DP Biology (first assessment 2025)

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Question 23M.1A.SL.TZ2.13

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Date May 2023 Marks available [Maximum mark: 1] Reference code 23M.1A.SL.TZ2.13
Level SL Paper 1A Time zone TZ2
Command term Question number 13 Adapted from N/A
13.
[Maximum mark: 1]
23M.1A.SL.TZ2.13

The pedigree chart shows the inheritance of three generations of Duane syndrome, a condition caused by a dominant allele that affects alignment of the eyes.

[Source: Yang, M.-M., Ho, M. et al., 2013. Pedigree of a Chinese family with Duane retraction syndrome. [diagram online]
Available at: https://www.researchgate.net/figure/Pedigree-of-a-Chinese-family-with-Duane-retraction-syndrome-
Squares-men-circles_fig1_236921765 [Accessed 5 October 2021]. Public domain.]

 

If individuals II:1 and II:2 had a third child, what is the probability that the child would have Duane syndrome?

A.  25 %

B.  50 %

C.  75 %

D.  100 %

[1]

Markscheme

B

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