Question 1
In a human sexual life cycle, a sperm cell fuses with an egg cell to form a zygote. What change in chromosome number occurs during this process?
A.
One haploid nucleus divides by meiosis to form a diploid zygote.
B.
One diploid nucleus divides by mitosis to halve the chromosome number.
C.
Two haploid nuclei fuse to restore the diploid chromosome number.
D.
Two diploid nuclei fuse to form a haploid zygote.
Question 2
A plant breeder wants to cross two pea plants while preventing self-pollination in the flower used as the female parent. The procedure that gives a controlled cross is shown in which diagram?
A.
B.
C.
D.
Question 3
In a plant, allele codes for a functional enzyme needed to make red pigment and allele codes for a non-functional enzyme. Both and plants have red flowers. What explains the phenotype of plants?
A.
The non-functional allele prevents transcription of the functional allele.
B.
One functional allele produces enough enzyme for red pigment formation.
C.
Both alleles are expressed equally to make an intermediate flower colour.
D.
The recessive allele changes into the dominant allele during development.
Question 4
A person with blood group AB has children with a person with blood group O. What blood group phenotypes are possible among their children?
A.
A and B only
B.
A, B, AB and O
C.
AB and O only
D.
A, B and AB only
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Question 5
A diploid organism has genotype . The two genes are unlinked. What gametes are expected from meiosis if independent assortment occurs?
A.
A, a, B and b as separate gametes
B.
AB, Ab, aB and ab in equal proportions
C.
AB and ab only, in equal proportions
D.
Aa and Bb only, in equal proportions
Question 6
In a dihybrid test cross, is crossed with . Both genes are unlinked autosomal genes with complete dominance. What phenotypic ratio is expected?
A.
B.
C.
D.
Question 7
In a sexually reproducing eukaryote, body cells contain homologous pairs of chromosomes. Gametes are produced before fertilization.
State the chromosome number of gametes relative to body cells.
[1]
Explain how meiosis and fertilization maintain chromosome number from one generation to the next.
[2]
Question 8
A data set for student height has one value more than above the third quartile. The correct box-and-whisker plot for the data is shown in which diagram?
A.
B.
C.
D.
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Question 9
The pedigree chart shows a genetic disorder in one family. What pattern of inheritance is most strongly suggested?
A.
Autosomal recessive inheritance
B.
Y-linked recessive inheritance
C.
Autosomal dominant inheritance
D.
Mitochondrial inheritance
Question 10
A student is using a human gene database to predict whether two genes are likely to assort independently. What database information is most directly needed?
A.
The number of introns in each transcribed gene
B.
The chromosome and locus of each gene
C.
The amino acid sequence of each polypeptide product
D.
The tissue where each gene is expressed most strongly
Question 11
An individual has two linked autosomal genes in the arrangement . The diagram that shows a recombinant gamete is which option?
A.
B.
C.
D.
Question 12
A breeder wants to cross two pea plants with different flower colours. The flowers produce both pollen and ovules, so self-pollination is possible unless it is prevented.
Identify the structure that contains the male gametes used in the cross.
[1]
Outline two procedures used to ensure that only the chosen pollen fertilizes the ovules.
[2]
State the meaning of F1 generation in this cross.
[1]
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Question 13
A plant species has a gene affecting stem length. The allele produces enough functional enzyme for tall stems and is dominant to the allele , which produces a non-functional enzyme.
State the genotype of a heterozygous plant for stem length.
[1]
Explain why plants with genotypes and have the same stem-length phenotype.
[2]
State the expected phenotypic ratio from a cross between two heterozygous plants if dominance is complete.
[1]
Question 14
A diploid cell is heterozygous at two unlinked autosomal genes, with genotype . The genes are on different chromosome pairs.
State the meaning of segregation for the alleles of gene A.
[1]
Explain why four gamete genotypes can be produced in equal proportions.
[3]
Question 15
A student used a gene database to compare four human genes and their polypeptide products.
