AQA GCSE Combined Science: Trilogy · 4.6

Inheritance, variation and evolution

50 revision questions with answers for 4.6 Inheritance, variation and evolution in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 4.6.1.1
What is sexual reproduction?
Answer:
Reproduction involving fusion of male and female gametes, producing offspring with a mixture of genetic information.
Question 2 · Spec 4.6.1.1
How does asexual reproduction differ from sexual reproduction?
Answer:
It involves one parent and no fusion of gametes, producing genetically identical clones through mitosis, except for mutations.
Question 3 · Spec 4.6.1.1
Name the male and female gametes in humans and flowering plants.
Answer:
Humans: sperm and egg cells. Flowering plants: male gametes are in pollen; female gametes are egg cells in ovules.
Question 4 · Spec 4.6.1.2
What does meiosis produce?
Answer:
Four genetically different gametes, each with half the original chromosome number, after two divisions following DNA replication.
Question 5 · Spec 4.6.1.2
Why must gametes have half the normal chromosome number?
Answer:
Their nuclei fuse at fertilisation, restoring the normal chromosome number instead of doubling it each generation.
Question 6 · Spec 4.6.1.3
What is DNA, and how is it organised in cells?
Answer:
DNA is the genetic material: a polymer arranged as a double helix and packaged into chromosomes.
Question 7 · Spec 4.6.1.3
What is a gene?
Answer:
A small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein.
Question 8 · Spec 4.6.1.3
What is a genome?
Answer:
The entire genetic material of an organism.
Question 9 · Spec 4.6.1.3
Give two reasons why understanding the human genome is useful.
Answer:
It helps identify genes linked to diseases and inherited disorders, develop treatments and trace human migration patterns.
Question 10 · Spec 4.6.1.4
What is an allele?
Answer:
A different version of a gene.
Question 11 · Spec 4.6.1.4
What does genotype mean?
Answer:
The combination of alleles an organism has for a particular gene or genes.
Question 12 · Spec 4.6.1.4
What does phenotype mean?
Answer:
An organism's observable characteristics, resulting from its genotype and interaction with the environment.
Question 13 · Spec 4.6.1.4
How do dominant and recessive alleles differ?
Answer:
A dominant allele affects the phenotype with one copy present. A recessive allele usually affects it only when two copies are present.
Question 14 · Spec 4.6.1.4
What do homozygous and heterozygous mean?
Answer:
Homozygous means having two identical alleles for a gene. Heterozygous means having two different alleles.
Question 15 · Spec 4.6.1.4
If B is dominant, compare the phenotypes of BB, Bb and bb.
Answer:
BB and Bb show the dominant characteristic; bb shows the recessive characteristic.
Question 16 · Spec 4.6.1.4
A supplied cross gives AA, Aa, Aa and aa. What proportion is homozygous recessive?
Answer:
One of four equally likely outcomes is aa: 1/4, or 25%.
Question 17 · Spec 4.6.1.4 · Higher only
Construct the possible offspring genotypes for Aa x aa.
Answer:
Gametes are A or a from the first parent and a from the second. Offspring: 50% Aa and 50% aa.
Question 18 · Spec 4.6.1.4
Does a 25% inherited-disorder probability mean exactly one affected child in every four?
Answer:
No. Each conception is a separate event; 25% is the probability for each child, not a guaranteed family ratio.
Question 19 · Spec 4.6.1.5
How is polydactyly inherited?
Answer:
It is caused by a dominant allele, so one copy can produce extra fingers or toes.
Question 20 · Spec 4.6.1.5
How is cystic fibrosis inherited?
Answer:
It is caused by a recessive allele. A person with one copy is usually an unaffected carrier; two copies cause the disorder.
Question 21 · Spec 4.6.1.5
Give one benefit and one ethical concern of embryo screening.
Answer:
It can reduce the chance of passing on an inherited disorder, but people may object to selecting or discarding embryos.
Question 22 · Spec 4.6.1.6
What sex chromosome combinations usually produce females and males?
Answer:
Females usually have XX; males usually have XY. Eggs carry X; sperm carry X or Y.
Question 23 · Spec 4.6.1.6
Why is the probability of a male or female offspring approximately equal?
Answer:
About half of sperm carry X and half carry Y, giving roughly equal chances of XX and XY at fertilisation.
Question 24 · Spec 4.6.2.1
What is variation within a population?
Answer:
Differences in characteristics between individuals of the same species.
Question 25 · Spec 4.6.2.1
Give examples of genetic, environmental and combined influences on variation.
Answer:
Blood group is inherited; scars are environmental; body mass is influenced by genes and environment.
Question 26 · Spec 4.6.2.1
What is a mutation, and do all mutations change phenotype?
Answer:
