Flashcards in Gene Pools And Mutations Deck (70):
What is a species
A group of individuals that share many characteristics and are able to interbreed under natural conditions to produce fertile offspring
What are alleles?
Alternative forms of a gene. The pairs of alleles each person inherits from their parents control and determine the characteristics of that individuals
What is a population?
A group of organisms of the same species living together in a particular place at a particular time
What is a geneticist?
Scientists who specialise in the study of inheritance; prefer to consider the characteristics of the population as a whole and not those of the individuals that make up the population. They find it convenient to pool genotypes of all the individuals capable of reproducing ‘gene pool’
What is a gene pool?
Sum of all the alleles carried by the members of a population
What are allele frequencies?
How often each allele of a gene occurs in a population
What are mutations?
A permanent change in a gene or chromosome leading to new characteristics in an organism, they may occur suddenly or purely by chance. There are 2 main types: gene mutations and chromosomal mutations
What is a mutant?
An organism with a characteristic resulting from a mutation
What is a gene mutations?
An alteration to a single gene, occur during replication of DNA before cell division. They are Changes to a single gene so that the traits normally produced by that gene are changed or destroyed
Eg. albinism, duchenne, cystic fibrosis
What is a chromosomal mutation?
A change to the structure and or number of chromosomes in a organism. A mutation in which all or part of a chromosome is affected
(a change to the structure and or number of chromosomes in an organism)
Define mutagenic agent/ mutagens?
An environmental agent that increases the rate of mutation Eg, mustard gas, Sulfur dioxide, X-rays and radiation from radioactive waste
What are somatic mutations?
A change occurring in a gene in a body cell( not gamete), reproductive cells are not affected as mutant body cell divides Eg. Many cancerous growths
What is germinal or Germaine mutation?
A change in the hereditary material in the egg or sperm that becomes incorporated into the DNA of every cell in the body of offspring. Eg. Diseases like phenylketonuria (PKU) can arise through mutation during formation of gametes and can be passed in to an offspring
What are point mutations?
- a change in just 1 base in a DNA molecule.
- it could alter a protein, have no effect at all of prevent the protein from being produced = DNA for a particular protein is altered= protein for which it codes may be abnormal of missing = can have an enormous effect on entire body
Eg. Albinism, duchenne dystrophy, cystic fibrosis
What is albinism?
Point mutation marked by absence of pigment from hair, skin and eye.
What is a lethal recessive?
Recessive alleles inherited from homozygous condition resulting in death of embryo, foetus or child.
- some lethal recessive masked by dominant allele
Eg. Tay each disease
How do lethal recessive affect the gene pool?
- affect gene pool as ppl who inherit two such alleles would die before their alleles could be passed onto next generation do proportion of lethal recessive alleles in the gene pool would generally be reduced
Types of chromosomal mutations?
What is deletion (chromosomal mutations)
When part of a chromosome is removed eg. cri du chat
What is duplication ( chromosomal mutations)
When a section of a chromosome occurs twice, this may happen if part of a chromosome breaks of and joins to the wrong chromatid
Eg. Charcot Marie tooth disease
What is inversion ( chromosomal mutations)
When a section of DNA breaks and is reattached in reverse order and orientation . This changes the order of genes on a chromosome and may disrupt the pairing of homologous chromosomes during meiosis
Eg. haemophilia A
What is translocation ( chromosomal mutations)
When part of a chromosome breaks of and is rejoined to the wrong chromosome
Wha is non-disjunction ( chromosomal mutations)
When during meiosis a chromosome pair does not seperate and one daughter cell has an extra chromosome and one daughter cell has one less than not,al number. ( sometimes referred to aneuplody- a change in chromosome number)
Trisomy – extra chromosome
Monosomy – lacking one chromosome
What is Down syndrome ?
- child has 3 of chromosome 21 instead of 2
- non disjunction
What is partial trisomy?
- when extra part of 1 chromosome attached to another chromosome
The gradual change in the characteristics of a species over a long period of time.
- the differences that exist between individuals or population of species
What is speciation?
The process of new species developing
What are the mechanisms for evolution?
- genetics and inheritance ( sexual reproduction, genetic disease, mutations)
- gene flow and barriers
- random genetic drift ( bottle necking and founder effect)
- natural selection
What are mutations?
A change in a gene of chromosome leading to new characteristics
What is a mutant?
An organism with a characteristic resulting from a mutation
What cells can be affected by mutations?
- somatic mutations: change occurring in a gene in a body cell ( not gamete)
- germline mutations: a change in the hereditary material in the egg or sperm that becomes incorporated into the DNA of every cell in the body of offspring eg. Phenylketonuria (PKU)
What are the types of mutations?
Gene mutations and chromosomal mutations
What processes can affect variation in humans?
- random assortment: of chromosomes during meiosis ( lots of possible combos )
- crossing over: of chromatids during meiosis ( changes in sequence, recombination of alleles)
-non disjunction: chromosomes fail to seperate during meiosis
- random fertilisation: sperm can fertilise any egg
- mutations: permanent changes in DNA of a chromosome
When does natural selection happen?
When nature favours one set of alleles at the expense of others - causing changes to allele frequencies in a gene pool, it is not random.
What is random genetic drift ( Sewell wright effect)?
The occurrence of characteristics in a population as a result of chance rather than natural selection; only occur in small populations.
- it is random/ non directional and only contributes to change in frequencies of alleles in a gene pool
What is the founder effect?
A type of genetic drift that occurs when a new population is formed by a small number of individuals; the small size of the sample can cause marked deviations in allele frequencies from the original population
What is migration?
- gene flow from one popular to another
- if immigrants from another country bring alleles not already in population allele frequencies for that gene will be altered
What are barriers to gene flow?
