A gene mutation is a change in the sequence of bases in a DNA molecule .

What is a substitution mutation ?

A substitution mutation occurs when a base in the DNA sequence is swapped for a different base .

An mutation occurs when a new nucleotide is added into a base sequence.

An insertion mutation occurs when a new nucleotide is added into a base sequence.

True or False? Insertion and deletion mutations both cause frameshift mutations.

True. Both insertion and deletion mutations can cause a frameshift mutation by changing every group of three bases downstream of the mutation.

A silent mutation is a substitution mutation that does not alter the amino acid sequence of the polypeptide due to the degenerate nature of the genetic code .

Why do most mutations not alter the polypeptide or its function?

Most mutations do not alter the polypeptide or its function because the genetic code is degenerate , so a change in the base sequence does not always change the amino acid.

A mutation can lead to a significantly altered , which may change the protein's appearance or function.

A mutation can lead to a significantly altered polypeptide , which may change the protein's appearance or function.

How can mutations drive evolution by natural selection?

Mutations that provide an advantage make individuals more likely to survive and reproduce, leading to the mutation becoming more common through natural selection .

A mutagen is an agent, such as ionising radiation, X-rays, or certain chemicals, that increases the likelihood of a mutation occurring .

In , a single substitution mutation causes haemoglobin proteins to clump together, affecting red blood cell shape.

In sickle-cell disease , a single substitution mutation causes haemoglobin proteins to clump together, affecting red blood cell shape.

How does a mutation in the CFTR gene cause cystic fibrosis?

A mutation in the CFTR gene leads to production of non-functional chloride channels , reducing water movement by osmosis and resulting in thick, sticky mucus.

True or False? Mutations that occur in gametes can be passed on to offspring.

True. Mutations in gametes can be inherited by the next generation, affecting every cell in the offspring.

A mutation occurs when a nucleotide is removed from a base sequence.

A deletion mutation occurs when a nucleotide is removed from a base sequence.

How can a gene mutation lead to cancer ?

A mutation in a gene that controls cell division can cause cells to divide uncontrollably, forming a tumour that may become cancerous.

An allele is a different form of a gene , usually arising by mutation and found at the same locus on homologous chromosomes.

What does homozygous mean?

An individual is homozygous when they have two identical alleles at a locus .

The phenotype is the observable characteristics of an organism, determined by its genotype and environment .

A is a length of DNA that codes for a single polypeptide.

A gene is a length of DNA that codes for a single polypeptide.

If both alleles are expressed in the phenotype at the same time, this is called .

If both alleles are expressed in the phenotype at the same time, this is called codominance .

What is the difference between a dominant and a recessive allele ?

A dominant allele is always expressed in the phenotype, even if only one copy is present, while a recessive allele is only expressed if no dominant allele is present.

What does a family pedigree diagram show?

A family pedigree diagram shows the pattern of inheritance of a specific trait through generations of a family.

True or False? In a pedigree diagram, squares represent males and circles represent females .

True. In pedigree diagrams, males are shown as squares and females as circles .

Which type of allele causes albinism according to pedigree analysis?

Albinism is caused by a recessive allele .

In pedigree diagrams, lines between male and female symbols show that they have produced children.

In pedigree diagrams, horizontal lines between male and female symbols show that they have produced children.

What is sex linkage in genetics?

Sex linkage refers to genes that are located on the sex chromosomes , meaning that inheritance of these genes depends on the sex of the individual.

Males (XY) will only have copy of a gene located on the X chromosome, whereas females (XX) will have two.

Males (XY) will only have one copy of a gene located on the X chromosome, whereas females (XX) will have two.

True or False? Males can be carriers of X-linked traits.

False. Males cannot be carriers of X-linked traits because they only have one X chromosome; if they have the allele, it will be expressed.

Why is red-green colour blindness more common in males than in females?

Red-green colour blindness is caused by an X-linked recessive allele . Males (XY) have only one X chromosome , so a single recessive allele causes the condition, whereas females (XX) would need two copies to be affected.

The phenotype is the observable characteristics or traits of an organism, resulting from the interaction of its genes and the environment.

What does a gene code for?

A gene codes for a single polypeptide , which can affect the phenotype of an organism.

Genetic disorders are often caused by a mutation that produces a or protein, altering the phenotype.

Genetic disorders are often caused by a mutation that produces a differently-functioning or non-functioning protein, altering the phenotype.