A mutation is a change in DNA. Most have no effect on phenotype; some affect characteristics.
Question 27 · Spec 4.6.2.2
Define evolution.
Answer:
A change in inherited characteristics of a population over time through natural selection, which can eventually produce new species.
Question 28 · Spec 4.6.2.2
How does natural selection change a population?
Answer:
Inherited variation affects survival and reproduction. Individuals with advantageous traits leave more offspring, making the associated alleles more common.
Question 29 · Spec 4.6.2.2
When are two populations considered different species in the GCSE model?
Answer:
When they can no longer interbreed to produce fertile offspring.
Question 30 · Spec 4.6.2.3
What is selective breeding?
Answer:
Humans choosing parents with desired characteristics to produce offspring with those characteristics.
Question 31 · Spec 4.6.2.3
Describe the main stages of selective breeding.
Answer:
Select parents with useful characteristics, breed them, select suitable offspring and repeat over many generations.
Question 32 · Spec 4.6.2.3
Give three characteristics humans may select in crops or livestock.
Answer:
Disease resistance, high yield or milk production, and desirable appearance or behaviour.
Question 33 · Spec 4.6.2.3
Why can selective breeding increase inherited-disease risk?
Answer:
Repeated breeding of related individuals reduces genetic variation and can increase the chance of harmful recessive alleles occurring together.
Question 34 · Spec 4.6.2.4
What is genetic engineering?
Answer:
Modifying an organism's genome by introducing a gene from another organism to give a desired characteristic.
Question 35 · Spec 4.6.2.4
Why are bacteria genetically engineered to produce human insulin?
Answer:
A human insulin gene enables them to make insulin that can be collected for treating diabetes.
Question 36 · Spec 4.6.2.4
Give two possible useful features of genetically modified crops.
Answer:
Resistance to insects or herbicides, improved yield, or altered nutritional content.
Question 37 · Spec 4.6.2.4
Give a possible concern about genetically modified crops.
Answer:
Introduced genes may spread to wild populations or affect ecosystems; proposed effects must be assessed using evidence.
Question 38 · Spec 4.6.2.4 · Higher only
Describe the main genetic-engineering steps.
Answer:
Use enzymes to isolate a gene and insert it into a vector, such as a plasmid or virus; transfer the vector into target cells.
Question 39 · Spec 4.6.2.4 · Higher only
Why are genes introduced early in an organism's development?
Answer:
As the modified cells divide, the introduced gene can be passed to many cells, allowing the organism to develop the desired characteristic.
Question 40 · Spec 4.6.3.1
Name two major sources of evidence for evolution.
Answer:
The fossil record and the development of antibiotic resistance in bacteria.
Question 41 · Spec 4.6.3.2
What is a fossil?
Answer:
Preserved remains or traces of organisms from the past, usually found in rocks.
Question 42 · Spec 4.6.3.2
Give three ways fossils can form.
Answer:
Hard parts may resist decay; conditions may prevent decay; or traces such as footprints and burrows may be preserved.
Question 43 · Spec 4.6.3.2
Why is the fossil record incomplete?
Answer:
Many early organisms were soft-bodied, many remains decayed, and geological activity destroyed or changed some fossil-bearing rocks.
Question 44 · Spec 4.6.3.3
Name three possible causes of extinction.
Answer:
Environmental change, new predators or competitors, new diseases, or catastrophic events.
Question 45 · Spec 4.6.3.4
Explain how an antibiotic-resistant bacterial population develops.
Answer:
A mutation produces resistance; antibiotic exposure kills susceptible bacteria; resistant survivors reproduce and pass on resistance.
Question 46 · Spec 4.6.3.4
How can the spread of antibiotic resistance be reduced?
Answer:
Avoid unnecessary antibiotic use, use appropriate prescriptions correctly, improve hygiene and develop new antibiotics.
Question 47 · Spec 4.6.4
State the Linnaean classification hierarchy.
Answer:
Kingdom, phylum, class, order, family, genus, species. Binomial names use genus and species.
Question 48 · Spec 4.6.4
What are the three domains in the modern classification system?
Answer:
Archaea, Bacteria and Eukaryota, based on evidence including molecular and biochemical differences.
Question 49 · Spec 4.6.4
What does an evolutionary tree show?
Answer:
Relationships and common ancestry between organisms; more recent common ancestors indicate closer evolutionary relationships.
Question 50 · Spec 4.6.4
Why have classification systems changed over time?
Answer:
Improved microscopy and molecular evidence, including genetic analysis, have revealed relationships that older systems did not show.

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