D3.2 Inheritance
Practice exam-style IB Biology questions for Inheritance, aligned with the syllabus and grouped by topic.
Question 1
In a sexual life cycle, meiosis produces gametes and fertilization produces a zygote. What change in chromosome number occurs at fertilization?
A.
The chromosome number is halved to form gametes.
B.
Homologous chromosomes separate into different gametes.
C.
Haploid nuclei fuse to restore the diploid number.
D.
Diploid nuclei fuse to form a tetraploid zygote.
Question 2
A pea plant has genotype Rr for seed shape. What term describes this genotype?
A.
Hemizygous
B.
Heterozygous
C.
Homozygous recessive
D.
Homozygous dominant
Question 3
In a controlled genetic cross in flowering plants, what is the purpose of removing immature anthers from the flower used as the female parent?
A.
To prevent self-pollination by pollen from the same flower.
B.
To stop the ovules from producing female gametes.
C.
To prevent pollen tubes growing down the style.
D.
To make the stigma unable to receive pollen.
Question 4
Which human trait is best described as resulting mainly from interaction between genotype and environment?
A.
Adult height
B.
A learned first language
C.
ABO blood group
D.
A scar from a cut
Question 5
In typical human sex determination, which gamete determines whether the zygote is XX or XY?
A.
The egg, because it carries no sex chromosome.
B.
The sperm, because it may carry an X or a Y chromosome.
C.
The egg, because it may carry an X or a Y chromosome.
D.
The sperm, because it carries two sex chromosomes.
Question 6
An individual has genotype AaBb for two unlinked autosomal genes. Which set of gametes is expected in equal proportions?
A.
AB and ab only
B.
AB, Ab, aB and ab
C.
AA, Aa, Bb and bb
D.
A, a, B and b
Question 7
Two human genes found in a database have loci on chromosome 7 and chromosome 12. What conclusion about their inheritance is most appropriate?
A.
They are unlinked because they are on different chromosomes.
B.
They are linked because all human genes are inherited together.
C.
They are alleles of the same gene because both are human genes.
D.
They must code for the same polypeptide product.
Question 8
Distinguish between a gene and an allele.
[1]
Question 9
Phenylketonuria is caused by a recessive autosomal allele. Two unaffected carriers have a child. What is the probability that the child will have phenylketonuria?
A.
1.00
B.
0.75
C.
0.25
D.
0.50
Question 10
What is the phenotype of a person with ABO genotype IᴬIᴮ?
A.
Blood group AB
B.
Blood group A
C.
Blood group B
D.
Blood group O
Question 11
Two double heterozygotes, AaBb × AaBb, are crossed. Both genes are unlinked autosomal genes with complete dominance. What phenotypic ratio is expected?
A.
1:1:1:1
B.
1:2:1
C.
3:1
D.
9:3:3:1
Question 12
A double heterozygote is test-crossed with a double homozygous recessive individual. The two genes are unlinked. What phenotypic ratio is expected among offspring?
A.
1:2:1
B.
3:1
C.
9:3:3:1
D.
1:1:1:1
Question 13
Why can linked autosomal genes fail to assort independently?
A.
They have the same nucleotide sequence.
B.
They are located on different homologous chromosome pairs.
C.
They are found only on the Y chromosome.
D.
They are physically close together on the same chromosome.
Question 14
A chi-squared goodness-of-fit test compares four phenotypic categories from a dihybrid cross. What is the number of degrees of freedom?
A.
4
B.
3
C.
2
D.
1
Question 15
The diagram shows a flower selected as the female parent in a controlled genetic cross.
Outline three procedures used to ensure that only pollen from the chosen male parent fertilizes ovules in this flower.
[1]
Question 16
For a gene coding for an enzyme, allele F produces a functional enzyme and allele f produces a non-functional enzyme.
Explain why genotypes FF and Ff may have the same phenotype, while ff has a different phenotype.
[1]
Question 17
Human skin can darken after increased exposure to sunlight.
