UNIT ____: Genetic Inheritance Name: _____________________
Essential Idea(s):
- The inheritance of genes follows patterns.
- Genes may be linked or unlinked and are inherited accordingly.
IB Assessment Statements and Class Objectives
3.4.U1: Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
- Describe Mendel’s pea plant experiments.
3.4.NOS: Making quantitative measurements with replicates to ensure reliability, Mendel’s genetic crosses with peas plants generated numerical data.
- Outline why Mendel’s success is attributed to his use of pea plants.
- List three biological research methods pioneered by Mendel.
3.4.U2: Gametes are haploid so contain only one allele of each gene.
- Define gamete and zygote.
- State two similarities and two differences between male and female gametes
3.4.U4: Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles
- Outline the possible combination of alleles in a diploid zygote for a gene with two alleles.
- Outline the possible combination of alleles in a diploid zygote for a gene with three alleles.
3.4.S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
- Define monohybrid, true breeding, P and F1.
- Determine possible alleles present in gametes given parent genotypes.
- Construct Punnett grids for single gene crosses to predict the offspring genotype and phenotype ratios.
3.4.U5: Dominant alleles mask the effect of recessive alleles but codominant alleles have joint effects.
- Define dominant allele and recessive allele.
- State an example of a dominant and recessive allele found in pea plants.
- State the usual cause of one allele being dominant over another.
- Define codominant alleles.
- Using the correct notation, outline an example of codominant alleles.
3.4.U9: Many genetic diseases have been identified in humans but most are very rare.
- List five example genetic diseases.
- Explain why most genetic diseases are rare in a population.
3.4.U6: Many genetic diseases in human are due to recessive alleles of autosomal genes.
- Define “carrier” as related to genetic diseases.
- Explain why genetic diseases usually appear unexpectedly in a population.
D.1.A2: Cause and treatment of phenylketonuria.
- Outline the genetic cause of phenylketonuria.
- List consequences of phenylketonuria if untreated.
3.4.U7: Some genetic diseases are sex-linked and some are due to dominant or codominant alleles.
- Describe why it is not possible to be a carrier of a disease caused by a dominant allele.
- Outline inheritance patterns of genetic diseases caused by dominant alleles.
- Explain sickle cell anemia as an example of a genetic disease caused by codominant alleles.
- Define sex linkage
3.4.A3: Inheritance of cystic fibrosis and Huntington’s disease.
- Describe the relationship between the genetic cause of cystic fibrosis and the symptoms of the disease.
- Outline the inheritance pattern of cystic fibrosis.
- Outline the inheritance pattern of Huntington’s disease.
- List effects of Huntington’s disease on an affected individual.
3.4.A1: Inheritance of ABO blood groups.
- Describe ABO blood groups as an example of complete dominance and codominance.
- Outline the differences in glycoproteins present in people with different blood types.
11.1.A1: Antigens on the surface of red blood cells stimulate antibody production in a person with a different blood group.
- Outline the difference between the ABO blood antigens.
- State the four human ABO blood types.
- Describe the consequence of mismatched blood transfusions, including agglutination and hemolysis.
3.4.U8: The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.
- Use correct notation for sex linked genes.
- Describe the pattern of inheritance for sex linked genes.
- Construct Punnett grids for sex linked crosses to predict the offspring genotype and phenotype ratios.
3.4.A2: Red-green color blindness and hemophilia as examples of sex-linked inheritance.
- Describe the cause and effect of red-green color blindness.
- Explain inheritance patterns of red-green color blindness.
- Describe the cause and effect of hemophilia.
- Explain inheritance patterns of hemophilia.
3.4.S3: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases
- Outline the conventions for constructing pedigree charts.
- Deduce inheritance patterns given a pedigree chart.
