DP Biology (first assessment 2025)

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

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

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.] 

(b)

Deduce reasons for the difference between the results of Cross 2 and Cross 3.

[2]

Markscheme
  1. (1:1 ratio) in cross 2 as banded parent is heterozygous/has one copy of each allele;
  2. (no unbanded offspring) in cross 3 as banded parent is homozygous/has two alleles for banded;
  3. (in crosses 2 and 3) banded parental phenotypes are the same but their genotypes are different;

 

 

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