GCSE Biology - Variation and Selection

Define natural selection.

The different survival and reproduction of individuals in a species due to differences in their phenotype.

Describe the advantages of producing plants by micropropagation.

Many plants produced.

Quicker than sexual reproduction.

Genetically identical/ clones produced.

With the desired characteristics.

Plants from endangered/rare plants.

Explain how a giraffe may have evolved a long neck.

There is genetic variation caused by random mutations in the genes that control neck length.

Those individuals with a longer neck can reach leaves higher up and obtain more food.

They have a greater chance of surviving and reproducing.

Those with shorter necks are outcompeted.

The alleles for longer necks are passed to the offspring.

Which increase in number.

Those with shorter necks decrease in number.

Explain how bacteria can become resistant to an antibiotic.

People do not finish their course of antibiotic.

Natural selection.

Some bacteria have a mutation that gives them resistance.

Resistant bacteria survive and reproduce.

Pass on allele for resistance to offspring.

The non-resistant bacteria die.

Give two possible uses of transgenic animals.

Pigs given human insulin gene to produce human insulin.

Cows produce milk with proteins to treat cystic fibrosis.

Host animal e.g. pig grows human organs for transplantation.

How does artificial selection differ from natural selection?

Carried out by humans.

Shorter time span.

Characters selected that are useful to humans.

How does genetic variation originate?

By random mutations.

What is meant by the term transgenic / genetically modified organism?

An organism that contains DNA from a different species.

What is the name of a part of a plant that is removed and used for cloning?

Explant.

What is the term for the condition in the environment which alters the survival of an individual in natural selection?

Selection pressure.

Why are the plants produced by micropropagation called clones?

They are genetically identical.

Compare the structure of DNA and RNA.

DNA is double-stranded, RNA is single-stranded.

DNA contains deoxyribose sugar, RNA contains ribose.

DNA contains thymine, RNA contains uracil.

Distinguish between transcription and translation.

Transcription occurs in the nucleus and forms a mRNA copy of a gene.

Translation occurs on a ribosome in the cytoplasm and forms a protein.

How many bases does it take to code for one amino acid?

Three.

How many chromosomes are there in a human ovum?

23

How many different amino acids are there?

20.

How many sets of chromosomes are there in a human ovum?

One.

How might a mutation affect the protein that the gene codes for?

Mutation results in a different base in the gene sequence.

This may code for a different amino acid.

The sequence of amino acids in the protein may therefore change.

The protein may not function because it has a different shape.

OR: the gene may code for the same amino acids, so the protein is unaffected.

Name the molecule that genetic material is made from.

DNA.

Name the process that occurs at ribosomes.

Protein synthesis / translation.

State the main stages of protein synthesis in a cell.

Transcription of a gene in the nucleus produces a molecule of messenger RNA.

mRNA leaves the nucleus and binds to a ribosome.

tRNA is attached to a specific amino acid.

Correct tRNA binds to mRNA at the ribosome.

Codon on mRNA binds to anticodon on tRNA.

Amino acids joined together to form polypeptide.

What does a gene code for?

The sequence of amino acids in a protein.

What is a chromosome?

A single molecule of DNA.

Packaged around histone proteins.

What is a codon?

A sequence of 3 bases on mRNA.

That codes for one amino acid.

What is a mutation?

A change in the DNA (sequence of bases) in a cell.

What is an allele?

An alternative form of a gene.

What is an anticodon?

A sequence of 3 bases on tRNA.

That will bind to a codon on mRNA.

What is DNA made up of?

Nucleotides: a sugar molecule, a base and a phosphate group.

When do mutations occur?

When DNA is replicating - the wrong base may be inserted by mistake.

Where are ribosomes found?

In the cytoplasm.

Where does transcription take place?

In the nucleus.

Which base will form a base pair with adenine?

Thymine.

Which base will form a base pair with cytosine?

Guanine.

Which bases are complementary to each other?

A is complementary to T.

C is complementary to G.

Which part of a cell contains genetic material?

Nucleus.

A fertilised egg divides many times. Name this type of cell division.

Mitosis.

Define clone.

A genetically identical individual.

Define diploid.

Having two sets of chromosomes.

Define haploid.

Having one set of chromosomes.

How many ova were fertilised when one pair of identical twins were conceived?

One.

What are the features of asexual reproduction?

Offspring are genetically identical.

Only one parent is required (no gametes involved).

What are the features of sexual reproduction?

Offspring are genetically different (variation).

Two gametes are required.

What happens before both mitosis and meiosis begin?

The chromosomes replicate.

What is the difference between binary fission and mitosis?

Mitosis occurs in Eukaryotic cells.

Binary fission occurs in bacterial (Prokaryotic) cells.

What is the function of mitosis?

To replace cells in tissue.

For growth of tissue.

In asexual reproduction.

Where in a plant would meiosis take place?

In anthers / stamens.

In ovary / ovules.

Define genotype.

The alleles a cell has for a particular trait (character).

Define phenotype.

The observable features for a particular genotype.

What does the term polygenic mean?

Many genes are involved in determining a trait (character).

What is meant by the term dominant allele?

Only one copy of the allele is needed to show the trait (character).

What is meant by the term homozygous recessive.

Both alleles are the same, and two are needed to show the trait (character) in an individual.

What is meant by the term recessive allele?

Two copies of the allele are needed to show the trait (character).

What would be the genotype of the offspring from crossing a plant with genotype AA with another plant with genotype aa?

Aa

What would be the genotype of the offspring from crossing a plant with genotype Aa with another plant with genotype aa?

50% would be Aa, 50% would be aa.

Which sex chromosomes do males have in humans?

XY