Gene | Chromosome | Locus / Mb | Polypeptide product |
|---|---|---|---|
F8 | X | 154.2 | coagulation factor VIII |
F9 | 4 | 187.9 | coagulation factor IX |
HBA1 | 16 | 3.02 | alpha-globin chain |
HBA2 | 16 | 3.05 | alpha-globin chain |
Identify one pair of genes in the table that is unlinked because the genes are on different chromosomes.
[1]
Identify one pair of genes in the table that may be linked because the genes are close together on the same autosome.
[1]
Explain how gene databases connect gene loci with inheritance patterns.
[2]
Question 16
The diagram shows stages in the sexual life cycle of a diploid flowering plant. The diploid chromosome number of the plant is .
State the chromosome number in a gamete of this plant.
[1]
Identify the process in the diagram that restores the diploid chromosome number.
[1]
Explain how meiosis and fertilization together allow inheritance without chromosome number doubling in each generation.
[2]
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Question 17
A student carried out a controlled cross in four o'clock flower, Mirabilis jalapa. A red-flowered plant was used as the pollen donor and a white-flowered plant was used as the female parent. The procedure and offspring phenotypes are shown.
Identify the structure that must receive pollen for the cross to occur.
[1]
Explain why the anthers of the female parent were removed before they released pollen.
[2]
Suggest why the F1 flowers all had a phenotype different from both P generation plants.
[1]
Question 18
In a dihybrid cross with four phenotype classes, the null hypothesis states that the observed frequencies fit a ratio. The calculated value is . The critical value at with degrees of freedom is . What conclusion should be made?
A.
Prove independent assortment because is not zero.
B.
Accept the alternative hypothesis because .
C.
Reject the null hypothesis because .
D.
Do not reject the null hypothesis because .
Question 19
A test cross is carried out using an individual heterozygous for two genes and an individual homozygous recessive for both genes. The offspring phenotypes are recorded.
| Phenotype | Number of offspring |
|---|---|
| Both dominant traits | 186 |
| Both recessive traits | 174 |
| First dominant, second recessive | 31 |
| First recessive, second dominant | 29 |
What is the best interpretation of these results?
A.
The genes are linked, with the two smaller classes being recombinants.
B.
The genes are sex-linked, because males and females differ in number.
C.
The genes are unlinked, because all four phenotype classes are present.
D.
The genes show incomplete dominance, with two intermediate classes.
Question 20
In the ABO blood group system, the alleles are , and . A person with blood group A has a child with a person with blood group B. The child has blood group O.
Deduce the genotypes of both parents.
[2]
Determine the probability that a future child of the same parents will have blood group AB.
[1]
State why blood group AB is an example of codominance rather than incomplete dominance.
[1]
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Question 21
Haemophilia is an X-linked recessive disorder. The normal clotting allele is represented by and the haemophilia allele by . A woman who is a carrier has a child with an unaffected man.
State the genotype of the carrier woman.
[1]
Determine the probability that a son will have haemophilia.
[1]
Explain why an affected father cannot pass this X-linked allele to his sons.
[2]
Question 22
A class collected data on student height and ABO blood group. Height was displayed using a box-and-whisker plot, while ABO blood group was summarized as counts in four categories.
Section | Item | Value / cm or students |
|---|---|---|
Height | lower whisker / minimum | 150 cm |
Height | first quartile () | 162 cm |
Height | median | 168 cm |
Height | third quartile () | 174 cm |
Height | upper whisker / maximum | 186 cm |
ABO blood group | A | 12 students |
ABO blood group | B | 8 students |
ABO blood group | AB | 4 students |
ABO blood group | O | 16 students |
Distinguish between height and ABO blood group as variables.
[2]
State two features of a box-and-whisker plot that show the spread of the height data.
[2]
Question 23
In a plant, purple flowers are dominant to white flowers , and round pollen is dominant to wrinkled pollen . The two genes are unlinked autosomal genes. Two plants with genotype are crossed.
State the four gamete genotypes produced by each parent.
[1]
Determine the expected phenotypic ratio in the offspring.
