An allele is one of the different versions of a particular gene.

Explain why individuals of the same species show differences in their inherited characteristics.

They inherit different combinations of alleles, and different alleles produce different versions of a characteristic.

Explain how a person can carry an allele that does not show in their appearance.

A recessive allele is masked whenever a dominant allele of the same gene is also present.

Two pea plants both have round seeds but only one of them can produce wrinkled-seeded offspring. Explain this.

That plant carries one round allele and one wrinkled allele, so it can pass the wrinkled allele on.

Edexcel GCSE Biology 1BI0

Key Concepts in Biology

Topic overview Eukaryotic and prokaryotic cells Specialised cells and their adaptations Microscopes and magnification calculations Size, scale and units in cell biology Enzyme action and denaturation Factors affecting enzyme activity Enzymes in synthesis and digestion, and rate calculations Food tests and the energy in food Diffusion, osmosis and active transport Osmosis in potatoes and percentage change in mass

Cells and Control

Topic overview Mitosis and the cell cycle Why mitosis matters: growth, repair and cancer Growth, differentiation and percentile charts Stem cells and their use in medicine The structure and function of the brain Investigating and treating the brain Neurones, receptors and the reflex arc The structure and function of the eye Eye defects and how they are corrected

Genetics

Topic overview Asexual and sexual reproduction Meiosis and the formation of gametes DNA structure, genes and the genome Extracting DNA from fruit Protein synthesis: transcription and translation Genetic variants in coding and non-coding DNA Mendel's work and the inheritance of blood groups Alleles, genotype and phenotype Monohybrid crosses and sex determination Probability and ratios from genetic crosses Sex-linked disorders Causes of variation: genes and environment The Human Genome Project Genetic variation and the effects of mutation

Natural Selection and Genetic Modification

Topic overview Darwin, Wallace and the theory of evolution Natural selection and antibiotic resistance Fossil evidence for human evolution Stone tool evidence for human evolution The pentadactyl limb and the three domains Selective breeding Tissue culture Genetic engineering and modern agriculture The stages of genetic engineering Benefits and risks of GM organisms

Health, Disease and the Development of Medicines

Topic overview Health, disease and susceptibility Pathogens and common infections How pathogens spread, and the virus life cycle Sexually transmitted infections How plants defend themselves and how plant disease is detected Physical barriers and chemical defences The immune system, immunisation and herd immunity Antibiotics and developing new medicines Aseptic technique in culturing microorganisms Testing antiseptics and antibiotics on bacterial cultures Monoclonal antibodies Lifestyle factors and non-communicable disease Treatments for cardiovascular disease

Plant Structures and Their Functions

Topic overview Photosynthesis as an endothermic reaction Limiting factors in photosynthesis Light intensity and the rate of photosynthesis Root hair cells, xylem and phloem Transpiration and translocation Leaf structure for photosynthesis and gas exchange Factors affecting the rate of transpiration Plant adaptations to extreme environments Plant hormones and their commercial uses

Animal Coordination, Control and Homeostasis

Topic overview Hormones, endocrine glands and homeostasis Adrenalin, thyroxine and negative feedback The menstrual cycle and its hormones Hormonal and barrier contraception Assisted reproductive technology and IVF Homeostasis and thermoregulation Controlling blood glucose, and type 1 diabetes Type 2 diabetes and body mass The urinary system and the production of urea The nephron, filtration and the effect of ADH Treating kidney failure: dialysis and transplants

Exchange and Transport in Animals

Topic overview Why multicellular organisms need exchange surfaces Alveoli and gas exchange Rate of diffusion and Fick's law The blood and its components Arteries, veins and capillaries The heart and the circulatory system Cellular respiration as an exothermic reaction Aerobic and anaerobic respiration compared Investigating the rate of respiration Cardiac output, stroke volume and heart rate

Ecosystems and Material Cycles

Topic overview Levels of organisation and interdependence Abiotic and biotic factors in a community Parasitism and mutualism Sampling with quadrats and transects Estimating population size from field data Energy transfer between trophic levels Human impact on ecosystems and biodiversity Food security The carbon cycle The water and nitrogen cycles Indicator species and pollution Factors affecting the rate of decomposition Calculating the rate of decay

Genetics

Alleles, genotype and phenotype

3 things to know
Paper 1

Overview

Alleles and why individuals of a species differ, dominant and recessive alleles and how a recessive allele can be carried unseen, chromosomes and genes, homozygous and heterozygous, genotype and phenotype, gametes and zygotes, and why one phenotype can hide different genotypes.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is an allele?

Key term

How many alleles of each gene does an individual normally have?

Key term

What happens to the characteristic when an individual inherits two different alleles of a gene?

Questions from this subtopic

Each one with the model answer underneath.

1
What is an allele?
Model answer
An allele is one of the different versions of a particular gene.
2
How many alleles of each gene does an individual normally have?
Model answer
Two, one inherited from each parent.
3
Explain why individuals of the same species show differences in their inherited characteristics.
Model answer
They inherit different combinations of alleles, and different alleles produce different versions of a characteristic.
4
What happens to the characteristic when an individual inherits two different alleles of a gene?
Model answer
If one allele is dominant and the other recessive, only the dominant allele is expressed in the characteristic.
5
Explain how a person can carry an allele that does not show in their appearance.
Model answer
A recessive allele is masked whenever a dominant allele of the same gene is also present.
6
Two pea plants both have round seeds but only one of them can produce wrinkled-seeded offspring. Explain this.
Model answer
That plant carries one round allele and one wrinkled allele, so it can pass the wrinkled allele on.

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Key Concepts in Biology

Cells and Control

Genetics

Natural Selection and Genetic Modification

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ANitrates cause an algal bloom that blocks the light.

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