Cystic fibrosis is a genetic disorder of cell membranes caused by a recessive allele of the CFTR gene on chromosome 7.

What is the function of the CFTR gene ?

The CFTR gene codes for the production of chloride ion channels needed for secretion of sweat, mucus, and digestive juices.

A mutation in the CFTR gene leads to chloride channels and production of mucus.

A mutation in the CFTR gene leads to non-functional chloride channels and production of thick, sticky mucus.

True or False? A person with only one recessive allele for cystic fibrosis will have the disorder.

False. A heterozygous person is a carrier but does not have cystic fibrosis; two recessive alleles are needed for the disorder.

A carrier is an individual who has one recessive allele for a genetic disorder but does not show symptoms.

If both parents are carriers for cystic fibrosis, the chance of having an affected child is .

If both parents are carriers for cystic fibrosis, the chance of having an affected child is 25% .

How does cystic fibrosis affect the digestive system ?

In cystic fibrosis, thick mucus can block the tube to the pancreas , reduce digestion, and inhibit absorption of nutrients in the intestines.

How does cystic fibrosis affect the gaseous exchange system ?

Thick, sticky mucus builds up in the airways and bronchioles, reducing airflow and the surface area available for gas exchange , and increasing the risk of lung infections.

How does cystic fibrosis affect the reproductive system ?

Thick, sticky mucus can block the sperm ducts in males and thicken cervical mucus in females, both of which reduce fertility.

Genetic screening is the testing of DNA to identify the presence of specific alleles associated with genetic disorders.

What is carrier testing and why is it offered?

Carrier testing is offered to individuals with a family history of genetic disorders , and it determines if someone carries an allele for a particular disorder even if they show no symptoms.

Couples can undergo genetic screening before having children to determine the of their children inheriting a genetic disorder.

Couples can undergo genetic screening before having children to determine the probability of their children inheriting a genetic disorder.

Preimplantation Genetic Diagnosis (PGD)

Preimplantation Genetic Diagnosis (PGD) is the analysis of DNA from embryos produced during IVF to screen for genetic disorders before implantation .

What are two main benefits of Preimplantation Genetic Diagnosis (PGD) ?

PGD reduces the chances of having a baby with a genetic disorder and avoids abortion as it is done before embryo implantation .

True or False? PGD can be ethically controversial because some people view embryos as having human status.

True. Some people believe that embryos are as worthy of human status as a foetus or a baby , so discarding affected embryos after PGD raises ethical issues.

Chorionic villus sampling

Chorionic villus sampling is a prenatal test that removes and analyses cells from the placenta to detect genetic disorders in a foetus .

What is amniocentesis and when is it usually performed?

Amniocentesis is a procedure that removes and tests a small sample of amniotic fluid containing foetal cells from the uterus, usually performed at around 15-20 weeks of pregnancy .

Chorionic villus sampling can be carried out at around weeks of pregnancy and provides results .

Chorionic villus sampling can be carried out at around 11-14 weeks of pregnancy and provides results rapidly .

True or False? Amniocentesis is always performed earlier than chorionic villus sampling.

False. Amniocentesis is usually performed at 15-20 weeks of pregnancy, which is later than chorionic villus sampling (11-14 weeks).

What is one important positive implication of prenatal genetic screening?

Prenatal genetic screening gives parents advance notice of a child with a genetic disorder , allowing them to make informed decisions and prepare for medical treatments.

International A Level (IAL)BiologyEdexcelFlashcards2. Membranes, Proteins, DNA & Gene ExpressionInheritance

Inheritance (Edexcel International A Level (IAL) Biology): Flashcards

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Cards in this collection (60)