[1]
Explain the conditions under which this ratio is expected.
[2]
Question 24
An organism is heterozygous for two linked autosomal genes. Its homologous chromosomes carry the allele combinations and . It is crossed with a double homozygous recessive organism, .
State the two parental gamete genotypes produced by the double heterozygote.
[1]
State the two recombinant gamete genotypes produced if crossing over occurs between the loci.
[1]
Explain why parental offspring phenotypes are expected to be more common than recombinant phenotypes in this cross.
[2]
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Question 25
In a fruit fly test cross, two autosomal genes affect body colour and wing shape. The offspring phenotypes occur mostly in two parental combinations, with much smaller numbers in the two recombinant combinations.
Body colour | Wing shape | Offspring count |
|---|---|---|
Grey | normal | 452 |
Black | vestigial | 448 |
Grey | vestigial | 52 |
Black | normal | 48 |
State the evidence from the results that the genes are linked.
[1]
Explain why linked autosomal genes can fail to assort independently.
[2]
State why this result is an exception to Mendel's second law rather than a contradiction of meiosis.
[1]
Question 26
The pedigree and screening results show inheritance of phenylketonuria (PKU) in one family. PKU is caused by a recessive allele of an autosomal gene coding for phenylalanine hydroxylase.
Deduce the genotype of the affected child, using for the normal allele and for the PKU allele.
[1]
Determine the probability that a future child of the same parents will be an unaffected carrier.
[2]
Explain why a low-phenylalanine diet can reduce symptoms in a child with PKU but does not change the inheritance of PKU.
[2]
Question 27
The table shows ABO blood groups in a family. One parent has blood group A and the other has blood group B. Their children include individuals with blood groups AB, A, B and O.
Family member | Blood group |
|---|---|
Parent 1 | A |
Parent 2 | B |
Child 1 | AB |
Child 2 | A |
Child 3 | B |
Child 4 | O |
Deduce the genotype of each parent, using , and .
[2]
State the expected phenotypic ratio among children from these parents.
[1]
Explain why blood group AB is an example of codominance.
[1]
Question 28
The pedigree shows inheritance of haemophilia in a human family. Haemophilia is an X-linked recessive disorder. Use for an X chromosome carrying the normal clotting allele and for an X chromosome carrying the haemophilia allele.
Identify one feature of the pedigree that supports X-linked recessive inheritance.
[1]
Deduce the genotype of an unshaded mother who has an affected son and an unaffected father.
[1]
Determine the probability that a son of this mother and an unaffected father will have haemophilia.
[1]
Explain why an affected father does not pass haemophilia directly to his sons.
[1]
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Question 29
The diagram shows two possible orientations of two homologous chromosome pairs during metaphase I of meiosis in an organism with genotype . The genes are on different chromosomes.
State the four gamete genotypes expected from this individual if the genes assort independently.
[1]
Explain how the movement of chromosomes in meiosis leads to independent assortment of these genes.
[2]
Predict the phenotypic ratio in the offspring of if both genes show complete dominance.
[1]
Question 30
In a dihybrid test cross in a plant, an individual with genotype was crossed with an individual with genotype . The genes are unlinked and show complete dominance. Offspring phenotypes are shown in the table.
Offspring phenotype | Number observed |
|---|---|
R dominant, Y dominant | 20 |
R dominant, y recessive | 20 |
r recessive, Y dominant | 20 |
r recessive, y recessive | 20 |
State the expected phenotypic ratio for this test cross if the genes are unlinked.
[1]
Determine the gametes produced by the parent.
[2]
Explain why the offspring phenotypes in this cross reveal the gametes produced by the parent.
[1]
Question 31
A database search was used to compare human genes, their chromosomal loci and their polypeptide products. Part of the output is shown.
Gene | Chromosome | Approximate locus | Polypeptide product |
|---|---|---|---|
PAH | 12 | 12q23.2 | phenylalanine hydroxylase |
CFTR | 7 | 7q31.2 | CFTR protein |
HBB | 11 | 11p15.5 | beta-globin |
HBD | 11 | 11p15.5 | delta-globin |
Identify one pair of genes in the table that would be unlinked because they are on different chromosomes.
