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IB Biology HL D3.2 Inheritance Questions

Practise IB Biology HL D3.2 with inheritance diagrams and data questions on alleles, pedigrees, linkage, variation, probability and genetic disorders.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Identify haploid gametes, genotype, phenotype and homozygous or heterozygous alleles.
  • Solve monohybrid crosses with Punnett grids; infer genotypes and dominant or recessive outcomes.
  • Explain recessive PKU from PAH deficiency to phenylalanine accumulation and treatment.
  • Explain environment-driven gene-expression changes that alter phenotype, not genotype.
  • Explain SNPs as single-base variants and identify multiple-allele crosses from a Punnett grid.
  • Deduce ABO inheritance and transfusion compatibility from IA, IB, i, antigens and antibodies.
  • Explain codominance and incomplete dominance and interpret their phenotype ratios in genetic crosses.
  • Explain XX/XY inheritance and the Y-chromosome SRY/TDF signal in testis development.
  • Infer X-linked or autosomal inheritance, genotypes and risks from haemophilia and pedigree data.
  • Interpret continuous height data using polygenic effects, environment and trait distributions.
  • Compare box plots by median and IQR; identify outliers with the 1.5 × IQR rule.
  • Explain allele segregation and independent assortment through meiosis I and random bivalent orientation.
  • Use 9:3:3:1 or 1:1:1:1 ratios to solve and interpret dihybrid crosses.
  • Infer linkage from parental and recombinant offspring; relate recombination to crossing over.
  • Use expected counts, degrees of freedom and p-values to test genetic ratios with χ².

Covered syllabus points

D3.2.1—Haploid gametes + fusion = diploid zygoteD3.2.2—Genetic crosses in flowering plantsD3.2.3—GenotypeD3.2.4—PhenotypeD3.2.5—Dominant and recessive allelesD3.2.6—Phenotypic plasticityD3.2.7—Phenylketonuria (PKU)D3.2.8—SNPs and multiple allelesD3.2.9—ABO blood groupsD3.2.10—Incomplete dominance and codominanceD3.2.11—Sex determinationD3.2.12—HaemophiliaD3.2.13—Pedigree chartsD3.2.14—Continuous variationD3.2.15—Box-and-whisker plotsD3.2.16 (HL)—Segregation and independent assortmentD3.2.17 (HL)—Dihybrid crossesD3.2.18 (HL)—Human gene lociD3.2.19 (HL)—Autosomal gene linkageD3.2.20 (HL)—RecombinantsD3.2.21 (HL)—Chi-squared test

Question 1

[Maximum number: 1]

What is always passed to the next generation as a result of sexual reproduction?

A

Homologous chromosomes from the mother

B

A chromatid from every chromosome of the father

C

A haploid set of chromosomes from the mother

D

All alleles from each parent

Question 2

[Maximum number: 1]

A pea plant that is homozygous for purple flowers is crossed with a pea plant having white flowers and the descendants are all plants with purple flowers. One of these F1\mathrm{F}_{1} plants is then crossed with a pea plant having white flowers. In the resulting offspring, what can be expected?

A

100 % of plants with purple flowers

B

100 % of plants with white flowers

C

75 % of plants with purple flowers, 25 % with white flowers

D

50 % of plants with purple flowers, 50 % with white flowers

Question 3

[Maximum number: 5]

In a strain of soybeans, high oil content (H) in seeds is dominant to low oil content (h) and four seeds in a pod (F) is dominant to two seeds in a pod (f). A farmer crosses two soybean plants, both with high oil content and four seeds in a pod. The offspring have a phenotypic ratio of 9: 3: 3: 1.

Question (a)

(a)

Identify the genotypes of the soybean plants with high oil content and four seeds in a pod that were used in the cross.

[ 1 ]

Question (b)

(b)

For the soybean cross HhFf × HhFf, determine the genotypes of the gametes and offspring using a Punnett grid.

[ 2 ]

Question (c)

(c)

Identify the phenotypes of each part of the phenotypic ratio.

Table for Question (c) — IB Biology HL
[ 2 ]
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