Inheritance, Variation and Evolution

Question 1

What is the structure of a DNA molecule?

Answer 1

Double helix structure (A double-stranded spiral)

Question 2

Each gene codes for…

Answer 2

… a particular sequence of amino acids which are put together to make a specific protein.

Question 3

What is a genome?

Answer 3

The entire set of genetic material in an organism.

Question 4

What can understanding the human genome do for science and medicine?

Answer 4

It can help to identify which genes are linked to inherited diseases and how to develop effective treatment. Scientists can look at genomes to trace the migration of certain populations.

Question 5

What is contained in each nucleotide (repeating unit of DNA)?

Answer 5

One sugar molecule, one phosphate molecule (‘backbones’ of DNA strands) and one ‘base’.

Question 6

What are the four bases that join to each sugar in DNA strands?

Answer 6

A and T, C and G

Question 7

Its the order of bases in a gene…

Answer 7

… that decides the order of amino acids in a protein.

Question 8

What is mRNA and its function?

Answer 8

mRNA acts as a messenger between the DNA and the ribosome - it carries the copied code between the two as DNA is too big to leave the nucleus. The correct amino acids are brought to the ribosomes in the correct order by carrier molecules.

Question 9

What is a mutation?

Answer 9

A random change in an organism’s DNA. They can sometimes be inherited.

Question 10

What is an insertion (mutation)?

Answer 10

Where a new base is inserted into the DNA base sequence where it shouldn’t be.

Question 11

What is a deletion (mutation)?

Answer 11

When a random base us deleted from the DNA base sequence.

Question 12

What is a substitution (mutation)?

Answer 12

When a random base in the DNA base sequence is changed to a different base.

Question 13

How are gametes produced?

Answer 13

By meiosis.

Question 14

Describe the stages of meiosis.

Answer 14

1) The cell duplicates us genetic information, forming two armed chromosomes. After replication, the chromosomes arrange in pairs.
2) In the first division in meiosis the chromosome pairs line up in the centre of the cell.
3) The pairs are then pulled apart so each new cell only has one copy of each chromosome. Someo f the father’s chromosomes and some of the mother’s chromosomes go into each new cell.
4) In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
5) You get four genetically different gametes, each with only a single set of chromosomes in it.
6) The resulting new cell divides by mitosis to make a copy of itself many times to form an embryo.

Question 15

Sexual vs. asexual reproduction

Answer 15

Sexual
- Genetic variation, increases chance of surviving a change in the environment

Asexual

• Faster
• Requires less energy (organisms don’t need to find a mate)

Question 16

What organisms reproduce by both methods?

Answer 16

Parasites of malaria - sexually in mosquito, asexually in human host.
Fungi - spores can be produced asexually or sexually depending on if the conditions change.
Strawberry plants - produce runners that form a plant at various points along the runner.

Question 17

What are alleles?

Answer 17

Different versions of genes (e.g. B or b).

Question 18

What inherited disorder is caused by a recessive allele?

Answer 18

Cystic Fibrosis

Question 19

What inherited disorder is caused by a dominant allele?

Answer 19

Polydactyly

Question 20

What did Gregor Mendel discover?

Answer 20

Mendel had shown that the height characteristic in pea plants was determined by separately inherited “hereditary units” passed on from each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants, T, was dominant over the unit for dwarf plants, t.

Question 21

What causes genetic variation?

Answer 21

Sexual reproduction (genetic variation), environmental variation and mutations.

Question 22

What causes extinction?

Answer 22

Fast environmental change, new predator or disease, a superior species that consumes most of food or a catastrophic event.

Question 23

What are problems with selective breeding?

Answer 23

Higher chance of inheriting harmful genetic defects, less genetic variation to defend from disease.

Question 24

How is a gene usually inserted into another organism?

Answer 24

A useful gene is isolated (cut) from one organism’s genome using enzymes and is inserted into a vector (a virus or bacterial plasmid). When the vector is introduced to the target organism, the useful gene is inserted into its cell(s).

Question 25

How are fossil formed?

Answer 25

• From gradual replacement by minerals
• From casts and impressions
• From preservation in places where no decay happens (e.g. glaciers, peat bogs)

Question 26

Describe the stages of speciation.

Answer 26

Two populations of the same species are separated by physical barriers. Populations adapt to new environments. Development of new species due to natural selection operating differently on the populations and populations changing so much that they can not breed to produce fertile offspring.