Explain how this is an example of phenotypic plasticity.
[1]
Question 18
Phenylketonuria (PKU) is caused by a recessive autosomal allele, p. Two parents are both heterozygous.
State the genotype of each parent.
[1]
Determine the probability that a child will be a carrier.
[1]
State why newborn screening and diet can reduce symptoms even though PKU is genetic.
[1]
Question 19
In a dihybrid cross, two unlinked autosomal genes are represented by A/a and B/b.
List the gametes produced by AaBb.
[1]
State the expected phenotypic ratio for AaBb × AaBb with complete dominance.
[1]
State the expected phenotypic ratio for AaBb × aabb.
[1]
Question 20
A gene database gives the chromosome, locus and polypeptide product for human genes.
State what is meant by the locus of a gene.
[1]
Explain how database information can help predict whether two genes may assort independently.
[1]
Question 21
A pure-breeding purple-flowered pea plant was crossed with a pure-breeding white-flowered pea plant. F1 plants were self-fertilized and F2 flower colours were counted.
| Generation | Plants recorded | Purple flowers / n | White flowers / n |
|---|---|---|---|
| P | pure-breeding parents | 1 | 1 |
| F1 | offspring from P cross | 96 | 0 |
| F2 | offspring from F1 selfing | 428 | 152 |
Identify the dominant flower colour using the F1 data.
[1]
Calculate the percentage of F2 plants with white flowers.
[1]
Compare the observed F2 phenotypic ratio with the expected ratio for a monohybrid cross with complete dominance.
[1]
Suggest one reason why the observed numbers may not exactly match the expected ratio.
[1]
Question 22
For a student height data set, Q₁ = 158 cm and Q₃ = 174 cm. According to the 1.5 × IQR rule, what is the upper boundary above which values are outliers?
A.
182 cm
B.
198 cm
C.
190 cm
D.
206 cm
Question 23
In a test cross, a heterozygote has linked alleles arranged as AB/ab. Which gametes are recombinant?
A.
Ab and aB
B.
AB and Ab
C.
AB and ab
D.
aB and ab
Question 24
In a chi-squared test at the p = 0.05 level, the calculated χ² value is greater than the critical value. What conclusion should be made?
A.
Conclude that sampling error is impossible.
B.
Reject the null hypothesis.
C.
Increase the expected frequencies until χ² is smaller.
D.
Accept that the null hypothesis has been proved.
Question 25
A parent with blood group A has genotype Iᴬi. A parent with blood group B has genotype Iᴮi.
List the possible gametes from each parent.
[1]
Determine the possible ABO phenotypes of their children.
[1]
Question 26
Haemophilia is an X-linked recessive disorder. A woman has genotype XᴴXʰ and a man has genotype XᴴY.
State the phenotype of the woman.
[1]
Determine the probability that a son will have haemophilia.
[1]
Explain why the father cannot pass the haemophilia allele to his sons in this cross.
[1]
Question 27
The box-and-whisker plot summarizes student heights.
| Plot feature | Height / cm |
|---|---|
| Minimum whisker | 146 |
| Q1 | 158 |
| Median | 166 |
| Q3 | 174 |
| Maximum whisker | 188 |
| Marked value | 201 |
Calculate the interquartile range.
[1]
State the median height.
[1]
State one reason why a box-and-whisker plot is suitable for these data.
[1]
Identify whether the marked extreme value is an outlier using the 1.5 × IQR rule.
[1]
Question 28
Explain how chromosome behaviour in meiosis results in segregation and independent assortment of alleles for two unlinked genes.
[1]
Question 29
A dihybrid cross produced 160 offspring in four phenotypic classes. The expected ratio under independent assortment is 9:3:3:1.
Calculate the expected number in the class corresponding to 9/16.
[1]
Calculate the expected number in each class corresponding to 3/16.
[1]
State a suitable null hypothesis for the chi-squared test.
[1]
State the formula for the chi-squared statistic.
