Chapter 9.2-9.5 Flashcards

Question

How is sickle celled anemia/disease caused? | Which Gene? What does the gene do?

Answer 1

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.

Answer 2

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.

Answer 3

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

Answer 4

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

Answer 5

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

Answer 6

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.

Answer 7

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

Answer 8

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

Answer 9

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.

Answer 10

``` 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 - 2. 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.

Answer 11

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.

Answer 12

``` Migration Genetic Drift Founder Effect Heterozygous Advantage Natural Selection ```

Answer 13

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

Answer 14

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.

Answer 15

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

Answer 16

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.

Answer 17

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.

Answer 18

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 ```

Answer 19

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

Answer 20

An extreme example of Genetic drift. Occurs when the size of a population is severely reduced due to a sudden event - 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.

Answer 21

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.

Answer 22

An inherited form of total colour blindness | Recessive allele

Answer 23

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

Answer 24

1. ISOLATION = BARRIER TO GENE FLOW REPRODUCTIVE ISOLATION may LEAD to the DEVELOPMENT OF SEPARATE GENE POOLS. 2. No 2 environments are the same exactly, so it would be expected that certain alleles would be favoured in one environment over another. 3. Hence, OVERTIME the ALLELE Frequencies of each gene pool will change, depending on which characteristics are favoured for survival. 4. OVER generations the populations become less and less alike as they develop characteristics that better suit them to their respective environments 5. 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. 6. 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. 7. IF THIS OCCURRED, THE 2 POPULATIONS COULD BE REGARDED AS SEPARATE POPULATIONS.

Answer 25

The natural process of producing species | - due to reproductive isolation (usually) which affect gene flow

Answer 26

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

Answer 27

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

Answer 28

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.

Chapter 9.2-9.5 Flashcards

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