Inheritance, Variation and Evolution

Question 1

What is DNA and what does it stand for?

Answer 1

It stands for DeoxyriboNucleic Acid which is a chemical a cell’s nuclear genetic material is made from.

[it is also a polymer made up of two strands coiled into a double helix]

Question 2

What are chromosomes?

Answer 2

Long molecules of DNA that normally come in pairs.

Question 3

What are genes?

Answer 3

A small section of DNA found on a chromosome.

Question 4

What are genomes?

Answer 4

An entire set of genetic material of an organism.

Question 5

What is sexual reproduction?

Answer 5

Where two parents go through the process of the cell division, meiosis and mitosis, to produce an offspring containing a mixture of the parents’ genes.

Question 6

What happens during meiosis?

Answer 6

[produces cells with half the normal number of chromosomes]

① the cell duplicates its genetic information.
② the cell divides and each new cell has one copy of each chromosome.
③ both cells divide again to make four gametes. Each gamete only has a single set of chromosomes.

[all the gametes produced are genetically different]

Question 7

What is an allele?

Answer 7

A version of a gene.

Question 8

What is a dominant allele?

Answer 8

An allele that is always expressed.

Question 9

What is the recessive allele?

Answer 9

An allele that is only expressed when two copies are present.

Question 10

What is homozygous?

Answer 10

When an organism has two alleles for a particular gene that are the same.

Question 11

What is heterozygous?

Answer 11

When an organism has two alleles for a particular gene that are different.

Question 12

What is a genotype?

Answer 12

Combination of alleles of an organism.

Question 13

What is a phenotype?

Answer 13

The characteristics an organism has.

Question 14

What are inherited disorders?

Answer 14

Disorders caused by certain alleles that are inherited from the parents.

Question 15

What is polydactyly?

Answer 15

A genetic disorder where a baby’s born with extra fingers or toes and is caused by a dominant allele.

Question 16

What is cystic fibrosis?

Answer 16

A genetic disorder of the cell membranes and is caused by a recessive allele.

Question 17

What are the disadvantages of embryonic screening?

Answer 17

> screening is expensive.
people might want to screen their embryos so they can pick the most ‘desirable’ one.
it implies that people with genetic problems are ‘undesirable’.

Question 18

What are the advantages of embryonic screening?

Answer 18

> it will help to stop people suffering.
testing disorders costs the government a lot of money.
there are laws to stop it going too far.

Question 19

What is meant by the term variation?

Answer 19

The differences in the characteristics of organisms.

Question 20

What do mutations do?

Answer 20

They cause the differences in genes and occur continuously.

Question 21

What is the effect of mutations on phenotype?

Answer 21

MOST MUTATIONS ⟶ none.
SOME MUTATIONS ⟶ slight.
VERY FEW MUTATIONS ⟶ new phenotype.

Question 22

What are fossils?

Answer 22

Remains of organisms from many thousands of years ago.

Question 23

What are the ways that fossils form?

Answer 23

> gradual replacement by minerals.
↳ happens to slow decaying parts.
casts and impressions.
↳ e.g. footprints, burrows and rootlet traces.
preservation.
↳ in places where conditions prevent decay, parts of organisms can be preserved.

Question 24

What is meant by the term extinction?

Answer 24

When no individuals of a species remain.

Question 25

What is Charles Darwin’s theory about evolution?

Answer 25

> he knew that organisms in species show wide variation in their characteristics and that organisms have to compete for limited resources in an ecosystem.
he concluded that the organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive.
↳ this is called ‘survival of the fittest’.
successful organisms that survive are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring.
the organisms that are less well adapted would be less likely to survive and reproduce therefore less likely to pass on their genes to the next generation.
over time, beneficial characteristics become more common in the population and the species changes.
↳ it evolves.

Question 26

What can we learn from fossils?

Answer 26

How much or how little different organisms have changed as life developed on Earth.

Question 27

How many nucleotides does DNA have?

Answer 27

4.

Question 28

What does each nucleotide consist of?

Answer 28

A common sugar and phosphate group with one of four different bases attached to the sugar.

Question 29

What are DNA’s four bases?

Answer 29

A ⇆ T

C ⇆ G