Pedigree IB questions
1.
Brachydactyly, abnormal shortness of the fingers, was the first human genetic disorder found to
be caused by a dominant allele.
The pedigree below shows a family with affected males ■, unaffected males □, affected females
● and unaffected females ○.
I
II
III
IV
V
VI
VII
What are the genotypes of the father and mother in the first generation, using the symbol B for
the dominant alleles and symbol b for recessive allele?
A.
bb and BB
B.
bb and Bb
C.
Bb and BB
D.
BB or Bb and bb
(Total 1 mark)
1
2.
Which feature of a genetic pedigree chart demonstrates that a characteristic is sex linked?
A.
Numbers of offspring carrying the characteristic decreased over several generations.
B.
One gender is more commonly affected than the other.
C.
Equal numbers of males and females inherit the characteristic.
D.
Boys and girls only inherit the characteristic from their mothers.
(Total 1 mark)
3.
(a)
Define sex linkage.
.....................................................................................................................................
(1)
(b)
State one example of sex linkage.
.....................................................................................................................................
(1)
2
(c)
Draw a simple pedigree chart that clearly shows sex linkage in humans. Use conventional
symbols. Start with an affected woman and an unaffected man.
(4)
(Total 6 marks)
4.
The diagram below shows the pedigree of a family with red green colour-blindness, a sex-linked
condition.
Key
1st generation
1
normal male
2
normal female
male with condition
2nd generation
1
2
1
2
3
4
5
3
4
female with condition
3rd generation
3
(a)
Define the term sex-linkage.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
Deduce, with a reason, whether the allele producing the condition is dominant or
recessive.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
(i)
Determine all the possible genotypes of the individual (2nd generation–1) using
appropriate symbols.
...........................................................................................................................
(1)
(ii)
Determine all the possible genotypes of the individual (3rd generation–4) using
appropriate symbols.
...........................................................................................................................
(1)
(Total 5 marks)
4
5.
The following diagram represents a two generation pedigree showing the blood groups of the
individuals. The female has been married to two different individuals.
O
A
AB
Key
1st generation
1
2
Male
3
Female
B
O
A
AB
2nd generation
1
(a)
2
3
4
Define the term co-dominant alleles.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
Deduce with a reason the probable father of 2nd generation–1.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
5
(c)
If 2nd generation–3 marries a man with blood group AB, predict the possible genotypes
of the children.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 6marks)
6.
The pedigree below shows which members of a family were Rhesus positive (■ and •) and
Rhesus negative (□ and O). The allele for Rhesus positive blood (Rh+) is dominant over the
allele for Rhesus negative blood (R-).
Rhesus positive male
I
II
III
Rhesus negative male
Rhesus positive female
Rhesus negative female
Which are possible genotypes of the individuals numbered I, II and III?
I
II
III
A.
Rh+ Rh+
Rh+ Rh+
Rh+ Rh–
B.
Rh+ Rh+
Rh+ Rh–
Rh+ Rh+
C.
Rh+ Rh+
Rh+ Rh–
Rh+ Rh–
D.
Rh+ Rh–
Rh+ Rh–
Rh+ Rh+
(Total 1 mark)
6
7.
Hemophilia is caused by an X-linked recessive allele. In the pedigree shown below which two
individuals in the pedigree must be carriers of hemophilia?
A.
I-1 and II-1
B.
I-4 and II-2
C.
II-1 and II-2
D.
III-2 and III-3
(Total 1 mark)
7
8.
In the pedigree shown below, the female, labelled I-2, is a carrier for colour blindness, however
neither male (I-1 or II-1) is colour blind
What is the probability that offspring III-1 will be colour blind?
A.
50%
B.
25%
C.
12.5%
D.
0%
(Total 1 mark)
9.
Colour blindness in humans is caused by an X chromosome linked recessive allele. In the
pedigree chart below which two individuals must, for certain, be carriers of colour blindness?
I
II
A.
II and IV
B.
I and III
C.
II and III
D.
I and II
III
IV
(Total 1 mark)
8