4B: Diversity and Selection

Question 1

What is a Diploid cell?

Answer 1

a cell that has the normal number of chromosomes for the organism, 2n

Question 2

What is a Haploid Cell?

Answer 2

a cell that has half the normal number of chromosomes for the organism, n

Question 3

What is fertilisation?

Answer 3

when the sperm fuses with the egg

Question 4

Give examples of Haploid cells

Answer 4

Sperm
Egg

Question 5

What processes during meiosis can lead to genetic variation?

Answer 5

• Homologous chromosomes pair up / form bivalents
• This can lead to the formation of a chiasma and crossing over can occur
• (Crossing over) results in a new combination of alleles
• Chromosomes can also align randomly
• This is known as independent segregation/assortment
• Which can produce varying combinations of chromosomes (alleles)

Question 6

Contrast Meiosis and Mitosis

Answer 6

Meiosis:
- produces haploid cells
- cells are genetically different
- produces 4 daughter cells
Mitosis:
- produces diploid cells
- cells are genetically identical
- produces 2 daughter cells

Question 7

Name 2 types of mutation

Answer 7

Substitution
Deletion

Question 8

What is Substitution?

Answer 8

one base is substituted with another

Question 9

What is deletion?

Answer 9

one base is deleted, causing a frame shift

Question 10

Describe the possible effects of a Substitution Mutation

Answer 10

may not always lead to a change in amino acid sequence because genetic code is degenerate
may cause a different amino acid to be coded for or a stop or start codon

Question 11

Describe the possible effects of a Deletion Mutation

Answer 11

will always cause a change is amino acid sequence
causes a frame shift

Question 12

What are Mutagenic Agents?

Answer 12

agents that increase the probability of a mutation occurring

Question 13

What is Chromosome non-disjuction?

Answer 13

a failure of the chromosomes to separate properly

Question 14

What is genetic Diversity?

Answer 14

the number of different alleles of genes in a species or population

Question 15

What is a Genetic Bottleneck?

Answer 15

an event that causes a big reduction in a population

Question 16

Describe the process of Natural Selection

Answer 16

1. Not all individuals are as likely to reproduce as eacother, this is called differential reproductive sucess. Individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes
2. This mens that a greater proportuion of the next generation inherits the beneficial allele
3. Those individuals will then be more likely to survive, reproduce, and pass on their alleles
4. So the frequency of the beneficial allele in the population increases from generation to generation
5. Over generations, this leads to evolution as advantagous alleles become more common in the population

Question 17

What are the 3 types of Adaptation?

Answer 17

Behavioural, Physiological, Anatomical

Question 18

What is a Behavioural Adaptation?

Answer 18

The ways an organism acts to increase its chance of survival

Question 19

What is a Physiological Adaptaion?

Answer 19

Processes inside an organism’s body that increase its chance of survival

Question 20

What are Anatomical Adaptations?

Answer 20

Structural features of an organism’s body that increase its chance of survival

Question 21

What is Directional Selection?

Answer 21

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This could be in response to an environmental change.

Question 22

What is Stabilising Selection?

Answer 22

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. This occurs when the environment isn’t changing, and reduces the range of possible characteristics

Question 23

What is Disruptive Selection?

Answer 23

When both extreme traits are favored in an environment