales include those found in:
Tobacco
Mustard gas
Nitrous Acid 61
Understandings
U9: Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
Key Terms
Mutagenic Chemicals

62. IB BIO – 3.4
Mutations that occur in adult cells can causes diseases such as cancer, but are not passed on to offspring.
However, mutations in cells that develop into gametes can be inherited by offspring.
So, mutations in gametes are the origin of genetic diseases. 62
Understandings
U9: Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
Key Terms

63. IB BIO – 3.4
Hiroshima was one of two Japanese cities hit with a number bomb during World War II. The explosion released radioactive isotopes into the environment which the people were then exposed to. 63
Applications
A4: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
Key Terms
Hiroshima

64. IB BIO – 3.4
Most who survived the blast died within a few months due to the radiation exposure.
The health of survivors were tracked for over 50 years. They showed a higher occurrence of tumors compared to control populations
In the following years, there was also an increase in mutations, causing:
Stillbirths
Malformations
Deaths 64
Applications
A4: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
Key Terms
Hiroshima

65. IB BIO – 3.4
In 1986, a nuclear power plant in Chernobyl, Ukraine released radioactive isotopes after an explosion in its nuclear core. 65
Applications
A4: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
Key Terms
Chernobyl

66. IB BIO – 3.4
Over 6 tonnes of radioactive material was released in the atmosphere, which had widespread and severe effects: 66
Applications
A4: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
4 km2 of downwind forest browned and died
Local cattle died from damaged thyroids
After humans left the area, local wildlife thrived nearby
Bioaccumulation of radioactive materials was seen across Europe
More than 6,000 cases of thyroid cancer were reported
Key Terms
Chernobyl

67. IB BIO – 3.4
PBS News: Health Effects of Hiroshima and Nagasaki Atomic Bombings Still Carefully Tracked
Veritasium: A Walk Around Chernobyl
Euronews: Chernobyl – 30 Years on, Health Issues Remain
NYT: The Animals of Chernobyl 67
VIDEOS

68. IB BIO – 3.4
List two examples of the following: - Mutation-causing radiation - Mutagenic chemicals
Outline consequences of the following events: - Nuclear bombing of Hiroshima - Chernobyl Power Plant Accident 68
REVIEW