Mutations

Question 1

Homo sapiens

Answer 1

All humans belong to same genus and species which are called Homo sapiens

Question 2

Species

Answer 2

Group of living organisms that share many characteristics and are able to interbreed under natural conditions to produce fertile offspring

Question 3

Alleles

Answer 3

Alternative forms of a gene

Question 4

Population

Answer 4

Group of organisms of the same species living together in a particular place at a particular time

Question 5

Gene pool

Answer 5

Sum of all alleles carried by members of a population

Question 6

Allele frequencies

Answer 6

How often each allele of a gene occurs in a population,

Question 7

evolution

Answer 7

is the change in characterisitics of a species over time it is a gradual change that occurs over a number of generations rather than a change of a particular individual or generation

Question 8

once new alleles are introduced into a population allele frequencies change due to ?

Answer 8

natural selection - new trait has beneficial adavantages to selective pressures present in the population

chance - genetic drift occuring whereby the characterisitc does not provide a survival advantage

Question 9

how do changes to gene pool occur ?

Answer 9

new alleles forming as a result of mutations
- migration introducing new alleles into the population
- Once new alleles are introduced into a population allele frequencies change due to:
- natural selection - new trait is beneficial to selective pressures present in the population
chance- genetic drift occurs whereby the characteristic does not provide a survival advantage

Question 10

how do you tell mutation has occured in a offspring ?

Answer 10

mutations occur when an offspring show variations that do not resemble any parent and have not occurred before in the history of the family

they are the result of a new allele being formed this occurs when DNA is changed by a mutation which results in a different variation of the trait

not all mutations are harmful but many are

the individual who expresses a characteristic as a result of a mutation is called a mutant

Question 11

what are the two types of mutations ?

Answer 11

gene mutation : changes in a single gene so that traits normally produced by that gene are changed or destroyed . Occurs during replication of DNA before cell division

Chromosomal mutation: all or part of chromosome is affected

Question 12

how do mutations occur ?

Answer 12

if a mistake occurs spontaneously when the DNA molecule is copied during mitosis or meiosis or when the chromosomes are seperated during meiosis , the change may have significant effects on the functioning on the cell

however, many mutations are repaired, and therefore don’t cause a problem. If they do remain when the cell divides the mutated DNA will be copied and passed on to daughter cells.

if the daughter cells are gametes, the mutations may be passed on from generation to generation

Question 13

what causes mutations ?

Answer 13

Induced mutations: mutagens in the environment increase the chance of mutations occuring

spontaneous mutations: occur due to a random error in biological processes such as mitosis or meiosis

Question 14

mutagenic agents or mutagens

Answer 14

an agent known to increase rate at which mutations occur
known mutagens:
- mustard gas
- formaldehyde
- sulfur dioxide
- some anitbiotics
- ionising radiation ( UV light, X-rays, cosmic rays, radioactive waste
- cigarettes
- Benzene

Question 15

what are the mutations that occur in different types of cells ?

Answer 15

somatic and germline mutations
somatic occur in body cells
germline mutations occur in reproductive cells

Question 16

somatic mutations

Answer 16

mutations occuring in body cells ( somatic cells)
only the individual with somatice mutation is affected
each time mutant body cell divides, mutation is passed on to daughter cells
reproductive cells are not affected and once the individual dies mutation is lost

many cancerous growths involve somatic mutations

Question 17

germline mutations

Answer 17

reproductive cells are affected mutation can occur in gametes and may then be passed on to the next and subsequent generations

individual in whom mutation occurs is not usually affected however individual produces gametes with changed DNA

if conception occurs involving one of the affected gametes, embryo is often naturally aborted early in pregnancy .

Question 18

what type of point mutation causes changes to a gene ?

Answer 18

point mutations: change in a single nucleotide, just one base, can alter protein have no effect at all or prevent protein from being produced

if DNA of a particular gene is altered the protien for which it codes may be missing or abnormal just one missing or abnromal protien can have an enormous effect on entire body

Question 19

what are the different types of point mutations ?

