AQA Biology GCSE Topic 6: Inheritance, Variation and Evolution

A comprehensive set of Q&A flashcards covering reproduction, DNA, inheritance, evolution, genetics, and classification based on the provided notes.

What is meiosis?

The process that forms four non-identical gametes from one parent cell.

What is mitosis?

The process that forms two identical daughter cells from one parent cell.

What characterizes sexual reproduction?

Joining of male and female gametes, each carrying genetic information from the parents; gametes are formed by meiosis.

What are the gametes in animals and in flowering plants?

Sperm and egg in animals; pollen and egg in flowering plants.

How many chromosomes do human gametes have?

23 chromosomes.

What happens to chromosomes during fertilisation?

Gametes fuse to form a zygote with 46 chromosomes; parental genetic information mixes to produce variation.

What characterizes asexual reproduction?

One parent, no gametes, mitosis, offspring that are genetically identical (clones).

Give examples of organisms that reproduce asexually.

Bacteria, some plants, and some animals.

How many chromosomes are in a normal human body cell?

46 chromosomes (23 pairs).

Why are gametes non-identical?

Because they are produced by meiosis and undergo genetic recombination.

What drives variation in offspring during sexual reproduction?

Mixing of parental genes during meiosis and fertilisation, plus crossing over and independent assortment.

What are the advantages of sexual reproduction?

Produces genetic variation, which helps species survive environmental changes; promotes natural selection.

What are the advantages of asexual reproduction?

Requires only one parent, rapid population growth, no need to find a mate.

Name organisms that can reproduce both sexually and asexually.

Malarial parasites, some fungi, and some plants (e.g., pollen-based reproduction or vegetative methods).

What is pollination?

The transfer of pollen to the female part of a flower, enabling sexual reproduction in plants.

How do strawberry plants reproduce asexually?

By producing runners that create new identical plants.

How do daffodils reproduce asexually?

They grow from bulbs, producing new identical plants.

What is DNA?

A polymer that stores genetic information; composed of two strands in a double helix.

What is a gene?

A small section of DNA on a chromosome that codes for a protein.

What is a genome?

All the genes that code for all the proteins in an organism.

What are nucleotides?

The building blocks of DNA, consisting of a sugar, a phosphate, and a base.

What are the four bases in DNA?

Adenine (A), Cytosine (C), Guanine (G), Thymine (T).

How do the two DNA strands pair?

A pairs with T, C pairs with G (complementary base pairing).

What is a codon?

A group of three bases on mRNA that codes for one amino acid.

How many amino acids are there?

20 amino acids.

What determines a protein’s function?

The sequence and type of amino acids and how the protein folds into its 3D shape.

What is transcription?

The process of copying DNA into mRNA in the nucleus.

Where does translation occur?

At the ribosome in the cytoplasm.

What is the role of tRNA?

Carrier molecules bring amino acids to the ribosome during protein synthesis.

What are the stages of protein synthesis?

DNA -> mRNA (transcription); mRNA -> protein at ribosome (translation); protein folding.

What is the function of enzymes, hormones, and structural proteins?

Enzymes catalyse reactions, hormones signal, and structural proteins provide support (e.g., collagen).

What are mutations?

Changes in DNA sequence; can be insertions, deletions, or substitutions.

How can insertions and deletions affect a protein?

They can shift the reading frame, altering many downstream amino acids and often changing protein function.

What is a substitution mutation?

One base is replaced, which may change one amino acid or have no effect if the same amino acid is coded.

What is the difference between coding and non-coding DNA?

Coding DNA codes for proteins; non-coding DNA controls gene expression and other regulatory functions.

What is a gene’s expression?

Whether a gene is turned on and produces its product (protein or RNA).

What is a genotype?

The combination of alleles an individual has (e.g., Aa, BB).

What is a phenotype?

The observable characteristics resulting from the genotype and environment.

What is a dominant allele?

Only one copy is needed for phenotype to be expressed.

What is a recessive allele?

Two copies are needed for phenotype to be expressed.

What does homozygous mean?

Both inherited alleles are the same (e.g., AA or aa).

What does heterozygous mean?

Two different alleles are inherited (e.g., Aa).

What is a Punnett square used for?

To predict the genotype and phenotype of offspring from two parents.

What is polydactyly and its mode of inheritance?

Having extra fingers or toes; caused by a dominant allele.

What is cystic fibrosis and its inheritance?

A recessive genetic disorder affecting mucus membranes; both parents must carry or have the condition.

What is embryonic screening?

Observing embryos to determine if genetic conditions are present.

What determines sex in humans?

The 23rd chromosome pair; females are XX, males are XY; sex is determined by the father's sperm.

What is variation and environment’s role in phenotype?

Genotype determines potential traits; environment influences how they are expressed.

What is natural selection?

Process where advantageous traits increase in frequency because organisms with them survive better and reproduce more.

What is speciation?

Formation of a new species when populations diverge and can no longer interbreed to produce fertile offspring.

Who proposed natural selection alongside Darwin?

Alfred Russel Wallace.

What did Mendel contribute to genetics?

Experiments with pea plants showing how traits are inherited via hereditary units (genes) that come in dominant and recessive forms.

What is a fossil used to show?

How anatomy and species have changed over time and relationships between organisms.

What is antibiotic resistance and how does it arise?

Bacteria acquire mutations that confer resistance; selection pressures from antibiotics increase resistant strains.

What are MRSA and how can resistance spread?

A ‘superbug’ resistant to many antibiotics; spreads in hospitals via close contact and movement of people.

How can antibiotic resistance be slowed?

Avoid unnecessary antibiotics, use targeted antibiotics, complete courses, reduce agricultural use, and maintain hygiene.

What are Linnaean and three-domain classification systems?

Linnaean: kingdoms to species with binomial names; three-domain system: Archaea, Bacteria, Eukaryota.

What is an evolutionary tree used for?

To show how closely related organisms are based on classification data and fossils.