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Human Biology: Unit 4 > Chapter 9.2-9.5 > Flashcards

Chapter 9.2-9.5 Flashcards

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1
Q

What changes the frequencies of the gene pool?

WHAT IS GENE FLOW? HOW?

A

Changes in alleles frequencies in a gene pool can also be due to GENE FLOW BROUGH BY MIGRATION.

GENE FLOW IS THE MOVEMENT OF GENETIC MATERIAL FROM ONE POPULATION TO ANOTHER.

When individuals move between populations, they enable gene flow.

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2
Q

What is Migration?

A

When individuals move between populations - FROM BIRTHPLACE TO ANOTHER REGION

Human migration involves the movement of people from one place to another with intentions of settling, permanently or temporarily, at a new location.

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3
Q

Example of gene flow affected - china

A

In the past, Chinese populations all had Rh-positive blood groups.

The Rh, or rhesus factor, is an antigen found on the surface of RBCs.

When European countries began trading with China in the 16th century, European immigrants and sailors INTRODUCED Rh -negative allele to the Chinese population.

HOWEVER, the FREQUENCY OF THE Rh- allele is very low in China compared to other countries.

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4
Q

AN example of how DISTRIBUTION OF ABO BLOOD GROUPS HAVE BEEN INFLUNECEC BY MIGRATION?

A

AN example of how DISTRIBUTION OF ABO BLOOD GROUPS HAVE BEEN influenced BY migration is the change in frequency of the I^B allele across Asia and Europe.

The inhabitants of Esat Asia, the MONGOLS, have a proportional higher frequency of the allele than those living to their est in Europe,

in fact, it is thought, that western Europeans did not have the I^B allele.

in the 12th and 13th centuries, the MONGOLS invaded Europe on a number of occasions, spreading not only their culture but genes as well.

Today, there is a steady decrease in the allele from central Asia to western Europe.

INteretsky, the lowest concentrations of the I^B allele is now in Pyrenees mountain and a few isolated locations in SCANDINAVIA.

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5
Q

Explain barriers to gene flow?

How to classify them?

List the two

A

Populations are often kept apart by barriers that inhibit the amount of interbreeding between them.

The isolation leads to separate gene pools forming.

Barriers to gene flows can be classified based on their cause.

  1. Geographical barriers
  2. Sociocultural barriers
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6
Q

Explain with examples the Geographical BARRIERS to gene flow

A
  1. Geographical barriers - include oceans, large lake systems, mountain ranges, deserts, and expansive ice sheets.

For example, the original inhabitants of Australia were isolated for 1000s of years by ocean barriers that formed as sea levels rose.

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7
Q

Explain with examples the Sociocultural BARRIERS to gene flow

A
  1. Sociocultural barriers - such as economic status, educational background, and social position are barriers to interbreeding

For example, statistics indicate Australians tend to marry people with similar educational backgrounds, members of particular religions favour partners who have the same faith.

RELIGION AND LANGUAGE CAN ALSO BE BARRIERS TO GENE FLOW.

Some religions do not allow marriages outside the religion,
it is unlikely that people who cannot communicate with one another will marry.

Sexual selection

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8
Q

What is known as the Special Creation?

A

The belief that a supreme being or a god had individually created all species

  • Prevalent belief until the 1800s
  • Still today some religious groups believe in this
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9
Q

What is Evolution?
Who proposed the theory?

What is Evolved?

A

The gradual change in the characteristics of a species.

The theory of evolution through natural selection was put forward independently by Charles Darwin and Alfred Russel in 1858

Evolved - having gone through the process of evolution

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10
Q

Who was Charles Darwin?
WHY WAS HE SIGNIFICANT?
WHAT INFLUENCED HIM?

A

Amateur naturalist, biologist.

  • Voyaged on expeditions (HMS BEAGLE) visiting other places like AUSTRALIA, NEW ZEALAND, AND GALAPAGOS ISLANDS.

QUESTIONED THE COMMONLY HELD BELIEF THAT LIVING SPECIES HAD ALWAYS BEEN EXACTLY THE SAME AS THEY APPEARED.
CONVINCED THAT SPECIES DID CHANGE.

