DP Biology (first assessment 2025)

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Question 23M.2.SL.TZ1.5a

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Date May 2023 Marks available [Maximum mark: 2] Reference code 23M.2.SL.TZ1.5a
Level SL Paper 2 Time zone TZ1
Command term Explain Question number a Adapted from N/A
a.
[Maximum mark: 2]
23M.2.SL.TZ1.5a

The spider Dolomedes plantarius usually has white bands down the left and right sides of its body, but some individuals lack these bands. The photograph shows the banded form of D. plantarius with a ball of spiderlings.



[Source: photo: Vėlavičienė, N., 2004. [Dolomedes.] [image online] Available at: https://commons.wikimedia.org/wiki/
File:Dolomedes_fimbriatus.jpg. [Accessed 14 March 2022]. Licensed under the Creative Commons Attribution-Share
Alike 3.0 Unported license (https://creativecommons.org/licenses/by-sa/3.0/deed.en).]

Crosses were performed to investigate the inheritance of this trait, by allowing specific males and females to mate. Numbers of banded and unbanded spiderlings that hatched out from all the eggs laid by the female were recorded. Results are shown in the table.

[Source: table: Baillie, A.L., Baillie, S.R. and Smith, H., 2019. The heritability of lateral banding in Dolomedes plantarius. Arachnology, [e-journal] 18(3), pp. 237–244. https://doi.org/10.13156/arac.2019.18.3.237.] 

(a)

Explain the conclusion that can be drawn from Cross 1.

[2]

Markscheme
  1. allele/trait/gene for banded is dominant/allele for unbanded is recessive;
  2. because two banded spiders produced some unbanded offspring
    OR
    because there is a ratio of 3 banded:1 unbanded;
  3. both parents are heterozygous;

Accept answers given in the form of Punnet squares.

 

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