[1]
Identify one pair of genes in the table that may be linked because they are close together on the same autosome.
[1]
Explain how information about gene loci can help predict inheritance patterns in a dihybrid cross.
[2]
Question 32
In a dihybrid test cross, the expected phenotypic ratio for unlinked genes is . The observed offspring numbers were 82, 18, 20 and 80 in the four phenotype classes. The calculated value of is . The critical value at for three degrees of freedom is .
State the null hypothesis for this chi-squared test.
[1]
State the expected number of offspring in each phenotype class.
[1]
Evaluate whether the data support independent assortment of the two genes.
[2]
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Question 33
Skin pigmentation index was measured in two groups of students with similar ancestry. One group had low recent sunlight exposure and the other had high recent sunlight exposure. The results are shown as box-and-whisker plots.
Group | Minimum / index units | Q1 / index units | Median / index units | Q3 / index units | Maximum / index units |
|---|---|---|---|---|---|
Low recent sunlight exposure | 20 | 25 | 32 | 38 | 68 |
High recent sunlight exposure | 34 | 42 | 50 | 60 | 69 |
State which group has the higher median skin pigmentation index.
[1]
Calculate the interquartile range for the high-sunlight group.
[1]
Explain why skin pigmentation is an example of continuous variation influenced by both genotype and environment.
[2]
Suggest why the median may be more useful than the mean for one of these groups.
[1]
Question 34
Two autosomal genes in a beetle are linked. A double heterozygote with alleles in the arrangement was crossed with a double homozygous recessive beetle, . Offspring phenotypes were recorded.
Offspring phenotype | Number observed |
|---|---|
A and B present | 160 |
A only | 44 |
B only | 36 |
Neither A nor B present | 160 |
Total | 400 |
Identify the recombinant offspring genotypes from this cross.
[1]
Calculate the percentage of recombinant offspring.
[2]
Explain why the recombinant classes are less frequent than the parental classes.
[1]
Question 35
A tomato breeder investigated two autosomal genes: one affecting leaf shape and one affecting fruit striping. A double heterozygote was crossed with a double homozygous recessive plant. The offspring phenotypes are shown.
Phenotype class | Number of offspring |
|---|---|
Normal leaves, striped fruit | 184 |
Curled leaves, striped fruit | 14 |
Normal leaves, unstriped fruit | 16 |
Curled leaves, unstriped fruit | 186 |
Evaluate whether the two genes are likely to be linked or unlinked.
[2]
State which offspring phenotype classes are parental types.
[1]
Explain why allele symbols for linked genes should be shown beside vertical lines representing homologous chromosomes.
[1]
Question 36
A plant breeder investigates inheritance of flower colour in a variety of pea plant. Purple flowers are produced by allele and white flowers by allele . Purple is dominant to white. A true-breeding purple-flowered plant is crossed with a true-breeding white-flowered plant to produce the generation. Several plants are then allowed to self-pollinate to produce the generation.
I.
Explain why removing immature anthers helps to make the cross controlled.
[1]
II.
Predict the genotype and phenotype of all offspring from this cross.
[2]
Explain how a Punnett grid predicts the phenotype ratio when plants self-pollinate.
[3]
Discuss one reason why the observed numbers in a real breeding experiment may not exactly equal the predicted ratio.
[1]
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Question 37
The ABO blood group system is controlled by three common alleles in the human gene pool: , and . A child has blood group O. One parent has blood group A and the other parent has blood group B.
I.
Deduce the genotype of the child.
[1]
II.
Deduce the genotypes of both parents and justify your answer.
[2]
Explain how the same gene can produce four ABO phenotypes in the population, although each individual inherits only two alleles.
[2]
Compare and contrast codominance and incomplete dominance using ABO blood group and four o'clock flower, Mirabilis jalapa, as examples.