  1. collected material, especially in Galapagos islands, became preparation for his later works.
    On these islands, Darwin was able to OBSERVE the similarities and differences between animals separated by
    - GEOGRAPHY; those living on the mainland of South America and those on various islands
    - TIME; animals recently extinct and species still alive.
  2. Influenced by the works of OTHERS
    - Carolus Linnaeus (1707-78) established the basis of the present system of CLASSIFICATION and BINOMIAL SYSTEM of NAMING ORGANISMS using generic (GENUS) and specific (SPECIES) names.
    - THIS SYSTEM WAS IMPORTANT TO DARWIN as it ENABLED HIM to CLASSIFY and ORGANISE the MATERIAL he COLLECTED.
  3. BOOK - “Principles of Geology”, written by his friend Charles Lyell.
    - Lyell hypothesized Earth’s surface has been gradually moulded over a very long period of time, by such simple forces as; temperature, running water and earth movements.
    THIS PROVIDED DARWIN WITH A CONCEPT OF CONSTANT CHANGE AGAINST WHICH HE COULD VIEW HIS OWN WORK.
  4. THOMAS MALTHUS, British clergyman and political economist,
    PROVIDED the IDEA for Darwin’s theory foundation for natural selection
    “AN ESSAY ON THE PRINCIPLE OF POPULATION” - pointed out that HUMAN POPULATION WAS INCREASING ATA A RATE FAR EXCEEDING THE RATE OF FOOD PRODUCTION.
    - Examples from natural populations of plants and animals Demonstrated the natural reproduction rates exceeded the available resources, THAT IS MORE PLANTS AND ANIMALS ARE PRODUCED THAN CAN POSSIBLY SURVIVE.
    DARWIN REALISED THAT UNDER THESE CIRCUMSTANCES A STRUGGLE FOR EXISTENCE WOULD OCCUR, WITH FAVOURABLE VARIATIONS BEING PRESERVED AND UNFAVOURABLE ONES BEING GRADUALLY LOST FROM THE POPULATION.
  5. In 1858, Darwin received a copy of an essay by ALFRED RUSSEL WALLACE, a naturalist then on the islands of Ternate in Indonesia.
    His essay ‘ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE ORIGINAL TYPE’
    - covered the same idea as Darwin has been working and refining on for 20 years.
    Was the stimulus for Darwin to publish his views.
    A joint essay was prepared by Both of them and READ BEFORE THE LINNEAN SOCIETY IN 1858.
  6. YEAR LATER, DARWIN PUBLISHED HIS FIRST BOOK = ‘ON THE ORIGIN OF SPECIES.
    lots of controversies, but with the support of other scientists darwin’s ideas became firmly established.
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11
Q

What is Darwin’s theory of natural selection?

A

Natural selection - The process by which a species becomes better adapted to its environment

  • those individuals with FAVOURABLE CHARACTERISTICS have a SURVIVAL ADVANTAGE and so PASS on those characteristics ON to SUBSEQUENT GENERATIONS.

SELECTION OF ALLELES IN A POPULATION THAT GIVE THE ORGANSISM SURVIVAL ADVANATGE.
- increase in allele frequency in that population gene pool, overtime characterics become more and more frequent in the species population.

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12
Q

What 3 Observations was Darwin’s theory of natural selection based on?

A
  1. VARIATION:
    - all members of a species vary
    - variations were passed on from generation to the next, where parents’ characteristics passed to offspring.
  2. BIRTH RATE:
    - all living organisms REPRODUCE AT A RATE FAR GREATER/FASTER than at which their FOOD AND OTHER RESOURCE INCREASE RATE.
    - RESULTING IN OVERCROWDING.
  3. NATURE’S BALANCE:
    - although the birth rate is high, EACH SPECIES TENDED TO REMAIN AT A RELATIVELY CONSTANT LEVEL.
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13
Q

List the INTERPRETATIONS OF DARWIN FROM HIS THREE OBSERVATIONS.

A
  1. STRUGGLE FOR EXISTENCE
  2. SURVIVAL OF THE FITTEST
  3. VARIATION
  4. SELECTIVE AGENT
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14
Q

What is the SURVIVAL OF THE FITTEST

A

A PRINCIPLE whereby organisms with FAVOURABLE CHARCTERITSICS SURVIVE,

but organisms with UNFAVOURABLE characteristics DIE BEFORE they have the CHANCE TO REPRODUCE.

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15
Q

What is the STRUGGLE FOR EXISTENCE

A

PRINCIPLE, whereby organisms with favourable characteristics is greater than the resources in the environment, can support

  • hence, there is a COMPETITION between the organism for these RESOURCES.
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16
Q

What is Variation?

A

Variation is the differences that exist between individuals or populations of a species.

