Transcript Genetics Human inheritance

Year 10 Genetics 2
Human inheritance
Chris Willocks 2006
1
Heritable traits
• Widow’s peak
• Cleft chin
• Tongue rolling
2
Heritable traits
• Attached and
unattached ears
• Concave nose
3
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?
4
Phenotypes and genotypes of
blood groups
Phenotype Genotype
A
AA, AO
B
BB, BO
O
OO
AB
AB
5
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
7
Pedigrees
8
Your family pedigree
• Draw your family as a pedigree
9
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 = albino
P
Aa X Aa
Gametes (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
12
Polydactyly
• Autosomal dominant
• Will a person with polydactyly pass it to their
children?
Let P = polydactyly
p = normal
P
Pp X pp
Gametes
(½P +½p) , p
F1 genotypes ½Pp + ½ pp
F1 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
15
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.
18
Queen Victoria’s pedigree
19
Rickets
• Sex linked dominant
XR = Rickets , X = normal
P
XR Y x XX
Gametes
XR, Y and X
F1 genotypes XR X, XY
F1 phenotypes Rickets, normal
• A male with Rickets will pass it to his daughters
20
Rickets pedigree
• Number and assign genotypes
• XR = Rickets , X = normal
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