Zadanie 8, Paper 2, maj 2022, TZ1, Biologia IB HL

(a) Ribose is drawn as a pentagon and labelled. ✔

A nitrogenous base is connected to the correct anomeric carbon (1′) and labelled. ✔

A phosphate group is connected through the 5′ position and labelled. ✔

(b) DNA samples are collected from the child and potential parents. ✔

A suitable source is used, such as cheek cells, saliva or blood cells. ✔

PCR amplifies the selected DNA regions. ✔

Short tandem-repeat regions are analysed. ✔

Repeat numbers differ between individuals. ✔

Matching at every tested variable locus is unlikely for unrelated individuals. ✔

Electrophoresis separates fragments according to length. ✔

A characteristic pattern of bands is obtained. ✔

The band pattern constitutes the DNA profile. ✔

At each tested locus the child’s inherited bands/alleles must be accounted for by the two parents. ✔

(c) Environmental conditions influence height. ✔

Nutrition affects growth OR another valid environmental example. ✔

Inherited alleles also influence height. ✔

Many genes contribute, making the trait polygenic. ✔

This produces continuous variation. ✔

A large population commonly has an approximately bell-shaped height distribution. ✔

Different alleles can increase or decrease height. ✔

Many combinations of these alleles are possible. ✔

Specific mutations can produce unusually short or tall stature. ✔

Meiosis produces new combinations of alleles. ✔

Mutation introduces new genetic variants. ✔

Sex-related differences contribute to variation in average adult height. ✔

Ageing can reduce standing height. ✔

Quality: the response is clear on first reading, concise and contains little repetition or irrelevant material. ✔

Part (a): 1 per correctly drawn and labelled feature, maximum 3; the phosphate–ribose connection must be at the 5′ position and the base at 1′. Part (b): any 5 distinct points, maximum 5. Part (c): any 7 distinct points, maximum 7. Award 1 independent quality mark for the stated communication criterion. Total maximum 16.