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6  Colour blindness is a characteristic that is inherited. Colour blindness is more common in males 

than in females.

 

Fig. 6.1 is a pedigree diagram showing the inheritance of colour blindness in a family.

1

2

3

5

6

7

8

4

male with normal

colour vision

male with colour

blindness

female with normal

colour vision

Key:

Fig. 6.1

 (a) 

Define the term inheritance.

 ...................................................................................................................................................

 ...................................................................................................................................................

 ............................................................................................................................................. [1]

 

(b)  (i)   Using the symbols B and b, state the genotypes of individual 5 and individual 8 in the 

pedigree diagram.

5  ........................................................................................................................................

8  ........................................................................................................................................

[3]

                            610/41 May 2020

it is the transmission of information from generation to generation

XBY

XBY

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   (ii) 

Individual 

3 is a carrier of colour blindness because she has one copy of the allele for 

colour blindness but has normal colour vision.

    

Describe the evidence from Fig. 6.1 that shows that individual 

3 is a carrier.

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ..................................................................................................................................... [3]

 

  (iii)   There was no history of colour blindness in the parents and grandparents of individuals 1 

and 

2.

    

Suggest how colour blindness first occurred in the family in Fig. 6.1.

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ...........................................................................................................................................

 ..................................................................................................................................... [2]

[Total: 9]

to individuals 5 and 6 copied X chromosomes of their mother and 3 is their 

mother. if she is not carier 5 and 6 won't be colour blindless

They may be gave this from environment during their life