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Describe inherited diseases case study I

Science - Genetics

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Questions (video)

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Your turn

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Match the pedigree to the mode of inheritance

Autosomal recessive

Autosomal dominant

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Your turn

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Who are the heterozygotes?

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Your turn

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Which individual expresses the autosomal recessive trait?

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Case study 1: The Addams

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What are George and Arlene’s genotypes?

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Case study 1: The Addams

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What are Ann and Michael’s genotypes?

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Case study 1: The Addams

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What is Sandra’s most likely genotype?

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Case study 1: The Addams

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Name three people who are most likely to be carriers of the disease (apart from George).

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Case study 2: The Bradys

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Fill in the blank genotypes.

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Case study 3: The Carters

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Why is this trait autosomal recessive?

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Case study 3: The Carters

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How are III4 and III5 connected or related?

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Case study 3: The Carters

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What are the chances of IV3 being a carrier?

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Case study 4: The Dunphys

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Fill in the blank genotypes.

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Questions (worksheet)

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Pause the video to complete your task

Resume once you’re finished

Autosomal dominant inheritance

Equal chance for _______ and females to inherit trait

Parent must have ______ to pass it on

Cannot skip a _________

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Pause the video to complete your task

Resume once you’re finished

Autosomal recessive inheritance

_______ chance for males and females to inherit trait.

Trait only expressed for ____________ recessive and can _______ generations. If the offspring express the trait but their parents don’t, then both parents are _________.

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Pedigree practice - 1

This pedigree tracks the presence of attached earlobes through a family’s generation.

How can you tell that attached earlobes follow an autosomal recessive pattern?

If individuals I-1 and I-2 had a fourth child, what is the chances that the child would have attached earlobes?

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Pedigree practice - 2

1. How many generations represented in the pedigree?

2. In generation I, which parent is heterozygous for the recessive allele?

3. Which individual in generation II marries a spouse who is homozygous dominant?

4. In which generation does the first case of sickle cell anaemia appear?

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Pedigree practice - 2

5. Which generation contains the most male carriers?

6. Can two carriers produce an individual with sickle cell anaemia?

7. Can a normal homozygous individual produce offspring with sickle cell anaemia?

8. Which parents produce two children with sickle cell anaemia?

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Pedigree practice - Autosomal dominance

List any observations from the pedigree that support Huntington’s disease (HD) being an autosomal dominant trait.
If the HD allele was represented as H and the healthy allele as h, copy the pedigree into your notebook and mark the possible genotypes for each of the individuals in the pedigree.
If Jo and Mark were to have another child, what would be the chance of it having HD?

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Create this pedigree:

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Two normal parents have 3 children. The first child (a girl) and their second child (a boy) have normal blood cells. Their third child (a girl) has sickle cell anaemia. That girl marries a normal male and they have four children. The first three (two girls and a boy) have normal blood cells. Their fourth child (a girl) has sickle cell anaemia like her mother. Shade the affected and definite carriers individually as appropriate.

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Answers (Video)

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Your turn

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Match the pedigree to the mode of inheritance

Autosomal recessive

Autosomal dominant

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Your turn

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Who are the heterozygotes?

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Your turn

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Which individual express the autosomal recessive trait?

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Case study 1: The Addams

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What are George and Arlene’s genotypes?

George: Ff

Arlene: ff

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Case study 1: The Addams

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What are Ann and Michael’s genotypes?

Ann: Ff

Michael: Ff

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Case study 1: The Addams

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What is Sandra’s most likely genotype?

Possible genotypes:

Ff - 50% chance of Daniel’s genotype

FF - 100% chance of Daniel’s phenotype

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Case study 1: The Addams

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Name three people who are most likely to be carriers of the disease (apart from George).

Sam

Ann

Michael

Daniel

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Case study 2: The Bradys

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Case study 3: The Carters

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Why is this trait autosomal recessive?

Males and females have trait
Skips multiple generations

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Case study 3: The Carters

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How are III4 and III5 connected or related?

Cousins
Married

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Case study 3: The Carters

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What are the chances of IV3 being a carrier?

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Case study 4: The Dunphys

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Fill in the blank genotypes

So the first step in these pedigree investigation is to fill in what absolutely must be true, what do we know already? We know that sickle cell anaemia is an autosomal recessive inheritance pattern so all individuals with the disoder must be homozygous recessive or capital S capital S. Lets fill these in to give us a bit more to work with © From this we can see that any parents that don’t have the disorder but do have children with the disorder must be carriers. So we can label I1 and and I2 as AS because they are normal but have two children with the disorder. We can also apply this rule to the pairs II3 and 4 © because they have the dominant phenotype but their child is homozygous recessive. What about individual 6 in the second generation? What's their genotype? Well their child is homozygous recessive. We know the father is homozygous recessive because he has the trait, and for the child ot be homozygous recessive the other parent must also carry the recessive gene. But the mother doesnt have the disorder, so she must be a carrier or heterozygous ©

Looking at the remaining offspring in gneration three, 1 and 2 must be heterozygous because they must get one of the dominant alleles from their homozygous mum and a recessive allele from their homozygous dad so we can write in these genotypes as AS ©

Last one here, III3. Now we know she must have at least one dominant allele as she doesn’t have the disorder. But she has a 50% chance of getting either recessive allele from either parent, or a 25% chance of getting another dominant allele. So we can only really write her as A- ©

And there you have it, mystery solved. Kind of.

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Answers (Worksheet)

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Pause the video to complete your task

Resume once you’re finished

Autosomal dominant inheritance

Equal chance for _______ and females to inherit trait.

Parent must have ______ to pass it on.

Cannot skip a _________.

males

trait

generation

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Pause the video to complete your task

Resume once you’re finished

Autosomal recessive inheritance

_______ chance for males and females to inherit trait.

Trait only expressed for ____________ recessive and can ______ generations. If the offspring express the trait but their parents don’t, then both parents are _____________ .

Equal

homozygous

skip

heterozygous

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Pedigree practice - 1

This pedigree tracks the presence of attached earlobes through a family’s generation.

How can you tell that attached earlobes follow an autosomal recessive pattern?

Some offspring of affected parent do not have the disorder.

If individuals I-1 and I-2 had a fourth child, what is the chances that the child would have attached earlobes?

I-1 must be heterozygous. Punnett square of Dd x dd: 50% chance of dd for offspring

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Pedigree practice - 2

1. How many generations represented in the pedigree? 4

2. In generation I, which parent is heterozygous for the recessive allele? I-2

3. Which individual in generation II marries a spouse who is homozygous dominant? II-4

4. In which generation does the first case of sickle cell anaemia appear? III

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Pedigree practice - 2

5. Which generation contains the most male carriers? III

6. Can two carriers produce an individual with sickle cell anaemia? Yes, 25% chance

7. Can a normal homozygous individual produce offspring with sickle cell anaemia? No, always pass on one A

8. Which parents produce two children with sickle cell anaemia?

II-8 and II-9

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Complete this pedigree:

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