Gene mutation
A gene mutation is a change in the sequence of bases in a DNA molecule.
What is a substitution mutation?
A substitution mutation occurs when a base in the DNA sequence is swapped for a different base.
An mutation occurs when a new nucleotide is added into a base sequence.
An insertion mutation occurs when a new nucleotide is added into a base sequence.
True or False?
Insertion and deletion mutations both cause frameshift mutations.
True.
Both insertion and deletion mutations can cause a frameshift mutation by changing every group of three bases downstream of the mutation.
Silent mutation
A silent mutation is a substitution mutation that does not alter the amino acid sequence of the polypeptide due to the degenerate nature of the genetic code.
Why do most mutations not alter the polypeptide or its function?
Most mutations do not alter the polypeptide or its function because the genetic code is degenerate, so a change in the base sequence does not always change the amino acid.
A mutation can lead to a significantly altered , which may change the protein's appearance or function.
A mutation can lead to a significantly altered polypeptide, which may change the protein's appearance or function.
How can mutations drive evolution by natural selection?
Mutations that provide an advantage make individuals more likely to survive and reproduce, leading to the mutation becoming more common through natural selection.
Mutagen
A mutagen is an agent, such as ionising radiation, X-rays, or certain chemicals, that increases the likelihood of a mutation occurring.
In , a single substitution mutation causes haemoglobin proteins to clump together, affecting red blood cell shape.
In sickle-cell disease, a single substitution mutation causes haemoglobin proteins to clump together, affecting red blood cell shape.
How does a mutation in the CFTR gene cause cystic fibrosis?
A mutation in the CFTR gene leads to production of non-functional chloride channels, reducing water movement by osmosis and resulting in thick, sticky mucus.
True or False?
Mutations that occur in gametes can be passed on to offspring.
True.
Mutations in gametes can be inherited by the next generation, affecting every cell in the offspring.
A mutation occurs when a nucleotide is removed from a base sequence.
A deletion mutation occurs when a nucleotide is removed from a base sequence.
How can a gene mutation lead to cancer?
A mutation in a gene that controls cell division can cause cells to divide uncontrollably, forming a tumour that may become cancerous.
Allele
An allele is a different form of a gene, usually arising by mutation and found at the same locus on homologous chromosomes.
What does homozygous mean?
An individual is homozygous when they have two identical alleles at a locus.
Phenotype
The phenotype is the observable characteristics of an organism, determined by its genotype and environment.
A is a length of DNA that codes for a single polypeptide.
A gene is a length of DNA that codes for a single polypeptide.
If both alleles are expressed in the phenotype at the same time, this is called .
If both alleles are expressed in the phenotype at the same time, this is called codominance.
What is the difference between a dominant and a recessive allele?
A dominant allele is always expressed in the phenotype, even if only one copy is present, while a recessive allele is only expressed if no dominant allele is present.
What does a family pedigree diagram show?
A family pedigree diagram shows the pattern of inheritance of a specific trait through generations of a family.
True or False?
In a pedigree diagram, squares represent males and circles represent females.
True.
In pedigree diagrams, males are shown as squares and females as circles.
Which type of allele causes albinism according to pedigree analysis?
Albinism is caused by a recessive allele.
In pedigree diagrams, lines between male and female symbols show that they have produced children.
In pedigree diagrams, horizontal lines between male and female symbols show that they have produced children.
What is sex linkage in genetics?
Sex linkage refers to genes that are located on the sex chromosomes, meaning that inheritance of these genes depends on the sex of the individual.
Males (XY) will only have copy of a gene located on the X chromosome, whereas females (XX) will have two.
Males (XY) will only have one copy of a gene located on the X chromosome, whereas females (XX) will have two.
True or False?
Males can be carriers of X-linked traits.
False.
Males cannot be carriers of X-linked traits because they only have one X chromosome; if they have the allele, it will be expressed.
Why is red-green colour blindness more common in males than in females?
Red-green colour blindness is caused by an X-linked recessive allele. Males (XY) have only one X chromosome, so a single recessive allele causes the condition, whereas females (XX) would need two copies to be affected.
Phenotype
The phenotype is the observable characteristics or traits of an organism, resulting from the interaction of its genes and the environment.
What does a gene code for?
A gene codes for a single polypeptide, which can affect the phenotype of an organism.
Genetic disorders are often caused by a mutation that produces a or protein, altering the phenotype.
Genetic disorders are often caused by a mutation that produces a differently-functioning or non-functioning protein, altering the phenotype.
Cystic fibrosis
Cystic fibrosis is a genetic disorder of cell membranes caused by a recessive allele of the CFTR gene on chromosome 7.
What is the function of the CFTR gene?
The CFTR gene codes for the production of chloride ion channels needed for secretion of sweat, mucus, and digestive juices.
A mutation in the CFTR gene leads to chloride channels and production of mucus.
