Why may a substitution mutation have no effect at all on the polypeptide produced?

The genetic code is degenerate, so the altered triplet may still code for the same amino acid, giving a silent mutation.

What is a frameshift mutation, and which kinds of mutation cause one?

A frameshift mutation shifts the reading frame of every triplet after the mutation, and it is caused by an insertion or deletion of a number of bases that is not a multiple of three.

Which gene is faulty in cystic fibrosis, and what does the normal protein do?

The CFTR gene on chromosome 7 is faulty, and the normal CFTR protein acts as a chloride ion channel in the cell surface membrane of epithelial cells.

How does a non-functional CFTR protein produce thick, sticky mucus?

Chloride ions are not secreted onto the epithelial surface, so less water follows by osmosis and the mucus becomes dehydrated, viscous and difficult to move.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

Topic overview The cell cycle and mitosis Apoptosis in growth and repair Stem cells and cell differentiation

The Developing Individual: Meiosis, Growth and Development

Topic overview Meiosis, haploid gametes and genetic variation The stages of meiosis Antenatal care and diet in pregnancy Alcohol, smoking and monitoring fetal growth Prenatal screening and karyotypes

The Development of Species: Evolution and Classification

Topic overview Classification and the species concept Evidence for classification and DNA barcoding Phylogenetic trees, hominids and the evolution of language Human adaptations, natural selection and evolution Plant adaptations and how they are investigated Measuring biodiversity and genetic diversity

Cells and Microscopy

Topic overview Microscopy and the cell theory Blood smears, staining and microscope drawings Blood cells and their structure Magnification and measuring cells Haemocytometer cell counts and dilutions Flow cytometry in blood analysis Ultrastructure of the animal cell Plant and prokaryotic cells Membrane lipids and the fluid mosaic model Movement of molecules across membranes The roles of membranes and the secretion of proteins

Water and Its Importance in Plants and Animals

Topic overview The properties of water Water as a transport medium and the composition of body fluids Detecting and measuring sugars and proteins Monomers, polymers and the carbohydrates Osmosis and water potential

Proteins and Enzymes

Topic overview Amino acids, peptide bonds and chromatography Globular protein structure: enzymes and haemoglobin Enzyme action and the rate of reaction Blood clotting and first aid Enzymes and inhibitors in medicine Blood donation and stored blood products

Nucleic Acids

Topic overview Nucleotides, ADP and ATP The structure of DNA and its extraction DNA replication and the genetic code RNA, transcription and translation

Patterns of Inheritance

Topic overview Monogenic inheritance and genetic terminology Gene mutations and inherited disease Codominance, multiple alleles and linkage Model organisms, dihybrid crosses and the chi-squared test Chromosome mutations and genetic counselling

Population Genetics and Epigenetics

Topic overview Natural selection, sickle cell and malaria The Hardy-Weinberg principle Genetic drift, the founder effect and speciation Epigenetics and gene expression

Gene Technologies

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The Principles and Importance of Homeostasis

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The Hormonal Control of Blood Glucose and the Management of Diabetes

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Kidney Functions and Malfunctions

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The Cellular Basis of Cancer and Treatment

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Respiratory Diseases and Treatment

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Cellular Respiration

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Metabolism and Exercise

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Pathogenic Microorganisms

Topic overview How pathogens cause communicable disease Tuberculosis HIV, AIDS and the structure of the virus Identifying bacteria: Gram staining and culture Epidemiology: incidence, prevalence and mortality Notifiable diseases and the control of HIV and TB

The Immune System

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Controlling Communicable Diseases

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Photosynthesis, Food Production and Management of the Environment

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The Impact of Population Increase

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Planning and Implementing Practical Work

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Analysing and Evaluating Practical Results

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Practical Skills, Apparatus and Techniques

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Fertility and Assisted Reproduction

Topic overview The urinogenital systems and gonad histology Gametogenesis and the structure of the gametes Hormonal control of gametogenesis and the menstrual cycle Fertilisation and pregnancy testing The causes and issues of infertility Assisted reproduction techniques

The Effects of Ageing on the Reproductive System

Topic overview Ageing and the female reproductive system Managing the menopause Ageing and the male urinogenital system

Plant Reproduction

Topic overview The control of flowering Adaptations of flowers for pollination Fertilisation, seed formation and germination Cereals as staple foods

The Nervous System and the Identification and Consequences of Damage

Topic overview Organisation of the nervous system and nervous tissue The structure and function of the human brain The structure of motor, sensory and relay neurones Resting potential and the action potential Synapses and the integration of responses Reflexes, reaction times and their investigation Brain scans and the consequences of nervous system damage Drugs, brain function and dependency

Monitoring Visual Function

Topic overview The structure of the eye The retina and its role as a transducer Assessing visual function by routine eye tests

The Effect of Ageing on the Nervous System

Topic overview Alzheimer's disease: symptoms and causes The effects of ageing on the senses and memory Investigating ageing, reaction times and memory

The Heart and Monitoring Heart Function

Topic overview The need for a mass transport system Structure and dissection of the mammalian heart The cardiac cycle Initiation and coordination of the heartbeat Heart rate, pulse rate and cardiac output Electrocardiograms and emergency cardiac treatment

Transport Systems in Mammals

Topic overview The closed double circulatory system Blood vessels and their microscopic structure Tissue fluid and capillary exchange Measuring and interpreting blood pressure

Gas Exchange in Mammals and Plants

Topic overview Tissues of the mammalian gas exchange system Gas exchange in the alveoli Pulmonary ventilation and lung volumes Expired air resuscitation Gas exchange and stomata in terrestrial plants

Transport Systems in Plants

Topic overview The need for transport systems in plants Vascular tissue in roots, stems and leaves Water uptake and movement through the plant Transpiration and Its Measurement Translocation in the Phloem

Patterns of Inheritance

Gene mutations and inherited disease

3 things to know
Components 01, 02 and 03

Overview

Recall questions on substitution, insertion, deletion and frameshift mutations, cystic fibrosis and the CFTR chloride channel, sickle cell anaemia and the GAG to GTG change, phenylketonuria and phenylalanine hydroxylase, and Huntington's disease and its CAG repeat.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is phenylketonuria described as a genetic disease whose phenotype depends on the environment?

Key term

What is a gene mutation?

Key term

What are the three main types of gene mutation?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a gene mutation?
Model answer
A gene mutation is a change in the base sequence of the DNA of a single gene.
2
What are the three main types of gene mutation?
Model answer
The three main types are substitution, insertion and deletion of one or more bases.
3
Why may a substitution mutation have no effect at all on the polypeptide produced?
Model answer
The genetic code is degenerate, so the altered triplet may still code for the same amino acid, giving a silent mutation.
4
What is a frameshift mutation, and which kinds of mutation cause one?
Model answer
A frameshift mutation shifts the reading frame of every triplet after the mutation, and it is caused by an insertion or deletion of a number of bases that is not a multiple of three.
5
Which gene is faulty in cystic fibrosis, and what does the normal protein do?
Model answer
The CFTR gene on chromosome 7 is faulty, and the normal CFTR protein acts as a chloride ion channel in the cell surface membrane of epithelial cells.
6
How does a non-functional CFTR protein produce thick, sticky mucus?
Model answer
Chloride ions are not secreted onto the epithelial surface, so less water follows by osmosis and the mucus becomes dehydrated, viscous and difficult to move.

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The Developing Cell: Cell Division and Cell Differentiation

The Developing Individual: Meiosis, Growth and Development

The Development of Species: Evolution and Classification

Cells and Microscopy

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