[1]
Question 30
Mendel's second law predicts independent assortment under specified conditions.
State one condition under which the 9:3:3:1 ratio is expected in a dihybrid cross.
[1]
Explain why this prediction is not an exception-proof biological law.
[1]
Question 31
The graph shows blood phenylalanine concentration in infants with PKU after diagnosis and dietary treatment.
State the trend in phenylalanine concentration after treatment begins.
[1]
Estimate the time taken for concentration to fall below the recommended upper limit.
[1]
Explain why a low-phenylalanine diet reduces the harmful phenotype of PKU.
[1]
State why the diet does not change the inheritance of the PKU allele.
[1]
Question 32
The graphs compare variation in ABO blood group and a skin pigmentation index in a sample of students.
Identify which variable is discrete.
[1]
Identify which measure of central tendency is most appropriate for ABO blood group.
[1]
Describe the distribution of the skin pigmentation index.
[1]
Suggest why skin pigmentation shows continuous variation.
[1]
Question 33
The table shows ABO blood groups of parents and children in three families.
| Family | Parent 1 group | Parent 2 group | Child 1 group | Child 2 group |
|---|---|---|---|---|
| 1 | A | O | A | O |
| 2 | B | B | B | O |
| 3 | AB | O | A | B |
Deduce one possible genotype for a child with blood group O.
[1]
Deduce whether a blood group AB parent can have a blood group O child with a blood group O parent.
[1]
Explain your answer to
[1]
using allele notation.
[1]
State why the ABO system is an example of multiple alleles.
[1]
Question 34
The graph shows recombination frequency between pairs of loci on the same autosome plotted against physical distance between the loci.
Describe the relationship shown by the graph.
[1]
State the approximate recombination frequency at which genes behave as if unlinked.
[1]
Explain why close genes have a low recombination frequency.
[1]
Suggest why recombination frequency does not increase indefinitely with distance.
[1]
Question 35
A database search produced information on four human genes.
| Gene | Chr | Cytoband | Position / bp | Polypeptide product |
|---|---|---|---|---|
| HBB | 11 | 11p15.4 | 5,225,464–5,227,071 | β-globin |
| HBD | 11 | 11p15.4 | 5,234,877–5,236,625 | δ-globin |
| CFTR | 7 | 7q31.2 | 117,120,016–117,308,718 | CFTR chloride channel |
| BRCA1 | 17 | 17q21.31 | 43,044,295–43,125,482 | BRCA1 protein |
Identify a pair of genes that is definitely unlinked.
[1]
Identify a pair of genes that may be linked.
[1]
State the polypeptide product for one named gene in the table.
[1]
Explain how the loci in the table support your answer to (b).
[1]
Question 36
The diagram and table show two possible orientations of homologous chromosome pairs during metaphase I in an AaBb cell, where the genes are on different chromosomes.
State the stage of meiosis in which the orientations shown occur.
[1]
Identify two gamete genotypes produced by one orientation.
[1]
Explain why the two orientations are equally likely.
[1]
Explain how this accounts for independent assortment in the offspring of a test cross.
[1]
Question 37
The diagram shows homologous autosomes carrying two linked genes in a double heterozygote.
Explain why allele symbols for linked genes are shown beside vertical chromosome lines.
[1]
State why parental combinations are usually more frequent than recombinant combinations when linked genes are close together.
[1]
Question 38
A double heterozygote with linked genes has the arrangement Ab/aB and is test-crossed with ab/ab.
Identify the parental gametes from the heterozygote.
[1]
Identify the recombinant gametes from the heterozygote.
[1]
Identify the recombinant offspring genotypes in the test cross.
[1]
Question 39
A student concludes that a dihybrid cross proves genes are unlinked because the calculated χ² value is less than the critical value at p = 0.05.
State the correct statistical conclusion.
[1]
Explain why the student's wording is too strong.
[1]
State two features of effective sampling that improve the reliability of such a test.
