Chapter 14 - Evolutionary Mechanisms

Question 1

What is random assortment?

Answer 1

The random separation of maternal and paternal chromosomes during the first division of meiosis.

Question 2

What is crossing over?

Answer 2

Crossing over of chromatids during meiosis may result in in pieces of chromatid being broken off and attaching to a different chromatid. This results in a changed sequence, or recombination, of alleles along the resulting chromosome.

Question 3

What is Non-disjunction?

Answer 3

Non- disjunction is where one or more members of a chromosome pair fail during meiosis. This results in gametes that have more or less than the correct number of chromosomes.

Question 4

What is random fertilisation?

Answer 4

The ability of any one sperm being able to fertilise any available egg, ultimately meaning there is an infinite number of possible combinations of alleles in offespring.

Question 5

What is natural selection?

Answer 5

The selection of favourable alleles (characteristics) that are passed on to future generations.

Question 6

What is random genetic drift?

Answer 6

Variation in allele frequencies (no obvious reason for it) in a population as a result of chance rather than natural selection.

Also known as the Sewall Wright Effect.

Question 7

Describe what the Founder effect is.

Answer 7

Similar to random genetic drift, the founder effect occurs when a small group moves away from it’s homeland to a totally new area and establishes their own population. After time, this new community will generally show features that are not genetically representative of the home land.

Question 8

What are geographical barriers to gene flow and what are some examples?

Answer 8

Geographical barriers are environmental barriers to gene flow between populations. Examples of these are oceans, mountain ranges and deserts.

Question 9

What are sociocultural barriers to gene flow and what are some examples?

Answer 9

Barriers that prevent people of different traits or characteristics from voluntarily interbreeding with one another. Examples may be, language barriers, economic status and religious groups.

Question 10

What are some examples of genetic diseases? (Hint 2)

Answer 10

• Thalassamia : a recessive Disease in which anaemia results from defects in the formation of haemoglobin. Leads to excess iron that tends to build up in the body.
• Sickle-cell anaemia : occurs mostly in people of black African ancestry. It results in the red blood cells being crescent in shape. Provides some immunity against malaria.

Question 11

What is special creation?

Answer 11

The belief that god had individually created each species.

Question 12

Who is Charles Darwin?

Answer 12

The theory of evolution through natural selection was put forward by Charles Darwin

Question 13

Define evolution.

Answer 13

Evolution is a gradual change in the characteristics of a species over time.

Question 14

What are Darwin’s 3 main observations about the theory of natural selection?

Answer 14

1. Variation - all members of a species vary.
2. Birth rate - living organising reproduce at a faster rate than at which their food supply increase.
3. Nature’s balance - each species numbers tended to remain at a relatively constant level.

Question 15

What are the 6 principles of evolution through natural selection?

Answer 15

1. There is a variation of characteristics within a species.
2. More offspring of a species are produced than can possibly survive to maturity.
3. Competition for survival.
4. Survival of the fittest.
5. Favourable characteristics are passed on to the next generations.
6. The proportion of alleles that produce favourable characteristics gradually increases.

Question 16

How does body stature correlate with the environments in which they occur?

Answer 16

Long bodies and short limbs = smaller surface area = colder environments

Short bodies and long limbs = larger surface area = warmer environments

Question 17

What is the name of the parasite that carries malaria?

Answer 17

The anopheles mosquito

Question 18

What is sickle cell anemia?

Answer 18

Sickle cell anaemia forms because of a mutation of the gene responsible for the production of normal haemoglobin. The mutant allele responsible for the sickle shape of the affected red blood cells caused the substitution of one amino acid (valine) for another (glutamic acid) during the formation of the haemoglobin protein

Question 19

What is a selective agent?

Answer 19

A selective agent is any factor that causes the death of organisms with certain characteristics but which has no effect on individuals without those characteristics.

Question 20

What is speciation?

Answer 20

Speciation is the process of a new species developing. If two populations are isolated for a very long time with different environmental demands, and interbreeding would no longer be possible the two populations would be regarded as a seperate species.

Question 21

What are the four stages of speciation?

Answer 21

Variation, isolation, selection and speciation.