Mutations & Gene Pools

Question 1

What does variation refer to?

Answer 1

The differences between members of a species

Question 2

List the sources of Variations

Answer 2

1. Random Fertilisation (sexual reproduction)
2. Random Assortment
3. Crossing over
4. Non disjunction
5. Mutations

Question 3

What does Random Fertilisation refer to?

Answer 3

Means that each person will produce a huge number of different sperm or eggs, there is an infinite number of possible combinations of alleles in the offspring

Question 4

What does Random Assortment refer to?

Answer 4

During anaphase 1 each pair of chromosomes segregates (goes either north or south of equator) independently of every other pair in a random process

Question 5

What is crossing over?

Answer 5

• Occurs during prophase 1
• Crossing over occurs when matching regions on a homologous chromosomes break then reconnect to the other chromosome, result is called genetic recombination

Question 6

What does Non Disjunction refer to?

Answer 6

-The failure of chromosomes to seperate during meiosis, this causes a gamete to have too many or too few chromosomes
Conditions of fault;
-Trisomy and Monosomy
-In monosomy daughter cells have one chromosome missing from one of its pairs
-Trisomy has one extra chromosome on a pair

Question 7

What is a gene pool?

Answer 7

A population is a group of organisms of the same species living together I’m a particular place at a particular time. A gene pool is a sum of all the alleles in a given population

Question 8

What is a Mutation?

Answer 8

When a change in a gene or chromosome takes place leading to new characteristics in an organism, which can beneficial or harmful. A mutant is something affected by a mutation

Question 9

What are the two types of mutations?

Answer 9

1. Somatic Mutations

2. Germline Mutations

Question 10

What are somatic mutations?

Answer 10

• DNA changes that occur within body cells
• Cannot be passed onto the offspring
• Only the individual with the somatic mutation is affected -Reproductive cells are not affected and once a person dies the mutation dies with them

Question 11

What are germline mutations?

Answer 11

• DNA changes that occur in the sperm or ova
• If the reproductive organs are affected the mutation can be passed to offspring
• The individual in whom the mutation occurs is not usually affected however the individual could produce gametes with changed DNA, usually aborted early

Question 12

What are gene mutations?

Answer 12

• Occurs during DNA replication before cell division
• Mutation is copied each time and therefore passed on to next generation
• A change in a base (nucleotide) which is code for an amino acid to build a protein, a change in just one base (point mutation) ) could alter a protein, have no effect at all, or prevent the protein from being produced could cause major to minor abnormalities
  e. g. Albinism, Duchenne form of muscular dystrophy, cystic fibrous, sickle cell anemia

Question 13

What is albinism in the form of a gene mutation?

Answer 13

The result of one missing protein, albinism is marked by an absence of pigment from the hair, skin and eyes. The hair of a person with albinism tends to be whitish blonde, and the skin tends to be extremely pale and the eyes pinkish.

Question 14

What is Duchenne form of muscular dystrophy in a gene mutation?

Answer 14

The disease is the wasting of leg muscles and later the arms, shoulders and chest. It usually becomes apparent around the age of 3-5 yeas old when muscle weakness becomes evident, eventually death occurs due to failure of the respirator muscles. Boys that suffer from the disease will usually wouldn’t live more than 20-25 years.

Question 15

What are lethal recessive gene mutations?

Answer 15

• Most gene mutations have a recessive allele
• If a person reproduced with a partner who had the same recessive mutation the recessive condition could appear in their offspring
• Some recessive mutations are lethal if they are not masked by a dominant normal allele. These lethal recessives cause the death of the embryo or foetus (a miscarriage or spontaneous abortion) or the early death of the child
  e. g. Tay Sachs Disease (TSD)

Question 16

What are chromosomal mutations?

Answer 16

Occurs in part of a chromosome or all of a chromosome and therefore affect not just one but a number of genes. Often so cause severe abnormalities that miscarriage often occurs in early pregnancy. Can occur due to deletion duplication, inversion, Translocation and non disjunction e.g. Trisomy and Monosomy

Question 17

What is Trisomy?

Answer 17

-One extra chromosome, these abnormalities can be detected before birth
-Partial Trisomy
-Trisomy X e.g
>Klinefelter syndrome (XXY) - a person is more feminine, a male have small tests and do not produce sperm, breasts are enlarged and body hair is sparse and oqccaiosnally mental retarded
>Jacobs syndrome (XYY) - a person is super male

Question 18

What is Monosomy?

Answer 18

• One less chromosome, these abnormalities can be detected before birth
• Partial Monosomy e.g. Cri-du-chat syndrome, a rare genetic disorder due to missing proportion of chrome 5. Infants cry and sound just like a meowing kitten due to problems with the larynx and nervous system
• Monosomy X e.g. Turners syndrome - females are short, infertile and lack secondary sex characteristics

Question 19

What causes changes in gene pools?