SURVIVAL OF THE FITTEST IS POSSIBLE DUE TO THIS.

Members of a species differ from one another in their PHYSICAL CHARACTERISTICS, BEHAVIOR, AND BODY FUNCTIONING.

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17
Q

What is a Selective agent?

A

A selective agent which is ANY FACTOR that CAUSES the DEATH of ORGANISIMS with CERTAIN CHARACTERISTICS, but which with NO EFFECT on individuals WITHOUT those characteristics.

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18
Q

What does a selective agent do to the species population?

A

THOSE THAT SURVIVE WILL PASS ON THOSE FAVOURABLE ALLELES.
- not impacted by the selective agent

  • GRADUALLY, over a period of time, the characteristics of a population change so that it becomes BETTER SUITED TO ITS ENVIRONMENT.
  • ENVIRONMENT IS ALSO CHANGING, CHARACTERISTICS THAT ENHANCE SURVIVAL ENABLE SUCCEEDING GENERATIONS TO GRADUALLY ADAPT TO IT.
  • INDIVIDUAL ORGANISM DOES NOT ADAPT.
    INSTEAD, THE SPECIES adapts to the environment by natural selection,
  • this process takes GENERATIONS.
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19
Q

Summarise the principles of evolution through natural selection.

A
  1. VARIATION of CHARACTERISTICS EXISTS within a SPECIES.
  2. MORE OFFSPRING of a species are PRODUCED THAN can POSSIBLY SURVIVE TO MATURITY.
  3. EXCESSIVE BIRTH RATE AND LIMITED RESOURCES = STRUGGLE FOR EXISTENCE or COMPETITION FOR SURVIVAL
  4. individuals with the BEST SUITED CHARACTERISTICS TO THE ENVIRONMENT HAVE A MORE CHANCE OF SURVIVING AND REPRODUCING = SURVIVAL OF THE FITTEST.
  5. favourable characteristics are PASSED TO NEXT GENERATION.
  6. in GENE POOL, the PROPORTION OF ALLELES THAT PRODUCE FAVOURABLE CHARACTERISTICS GRADUALLY DECREASES.
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20
Q

Explain an example of natural selection: BODY STATURE

A
  1. initially, human gene pool = ALLELES for a RANGE OF STATURES
    EXAMPLE
    - short-bodied, long-limbed physique of present-day BLACK AFRICAN
    - long-bodied, short-limbed stature of INUIT people of today.
  2. LONG BODY and SHORT LIMBS = smaller SURFACE AREA in relation to BODY VOLUME, comparatively
  3. Hence they LOSE LESS HEAT in VERY COLD ENVIRONMENTS. = SURVIVAL ADVANTAGE
  4. they WILL REPRODUCE AND PASS ON THIS CHARACTERISTIC (short limbs and long body) to OFFSPRING.
    Others DIE YOUNG before THEY REPRODUCE.
  5. Gradually, FREQUENCY OF UNFAVOURABLE ALLELES in GENE POOL DECREASE.
    OVERTIME, those ALLELES DECREASE TO THE EXTENT THAT the unfavourable CHARACTERISTIC would NO LONGER OCCUR IN POPULATION.
  6. long-body short-limbed characteristic alleles would have increased in the gene pool.
  7. EVOLUTION OR GENETIC CHANGE HAS TAKEN PLACE.
    WITHIN A PARTICULAR GENE POOL, THE FREQUENCY OF ALLELES HAVE CHANGED OVER TIME.
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21
Q

What is Sickle-celled anemia?

A

An inherited disease-causing early death; results from the inheritance of recessive 2 alleles for sickle-celled anaemia

EXAMPLE OF NATURAL SELECTION OPERATING IN HUMAN POPULATIONS.

22
Q

Explain Malaria; Why has it INCREASED?

A
  1. The ‘Anopheles’ mosquito TRANSMITS MALARIA PARASITE.
  2. Found in QUIET, STAGNANT POOLS OF WATER (BREEDING SITES)
    - habitat Found in open areas
    - NOT NORMALLY FOUND IN TROPICAL FORESTS.
  3. DEFORESTATION IN AFRICA for AGRICULTURE = changed the environment in a manner CREATING ADDITIONALLY BREEDING AREAS for these MOSQUITOS.
  4. INCREASED FOOD SUPPLY from AGRICULTURAL PRODUCTION allowed the HUMAN POPULATION TO INCREASE = MORE BODIES FOR MOSQUITOS TO FEED ON.
  5. incidence of malaria increased
23
Q

Explain Malaria; disease, and symptoms

A

Symptoms of malaria include fever and flu-like illness, including shaking chills, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhea may also occur. Malaria may cause anemia and jaundice (yellow coloring of the skin and eyes) because of the loss of red blood cells.

