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Question 18N.2.SL.TZ0.6a

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Date November 2018 Marks available [Maximum mark: 3] Reference code 18N.2.SL.TZ0.6a
Level SL Paper 2 Time zone TZ0
Command term Describe Question number a Adapted from N/A
a.
[Maximum mark: 3]
18N.2.SL.TZ0.6a
(a)

Isolated communities in rural Finland, Hungary and some of the Scottish islands have a high incidence of red-green colour blindness. Describe the inheritance of red-green colour blindness.

[3]

Markscheme

a. sex linked/gene is on the X chromosome ✔

b. allele «for red-green colour blindness» is recessive/colour blindness is recessive trait/disorder ✔

c. heterozygous females are unaffected/carriers ✔

d. XB denotes normal allele and Xb denotes colour blindness allele ✔

e. more frequent in males because they only have one X chromosome ✔

f. 50 % chance of colour blindness in sons whose mother who is heterozygote/XBXb ✔

 

Accept any other letter for the alleles.

Award mpb, mpc, mpd and mpf if these points are clearly made on a Punnett grid.

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