Chris Willocks 2006 1

Year 10 Genetics 2Human inheritance

2

Heritable traits

• Widow’s peak• Cleft chin• Tongue rolling

3

Heritable traits

• Attached and unattached ears

• Concave nose

4

Blood groups

• 4 blood groups – A, B, O, AB• Blood group A has A antigens on red blood cells• What antigens are on the other blood groups?

5

Phenotypes and genotypes of blood groups

Phenotype Genotype

A AA, AO

B BB, BO

O OO

AB AB

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Blood group inheritance

• Can a couple of blood groups A and B have a child with blood group O?

P AO X BO

Gametes (½A +½O) , (½B +½O)

F1 genotypes ¼AB + ¼AO + ¼BO + ¼OO

F1 phenotypes ¼AB + ¼A + ¼B + ¼O

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Karyotypes

8

Pedigrees

9

Your family pedigree

• Draw your family as a pedigree

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Types of inheritance

4 types of inheritance:

1. Autosomal recessive eg Albinism

2. Autosomal dominant eg Huntington’s disease

3. Sex-linked recessive eg Haemophilia

4. Sex-linked dominant eg Rickets

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Albinism

• Autosomal recessive• How can 2 normal parents have

an albino child?

A = normal a = albinoP Aa X AaGametes (½A +½a) (½A +½a)

F1 genotypes ¼AA + ½Aa + ¼aa

F1 phenotypes ¾normal + ¼albino

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Albinism pedigrees

• Assign genotypes to each person in the pedigrees • Let A = normal, a = albino

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Polydactyly

• Autosomal dominant• Will a person with polydactyly pass it to their

children?

Let P = polydactyly p = normalP Pp X ppGametes (½P +½p) , pF1 genotypes ½Pp + ½ ppF1 phenotypes ½polydactyly + ½normal

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Polydactyly pedigree

• Let P = polydactyly, p = normal• Assign genotypes to the pedigree• Number the generations and individuals using the standard notation

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Haemophilia

• Haemophiliacs lack blood clotting factors

• Need clotting factors from blood donations to survive

• Blood is screened to remove any viruses before being used

• Many haemophiliacs were infected with hepatitis or HIV

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Haemophilia inheritance

• Haemophilia gene is on the X chromosome• Sex-linked recessive

X = normal, Xh = haemophilia

P X Xh x XY

Gametes X, Xh and X, Y

F1 genotypes XX, X Xh , XY, XhY

F1 phenotypes normal, carrier, normal, haemophiliac

• Carrier females pass it to half their sons

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Haemophilia pedigree

• Assign genotypes to the pedigree• Let X = normal, Xh = haemophilia

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Haemophilia in the Royal Family

• Queen Victoria was a carrier for haemophilia

• Due to a chance mutation.

• Her children married other royalty and passed the trait throughout the royal families of Europe.

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Queen Victoria’s pedigree

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Rickets

• Sex linked dominant

XR = Rickets , X = normal P XR Y x XXGametes XR, Y and X

F1 genotypes XR X, XY

F1 phenotypes Rickets, normal

• A male with Rickets will pass it to his daughters

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Rickets pedigree

• Number and assign genotypes• XR = Rickets , X = normal