4.6 - Inheritance , variation & evolution

What is asexual reproduction?

Reproduction involving one parent and producing genetically identical offspring.

What is sexual reproduction?

Reproduction involving two parents and producing genetically different offspring.

What is DNA?

Genetic material that carries instructions for making proteins.

Where is DNA found?

Mainly in the nucleus of cells.

What is a chromosome?

A long DNA molecule containing many genes.

What is a gene?

A section of DNA that codes for a particular protein.

What is a genome?

The entire genetic material of an organism.

What is an allele?

A different version of a gene.

What is a dominant allele?

An allele expressed when at least one copy is present.

What is a recessive allele?

An allele only expressed when two copies are present.

What is a homozygous organism?

An organism with two identical alleles for a gene.

What is a heterozygous organism?

An organism with two different alleles for a gene.

What is a genotype?

The alleles an organism has.

What is a phenotype?

The observable characteristics of an organism.

What are gametes?

Sex cells such as sperm and egg cells.

How many chromosomes are in a human body cell?

46.

How many chromosomes are in a human gamete?

23.

Why do gametes have half the number of chromosomes?

So fertilisation restores the normal chromosome number.

What is fertilisation?

The fusion of two gametes.

What is a Punnett square used for?

Predicting possible genetic combinations in offspring.

What does a dominant allele do in a heterozygote?

It determines the phenotype.

When is a recessive characteristic expressed?

When the individual has two recessive alleles.

What is a genetic cross?

A cross between organisms used to predict inheritance.

What is the probability of an outcome?

The likelihood that it will occur.

What determines biological sex in humans?

The sex chromosomes.

What sex chromosomes do females usually have?

XX.

What sex chromosomes do males usually have?

XY.

Which parent determines the sex of the child?

The father, because sperm carry either X or Y.

What happens if an X sperm fertilises the egg?

XX, usually female.

What happens if a Y sperm fertilises the egg?

XY, usually male.

What is the expected probability of a male or female child?

Approximately 50% each.

What is a genetic disorder?

A condition caused by changes in genes or chromosomes.

What causes cystic fibrosis?

A recessive allele.

What does cystic fibrosis affect?

The lungs and digestive system.

Why does cystic fibrosis cause thick mucus?

The faulty gene affects the movement of chloride ions and water.

What causes Huntington's disease?

A dominant allele.

Why can Huntington's disease be inherited from one affected parent?

It is caused by a dominant allele.

What is embryo screening?

Testing embryos for genetic disorders before implantation.

What is a concern about embryo screening?

Ethical concerns about selecting which embryos are implanted.

What is variation?

Differences between individuals of the same species.

What causes genetic variation?

Genetic differences inherited from parents.

What causes environmental variation?

Differences caused by surroundings or lifestyle.

What can cause variation?

A combination of genetic and environmental factors.

Give an example of environmental variation.

A person's diet affecting their mass.

Give an example of genetic variation.

Blood group.

Why are offspring produced by sexual reproduction genetically different?

They inherit different combinations of alleles from two parents.

What is a mutation?

A random change in DNA.

Can mutations be harmful, neutral or beneficial?

Yes.

How can mutations cause variation?

They can create new alleles.

What is evolution?

A change in the inherited characteristics of a population over generations.

What is natural selection?

The process where individuals with advantageous characteristics are more likely to survive and reproduce.

What is an adaptation?

A characteristic that helps an organism survive and reproduce.

Why does variation help natural selection?

Some variations give individuals an advantage in their environment.

What happens to organisms with advantageous characteristics?

They are more likely to survive and reproduce.

What happens to advantageous alleles over generations?

Their frequency can increase in the population.

What happens to disadvantageous characteristics?

They may become less common over generations.

What is selective pressure?

An environmental factor that affects survival and reproduction.

What is an example of selective pressure?

Predators, disease or competition.

Why does natural selection take many generations?

Changes in allele frequency occur gradually as organisms reproduce.

What is extinction?

When no individuals of a species remain alive.

What can cause extinction?

Environmental change, new predators, new diseases, competition or catastrophic events.

How does antibiotic resistance develop?

Random mutations can produce resistant bacteria.

What happens when antibiotics are used?

Susceptible bacteria are killed while resistant bacteria survive.

Why do resistant bacteria reproduce?

They survive the antibiotic and pass on their resistance genes.

Why should antibiotics not be overused?

Overuse increases selection for resistant bacteria.

Why don't antibiotics kill viruses?

Viruses reproduce inside cells and do not have the structures targeted by antibiotics.

How can antibiotic resistance be reduced?

Only use antibiotics when necessary and complete prescribed courses.

What is classification?

Organising organisms into groups based on similarities and differences.

What is a species?

A group of organisms that can reproduce to produce fertile offspring.

What is the binomial system?

Naming organisms using their genus and species.

What is a fossil?

The preserved remains or traces of organisms from the past.

How do fossils provide evidence for evolution?

They show how organisms and their characteristics have changed over time.

Why is the fossil record incomplete?

Fossils form only under certain conditions and many are destroyed.

What is extinction evidence?

Fossils show that some species existed in the past but no longer exist.

What is selective breeding?

Humans choosing organisms with desired characteristics to reproduce.

How is selective breeding carried out?

Select parents with desired characteristics, breed them, then select offspring with the desired characteristics.

Why is selective breeding repeated over generations?

To increase the desired characteristic in the population.

What are disadvantages of selective breeding?

Reduced genetic variation and increased risk of inherited disorders.

Why can selective breeding reduce genetic variation?

Only a small number of individuals with desired characteristics are repeatedly bred.

What is genetic engineering?

Modifying an organism's genome by inserting a gene from another organism.

What is a vector?

A carrier used to transfer a gene into a cell.

What is a common vector used in genetic engineering?

A bacterial plasmid.

What enzyme cuts out a desired gene?

A restriction enzyme.

What enzyme joins DNA fragments together?

DNA ligase.

How can bacteria be genetically modified?

A desired gene can be inserted into a bacterial plasmid.

Why are genetically modified bacteria useful?

They can produce useful substances such as human insulin.

What is a genetically modified organism (GMO)?

An organism whose genetic material has been deliberately altered.

What is a benefit of genetic engineering in crops?

Crops can be given useful characteristics such as pest resistance.

What is a concern about genetic engineering?

There may be unknown long-term environmental effects.

Why does natural selection change allele frequency?

Individuals with advantageous alleles are more likely to reproduce and pass them on.

Why can a mutation become common in a population?

If it provides an advantage, natural selection can increase its frequency.

Why doesn't natural selection give organisms characteristics because they need them?

Mutations occur randomly; selection acts on existing variation.

Why can antibiotic resistance spread rapidly?

Bacteria reproduce quickly and resistant bacteria can pass resistance genes to offspring.

Why is sexual reproduction important for evolution?

It creates genetic variation, providing differences for natural selection to act on.

Why can selective breeding cause health problems?

Repeatedly breeding closely related organisms reduces genetic variation and can increase harmful recessive alleles.

Why can two parents with a recessive genetic disorder allele have an unaffected child?

The child may inherit a dominant normal allele from one or both parents.

Why can two unaffected parents have a child with a recessive disorder?

Both parents may be carriers and pass on the recessive allele.

Why are mutations important for evolution?

They create new alleles, increasing genetic variation.