Inheritance

Question 1

What is a nucleus?

Answer 1

Contains all of the body’s genetic information in the form of 46 chromosomes

Question 2

What is a chromosome?

Answer 2

Long lengths of DNA coiled up

Humans have 46 chromosomes or 23 pairs

Question 3

What is a gene?

Answer 3

A short section of DNA.

It is a chemical instruction that codes for a particular protein

Question 4

What is DNA?

Deoxyribo-Nucleic Acid

Answer 4

A long list of instructions on how to put an organism together and make it work

Question 5

Describe the structure of a DNA molecule.

Answer 5

1. Two strands coil together in a double helical shape
2. Strands are held together by bases (special chemicals)
3. The bases are paired and they will always pair up in the same way: A-T and C-G (complementary base pairing)

Question 6

What are the four bases in a DNA molecule and which pair with which?

Answer 6

Adenosine
Thymine
Guanine
Cytosine

Adenosine + Thymine
Cytosine + Guanine

Question 7

What is DNA’s role in a cell?

Answer 7

Controls the production of proteins (protein synthesis)

Question 8

How does a gene decide which protein is made?

Answer 8

The order of the bases in a gene decides the order of the amino acids

Question 9

What is a codon?

Answer 9

A sequence of three bases in a gene. Codes for one amino acid

Question 10

How many amino acid combinations are possible from one gene?

Answer 10

64

4 x 4 x 4

Question 11

How many amino acids can be made?

Answer 11

20

Therefore some codons form the same amino acid

Question 12

How many amino acids can be made?

Answer 12

20

Therefore some codons form the same amino acid

Question 13

What are the two stages of protein synthesis?

Answer 13

Transcription
Translation

Question 14

Where does protein synthesis occur?

Answer 14

In the nucleus (transcription) and in ribosomes (translation)

Question 15

What is mRNA and why is it needed?

Answer 15

Messenger RNA

DNA can’t leave the nucleus because it’s too big, so mRNA transfers the gene data

Question 16

What are the four bases in mRNA and which pair with which?

Answer 16

Adenosine
Uracil
Guanine
Cytosine

Adenosine - Uracil
Guanine - Cytosine

Thymine is replaced with Uracil

Question 17

What is RNA-polymerase?

Answer 17

The enzyme that joins together the base sequences to form mRNA

Question 18

How does transcription work?

Answer 18

1. RNA-polymerase binds to a region of non-coding DNA
2. The two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA
3. It uses the coding DNA in the gene as a template to make the mRNA
4. Once made, the mRNA moves out of the nucleus and joins with a ribosome in the cytoplasm

Question 19

How does translation work?

Answer 19

1. Amino acids are brought to the ribosome by tRNA (t = transfer)
2. The order which the amino acids are brought to the ribosome matches the order of the codons in the mRNA
3. The anti-codon on the tRNA is complementary to the codon on the amino acid.
4. The pairing between codon and anti-codon makes sure that the amino acids are in the right order
5. The amino acids are joined together by the ribosome, making a protein

Question 20

What is the definition of asexual reproduction?

Answer 20

Reproduction involving one parent. The offspring have identical genes to the parent so there’s no variation between parent and offspring

Question 21

What is mitosis?

Answer 21

When a cell reproduces by splitting itself in half to form two cells with identical sets of chromosomes

Question 22

What are the steps of mitsosis?

Answer 22

1. Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome)
2. Chromosomes line up at centre of cell and cell fibres pull them apart
3. Membranes form around each of the new set of chromosomes (become nuclei) and cytoplasm divides
4. Two genetically identical daughter cells are made

Question 23

What is the definition of sexual reproduction?

Answer 23

The fusion of male and female gametes (haploid cells). Because there are two parents, the offspring contain a mixture of their parents’ genes

Question 24

What is meiosis?

Answer 24

Produces four haploid cells whose chromosomes are not identical.

Two divisions occur. The first is like mitosis, the second is different

Question 25

What are the steps of meiosis?

Answer 25

1. Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome) 2. The chromosomes line up in pairs in the centre of the cell. Each pair will have a chromosome each from the mother and father 3. The pairs are pulled apart so each cell will have both the father's and mother's chromosomes in each cell. This creates genetic variation 4. In the second division, the chromosomes line up in the centre of the cell and the arms are pulled apart 5. Four haploid gametes that are all genetically different. Each gamete only have a single set of chromosomes

Question 26

What are alleles?

Answer 26

Different variations of the same gene

Question 27

What is your genotype?

Answer 27

The alleles that you have

Question 28

What is your phenotype?

Answer 28

The physical characteristics the alleles produce

Question 29

What alleles can you have if you're homozygous?

Answer 29

Two alleles of the same type for that gene e.g. AA or aa

Question 30

What alleles can you have if you're heterozygous?

Answer 30

Two different alleles for that gene e.g. Aa

Question 31

What is a codominant allele?

Answer 31

When neither allele is recessive, so you show characteristics from both alleles. E.g. blood group AB

Question 32

What is a mutation?

Answer 32

A rare, random change in an organism's DNA that can be inherited

Question 33

What can increase the chance of a mutation?

Answer 33

Ionising radiation e.g. X-rays, gamma rays, UV rays Chemicals called mutagens (e.g. tobacco smoke)

Question 34

How can bacteria evolve to become antibiotic resistant?

Answer 34

1. Bacteria develop random mutations in their DNA which mean they're less affected by that antibiotic 2. This newly-resistant bacteria lives for longer and reproduces many times 3. This leads to the allele for resistance being passed on to most of its offspring