The malaria parasites enter that person’s bloodstream and travel to the liver. When the parasites mature, they leave the liver and infect red blood cells. Malaria is caused by a single-celled parasite of the genus plasmodium. The parasite is transmitted to humans most commonly through mosquito bites

24
Q

What is Sickle-celled anaemia (in detail)

  • SYMPTOMS
  • 1ST CASE
  • EFFECTS
A

1ST CASE - young west Indian student in Chicago in 1910

AFFECTS HEMOGLOBIN MOLECULES

SYMPTOMS INCLUDE:
- Clogged/blockages in blood vessels, pneumonia, rheumatism, heart disease, inflammation of the hands and feet, inflexible and ANAEMIA.
ORGAN DAMAGE (KIDNEYS, LUNGS, BRAIN), JAUNDICE, FATIGUE, HIGH BP AND HEART FAILURE.

  • Doctors took BLOOD SAMPLE and OBSERVED UNDER A MICROSCOPE =
    WHEN AIR WAS EXCLUDED FROM THE SAMPLE, THE RBCS showed a DRAMATIC CHANGE IN SHAPE.
    FROM ROUND BICONCAVE DISC SHAPE TO SICKLED/CRESENT-LIKE SHAPE.
25
Q

How is sickle celled anemia/disease caused?

Which Gene? What does the gene do?

A

Results when IN a HOMOZYGOUS RECESSIVE ALLELE person.

  • This allele is due to POINT MUTATION in the DNA sequence of the HBB gene.
  • The HBB gene codes for ONE OF THE BETA-GLOBULIN PROTEINS that make up HAEMOGLOBIN IN RBCs.
  • The DIFFERENT BASE SEQUENCE MEANS THAT THE AMINO ACID ‘VALINE’ IS ADDED INSTEAD OF GLUTAMIC ACID.
  • this RESULTS in a DIFFERENT FORM OF THE PROTEIN,, ALTERNATING THE HAEMOGLOBIN PRODUCED
  • DISTORTING THE SHAPE OF RBCs.
26
Q

What happens to Heterozygous people with allele Sickle celled disease.

or HOMOZYGOUS NORMAL?

A

It is a recessive allele, the dominant allele in the genotype will ‘mask’ the charactertictic.
= CARRIERS and are called HAVING SICKLED-CELL TRAIT

SHOWS NO ILL EFFECTS, UNLESS O2 IS IN SHORT SUPPLY.
- when this occurs RBCs Show MILD SICKLING.

homozygous normal = blood that shows no sign of the sickling phenomenon.

27
Q

What is Anaemia?

A

A condition in which there is a reduced amount of haemoglobin in the blood or a reduced number of RBCs,

28
Q

Why is the ‘ratio of mutation theory not the reason for the Sickle-celled anemia to prevalent?

A

If a person if SCA disease dies before reproducing = trait not passed to next-generation Hence, expect the frequency of the allele gradual decrease and be eliminated from the population.
BUT IT IS STILL COMMON IN SOME POPULATIONS

otherwise; if RATIO OF MUTATION of NORMAL ALLELE: SICKLE-CELL ALLELE was LARGE ENOUGH,
- COULD CANCEL OUT OUT LOSS OF ALLELES THROUGH THE DEATH OF AFFECTED INDIVUALS IN THE POP.

HOWEVER, this is NOT THE CASE
as investigation shows = RATE OF ALLELES LOST FROM POPULATION IS 100X GREATER AVERAGE RATE OF MUTATION AT ANY POINT ALONG HUMAN CHROMOSOME.

SOME OTHER MECHANISM MUST WORK TO MAINTAIN THE SICKLE CELL ALLELE IN THE POPULATION

29
Q

What Maintains Sickle-cell in populations of humans?

where prevalent?

observed by who?

what observations?

suggested what?

survival advantage?