Answer 19

substituition : where an exisitng nucleotide is replaced by another
inversion: two nucleotides are switched
insertion : a new nucleotide
is added to the DNA strand
Deletion : a nucleotide is removed from the DNA strand

Question 20

point mutations can cause frameshift mutations

Answer 20

occur when the addition ( insertion) or removal ( deletion) of a base alters the reading frame of the gene this change ( permance ) will affect every codon beyond the point of mutation and thus may dramatically change the amino acid sequence

Question 21

effects of point mutations

Answer 21

Missense mutations – cause a change in the amino acid, and therefore in the protein produced.

Nonsense mutations – change the base sequence to the code to STOP. This means that the synthesis of the protein will stop, and so a shorter protein is produced that is unlikely to be able to fulfil its function.

Neutral mutations – cause a change in an amino acid; however, the amino acid is of the same type (functionally similar) and does not change the structure of the protein enough to change its function. GAG (Glu) à GAC (Asp)

Silent mutations – do not cause any change in the amino acid, and therefore the protein produced. This is possible, as most amino acids are coded for by more than one base sequence. GAG (Glu) à GAA (Glu)

Question 22

gene mutations

Answer 22

Most gene mutations produce a recessive allele because they prevent gene from producing protein that will be able to function in the body.

A person could have a large number of mutations in the genes & be totally unaware of them. If this person reproduced with a partner had same recessive mutation, recessive condition could appear in offspring
This happens when couples unexpectedly have child with Cystic Fibrosis (both mother & father carry the recessive allele)

Question 23

examples of gene mutations

Answer 23

Albinism: result of one missing protein. Marked by an absence of pigment from hair, skin & eyes
Duchenne muscular dystrophy: May arise in gene mutation in mother, which can then be inherited by her sons. Mutation may also occur in male zygote and child develops condition. Results in wasting of leg muscles, arms, shoulders, chest.

Usually becomes apparent around age of 3 – 5 years. Death occurs due to failure of respiratory muscles. Death usually results at 20-25 years

Cystic Fibrosis: Mutation occurs in huge gene on chromosome number 7. Recessive (mutant allele passed from both parents). Gene has the code for 1480 amino acids that make up a protein that regulates passage of chloride ions across the cell membrane. Symptoms: salty tasting skin, persistent coughing, wheezing or pneumonia, digestive & other problems.

Question 24

lethal recessive

Answer 24

Lethal recessive: recessive mutation that is lethal if not masked by dominant normal allele. These cause death of embryo or foetus (a miscarriage or spontaneous abortion) or early death of child
Due to lethal recessive causing death of individuals, proportion of lethal recessive alleles in gene pool gradually is reduced

Question 25

lethal recessive examples

Answer 25

Tay-Sachs disease (TSD): disorder of lipid metabolism that is inherited in an autosomal recessive pattern. Missing enzyme results in accumulation of fatty substance in the nervous system. A baby with 2 recessive alleles for TSD develops normally for first few months, then deterioration causing mental & physical disabilities begin. Death usually occurs in early childhood

Sickle Cell Anaemia: Caused by gene mutation. Disease allele arose from a base substitution mutation (single base changed in gene sequence). The amino acid change alters structure of the haemoglobin (Hb), causing it to form insoluble fibrous strands. This Hb cannot carry O2 as effectively causing individual to feel constantly tired. Sickle cells form clots within capillaries & are destroyed more rapidly than normal cells, leading to a low RBC count (anaemia). Individual is homozygous recessive.

Question 26

chromosomal mutations

Answer 26

involve all or part of a chromosome and therefore affect not just one but a number of genes

chromosomal mutations cause abnormaltiies so severe that miscarriage often occurs early in pregnancy

Question 27

what are the types of chromosomal mutations

Answer 27

Deletion
*Duplication
*Insertion
*Inversion
*Translocation
*Non-disjunction

Question 28

deletion

Answer 28

Deletion: part of chromosome lost. Results in loss of a number of genes, it usually has a significant effect on individual’s development, often proving lethal

Question 29

inversion

Answer 29

Inversion: Breaks occur in chromosome & broken piece joins back in, but wrong way around. This changes order of genes on chromosome & may disrupt pairing of homologous chromosome during meiosis

Question 30

duplication and insertion

Answer 30

Duplication: a section of chromosome occurs twice (or more than once). This may happen if part of a chromatid breaks off & joins on to wrong chromatid.
Insertion: a section of a different chromosome is added a new chromosome.