Answer 19

1. Random Genetic Drift
2. Founder effect
3. Genetic diseases
4. Migration
5. Barriers to gene flow
6. Mutations
7. Natural selection

Question 20

What is Random Genetic Drift? and give an example

Answer 20

• Can change frequencies of alleles in gene pools
• Totally random
• Non directional
• Purely chance
• An allele that is rare in a large population may by chance become frequent in a small population e.g Dunkers, Bentick Island

Question 21

Explain Dunkers with reference to random genetic drift

Answer 21

Dunkers lived in Pennsylvania, came from the Hesse community in Germany in 18th century, there religion does not allow them to marry outside of their group and therefore they became an isolated breeding population within the US. Study’s measuring blood types etc found that Dunkers varied in allele frequency from the present day Hesse and surrounding American population. The size of Dunkers allowed certain alleles to became more common by chance

Question 22

Explain Bentinck Islanders with reference to random genetic drift

Answer 22

Bentinck Island was originally apart of the Mainland Australia however rising sea levels cut them off and became isolated and had no contact with the mainland therefore had limited alleles. Studies show that blood group of people on Bentinck Island fall outside the Aborigines in the rest of Australia. Showed high lB and low IA opposite to mainland. Thus RGD was responsible as the size of Bentinck Island allowed certain alleles to become more common purely by chance

Question 23

What is the founder effect?

Answer 23

• Similar to random genetic drift
• Occurs when a very small group moves away form homeland to a new area and establishes a community which expands and grows
• Small group which is relatively isolated leads to a loss os genetic variation and can lead to an evolution of a new species
  e. g. Pitcairn island, Pingelup, Tristan Da Cuncha, Finland

Question 24

In reference to the founders effect describe the Pingelup situation

Answer 24

• A Typhoon hit the island of Pingelup in Micronesia and killed all but 20 people
• 20 people formed the founding population of current inhabitants
• One person who carried the heterozygous allele for Achromatopsia (total colour blindness) and this allele became more frequent purely by chance
• In Pingelup = 5% of occurrence of Achromatopsia, In world = 0.0033& occurrence, furthermore 30% of Pingelup are carriers thy are not colour blind but they do have the affected allele
• The founder effect was due to a small group relatively isolated with little immigration, gene pool was different to the original population, this founder population is unrepresentative of the original population

Question 25

In reference to the founder effect explain the Finland situation

Answer 25

• About 2000 years ago, a small population settled in South West of Finland
• Population has remained relatively isolated
• Little immigration and migration occurred
• Different gene pool to neighbouring European population
• The founder effect was due to a small group relatively isolated with little immigration, gene pool was different to the original population, this founder population is unrepresentative of the original population

Question 26

In reference to the founder effect explain the Tristan Da Cunha Situation

Answer 26

• Group of islands in South Atlantic Ocean between south Africa and South America
• 7 surnames on the Island which were traced to 15 British Immigrants in 1817
• Few migrations occurred
• 250 inhabitants
• Have a different gene pool to British population today
• The founder effect was due to a small group relatively isolated with little immigration
• The gene pool was different to the original population
• This founder effect is unrepresentative of the original population

Question 27

List some examples of Migration

Answer 27

China: In the east had Rh+ allele. In 16th century, European countries started trading with China, sailors introduced Rh- allele to the Chinese population
-Now China has some Rh- which they didn’t have before due to immigration
Mongols (East Asia): In the past Mongols had a high lB allele than those living to their west in Europe, it is thought that most Western Europeans originally did not have the IB allele
-In the 12th and 13th century, Mongols invaded Western Europe and spread their genes due to migration

Question 28

What are barriers of gene flow?

Answer 28

• Populations are often kept apart by barriers that inhibit the amount of interbreeding between them
• No two environments are the same
• environmental pressures on one side of the population ill be different from the pressure
• Isolation results in different gene pools
• Two examples are geographical and sociocultural

Question 29

What are geographical barriers?

Answer 29

• Oceans, large lakes, mountain rangers, desserts, ice sheets
• E.g. Australians were isolated for many years due to ocean barriers, Bentick islanders were isolated from mainland Australia

Question 30

What are sociocultural barriers?

Answer 30

• Religion, language e.g. Basque people = Pyrenees between France and Spain, developed their own language that was different to French and Spanish
• Even though they had the same religion and occupations as neighbours they isolated themselves in terms of sociocultural barrier
• Resulted in broad foreheads, narrow jaws, distinctive patterns in blood groups e.g. 30% have Rh- compared to 16% Rh-

Question 31

What are genetic diseases?

Answer 31

• Genetic dies seas result in changes to the allele frequencies in a gene pool
• Usually an allele that causes death seem to disappear but some stay i.e. Tay Sachs Disease (TSD) and Sickle Cell Anaemia

Question 32

What is natural selection?

Answer 32

Natural selection is a process where a species become adapted to the environment, certain allies can become preferred and can be a survival advantage

Question 33

What are the 5 principles of Natural Selection?

Answer 33

1. Variation - there is variation within species meaning there are different characteristics within a species
2. Birth Rate - Offsprings reproduce at a rate greater than that at which their food supply and other resources increase, there for creating overcrowding with limited resources
3. Struggle for existence - Individuals with characteristics best suited to their environment have a greater chance of serving and reproducing
4. Favourable characteristics - Are passed onto the next generation
5. Allele Frequencies - The proportion of alleles that produce favourable characteristics increase in the gene pool

Question 34

Give two examples of Natural Selection occurring in humans

Answer 34

Eskimos - Have short lips and long bodies —> low surface area –> less heat loss
Black Africans - Have long limbs and short bodies —> high surface area —> leads to more heat loss and can survive

Question 35

What is speciation?

Answer 35

Over a long period of time the cognates in the gene frequencies may be great enough to prevent the productive of fertile offspring by interbreeding between the two populations from ever occurring again when this happens, two species exist