Unit 1 KA5-6

Question 1

Genome

Answer 1

All the hereditary information of an organism, encoded in its DNA (in a complete set of its chromosomes).

Made of genes and non-coding sequences.

Question 2

Homologous chromosomes

Answer 2

A matching pair of chromosomes, carrying the same genes (but the alleles could be different).

One chromosome from each pair came from each parent.

Humans have 46 chromosomes - 23 homologous pairs.

Question 3

Regulation of transcription

Answer 3

Transcription is controlled by activators which are bound to regulator DNA sequences.

These fold over and combine with transcription factors and RNA polymerase at the promoter site next to a gene, to initiate transcription.

Question 4

Telomeres

Answer 4

Repetitive sequences at the ends of chromosomes, which prevent them from fraying.

They are protective structures.

Question 5

Non-translated RNA

Answer 5

tRNA and rRNA are transcribed (made by copying sections of DNA) but are never translated.

They remain as RNA and are used to assist translation (by moving amino acids into position and by forming the structure of ribosomes).

Question 6

Mutation

Answer 6

A change in the genetic material of an organism.

They are usually random, spontaneous and rare, and can affect the base sequence of a gene, or the structure of whole chromosomes.

Question 7

Mutant

Answer 7

An organism with an altered phenotype as a result of mutation.

Question 8

Mutagenic agents

Answer 8

Increase the rate of mutation. eg. radiation (UV, X-rays) or chemicals (nerve gas, Agent Orange).

Question 9

Single gene (point) mutations

Answer 9

Alter the nucleotide sequence in a gene.

There are 3 types - substitution, deletion and insertion.

Question 10

Substitution

Answer 10

One nucleotide in a gene is swapped for a different one, which affects one codon.

There are 2 types : missense and nonsense.

Question 11

Missense substitution

Answer 11

One amino acid is swapped for a different one. This produces an altered protein which may be abnormal and non-functioning.

Question 12

Nonsense substitution

Answer 12

An amino acid is replaced with a STOP codon which results in a shortened polypeptide chain which doesn’t fold properly.

Question 13

Insertion

Answer 13

An extra nucleotide is inserted into a gene.

This is a frameshift mutation - all subsequent codons are altered which has a major impact on the structure of the protein produced.

Question 14

Deletion

Answer 14

A nucleotide is removed from the gene.

This is a frameshift mutation - all codons after the mutation are altered, which has a major impact on the protein molecule produced.

Question 15

Splice site mutation

Answer 15

Occurs where introns meet exons at splice sites on a primary mRNA transcript.

It may result in an intron being retained in error, which has a major impact on the structure of the protein produced.

Question 16

Chromosome structure mutations

Answer 16

A whole section of chromosome, carrying many genes, breaks off and re-joins onto another chromosome or in a different position.

This alters the number and sequence of genes.

Question 17

Chromosome deletion

Answer 17

A chromosome breaks in 2 places, which results in a section of chromosome, containing many genes, being lost.

Question 18

Translocation

Answer 18

A section of one chromosome breaks off and re-joins onto another non-homologous chromosome.

Question 19

Duplication

Answer 19

An extra section is added to a chromosome from its homologous partner, resulting in multiple copies of genes.

Question 20

Evolutionary importance of duplications.

Answer 20

Mutations can occur in the ‘extra genes’ without affecting the functioning of the original ones. These mutations may prove to be advantageous (eg. anti-freeze protein in ice fish).

Question 21

Inversion

Answer 21

A section of chromosome containing many genes, is turned upside down.

Question 22

Genetic conditions caused by chromosome mutations.

Answer 22

Many chromosome mutations are lethal, but some are survivable and result in genetic conditions characterised by an altered phenotype. eg. Cri-du-chat, haemophilia.

Question 23

Evolutionary importance of gene mutations.

Answer 23

Mutation is the only source of new alleles, and is therefore responsible for variation.

New alleles code for new proteins, which may result in the organisms carrying them having a survival advantage.

Natural selection allows these advantageous alleles to be passed on to the next generation.