- environmental pressures that inhibit the amount of interbreeding in populations
- isolation results in development f seperate gene pools
Geographical barriers- oceans, mountains, large lake systems, deserts, expansive ice sheets ( most common barriers for early humans)
Sociocultural barriers- people of different religions, who speak different languages, economic statuses, educational backgrounds, social positions
What is population bottlenecking?
When populations are reduced to low numbers by disease, predation or periods of climate change. ( population crash is not selective but may affect all phenotypes equally)
- populations may recover ( having squeezed through a ‘bottleneck’ of low numbers) and return to previous levels but with reduced genetic diversity
How can organisms be ‘carried’ to an offshore island
Wind, ocean, human interference, animals, swimming, finding their way onto a boat,
Define 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 those characteristics on to subsequent generations.
What influences natural selection?
Selective pressures- any phenomena which impacts upon the behaviour and fitness of living organisms within a given environment
What are the types of selective pressures?
Abiotic ( non living) and biotic ( living)
Examples of abiotic pressures?
Access to water, ability of bodies to use water, access to clothing and shelter, exposure to UV
Examples of biotic pressures
Eg. Access to food, availability of mates, predators/ prey relationships, diseases
Define special creation?
Belief that God Individually created each species
Darwin’s theory of evolution was based on what 3 observations?
- variation: all members of a species may vary. Variations are passed on.
( favourable characteristics suited for environment = survival of the fittest)
- birth rate: all organisms reproduce at a rate far greater than that at which their food supply and other resources increase. ( normally resulting in overcrowding)
(Exessive birthrate + limited resources =struggle for existence )
- natures balance- although birth rate of organisms is high, each species numbers tended to remain at relatively constant level
Examples of natural selection in humans?
Ppl with long bodies and short limbs ( eskimos) have smaller SA in relation = lose heat less in very cold environments
Ppl with short bodies and long limbed ( black Africans have larger SA so lose heat more effectively and survive better in hotter environments
+ also sickle cell Armenia is an example ( presence of malaria acts as a selective agent for sickle cell allele)
What is a selective agent?
Any factor that causes the death of organisms with certain characteristics but has no effects on individuals without those characteristics
Speciation, isolation, variation and selection worksheet)
What are Genetic diseases
Diseases that result in changes to allele frequencies in a gene pool. An allele causing an inherited fatal disease is expected to gradually be eliminated from a population because people with the allele would die and would not pass it on to the next generation.
Eg, tay Sachs, sickle cell amenia ,thassemia
Cause of tay Sachs?
Causes: disorder of lipid metabolism that is inherited in an autosomal recessive pattern. Missing enzyme results in accumulation of fatty substance in nervous system.
Effects of tay Sachs?
lethal recessive condition, leads to early childhood death
Sufferers deal with muscle weakness, problems with coordination, rhythmic muscle contractions, stiff muscles, feeling faint or wasting away, difficulty swallowing, hearing loss, impaired voice, seizures, or vision loss
Mode of inheritance for tay Sachs ?
Populations which are most likely to be affected by tay Sachs?
Ashkenazi Jew population due to population being small and isolated while heterozygous form of tay Sachs has increased resistance to tuberculosis.
Causes Of Sickle cell Amenia
disorder of the blood caused by an inherited mutation in the gene hemoglobin. The abnormal hemoglobin causes distorted (sickled) red blood cells, red blood cells to become rigid, sticky and misshapen.
Effects of sickle cell amenia?
amenia - Sickle cells break apart easily and die leaving you without enough red blood cells
Pain- when sickle-shaped red blood cells block blood flow through tiny blood vessels to your chest, abdomen and joints, Pain can also occur in bones
swelling of hands and feet
Mode of inheritance for sickle cell amenia?
Autosomal recessive condition
Populations which are most likely to be affected by sickle cell amenia?
Africa and India
Causes of Thalassemia
Causes: Blood disorder characterized by less hemoglobin and fewer red blood cells in your body than normal. It’s caused by mutations in the DNA of cells that make hemoglobin, the mutations associated with thalassemia are passed from parents to children, it is an inherited disorder.
Effects of thalassemia?
-fewer haemoglobin and red blood cells, may cause amenia.
-Symptoms include fatigue, weakness, pale or yellowish skin, facial bone deformities, slow growth, abdominal swelling and dark urine
Mode of inheritance for thalassemia
Autosomal recessive inheritance
Populations which are most likely to be affected by thalassemia
occurs mostly in African-American populations, people of Mediterranean, particularly Greece and Italy. and in people of southeast Asian ancestry.
Example of geographical barrier
Eg. Early Indigenous Australians were isolated for thousands of years by ocean barriers that formed as sea levels rose
Example of sociocultural barriers?
Eg. Basque people fro, Pyrenees in France and Spain have a language that is unrelated to any other. They are characterised by distinctive features that remain in their populations including the blood type Rh- which accounts for 35% of basque people which is almost double to the rest of Europe. The language difference acts as a sociocultural barrier.
Example of random genetic Drift
Eg. Isolated populations of Bentinck and Mornington in gulf of Carpentaria, were originally part of the mainland before cut off by rising sea level. Scientists observed a great differences in allele frequency values for blood groups on the islands compared to the mainland. One allele was completely absent from the island population.
Example of population bottlenecking
Eg. Northern elephant seals due to being hunted which reduced their population to less than 20 at the end if the 19th century. Since then their population has grown to over 30,000 but as a result of bottleneck genetic variation has greatly reduced.
Example of founder effect
Eg.island population of Tristan da Cunha is an isolated group of islands in south Atlantic Ocean that migrated from Britain. There have been few migrations since and isolation has resulted in a gene pool very different to the current British population.