Question 31

translocation

Answer 31

Translocation: part of a chromosome breaks off & is rejoined to wrong chromosome. Similar to crossing over, except it occurs between non-homologous chromosomes

Question 32

non-disjunction

Answer 32

Non-disjunction: during meiosis, a chromosome pair does not separate & so one daughter cell has an extra chromosome & one daughter cell has one less than normal number. These are sometimes not referred to as mutations but as aneuploidy (a change in chromosome number)

Question 33

examples of chromosomal mutations are

Answer 33

trisomy and monosomy

Question 34

diagnosis of chromosomal

Answer 34

Chromosomal abnormalities can frequently be diagnosed before birth by analysing cells in amniotic fluid or from the placenta

Chromosome analysis (blood sample, cells from amniotic fluid or placenta) would provide parents information about karyotype of foetus

Question 35

trisomy 21- down syndrome

Answer 35

Down syndrome (trisomy 21): child has 3 of chromosome 21 instead of normal 2. Results from non-disjunction. Affected gamete has an extra chromosome 21

Partial trisomy: Extra copy of chromosome 21 is attached to one of other chromosomes, resulting in many of the symptoms of Down syndrome

Question 36

trisomy 13 and 16

Answer 36

Patau syndrome (trisomy 13): extra chromosome 13 produces individuals with mental retardation, a small head, extra finger on each hand, cleft palate, malformations of ears & eyes. Features of trisomy 13 result from having extra chromosome in each of body’s cells. Occurs in about 1/ 5000 live births. More than 80% children with this condition die within a month of birth

Trisomy 16: most common trisomy in humans, occurring in more than 1% pregnancies. Condition usually results in spontaneous miscarriage in first 3 months of pregnancy

Question 37

trisomy in sex chromosomes

Answer 37

Trisomy can occur with sex chromosomes. In males, non-disjunction may occur either first or second meiotic division, producing individuals with either extra X chromosome (XXY) or an extra Y chromosome (XYY)

Individuals with trisomy XXY are normal as boys but develop Klinefelter’s syndrome as adults
Klinefelter’s syndrome: small testes that do not produce sperm, breasts are enlarged & body hair is sparse. Occasionally individual is mentally retarded. Affects about 1 in 650 men

Question 38

monosomy

Answer 38

Monosomy: where individual is missing chromosome
If autosome is completely missing, monosomy usually results in severe malformations & miscarriage
Partial monosomy: only part of chromosome is missing
Cri-du-chat (‘cry of the cat’) syndrome: rare genetic disorder due to a missing portion of chromosome 5. Infant sounds like a meowing

Question 39

monosomy in sex chromosomes

Answer 39

Turner’s syndrome: individuals with a chromosome set with only one X chromosome. Genotype is XO. Often individuals with this condition don’t survive pregnancy. These females are short in stature, lack secondary sex characteristics, are infertile

Question 40

what process contribute to variation in the gene pool

Answer 40

• non-disjunction : when one or more members of a chromosome pair fail to seperate during meiosis. Gametes then contain more or less than the correct number of chromosomes

random assortment of chromosomes:
occurs during meiosis are results in gametes that have a huge number of possible combinations of the chromosomes that originally came from the male and female parent

random fertilisation: each person produced a huge number of different gametes with respect to the number of alleles each contains and because any sperm can fertilse any egg there is an infinite number of possible combinations of alleles in the offspring

crossing over
occurs during meiosis and may result in pieces of chromatid being being broken off and attaching to a different chromatid Results in recombination of the alleles along the resulting chromosomes

mutation
permenanent change in DNA of a chromosome and may result in totally new characterisitics in an individual mutations in gametes can be passed from generation to generation

Question 41

large vs small populaations

Answer 41

feature : contribution of individual to the gene pool
small population it is a large contribution
for a large population it is a relatively small contribution

feature: adaptive/ non: adaptive changes in allele frequnency small population : often non-adaptive = random changes for large population it is adaptive changes.

