Natural Selection

Question 1

Observations by Charles Darwin

Answer 1

Variation - all members vary, parent traits passed on.
Birth Rate - reproduce faster than resources etc increase
Natures Balance - population numbers remain fairly constant

Question 2

Survival of the fittest

Answer 2

organisms with favorable characteristics survive but organisms with unfavorable characteristics die before they reproduce.

Question 3

Selective agent

Answer 3

any agent that causes the death of organisms with certain characteristics → no effect on those without.

Question 4

Body stature

Answer 4

Long bodies and short limbs have a smaller SA:V ratio → lose less heat in cold environments → survival advantage. Thus reproduce and pass down favorable alleles. Unfavorable alleles decrease in population.

Question 5

Sickle cell anaemia cause

Answer 5

RBCs are crescent-shaped. SCA occurs when a person is homozygous for a particular recessive allele that occurs due to a point mutation on the DNA sequence of HBB gene. This means the amino acid valine is added instead of glutamic acid in the haemoglobin → alters RBC shape. Sickle-shaped RBCs die early → anaemia, and can get stuck in blood vessels → blockage.

Question 6

Sickle cell anaemia and malaria

Answer 6

Rate of SCA alleles being lost from the population is 100x greater than the average rate for regular mutations. Anthony Allison observed SCA had highest frequencies where malarial parasites are prevalent. Heterozygous individuals are less susceptible to infection from malaria than regular people → survival advantage.

Question 7

Heterozygous advantage

Answer 7

when heterozygous genotype has a higher survival chance than either homozygous genotypes.

Question 8

Steps for speciation

Answer 8

1 - Variation
2 - Isolation
3 - Selection
4 - Speciation

Question 9

speciation variation

Answer 9

1. A population of the same species exists.
2. Range of variations in a population.
3. Share a common gene pool

Question 10

speciation isolation

Answer 10

1. Can occur within parent population or from parent population.
2. Interbreeding (gene flow) between two populations is disrupted = two new gene pools.
3. Due to a barrier forming.

Question 11

speciation selection

Answer 11

1. Sub-populations adapt to new environment.
2. New different selection pressures.
3. If sub-population is small, random genetic drift amplifies gene pool changes.

Question 12

speciation speciation

Answer 12

1. Reproductive isolation occurs when two populations become sufficiently different that they can no longer interbreed or produce fertile offspring.
2. Will be regarded as different species.

Question 13

mutation

Answer 13

A change in a gene or chromosome leading to new characteristics in an organism.

Question 14

Describe two ways in which two different populations could be both missing allele A.

Answer 14

Founder effect / original populations didn’t have the allele and they were reproductively isolated, so allele A was not introduced into the population. A allele was disadvantageous and individuals with the gene did not survive.

Question 15

How a mutation can change the allelic frequencies of a population:

Answer 15

• The mutation occurs in the gametes.
• This mutation may give the organism a survival advantage.
• Due to the survival advantage the organism is more likely to survive.
• This allows the organism’s favourable genes to be passed onto the next generation.
• Over time the mutations frequency in the gene pool will increase as those that possess it will have a higher chance of surviving.

Question 16

Migration example

Answer 16

• China:
  
  • Only RH+ blood type originally.
  • As trade increased, European immigrants and sailors introduced blood type RH- to population via interbreeding.

Question 17

Inbreeding example

Answer 17

The Old Order Amish Community in Pennsylvania USA do not marry outside of their sect, and only share 8 family names. They have an above average incidence of inherited illnesses.

Question 18

Body stature

Answer 18

• Long bodies and short limbs have a smaller SA:V ratio → lose less heat in cold environments → survival advantage.
• Thus reproduce and pass down favorable alleles.
• Unfavorable alleles decrease in population.

Question 19

Founder effect example

Answer 19

• The Dunkers who migrated from Germany to America.
• Interbreeding produced allele frequencies quite different from original population and American population.

Question 20

The majority of the population in the town has brown hair, the original settlers of the town were from Germany, a country which has a higher proportion of blonde hair. Explain what evolutionary mechanism this involves and how it causeda large number of brown hair people.

Answer 20

• The founder effect
• Small sample of original population
• Sample not genetically representative of original population
• With more individuals carrying the gene for brown hair
• Restricted breeding/inbreeding amongst population results in brown hair gene being maintained over time

Question 21

Bottleneck effect example

Answer 21

• Typhoon on Pingelap greatly reduced population size.
• A survivor has achromatopsia (inherited total colour blindness)
• Now 5% of Pingelap population has achromatropsia.

Question 22

mutagenic agents

Answer 22

• Physical agents - heat, radiation.
• Chemical agents - base analogs, intercalating agents
• Biological agents - bacteria, viruses.

Question 23

Missense vs nonsense mutation

Answer 23

• Missense mutation - change in amino acid that causes a change in protein created.
• Nonsense mutation - base sequence gets coded to STOP, so protein produced is too short.

Question 24

Neutral vs silent mutation

Answer 24

• Neutral mutation - Change in amino acid but no effect due to amino acid being of same type, and structure isn’t changed enough to change its function.
• Silent mutation - No change in amino acid and thus protein produced. Due to most amino acids being coded for by more than one base sequence.

Question 25

Ways to detect lethal recessives:

Answer 25

• Genetic counselling.
• Using pedigrees to determine child’s chance of inheriting.
• Can be tested for the gene.

Question 26

Four ways variation can occur independently of environmental factors:

Answer 26

1. Mutations
2. Crossing over
3. Random assortment of chromosomes across equator in metaphase of meiosis
4. Random fertilisation

Question 27

Gene frequency stability

Answer 27

The larger the population, the more stable the gene frequency from one generation to the next. Random loss of alleles are buffered by the large numbers of the population. Smaller population has a greater effect as there is a higher proportion of the alleles.

Question 28

Founding population has:

Answer 28

• Different allele frequency than original population.
• Decreased genetic variation.

Question 29

Explain three factors that could influence different populations having different carrier rates of the t allele.

Answer 29

1: Small population = increased inbreeding rates of those carrying the allele.
2: Population isolation = decreased migration = decreased gene flow.
3: Social/cultural traditions that don’t allow mating outside of the group.

Question 30

Explain how the use of DNA technology could reduce the frequency of Tay-Sachs in the population of Ashkenazy Jews living in Australia today.

Answer 30

Genetic profiling of embryos can identify those carrying the T-S allele. Selection of T-S-free embryos to implant via IVF. Genetic profiling of parents to advise on prohibitions of producing a child with T-S.

Question 31

Gene and chromosomal mutation

Answer 31

A gene mutation involves changes in a single gene so that the traits normally produced by the gene are changed or destroyed.
A chromosomal mutation involves changes in all or part of the chromosome and affect not just one but a number of genes.