[1]
Question 40
The pedigree shows inheritance of a rare genetic disorder in a family.
State the sex of individual II-3.
[1]
Deduce whether the disorder is more likely dominant or recessive.
[1]
Explain the evidence from the pedigree for your answer to (b).
[1]
Deduce the genotype of the unaffected parents of an affected child, using A and a.
[1]
Distinguish between the inductive and deductive reasoning used in this pedigree analysis.
[1]
Question 41
A dihybrid cross between AaBb plants produced four phenotypic classes. The expected ratio for unlinked genes with complete dominance is 9:3:3:1.
| Phenotypic class | Observed offspring / count | Expected ratio |
|---|---|---|
| A_B_ | 96 | 9 |
| A_bb | 34 | 3 |
| aaB_ | 27 | 3 |
| aabb indicated | 3 | 1 |
| χ² critical value, df = 3, p = 0.05 | 7.815 |
Calculate the expected number for one phenotypic class using the total offspring and the expected ratio.
[1]
Calculate one contribution to χ² using (O − E)²/E for the class indicated.
[1]
State the degrees of freedom for this test.
[1]
Use the critical value provided to decide whether to reject the null hypothesis at p = 0.05.
[1]
Suggest one biological reason why the data might not fit 9:3:3:1.
[1]
Question 42
A double heterozygote with linked genes was test-crossed with a double homozygous recessive individual. The offspring phenotypes are shown.
| Offspring phenotype | Alleles from heterozygote | Offspring / count |
|---|---|---|
| Grey body, normal wings | AB | 418 |
| Black body, vestigial wings | ab | 412 |
| Grey body, vestigial wings | Ab | 86 |
| Black body, normal wings | aB | 84 |
| Total | — | 1000 |
Identify the two parental phenotype classes.
[1]
Identify the two recombinant phenotype classes.
[1]
Calculate the recombination frequency.
[1]
Explain why the data indicate linkage rather than independent assortment.
[1]
Suggest how crossing over produces the recombinant classes.
[1]
Question 43
Outline how haploid gametes are produced and how a diploid zygote is formed in a sexual life cycle.
[1]
Explain how this process allows alleles of autosomal genes to be inherited from both parents.
[1]
Question 44
Define phenotype and phenotypic plasticity.
[1]
Discuss the roles of genotype and environment in producing human phenotypes, using examples.
[1]
Question 45
Outline the inheritance of ABO blood groups using the alleles Iᴬ, Iᴮ and i.
[1]
Compare and contrast codominance and incomplete dominance, using ABO blood group and four o'clock flower (Mirabilis jalapa) as examples.
[1]
Question 46
A pedigree for a rare disorder shows several affected males and females born to unaffected parents. In another branch, a carrier female for haemophilia has children with an unaffected male.
Outline two conventions used in pedigree charts and one reason pedigrees are used in human genetics.
[1]
Evaluate how pedigrees can be used to deduce autosomal recessive and X-linked recessive inheritance patterns, including haemophilia and marriage between close relatives.
[1]
Question 47
Outline the processes of segregation and independent assortment in meiosis.
[1]
Explain how these processes produce the expected phenotypic ratios in dihybrid crosses involving two unlinked autosomal genes.
[1]
Question 48
Outline what information about a human gene can be obtained from a gene database.
[1]
Discuss how gene loci and polypeptide products help explain inheritance patterns, including exceptions to Mendel's second law.
[1]
Question 49
Outline how linked alleles should be represented in a double heterozygote.
[1]
Discuss how offspring from a test cross can be used to identify linkage and recombinants.
[1]
Question 50
A researcher obtains offspring counts from a dihybrid cross and wants to test whether the data fit a 9:3:3:1 ratio.
State the null hypothesis, alternative hypothesis and degrees of freedom for a chi-squared test with four phenotypic classes.
[1]
Evaluate the use of a chi-squared test for these data, including expected values, significance at p = 0.05 and sampling.
[1]
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