Inheritance, variation and evolution

State two features of asexual reproduction.

Compare the production and genetic features of offspring made by sexual and asexual reproduction.

A plant can produce seeds after pollination and can also produce new plants from runners. Explain why the offspring from these two methods differ genetically.

State the type of cell division that produces gametes and the number of gametes produced from one cell.

Explain how meiosis and fertilisation maintain the chromosome number from one generation to the next.

Describe the sequence from one cell in a reproductive organ to a differentiated embryo, including the divisions involved and the genetic relationship between cells.

State one advantage of sexual reproduction and one advantage of asexual reproduction.

A fungus reproduces rapidly by asexual spores when conditions are stable but sometimes reproduces sexually. Explain the advantage of each strategy.

Evaluate whether a farmer should propagate a disease-resistant crop asexually or continue sexual breeding. Use benefits and risks of both methods.

Define the genome of an organism.

Describe the relationship between DNA, chromosomes, genes and proteins.

Explain three medical or historical benefits of studying the whole human genome, and state one limitation when predicting disease.

Name the three components of a DNA nucleotide.

Describe the structure of a DNA strand and explain how it can carry different genetic information.

Higher tier: A mutation changes the order of bases in a gene. Explain how this may change the protein made, using the relationship between bases and amino acids.

Define the terms allele and heterozygous.

In mice, black fur allele B is dominant to white fur allele b. Explain the phenotypes of mice with genotypes BB, Bb and bb.

Higher tier: Two heterozygous black mice, Bb and Bb, are crossed. Construct the genetic cross and predict the genotype ratio, phenotype ratio and probability of a white offspring.

State which disorder is caused by a dominant allele and which is caused by a recessive allele: polydactyly and cystic fibrosis.

Two parents do not have cystic fibrosis, but each carries its recessive allele. Explain how they can have a child with the disorder.

Evaluate the use of embryo screening by parents who risk passing on a serious inherited disorder.

State the sex-chromosome combination usually found in females and in males.

Use a genetic cross to explain why the probability of an XX child is $1/2$.

A family has three XY children. A parent claims that the next child is now more likely to be XX. Evaluate the claim using chromosome inheritance and probability.

State the three broad causes of variation in phenotype.

Explain why genetically identical plant cuttings can grow to different heights in two gardens.

A pesticide is introduced into an insect population. Explain how a rare mutation may contribute to a rapid population change without the pesticide causing the useful mutation.

Define evolution.

Explain how natural selection can make a favourable inherited characteristic more common in a population.

Two populations descended from one species now differ strongly in phenotype. Explain what further evidence would show that speciation has occurred, and how natural selection could have produced the differences.

Define selective breeding.

Describe how a breeder could develop a variety of crop in which most plants resist a fungal disease.

Evaluate a programme that selectively breeds dairy cattle only from the highest-milk-producing animals.

Define genetic engineering.

Evaluate the use of a genetically modified crop that resists insect attack.

Higher tier: Describe how a human gene can be transferred into bacterial cells so that the bacteria develop the desired characteristic.

State one use of plant tissue culture and explain why the new plants are clones.

Describe how embryo transplants produce several genetically identical farm animals.

Describe adult cell cloning from an unfertilised egg cell to the birth of a cloned animal, and identify which animal supplies most of the clone's genetic information.

State two reasons why many people did not immediately accept Darwin's explanation of how species change.

Describe Darwin's explanation of evolution by natural selection.

Compare Darwin's and Lamarck's explanations for a population becoming better suited to its environment, and explain why Darwin's theory became accepted.

State one contribution made by Alfred Russel Wallace to evolutionary biology.

Describe how the work of Wallace affected the development and publication of evolutionary theory.

A physical barrier separates two populations of one species into different environments. Explain the steps by which two new species may arise.

State the main conclusion Mendel drew from his plant breeding experiments.

Explain how observations of chromosomes helped scientists connect Mendel's units with genes.

Describe how understanding of genetics developed from Mendel's experiments to modern gene theory, and explain why this is an example of science developing over time.

State two sources of evidence for evolution.

Explain how modern genetics strengthened the evidence for Darwin's theory.

Explain why fossil evidence and antibiotic resistance together provide stronger support for evolution than either source alone.

State two ways in which a fossil may form.

Explain why the fossil record gives an incomplete account of the earliest life on Earth.

An evolutionary tree places species P and Q on branches that share a more recent common branch point than either shares with species R. Interpret this evidence and state one reason the proposed tree could later change.

Define extinction.

Describe three factors that may contribute to the extinction of a species.

A small island species loses most of its habitat while a new predator and disease arrive. Explain why this combination creates a high risk of extinction.

State why bacterial populations can evolve antibiotic resistance rapidly.

Explain how treating a mixed bacterial population with an antibiotic can increase the proportion of resistant bacteria.

Evaluate three measures intended to slow the emergence and spread of antibiotic-resistant bacterial strains.

State the two taxonomic groups used in a binomial name.

Explain why biological classification systems have changed since Linnaeus developed his system.

Compare Linnaean classification, the three-domain system and evolutionary trees as ways of organising biological evidence.