IB DP Biology Mock Exam HL Paper 2 Set 5 - 2025 Syllabus
IB DP Biology Mock Exam HL Paper 2 Set 5
Prepare for the IB DP Biology Exam with our comprehensive IB DP Biology Exam Mock Exam HL Paper 2 Set 5. Test your knowledge and understanding of key concepts with challenging questions covering all essential topics. Identify areas for improvement and boost your confidence for the real exam
Question
(a) Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.
(b) Outline the causes of sickle cell anemia.
(c) The karyogram shown is for the African marsh rat (Dasymys incomtus). In this species, sex is determined by X and Y chromosomes. Females are XX and males are XY.
i. Identify, with a reason, the sex of this individual.
ii. State the haploid number for this nucleus.
(d) Thomas Hunt Morgan established that genes for body colour and wing size in Drosophila are autosomally linked. The allele for grey body ($b^+$) is dominant over that for black body (b) and the allele for normal wing size ($vg^+$) is dominant over that for vestigial wing (vg).
(i). A fly that is homozygous dominant for both body colour and wing size mates with a fly that is recessive for both characteristics. In the table, draw the arrangement of alleles for the offspring of this mating and for the homozygous recessive parent.
(ii). The offspring, which were all heterozygous for grey body and normal wings, were crossed with flies that were homozygous recessive for both genes. The table shows the percentages of offspring produced.
Explain these results, based on the knowledge that the genes for body colour and wing size are autosomally linked.
Answer/Explanation
Ans:
a)
a. prokaryotes have circular DNA/chromosome but eukaryote chromosomes linear/OWTTE
OR
eukaryotes have telomeres/centromeres whereas prokaryotes do not
b. some prokaryotes have plasmids whereas eukaryotes do not
c. eukaryotes have multiple chromosomes whereas prokaryotes «typically» have only one
d. histones/nucleosomes/proteins associated with DNA in eukaryotes but not in prokaryotes/naked DNA in prokaryotes
OR
eukaryote DNA can coil/supercoil/condense «due to histones» but not prokaryote DNA
b)
a. genetic disease/caused by a gene
OR
inherited «from parents»
OR
caused by mutation «of a gene»
b. base substitution OR
GAG → GTG
c. hemoglobin gene mutated / different allele/form/version of hemoglobin gene
OR
HbA → HbS
d. leads to change in amino acid sequence «in hemoglobin»
OR
glutamic acid → valine
e. only homozygotes have full disease/sickled cells / heterozygote has milder form
OR
hemoglobin crystallizes at low oxygen concentration
f. «selected for/spreads in population» as it gives resistance to malaria
c (i) male because «X and» Y chromosome present OR male because sex chromosomes/last two chromosomes/pair 21 are unpaired/different «from each other»/not homologous
c (ii) 21
d (i)
d (ii)
a. not a 1:1:1:1 ratio «because of linkage»
OR
not independent assortment
OR
grey normal and black vestigial types/parental combinations/double dominant and double recessive were commoner than 25 %/commoner than expected
b. «linked genes» so were on the same chromosome
c. grey body vestigial wing and black body normal wing are recombinants
OR
2 % plus 3 % of the offspring are recombinants
d. recombinants due to crossing over/exchange of genes between «non-sister» chromatids
OR
2 % and 3 % of offspring were due to crossing over
OR
genes inherited together unless separated by crossing over
e. crossing over between the two loci/between the two genes on the chromosomes