A
  1. SICKLE-CELL ALLELE OCCURS IN AREAS WHERE MALARIA IS PREVALENT.
    - first noticed by ANTHONY ALLISON this relationship
  2. observations published in the BRITISH MEDICAL JOURNAL 1954,
  3. noting SICKLING ALLELEM TENDED TO HIGHER FREQUENCY IN AREAS WHERE THE RISK FROM MATERIAL PARASITES was THE GREATEST.
  4. he SUGGESTED THAT INDIVIDUALS with ONE SICKLE-CELLED ALLELE WERE MORE RESISTANT TO MALARIA THAN THOSE WITH NORMAL HAEMOGLOBIN IN RBCs.
  5. ‘Sicklers’ had fewer malarial parasites, compared to non-‘sickler’ patients.
  6. FROM HIS INOCULATED EXPERIMENT (TO CONFIRM OBSERVATION)
    - HETEROZYGOUS people were LESS SUSCEPTIBLE TO MALARIA THAN TO HOMOZYGOUS NORMAL PEOPLE.
  7. HENCE PEOPLE WITH SICKLE CELLED TRAIT (HETEROZYGOUS) HAVE A SURVIVAL ADVANTAGE IN AREAS WHERE MALARIA IS PREVALENT
30
Q

How does Sickle-cell example show how natural selection occurs in human populations?

A
  1. A MUTATION ESTABLISHED a NEW ALLELE in the population
  2. Having 1 of these alleles gave the individuals living in malarial prone areas a SURVIVAL ADVANTAGE
    KNOWN AS HETEROZYGOUS ADVANTAGE.
  3. 2 sickle-celled alleles usually die (due to disease-causing anemea)
  4. homozygous normal was susceptible to malaria.
  5. THEREFORE, THE PRECSNE ON MALARIA ACTED AS A ‘SELECTIVE AGENT’ FOR THE SICKLE-CELLED ALLELE.
31
Q

What is a Heterozygous advantage?
AFFECT GENE POOL?
EXAMPLES OF HOW?

A

A situation where a heterozygous genotype has a higher chance of survival than either homozygous genotype.

THE HETEROZYGOUS ADVANTAGE PROVIDED BY THE HETEROZYGOUS GENOTYPE INCREASES THE PERCENTAGE OF THE RECESSIVE ALLELE IN THE GENE POOLS

  1. TAY - SACHS
  2. SICKLED CELLED ANEMIA
32
Q

What Is Tay-Sachs Disease?

Effects in general?

A
  1. Lethal Condition caused by the Mutation that Results in the ABSENCE OF THE ENZYME BETA-HEXOAMINIDASE
    = his enzyme is found in lysosomes, which are structures in cells that break down toxic substances and act as recycling centers.
  2. appears RECESSIVE ALLELE ON CHR. 15
    OCCURS
  3. CONDITION LEADS TO THE DETEROIATION OF THE NERVOUS SYSTEM
  4. DEATH USUALLY OCCURS AT A YOUNG AGE

HETEROZYGOUS = REDUCED amount of the enzyme

TSD IS AN EXAMPLE OF LETHAL RECESSIVES
IN SOMATIC CELLS

Disorder of lipid metabolism that is inherited in an autosomal recessive pattern.

A lethal recessive condition caused by a mutation in the HEXA GENE that codes for the ENZYME BETA-HEXOSAMINIDASE.
- enzyme is responsible for BREAKING DOWN TOXIC SUBSTANCES including a fatty substance called GM2 GANGLIOSIDE, IN THE BRAIN.

The missing enzyme results in the ACCUMULATION OF GM2 ganglioside in the nervous system, which destroys the neurons.

A baby with 2 recessive alleles of TSD develops ABNORMALLY FOR FIRST FEW MONTHS, AND THEN DETERIORATION THAT CAUSES INTELLECTUAL AND PHYSICAL DISABILITIES BEGIN/

DEATH USUALLY OCCURS IN EARLY CHILDHOOD = APPROX 5YRS

33
Q

Explain the distribution of alleles for Tay-Sachs disease and how it affects the gene pool and why.

Normal Homozygous, Homozygous Recessive, Heterozygous

A

HETEROZYGOUS = REDUCED amount of the enzyme BETA-HEXOAMINASE

These individuals have some protection from TUBERCULOSIS; an infectious disease that primarily affects the lungs.

This means that people who are:

  1. HOMOZYGOUS RECESSIVE DIE BEFORE REPRODUCING, due to Tauy-Sachs, and therefore do not pass on the recessive allele
  2. HETEROZYGOUS SURVIVE TUBERCULOSIS, REPRODUCE, AND PASS ON BOTH ALLELES.
  3. HOMOZYGOUS NORMAL DOMINANT ARE AFFECTED BY TB and may die before reporduing.