A mutation in the CFTR gene leads to non-functional chloride channels and production of thick, sticky mucus.
True or False?
A person with only one recessive allele for cystic fibrosis will have the disorder.
False.
A heterozygous person is a carrier but does not have cystic fibrosis; two recessive alleles are needed for the disorder.
Carrier
A carrier is an individual who has one recessive allele for a genetic disorder but does not show symptoms.
If both parents are carriers for cystic fibrosis, the chance of having an affected child is .
If both parents are carriers for cystic fibrosis, the chance of having an affected child is 25%.
How does cystic fibrosis affect the digestive system?
In cystic fibrosis, thick mucus can block the tube to the pancreas, reduce digestion, and inhibit absorption of nutrients in the intestines.
How does cystic fibrosis affect the gaseous exchange system?
Thick, sticky mucus builds up in the airways and bronchioles, reducing airflow and the surface area available for gas exchange, and increasing the risk of lung infections.
How does cystic fibrosis affect the reproductive system?
Thick, sticky mucus can block the sperm ducts in males and thicken cervical mucus in females, both of which reduce fertility.
Genetic screening
Genetic screening is the testing of DNA to identify the presence of specific alleles associated with genetic disorders.
What is carrier testing and why is it offered?
Carrier testing is offered to individuals with a family history of genetic disorders, and it determines if someone carries an allele for a particular disorder even if they show no symptoms.
Couples can undergo genetic screening before having children to determine the of their children inheriting a genetic disorder.
Couples can undergo genetic screening before having children to determine the probability of their children inheriting a genetic disorder.
Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis (PGD) is the analysis of DNA from embryos produced during IVF to screen for genetic disorders before implantation.
What are two main benefits of Preimplantation Genetic Diagnosis (PGD)?
PGD reduces the chances of having a baby with a genetic disorder and avoids abortion as it is done before embryo implantation.
True or False?
PGD can be ethically controversial because some people view embryos as having human status.
True.
Some people believe that embryos are as worthy of human status as a foetus or a baby, so discarding affected embryos after PGD raises ethical issues.
Chorionic villus sampling
Chorionic villus sampling is a prenatal test that removes and analyses cells from the placenta to detect genetic disorders in a foetus.
What is amniocentesis and when is it usually performed?
Amniocentesis is a procedure that removes and tests a small sample of amniotic fluid containing foetal cells from the uterus, usually performed at around 15-20 weeks of pregnancy.
Chorionic villus sampling can be carried out at around weeks of pregnancy and provides results .
Chorionic villus sampling can be carried out at around 11-14 weeks of pregnancy and provides results rapidly.
True or False?
Amniocentesis is always performed earlier than chorionic villus sampling.
False.
Amniocentesis is usually performed at 15-20 weeks of pregnancy, which is later than chorionic villus sampling (11-14 weeks).
What is one important positive implication of prenatal genetic screening?
Prenatal genetic screening gives parents advance notice of a child with a genetic disorder, allowing them to make informed decisions and prepare for medical treatments.
True or False?
Prenatal genetic screening is always 100% accurate.
False.
Prenatal genetic screening is not 100% accurate, and can give false positives or false negatives.
Genetic screening
Genetic screening is a process used to determine whether an individual has a particular allele present in their genome, often to assess risk of genetic disorders.
What is the role of genetic counsellors for couples considering genetic screening?
Genetic counsellors provide information, support, and explain the possible outcomes and implications of genetic screening for couples before and after the screening process.
Genetic counsellors may discuss the of the couple having a child with a genetic disorder, as well as possible and ethical issues.
Genetic counsellors may discuss the probability of the couple having a child with a genetic disorder, as well as possible treatments and ethical issues.
List three possible concerns or issues that genetic counsellors might discuss with parents before or after genetic screening.
Possible concerns include the probability of having a child with a genetic disorder, ethical issues surrounding termination of pregnancy, and the financial implications of raising a child with a disorder.
True or False?
Ethical concerns about genetic screening are identical for everyone, regardless of personal beliefs.
False.
Ethical concerns differ depending on an individual's religious, moral, and social position.
Some believe that embryos are human beings from conception, so discarding embryos or abortion at any stage is considered .
Some believe that embryos are potential human beings from conception, so discarding embryos or abortion at any stage is considered unacceptable.
What is a potential social concern about the use of genetic screening and embryo selection beyond health reasons?
A potential social concern is the possibility of selecting embryos for non-medical traits such as sex or intelligence, raising ethical issues about the future of 'designer babies'.
Designer baby
A designer baby is an embryo that has been selected or genetically altered for specific traits, such as health, sex, or intelligence, raising ethical and social concerns.

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