[2]
Question 38
Genetically identical cuttings of a plant species were grown under different light conditions. The same genotype produced broad, dark-green leaves in shade and smaller, thicker leaves in high light.
I.
State the term for the capacity of one genotype to develop different traits in different environments.
[1]
II.
Explain why this example is not evidence of mutation during growth.
[1]
Discuss how genotype and environment can both contribute to phenotype, using one human example.
[2]
Evaluate one possible advantage of phenotypic plasticity for plants living in variable environments.
[2]
Question 39
A student uses a human genome database to compare four genes. Two genes are on different chromosomes, and two genes are close together on the same autosome. The database entries include chromosome number, locus and polypeptide product.
Gene | Chromosome | Locus | Polypeptide product |
|---|---|---|---|
RHD | 1 | 1p36.11 () | RhD protein |
RHCE | 1 | 1p36.11 () | RhCE protein |
CFTR | 7 | 7q31.2 () | CFTR chloride channel protein |
HBB | 11 | 11p15.4 () | -globin polypeptide |
I.
State what is meant by the locus of a gene.
[1]
II.
Explain why a gene database may list a polypeptide product for a gene.
[1]
Discuss how the database information could be used to predict whether two genes are likely to assort independently.
[2]
Evaluate one limitation of using only database locus information to predict the offspring ratios from a cross.
[2]
Question 40
In an generation from a dihybrid cross, offspring were classified into four phenotype categories. The null hypothesis was tested against the expected ratio for two unlinked autosomal genes with complete dominance.
Category | Observed | Expected (9:3:3:1) | critical value |
|---|---|---|---|
Phenotype 1 | 95 | 90 | — |
Phenotype 2 | 29 | 30 | — |
Phenotype 3 | 29 | 30 | — |
Phenotype 4 | 7 | 10 | — |
Critical value (df=3, p=0.05) | — | — | 7.815 |
State a suitable null hypothesis for this chi-squared test.
[1]
Calculate the chi-squared value for the data.
[2]
Evaluate the null hypothesis at the level. The degrees of freedom are .
[2]
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Question 41
Phenylketonuria, PKU, is caused by a recessive allele of an autosomal gene coding for phenylalanine hydroxylase. The pedigree shows part of a family in which one child has PKU.
I.
Deduce the most likely pattern of inheritance shown by the pedigree.
[1]
II.
Using for the normal allele and for the PKU allele, deduce the genotypes of the unaffected parents of the affected child.
[2]
Explain the biochemical basis of the PKU phenotype and why a carrier usually does not show PKU symptoms.
[3]
Evaluate the statement: “PKU is entirely determined by genotype, so environmental management cannot affect the phenotype.”
[2]
Question 42
A class collected data on student height and ABO blood group. The height data are displayed as a box-and-whisker plot, and the blood group data are displayed as counts in categories.
Data set | Statistic / category | Height / cm | Count |
|---|---|---|---|
Height | Minimum | 148 | |
Height | Lower quartile () | 153 | |
Height | Median | 158 | |
Height | Upper quartile () | 162 | |
Height | Maximum | 169 | |
ABO blood group | A | 7 | |
ABO blood group | B | 4 | |
ABO blood group | AB | 2 | |
ABO blood group | O | 8 | |
ABO blood group | Total | 21 |
I.
Identify two features of the height data that are shown by the box-and-whisker plot.
[2]
II.
State how an outlier is categorized using the interquartile range.
[1]
Compare height and ABO blood group as types of variation.
[3]
Evaluate whether the mean, median or mode is most appropriate as the measure of central tendency for the ABO blood group data.
[2]
Question 43
Haemophilia is an X-linked recessive genetic disorder. The normal clotting allele is written and the haemophilia allele is written . A pedigree shows a family in which haemophilia occurs in several males.
I.
Explain why haemophilia affects males more frequently than females in this pattern of inheritance.
[2]
II.
State why a father with haemophilia does not pass the haemophilia allele to his sons.
