Genetics:Inheritance

And Variation

Made just for You by theGrade 10 Science Team

International School Bangkok

Human Genetics

Human Genetic Illness Examples

• Dominant: Huntington’s Disease– H, h

• Recessive: Cystic Fibrosis– F, f

• Codominant: Sickle-cell anemia– HbA, HbS

• X-linked (recessive): Hemophilia– XH, Xh

The Human Condition Cystic Fibrosis: A Recessive Allele

Genotypes:FF = normalFf = normalff = Cystic Fibrosis

A sad story. A hopeful story.Informational Video

Cystic Fibrosis Punnett Grids

Claire’s parents are both carriers of cystic fibrosis. If they have another child, what is the chance it will have CF?

Kerry has CF. Her husband is homozygous normal. What is the chance that their son would have CF? What is the chance he would be a carrier of CF?

Ff

Ff

ff

FFF f

F f

25% Ff

f

F

0%100%

The Human ConditionHuntington’s Disease: A Dominant Allele

A degenerative brain disorderOnset usually occurs later in life (30’s to 40’s)People lose the ability to walk, reason, talkAssociated with aggression and other personality changes

Informational Video Personal Story

Huntington’s Disease: A Dominant Allele

Genotypes:Hh = Huntington’s Diesasehh = normalHH = Huntington’s Disease (but very rare)

A pregnant woman was just diagnosed with Huntington’s Disease. Her husband has tested negative for the Huntington’s allele. What is the chance that the baby will also have Huntington’s Disease?

Hh hhh

H h

50%

The Human Condition Hemophilia: A Sex-Linked (Recessive) Allele

Informational Video Teens Speak about Hemophilia

Hemophilia Punnett GridsA woman who carries hemophilia has children with a man with normal blood. What is the chance of a son having hemophilia? What is the chance for a daughter?

A man with hemophilia has children with a women who is homozygous normal. What is the chance that their child will have hemophilia? What is the chance that a son will be a carrier?

XHXhXHYXH

Xh Y 0%0%

XHXH XHYXH

Xh

XH Y 50%0%

XHXhXhY

The Human ConditionSickle-Cell Anemia : Codominant Alleles

Genotypes:HbAHbA = normalHbAHbS = protection from malariaHbSHbS = Sickle Cell Anemia

Informational Video Personal Story

The Human Condition Sickle-Cell Anemia: Codominant Alleles

% of Population with the HbS allele

Two parents are both heterozygous for the sickle-

cell allele. What is the chance that their child will

have protection against malaria? What is the

chance that their child will have sickle cell disease?

HbAHbAHbA

HbS

HbA HbS

50%25%HbAHbS

HbAHbS

HbSHbS

Pedigrees

Pedigrees

• Visually represent genetic relationships over generations

Symbols in Pedigrees

Male Female

Marriage / Mating

Offspring / Children

I

II

Marriage / Mating

Generation Number

1 2

1 2

What is the relationship of person II 2 to person I 1?

Individuals with the trait being studied are shaded.

Daughter

Number of individual

Do you have a Pedigree?

Of course you do!

Ms. Soule’s Pedigree

How many children does Ms. Soule have? How many sons and daughters?How many cousins does Ms. Soule have?How many brothers and sisters does Ms. Soule’s mother have?How many brothers and sisters does Ms. Soule’s father have?

2, 1, 141, 10, 1

Ms. Soule’s Pedigree

The trait is “red hair”. Assume it is a recessive single-gene trait.What is the chance than Ms. Soule’s sister is a carrier?What is the chance that Ms. Soule is a carrier if her father does not have the allele?

100%

50%

What pattern of inheritance does this show?

Recessive! How can you tell?

What pattern of inheritance does this show?

Sex-linked recessive! How do you know?

What pattern of inheritance does this show?

Dominant! How do you know?

What pattern of inheritance does this show?

Recessive! How do you know?

Pedigrees, Probability, and Punnett Grids!

1. What is the chance that person III 1 is a carrier?2. What is the chance that a new child of people II 3 and II 4 would have

the trait?3. What is the chance that the next child of people III 2 and III 3 will have

the trait?4. What is the chance that a sister of person II 1 would have at least one

copy of he allele? 5. What is the chance that the grandchild of person III 5 will be a carrier if

no people marrying into the family have the allele?

100%

25%

100%

100%

25%

Remember Karyotypes?

Turning a picture of a jumble of chromosomes into . . .

an orderly array like this!

Could you diagnose conditions like Cystic Fibrosis or Sickle-Cell Anemia with a Karyotype?

No, those alleles involve changing only a few base pairs. Karyotypes show chromosomes which are many millions of base pairs long