feature : changes in allele frequency over time small populations more likely to change often as result of chance large population; tends to stay the same - more stable due to high frequency of favourable alleles

feature is speed of evoultion in small population can occur quite rapidly and in large populations occurs slowly

Question 42

what is the largest source of variation in the gene pool

Answer 42

mutations they introduce new and different alleles into the gene pool
if the new allele helps the individual survive, the allele frequency of the gene pool may change ( increase )

Question 43

gene flow

Answer 43

changes in allele grequencies in a gene pool cna also be due to gene flow brought about migration

gene flow is the movement of genetic material from one population to another
immigrants to a certain country can bring alleles that are not already in the population they immigrate to or they can alter exisitng allele frequencies

Question 44

barriers to gene flow

Answer 44

barrier inhibt the amount of interbreeding between them and preventing gene flow

this isolation leads to seperate gene pools forming

as no two environments are exaxtly the same the environmental pressures that one population experiances will be different to the other

this lead to particular characterisitcs ( alleles) being favoured in different populations and therefore altering the frequency of the alleles in each gene pool

in extreme cases isolation can lead to seperate gene pools in different location can lead to speciation

Question 45

types of barriers

Answer 45

oceans, mountain ranges, large lake systems, deserts and expansive ice sheets are geographical barriers

socio-cultural barriers
economic status, educational background, social position, religon and language

Question 46

natural selection

Answer 46

in a large population generally the allele frequency of the gene pool stays quite constant ( or similar) from one generation to another this is particulary evident in non-adaptive alleles-those that do not provide a survival advantage

when an allele provided a survival advantage we typically see the frequency of that allele increase and the non- favourable allele frequency decrease - this process is not random

natural selection occurs when nature favours on set of alleles over another. This causes major changes to the allele frequency in the gene pool of the population

Question 47

Darwin’s theory of Evolution through natural selection

Answer 47

1.Variation – All members of a species show variation/differences. These traits were passed down through generations where the characteristics of the parents were seen in their offspring.
2.Birth Rate – All living things reproduce at a rate that is greater than the rate at which their food supply and other resources increases. Normally this would result in overcrowding.
3.Natures Balance – Even though birth rate was very high, the number of individuals of each species remained relatively constant in the population

Question 48

survival of the fittest

Answer 48

Organisms with favourable characteristics survive and pass this favourable characteristic on to their offspring – increasing the allele frequency of the favourable/adaptive allele in the gene pool of the population.

Organisms with the un-favourable characteristic die and are unable to pass on this characteristic which decreases the allele frequency of the un-favourable allele in the gene pool of the population.
The environmental factor that acts on a populations and determines which characteristics are favourable is called the selective agent/factor.
This process is possible due to variation within the gene pool of a population.

Question 49

evouloution through natural selection

Answer 49

1. there is a variation of characterisitcs within a species
2. More offspring of a species are produced than can possibly survive to maturity
3. Because of excessive birth rate and limited resources, there is a struggle for exisitence - competition for survival
4. individuals with characterisitics best suited to the enviornment have more of a chance of surviving and reproducing - survival of the fittest
   5 favourable characterisitcs those with survival value are passed on to the next generation
   6 in the gene pool the porportion of alleles that produce favourbale characterisitcs gradually increases

Question 50

example of natural selection

Answer 50

Pigmentation of Skin
Why is it that people who originate from sunny regions have dark skin, whereas those from less sunny places have lighter skin?
Skin pigmentation is a good example of an adaptive feature (a feature that allows a person to survive in their natural environment).
Skin colour depends mainly on the amount of the pigment melanin. Melanin is produced by special skin cells called melanocytes. Production of melanin is catalysed by a number of enzymes.

Question 51

what are the survival advantages of pigmentation of the skin and of light skin ?