[1]
A carrier female has children with a male without haemophilia. Deduce the possible genotypes and phenotypes of their sons and daughters.
[3]
Discuss how a pedigree can be used by both inductive and deductive reasoning in studying this disorder.
[2]
Question 44
In a diploid organism, two unlinked autosomal genes affect seed shape and seed colour. The organism is heterozygous for both genes, . Allele gives round seeds and gives wrinkled seeds; allele gives yellow seeds and gives green seeds.
I.
Explain segregation for the gene during meiosis.
[1]
II.
Explain why and assort independently in this organism.
[2]
Predict the gamete genotypes produced by the individual and their relative frequencies.
[2]
Explain how independent assortment in meiosis leads to a phenotypic ratio in a cross between two double heterozygotes, assuming complete dominance.
[2]
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Question 45
In a dihybrid test cross, a tomato plant heterozygous for fruit colour and leaf shape is crossed with a plant homozygous recessive for both genes. Red fruit, , is dominant to yellow fruit, , and lobed leaves, , are dominant to entire leaves, . The two genes are known to be unlinked.
Gamete from | Gamete from | Offspring genotype | Offspring phenotype | Expected frequency |
|---|---|---|---|---|
red lobed | ||||
red entire | ||||
yellow lobed | ||||
yellow entire |
I.
Identify the gametes produced by the heterozygous parent.
[1]
II.
Deduce the expected offspring phenotypes from this test cross.
[2]
Explain why a test cross can reveal the gametes produced by the heterozygous parent.
[2]
Evaluate why Mendel's second law is a useful prediction but not an exception-proof rule in this cross.
[3]
Question 46
In a plant species, two autosomal genes are linked. A plant heterozygous for both genes has the allele arrangement , where the slash separates homologous chromosomes. It is test-crossed with a plant . Offspring phenotypes are recorded.
Offspring phenotype | Number of offspring |
|---|---|
Both A and B traits | 400 |
A trait only | 100 |
B trait only | 100 |
Neither A nor B trait | 400 |
I.
Identify the parental gamete types produced by the heterozygous parent.
[1]
II.
Identify the recombinant gamete types produced by the heterozygous parent.
[1]
III.
Explain why a test cross allows recombinant offspring phenotypes to be identified.
[1]
Explain why the parental offspring classes are expected to be more frequent than recombinant classes in this cross.
[3]
Discuss why allele symbols for linked genes are often written beside vertical lines representing homologous chromosomes rather than as a simple genotype such as .
[2]
Question 47
In an generation from a dihybrid cross, four phenotypes are counted. A student tests whether the data fit the ratio expected for two unlinked autosomal genes with complete dominance. The critical value of for degrees of freedom at is .
Phenotype | Observed count | Expected count () |
|---|---|---|
Both dominant traits | 85 | 90 |
Trait A dominant only | 35 | 30 |
Trait B dominant only | 25 | 30 |
Both recessive traits | 15 | 10 |
I.
State an appropriate null hypothesis for the chi-squared test.
[1]
II.
Explain why the degrees of freedom are for this test.
[1]
III.
State the formula used to calculate the chi-squared statistic.
[1]
Explain how observed and expected results are used to decide whether the deviation from is statistically significant at .
[2]
Evaluate why using the generation as a sample may affect the reliability of the conclusion.
[3]
Question 48
A breeder studies two genes controlling coat traits in a mammal. A double heterozygote is test-crossed with a double homozygous recessive individual. The offspring show many parental combinations and fewer recombinant combinations.
Offspring phenotype class | Number of offspring |
|---|---|
Dark coat, short fur | 45 |
Light coat, long fur | 45 |
Dark coat, long fur | 5 |
Light coat, short fur | 5 |
I.
Deduce whether the genes are linked or unlinked.
[1]
II.
Justify the deduction using the offspring phenotypes.
[2]
Explain the cellular mechanism that produces the recombinant offspring in a cross involving linked autosomal genes.
[2]
Discuss how the distance between two loci on the same autosome affects recombination and inheritance ratios.
[2]
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