THE HETEROZYGOUS ADVANTAGE PROVIDED BY THE HETEROZYGOUS GENOTYPE INCREASES THE PERCENTAGE OF THE RECESSIVE ALLELE IN THE GENE POOLS
***IN AREAS AFFECTED BY TB.

34
Q

What is Thalassemia?

How is hemoglobin formed?

TYPES?

HOW INHERITED?

EFFECTS?

SEVERITY?

SYMPTOMS?

A 
A disorder that alters the STRUCTURE  of HAEMOGLOBIN IN BLOOD.
####haemoglobin is made up of 4 protein chains that fit together

***2 FORMS
- 1. ALPHA THALASSEMIA
due to a MUTATION in the HBA gene on CHROMOSOME 16 WHICH REDUCES THE LEVEL OF ALPHA GLOBIN IN HAEMOGLOBIN

    1. BETA THALASSEMIA
      due to mutation of HBB gene on CHROMSOME 11 WHICH REDUCES LEVEL OF BETA GLOBIN IN HAEMOGLOBIN.

BOTH ARE INHERITED IN AN AUTOSOMAL RECESSIVE MANNER.

EFFECTS:
- have LESS HAEMOGLOBIN in RBCs and THEREFORE CAN NOT CARRY MUCH O2 IN THEIR BLOOD.

SEVERITY - VARIES
depends on the NUMBER OF GENES AFFECTED

SYMPTOMS RANGE FROM MILD ANEMIA AND FATIGUE
TO ENLARGED LIVER AND HEART.

35
Q

Where is Thalassemia common?
for both types?
What is the selective agent?
WHY?

A

Thalassemia is present and prevalent in AREAS AFFECTED BY MALARIA.

  • Alpha thalassemia is more PREVALENT IN SOUTH-EAST ASIA
  • Beta thalassemia is more PREVALENT IN MEDITERRANEAN BASIN

SELECTIVE AGENT - research shows MALARIA can act as a SELECTIVE AGENT
- RESULTING IN THE FREQUENCY OF ALLELES OF ALPHA THALASSEMIA.

WHY?
lower amounts of hemoglobin give some PROTECTION AGAINST MALARIA.
Patients seem to RECOVER more QUICKLY than those W/O THALLASEMIA
POSSIBLY DUE TO THE INCREASED NO. OF RBCs.

Possible FOR BETA THALASSEMIA CASE ALSO however has not been supported by research.

36
Q

What factors may affect allele frequency in a population?

A 
Migration 
Genetic Drift 
Founder Effect 
Heterozygous Advantage 
Natural Selection
37
Q

Define Genetic Drift?
how it affects evolution?

Other names

A

The Random, non-directional change in allele frequency between generations.

Not affected by whether an allele is beneficial or harmful; instead, it is purely BY CHANCE.

OCCURS IN POPULATIONS OF ALL SIZES

  • PLAYS A MUCH MORE IMPORTANT ROLE IN EVOLUTION IN SMALL POPULATIONS
  • significant in causing changes to allele frequencies

GENETIC DRIFT = RANDOM GENETIC DRIFT = SEEWALL WRIGHT EFFECT

100 - 60:40 HENCE BY CHANCE

38
Q

Example of the effect of GENETIC DRIFT.

ISOLATED POPULATIONS OF ABORIGIBNALS

A

BENTINCK AND MORNINGTON ISLANDS IN THE GULF OF CARPENTARIA.

  1. Originally islands were part of the mainland, but rising sea levels cut them off and their POPULATIONS BECAME ISOLATED.
  2. Mornington Islanders maintained some contact with the Mainland by using smaller islands as ‘stepping stones’
  3. The blood group frequencies of the islanders have been studied and compared with the population occupying BAYLEY POINT ON THE MAINLAND.
  4. Occupants of BENTINCK ISLAND SHOW ALLELE FREQUENCY VALUES FOR BLOOD GROUPS THAT FALL OUTSIDE THE RANGE FOR THE ABORIGINAL PEOPLE IN THE REST OF AUS.
  5. They show a HIGHER PROPORTION of the I^B allele and a COMPLETE ABSENCE OF THE ALLELE I^A
    - unlike the mainland population which has a low proportion of the I^B allele and a relatively high proportion of I^A.
39
Q

What is the Founder effect?