Answer 51

survival advantage
- melanin acts as a natural sunscreen
reduced risk of sunburn and skin cancer
- absorbs heat and activates sweating ( important for hunters?
- prevents folate deficiency ( associated with neural tube defects in babies, miscarriages and male fertility
reduces risk of damage to sweat glands

survival advantage of light skin
- most vitamin D is synthesised in the skin by the action of ultra violet radiation ( sunshine ) on carotene pigments
- melanin is a natural sunscreen so people with less of it can absorb more vitamin D than people with darker skin

• Vitamin D deficiency causes bone disease, rickets. People with lighter skin have less chance of rickets and therefore have stronger bones these people were probably better hunters and could obtain more food thus enabling them to survive harsh winters

Question 52

sickle-cell anaemia

Answer 52

The mutant gene responsible for the sickle cell condition is a potentially lethal gene but in some regions up to 40% of the population carries the gene. (most commonly found in people of African ancestry)
Due to a point mutation in one of the genes that codes for haemoglobin, the blood protein that carries oxygen.
shows CODOMINANCE – form of polymorphism (two or more forms)
HAHA – Homozygous normal RBCs
HAHS – Heterozygous normal (mild sickling)
HSHS – Homozygous sickle cell RBCS

Question 53

sickle -cell anaemia : homozygous recessive

Answer 53

People with sickle cell anaemia have inherited two copies of the recessive allele (HSHS).
This mutation causes the red blood cells to take on a sickle shape, rather than their characteristic donut shape.
Individuals who suffer from sickle cell anaemia are chronically anaemic, experience significant damage to their heart, lungs, and kidneys, and often die young (in infancy).

Question 54

sickle-cell anaemia: heterozygotes

Answer 54

People who inherit only one copy of the mutant allele (heterozygotes) have a mix of normal red blood cells and some abnormal cells.
These people are said to have the sickle cell trait and lead normal, healthy lives.
If oxygen is in short supply their red blood cells show mild sickling.

Question 55

sickle-cell anaemis: heterozygous advantage

Answer 55

People with sickle cell trait (heterozygous) have an improved immunity to malaria than people with the normal genotype (i.e. homozygous dominant) = heterozygous advantage for this selective agent.
The sickle cell mutation is believed to have occurred on several occasions in Africa in the past 150 000 years.
Malaria kills millions of people in Africa every year.
Most people with sickle cell trait live in the African malaria belt.
Since sickle cell trait provides some degree of immunity to malaria, the allele is maintained in this population.

Question 56

other conditions providing a heteroxygous advantage

Answer 56

tay-sachs disease= immunity to TB
Thalassemia=immunity to malaria

Question 57

what is random genetic drift RGD

Answer 57

random genetic drift is a random, non-directional variaiton in allele frequency
random genetic drift occurs in small populations

occurs when variant forms of a gene ( alleles increase or decrease by chance over time . this changes the allele frequences over time

Question 58

effects of RGD

Answer 58

Random Genetic drift can result in:
Traits being lost from small populations.
Unusual traits, not commonly found in the parent population, and that are often non-adaptive, becoming more frequent

and can only be amplified by differences in the number of children raised by couples or premature dying

Question 59

founder effect

Answer 59

occurs when a small number of people migrate away from their homeland and settle in a new area to establish a new community. This population then reproduces and members of the population increase

the migrant group being only a small sample of the original population usually not genetically representitative of them and generally shows less variation the new community therefore generally shows feature that are not typically with the original population

Question 60

bottleneck effect

Answer 60

situations which can cause a sudden drop in population size/ reduces mating possibilities include
- natural disasters
- wars
- migration
genetic bottleneck are a result of inbreeding bought about by limited mating possiblities

inbreeding can amplify desirable traits, but it can also greatly increase the risk of unusual, often harmful taits being expressed eg, haemophilia

Question 61

speciation

Answer 61

if two population are isolated for a very long time and the enviormental infleucnes on each other are different enough major changes in the allele frequencies within each population could occur

members of the two populations can become so different that even if the barriers to reproduction are removed interbreeding would no longer be possible a new species has formed
- called speciation

Question 62

speciation - the process

Answer 62

1. variation: range of variations exist within the population which shares a common gene pool
2. isolation: A barrier is formed which is divided the population interbreeding can occur Each population has a seperate gene pool
3. selection : different selection pressures exist in each population
   change in gene frequencies occurs due to natural selection
   evolution of a separate subspecies occurs

4.speciation: over long period of time gene frequencies are so different that interbreeding will no result in fertile offspring two new speicies are formed.