Gregor Mendel “The Father of Genetics”
What people thought before Mendel: | 
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What Mendel’s experiments showed: | 
Mendel was a “pioneer” because he:
- _______________________________
- _______________________________
- _______________________________
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Test Cross
What is it?
| Why is it done? |
Foundations of Basic Genetics
Gene:
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Allele:
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Dominant allele:
| Definition:
Cause:
Example:
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Recessive allele:
| Definition:
Cause:
Example:
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Codominant alleles:
| Definition:
Notation:
Example:
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Genotype:
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Heterozygous:
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Homozygous:
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True Breeding:
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Phenotype:
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From Gametes to Zygotes
GAMETES | ZYGOTE |
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Possible allele combinations in the zygote if there are two alleles of a gene in the population:
The pea flower position gene has two alleles:
- “A” (axial)
- “a” (terminal)
Possible allele combinations in a diploid zygote:
Possible allele combinations in the zygote if there are three alleles of a gene in the population:
The human blood type gene has three alleles:
- “IA” (type A)
- “IB” (type B)
- “i” (type O)
Possible allele combinations in a diploid zygote:
Note: even though there are three alleles in the population, there are a maximum of two alleles in any single individual.
Punnett Squares
- Determine gene, alleles and parental 2n genotypes
- Determine the unique gametes from each parent
- Draw a Punnett Square using unique gametes only
- Fill in the Punnett Square with the possible genotypes of the offspring.
- Summarize possible genotypes and phenotypes of offspring, with expected ratios
- Celebrate and feel proud
Which of Mendel’s Laws is indicated by the arrows from the diploid parent to the haploid gamete?
What does the bringing together of parent alleles in a box represent?
What does each square represent?
Human Blood Types
What causes blood types?
- Allele IA is ____________ to allele i and is ____________________ with allele IB.
- Allele IB is ____________ to allele i and is ____________________ with allele IA.
- Allele i is ____________ to both allele IA and IB.
Blood Typing
Sex Linked Traits
Definition:
Why are most sex linked traits on the X chromosome?
Notation:
Non-diseased homozygous female
| Heterozygous female (carrier) | Diseased female | Normal Male | Diseased Male |
Human Genetic Diseases
What is a genetic disease?
Contrast genetic diseases caused by:
Dominant alleles
| Recessive alleles | Codominant alleles | Sex linked genes |
Why are genetic diseases rare in the human population?
What does it mean if an individual is a “carrier” of a genetic disease?
Disease | Caused by a Dominant or Recessive Allele | Sex Linked (Y or N) | Effect of the mutation associated with the disease causing allele |
Sickle Cell Anemia |
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Cystic Fibrosis |
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Hemophilia |
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Huntington’s Disease |
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Phenyketonuria (PKU) |
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Red-green Color Blindness |
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PEDIGREES
What are the common notations used in pedigrees? Create a key:
Patterns of inheritance shown in pedigrees:
Autosomal Dominant - Males and females are equally likely to be affected.
- There are affected people in every generation (generally).
- There is male to male transmission of the disease.
- DD and Dd are affected, dd is not.
| Autosomal Recessive - Males and females are equally likely to be affected.
- Disease often skips generations.
- Disease may appear in siblings without appearing in their parents.
- If a parent has the disease, those offspring who do not have the trait are heterozygous carriers.
- dd is affected, DD and Dd are not.
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X-linked Dominant - All daughters of a male who has the disease will also have the disease
- There is no male to male transmission.
- A female who has the trait may or may not pass the gene for the disease to her son or daughter.
- XDXD and XDXd are diseased females; XdXd are females without the disease.
- XDY are affected males; XdY are males without the disease.
| X-linked Recessive - The disease is far more common in males than in females.
- All daughters of a male who has the disease are diseased or heterozygous carriers.
- The son of a female carrier has a 50% chance of having the trait.
- There is no male to male transmission.
- Mothers of males who have the trait are either heterozygous carriers or have the disease.
- Daughters of female carriers have a 50% chance of being carriers.
- XDXD and XDXd are normal females; XdXd are females with the disease.
- XDY are normal males; XdY are males with the disease.
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What two questions should you ask yourself when determining the mode of inheritance in a pedigree?
DIRECTIONS: Identify the inheritance pattern and genotypes of all individuals in the pedigrees C – H.