A

EXTREME EXAMPLE OF GENETIC DRIFT

A type of genetic drift where a new population is formed by a small number of individuals;

  • the small sample size can cause marked deviations in allele frequencies from the original population

ISOLATED GROUPS SHOW THIS EFFECT

40
Q

How is the Founder effect an extreme example of genetic drift?

A

Because the population size is very small, CHANCE can cause the new groups to have:

  1. A DIFFERENT ALLELE FREQUENCY FROM THE ORIGINAL POPULATION
  2. DECREASED GENETIC VARIATION

This means the NEW POPULATION MAY SHOW a FREQUENCY OF FEATURES THAT ARE NOT TYPICAL OF THE ORIGINAL HOMELAND PEOPLE/POPULATON.

41
Q

Example of the Founder Effect

DUNKERS

A

A study was done by BENTLEY GLASS AND CO-WORKERS
The 1950s, US, PENNSYLVANIA STATE

  1. originally from Hesse, germany, The ‘DUNKERS’ is an isolated population
  2. DESCENDED FROM OLD GERMAN BAPTIST BRETHREN who came to the US in the 1700s.
  3. RELIGION DOES NOT ALLOW THEM TO MARRY OUTSIDE THEIR GROUP, and thus THEY CONSTITUTED TO ISOLATED BREEDING POPULATION WITHIN THE TOTAL POPULATION OF US.
  4. STUDY investigated a number of easily measurable physical traits; frequency of
    - ABO, Rh, and Mn blood groups
    - mid-digital hair,
    - left or right handedness
    - attached or free earlobes.
  5. For most of these traits studied, the Dunkers varied in allele frequencies from the present-day population of Hesse and the surrounding US population.
    THE ENVIRONMENT FOR DUNKERS AND SURROUNDING US POP. = ESSENTIALLY THE SAME
    - HENCE, THERE WOULD HAVE NOT BEEN ANY NATURAL SELECTION FOR THE DIFFERENCES OF ALLELES.

HENCE IT CAN BE CONCLUDED THAT GENETIC DRIFT WAS RESPONSIBLE FOR THE VARIATION OF AS THE SMALL SIZE OF THE DUNKER POPULATION ALLOWED CERTAIN CHARACTERISTICS TO BECOME MORE COMMON PURELY BY ***CHANCE.

42
Q

EXAMPLE OF FOUNDER EFFECT - ASHKENAZI JEWS

A

incidence of Tay-Sachs Disease IN THE POPULATION OG of Ashkenazi jews. = MUCH HIGHER

LETHAL RECESSIVE DISEASE

Approx. 1 in 27 AKJ carries the altered allele
Compared to 1 in 300 Non-AKJ.

AKJ descended from Central or Eastern Europe

  • This Group was initially isolated GEOGRAPHICALLY
  • Additional isolation through the CUSTOM odf ENDOGAMY (only marrying within the community)

THIS CREATED A FOUNDER EFFECT.

INCIDENCE OF TAY-SACHS DISEASE VIA MUTATED ALELEL WAS HIGHER IN ANCESTORS, HENCE GENETIC DRIFT IS RESPONSIBLE FOR THE PREVALENCE OF THE DISEASE IN THE AKJ POPULATION.

FREQUENCY = 1 IN 500 000
EASTERN EUROPEAN JEWISH PPL 
- Ashkenazi Jewish heritage (of central and eastern European descent)
= 1 IN 2500
DUE TO GENETIC DRIFT, SMALL COMMUNITIES
43
Q

What is Tay-Sachs Disease.. part 2

A

TSD IS AN EXAMPLE OF LETHAL RECESSIVES
IN SOMATIC CELLS

Disorder of lipid metabolism that is inherited in an autosomal recessive pattern.

A lethal recessive condition caused by a mutation in the HEXA GENE that codes for the ENZYME BETA-HEXOSAMINIDASE.
- enzyme is responsible for BREAKING DOWN TOXIC SUBSTANCES including a fatty substance called GM2 GANGLIOSIDE, IN THE BRAIN.

The missing enzyme results in the ACCUMULATION OF GM2 ganglioside in the nervous system, which destroys the neurons.

A baby with 2 recessive alleles of TSD develops ABNORMALLY FOR FIRST FEW MONTHS, AND THEN DETERIORATION THAT CAUSES INTELLECTUAL AND PHYSICAL DISABILITIES BEGIN/

DEATH USUALLY OCCURS IN EARLY CHILDHOOD = APPROX 5YRS

44
Q

What is the Bottleneck Effect?

A

An extreme example of Genetic drift.

