science test

What are the four bases in DNA?

Adenine (A), thymine (T), cytosine (C) and guanine (G).

What is complementary base pairing?

Adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

What is the structure of DNA?

DNA consists of two strands twisted into a double helix. Each strand has a strong sugar-phosphate backbone, with complementary nitrogen bases joined by weak hydrogen bonds.

How does DNA store genetic information?

Genetic information is stored in the sequence or order of bases along the DNA molecule.

Why is the sugar-phosphate backbone important?

It is held together by strong covalent bonds, making DNA stable and protecting the genetic information stored in the base sequence.

Why are weak hydrogen bonds important in DNA?

They hold the two DNA strands together but are weak enough to break so the strands can separate during DNA replication.

How does complementary base pairing allow DNA to be copied accurately?

Each original strand acts as a template. A pairs with T and C pairs with G, allowing the correct complementary strand to be produced.

How does DNA code for proteins?

The sequence of bases in DNA provides instructions for the order of amino acids used to make a protein.

What did Rosalind Franklin contribute to the discovery of DNA?

She used X-ray diffraction to produce images of DNA, including Photo 51, which provided important evidence that DNA had a helical structure.

What did Maurice Wilkins contribute to the discovery of DNA?

He also studied DNA using X-ray diffraction and worked in the same laboratory as Franklin. His work contributed evidence about DNA's structure.

What did Erwin Chargaff discover?

Chargaff found that DNA contains approximately equal amounts of adenine and thymine and equal amounts of cytosine and guanine. This helped establish complementary base pairing.

What did James Watson and Francis Crick contribute?

They used evidence from Franklin, Wilkins, Chargaff and others to construct the double-helix model of DNA in 1953.

Who is generally credited with discovering the structure of DNA?

James Watson and Francis Crick are generally credited with developing the double-helix model, although Rosalind Franklin, Maurice Wilkins and Erwin Chargaff provided crucial evidence.

What is a codon?

A sequence of three bases that codes for a particular amino acid or a start/stop signal during protein production.

What is a protein?

A large biological molecule made from a chain of amino acids folded into a specific shape.

Why is the order of amino acids in a protein important?

The amino acid sequence determines how the protein folds, and its shape determines its function.

What can happen if the amino acid sequence of a protein changes?

The protein may fold differently and its function may change or be lost, although some changes have little or no effect.

What is mitosis?

Cell division that produces two genetically identical diploid daughter cells. It is used for growth, repair and replacement.

What is meiosis?

Cell division that produces four genetically different haploid sex cells, or gametes, with half the normal chromosome number.

How many cells are produced by mitosis?

Two genetically identical daughter cells.

How many cells are produced by meiosis?

Four genetically different haploid cells.

What happens to chromosome number in mitosis?

It stays the same as the parent cell.

What happens to chromosome number in meiosis?

It is halved.

Why is meiosis important?

It produces gametes for sexual reproduction and creates genetic variation.

What is a mutation?

A change in the DNA base sequence.

What is a substitution mutation?

A mutation where one DNA base is replaced by another base.

What is an insertion mutation?

A mutation where one or more extra bases are added to the DNA sequence.

What is a deletion mutation?

A mutation where one or more bases are removed from the DNA sequence.

Why can insertions and deletions have large effects?

They can cause a frameshift, changing how bases are grouped into codons and potentially changing many amino acids after the mutation.

Can all mutations be harmful?

No. Mutations can be harmful, beneficial or neutral depending on their effect and the environment.

Give an example of a beneficial mutation.

A mutation that gives bacteria antibiotic resistance can help the bacteria survive when antibiotics are present.

Give an example of a harmful mutation.

A mutation in a gene controlling cell division can contribute to cancer, or inherited mutations can cause genetic disorders such as cystic fibrosis.

What is an allele?

An alternative version of a gene.

What is a genotype?

The combination of alleles an organism has for a characteristic, such as BB, Bb or bb.

What is a phenotype?

The observable characteristic produced by the genotype and often influenced by the environment.

What is a dominant allele?

An allele that is expressed in the phenotype when at least one copy is present. It is usually represented with a capital letter, such as B.

What is a recessive allele?

An allele that is only expressed in the phenotype when two recessive copies are present. It is usually represented with a lowercase letter, such as b.

What does homozygous mean?

Having two identical alleles for a gene, such as BB or bb.

What does heterozygous mean?

Having two different alleles for a gene, such as Bb.

What is the relationship between genotype and phenotype?

Genotype is the combination of alleles an organism has, while phenotype is the observable characteristic produced by those genes and environmental influences.

What did Gregor Mendel investigate?

Mendel investigated inheritance by breeding pea plants with different characteristics such as flower colour, seed shape and plant height.

What did Mendel conclude?

Characteristics are passed from parents to offspring through inherited factors, now called genes, and some alleles can be dominant while others are recessive.

Why are identical twins useful for studying genes and environment?

Identical twins have almost identical DNA. Comparing twins raised in different environments helps scientists investigate which characteristics are strongly influenced by genes and which are influenced by the environment.

What does a square represent on a pedigree?

A male.

What does a circle represent on a pedigree?

A female.

What does a shaded symbol represent on a pedigree?

An individual who has the characteristic being studied.

What does a horizontal line between two people on a pedigree represent?

A reproductive partnership or parents.

What does a vertical line on a pedigree represent?

A line of descent to offspring.

How are generations labelled on a pedigree?

Generations are usually labelled with Roman numerals such as I, II and III, while individuals are numbered from left to right.

What particles are involved in chemical reactions?

Electrons, particularly the outer or valence electrons.