An event such as a natural disaster severely REDUCES the SIZE OF THE POPULATION.

The allele frequency after the disaster, may by CHANCE, be different from before the event.
- allele frequency of survivors may not reflect that of the original population.

THE CHANCE OF SURVIVAL IS BY CHANCE AND NOT DUE TO A SPECIFIC TRAIT.

45
Q

Example of BottleNeck effect - Achromatopsia

A

In 1775 when Typhoon reduced the population of Pingelap, an Island in Micronesia to ONLY 20.

The SURVIVORS formed the FOUNDING POPULATION FOR THE CURRENT INHABITANTS.

1 survivor was heterozygous for ACHROMATOPSIA.

Allele is Recessive

Today, after a number of generations, the incidence of the ACHROMATOPSIA IN Pingelap is 5%
Other parts of the world = 0.0033%

30% on the ISLAND ARE CARRIERS (not colour, blind, but have the affected allele)

HENCE ALLELE FREQUENCIES CAN CHANGE IN SMALL, ATYPICAL POPULATIONS.

46
Q

What is Achromatopsia?

A

An inherited form of total colour blindness

Recessive allele

47
Q

What is a Species?

A

The basic unit of biological classification;

Groups of individuals who share many characteristics and are capable of interbreeding in natural conditions to produce fertile offspring

Hence Humans belong to the same species

48
Q

How does REPRODUCTIVE isolation AN EXAMPLE/ INSTANCE WHICH MAKES ‘SPECIATION’ OCCUR?

A
  1. ISOLATION = BARRIER TO GENE FLOW

REPRODUCTIVE ISOLATION may LEAD to the DEVELOPMENT OF SEPARATE GENE POOLS.

  1. No 2 environments are the same exactly, so it would be expected that certain alleles would be favoured in one environment over another.
  2. Hence, OVERTIME the ALLELE Frequencies of each gene pool will change, depending on which characteristics are favoured for survival.
  3. OVER generations the populations become less and less alike as they develop characteristics that better suit them to their respective environments
  4. if 2 populations are isolated for a very long period of time, and the environmental influences on each are different enough, major changes in the allele frequencies within each population could occur.
  5. in such a situation, the members of those populations may become so different that, even if the barriers of reproduction were removed, INTERBREEDING WILL NO LONGER BE POSSIBLE.
  6. IF THIS OCCURRED, THE 2 POPULATIONS COULD BE REGARDED AS SEPARATE POPULATIONS.
49
Q

Define Speciation

A

The natural process of producing species

- due to reproductive isolation (usually) which affect gene flow

50
Q

List and explain the steps for SPECIATION

A
  1. VARIATION - there is variation between individuals of a species but shares A COMMON GENE POOL
  2. ISOLATION - populations of the same species are isolated without gene flow
    - via a barrier formed and DIVIDES the populations
    - no interbreeding occurs BETWEEN THE 2 POPULATIONS
    - EACH HAVE A SEPARATE GENE POOL
  3. SELECTION - each population is subjected to different selective agents
    - different selective pressures act on each population
    - change in gene frequency of each gene pool
    - leading to the evolution of separate SUBSPECIES
  4. SPECIATION - the allele frequency changes until they become so different that the 2 groups are no longer able to interbreed
    - CHANGEs in gene frequency may be great enough to prevent the PRODUCTION of fertile offspring via natural inbreeding between 2 populations for EVER OCCURING AGAIN
51
Q

Explain populations, gene pools, and allele frequencies

A

Populations that differ in the characteristics they possess are likely to have different frequencies of the various alleles of a gene in their irrespective gene pools.

Thus two populations having different characteristics are likely to have different gene pools.

Example: Scandinavians commonly have blue eyes, whereas black Africans have brown eyes.

  • THE FREQUENCY OF THE ALLELE FOR BLUE EYES WOULD BE MUCH HIGHER IN THE SCANDINAVIAN GENE POOL THAN IN THE AFRICAN GENE POOL
52
Q

What is Gene pool?

A

Gene pool is the sum of all the alleles in a given population

GENETICISTS Prefer to consider the characteristics of the population as a whole and those of the individuals that make up the population.

They find it convenient to pool the genotypes of all the individuals capable of reproducing as refers to this as a GENE POOL.

A genome is the complete set of genetic information in an organism.

Allele frequency, or gene frequency, is the relative frequency of an allele at a particular locus in a population, expressed as a fraction or percentage.

Human Biology: Unit 4 (7 decks)

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