Mutations/evolution 2

Question 1

Define evolution

Answer 1

Change in characteristics of a species overtime due to changes in allele frequencies

Question 2

Distinguish difference between genotypes and phenotypes

Answer 2

phenotype: observable characteristics in an individual resulting from expression of gene

genotype: genetic makeup of an organism (specific alleles inherited for particular trait)

Question 3

Define population

Answer 3

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

Question 4

Define gene pool

Answer 4

sum of all alleles in a given population

Question 5

Define allele frequency. What can be determined by allele frequency variation

Answer 5

how common an allele is in a given population. Variation in allele frequencies reflect differences in characteristics

Question 6

Define mutation. What are the two main types

Answer 6

Change in the DNA sequence of an organism leading to new characteristics in said organism
- Chromosomal; effect multiple genes, therefore, all/part of chromosome affected. May change chrom. structure/number
- Gene; changes in single gene so traits normally produced by gene are destroyed/changed

Question 7

Explain the causes of organism mutations.
Include examples

Answer 7

May often occur spontaneously due to random errors in meiosis/mitosis or…
Mutagenic agents/mutagens- environmental agents that increase the rate of/induce mutation e.g. mustard gas, xrays

Question 8

How are mutations classified

Answer 8

1.Induced or spontaneous
2.Hereditary or not
3.Effect
4.Extent of mutation

Question 9

Define somatic mutations

Answer 9

Occur to all somatic/body cells excluding gametes.
Cannot be passed onto offspring
Only tissues derived from the mutated cell are effected i.e. cancer

Question 10

Define germinal/germline mutations

Answer 10

Occur in gametes/reproductive cells
can be passed onto offspring/inherent
Every cell in entire organism will be effect
e.g. PKU(phenylketonuria-prevent AA phenylalanine breakdown

Question 11

What are the effects of protein mutations

Answer 11

Missense: change in the amino acid and therefore protein production

Nonsense: change in base sequence to code to STOP (synthesis of protein will stop=short, less well functioning strand)

Neutral: change in amino acid (same type) does not change the protein’s structure enough to alter it’s function

Silent: do not cause any change in amino acid and therefore protein produced

All substituted nucleotide

Question 12

Define point mutation. What are the three changes in DNA as a result of gene mutation

Answer 12

Due to change in single nucleotide (one base changed)
Substitutions-existing nucleotide replaced with another one, with different base
Insertion-new nucleotide added to DNA strand
Deletion-nucleotide removed from DNA strand

Question 13

Define frameshift. How does it occur

Answer 13

Result form point mutations-occurs when base is inserted/deleted and changes the way codons are read from point in DNA

Question 14

What changes in long DNA segments/chromosomes come as a result of chromosomal mutation

Answer 14

Duplication: section of chromosome occurs twice
Deletion: piece of DNA is removed
Inversion: breaks occur in a chromosome and the broken piece joins back in, but wrong way around
Translocation: part of chromosome breaks off and is re-joined to wrong chromosome
Non-disjunction: during meiosis, chromosome pair does not separate and so one daughter cell has extra chromosome and one daughter cell has one less than normal number (aneuplody)

Question 15

Conditions caused by gene mutation

Answer 15

Duchenne muscular dystrophy
Cystic fibrosis: inherited from both parents only. Salty skin taste, coughing, wheezing
Tay-sachs disease (lethal recessive)- fatal, inherant condition lethal if not masked by dominant allele. Death in early childhood due to disorder of lipid metabolism

Question 16

Conditions caused by chromosomal mutation

Answer 16

Trisomy (result of non-disjunction) failure of one or more chromatid separations in second division of meiosis=down syndrome or trisomy-21, child has three of chromosome-21
Monosomy missing a chromosome either full or partially.

Question 17

Define gene flow. Attachment to migration?

Answer 17

movement of alleles from one population to another through migration

Question 18

What are the barriers of gene flow? Include examples

Answer 18

Inhibit interbreeding between populations due to enforced isolation
Geographical: oceans, mountain ranges, large lake systems, deserts and expansive ice sheets.
Sociocultural: economic status, educational background, social position, religion and language, ethnic origin

Question 19

Define species

Answer 19

group of organisms that shares similar characteristics and are able to interbreed to produce fertile offspring

Question 20

Define geneticists

Answer 20

specialise in studying inheritance

Question 21

Define allele

Answer 21

alternate form of same gene

Question 22

Describe Darwins observations

Answer 22

Variation: all individual in species vary
Birth rate: organisms reproduce at a rate greater than that at which food supply and other resources increase
Natures balance: species numbers remain at a constant level despite high birth rate

Question 23

Define variation

Answer 23

The differences that exist between individuals of a population or species

Question 24

Describe survival of the fittest

Answer 24

Organisms with favourable characteristics will survive, while those with unfavourable died before reproducing and passing on trait

Question 25

Describe struggle for existence

Answer 25

due to larger birth-rate to resources and food available for all organisms, there is competition for resources

Question 26

Define selective agent

Answer 26

Any factor that cause death of organisms with certain characteristics, but which has no effect on individuals without those characteristics

Question 27

Define the principles of evolution/natural selection

Answer 27

1. Variation within species
2. More offspring produced than can survive till adulthood
3. Struggle for existence
4. Individuals with favourable characteristics will survive and reproduce
5. Favourable characteristics passed onto offspring
6. Proportion of favourable alleles gradually increases

Question 28

Provide and example of evolution due to natural selection
(e.g. body stature?)

Answer 28

Body stature
- long bodies and short limbs have smaller SA to body volume ratio
-less heat loss in cold environments
-survival advantage
Sickle cell anaemia
-immunity to malaria

Question 29

Explain how the incidence of sickle-cell alleles increase in areas prone to malaria

Answer 29

1. Variation in genes
2. More offspring than can survive adulthood
3. Struggle for existence
4. Individuals heterozygous for sickle cell anaemia were less susceptible to malaria = heterozygote advantage
5. Presence of malaria acted as selective agent for the sickle cell allele, where heterozygous individuals had selective advantage

Question 30

What are the symptoms and effects of sickle cell anaemia
What is it’s population frequency

Answer 30

Inflexible, crescent shaped sickle cell red blood cells cause blockage of blood vessels, fatigue, jaundice, heart failure, etc
-black african community

Question 31

What causes speciation? Describe the steps involved

Answer 31

Isolation prevents reproduction between two populations (no gene flow as a result), causing them to be regarded as separate species overtime
1. Variation: Variation between individuals of a species
2. Isolation: Populations of same species are isolated without gene flow (barriers w/examples)
3. Selection: no two environments same therefore each population is subjected to different selective agents
4. Speciation: Allele frequency changes until they become so different that the two groups no longer are able to interbreed and produce fertile offspring

Question 32

Define genetic drift. Differentiate it’s presence in opposingly sized populations.

Answer 32

Random, non-directional change in allele frequencies between generations, usually more noticeable in smaller populations.
Rare allele in large population can become frequent in small

Question 33

Describe founder effect (genetic drift) providing an example

Answer 33

When small groups move away from homeland to establish new, smaller population which later expands. Causes
- different allele frequency from original population
- decreased genetic variation

Bentley glass and dunkers
-religion opposed outside of group marriage, causing isolated breeding within population causing certain characteristics to become more common in comparison to surrounding society

Question 34

Describe bottle effect (genetic drift) providing an example

Answer 34

When population is sharply reduced due to an event such as a natural disaster.

Pingelap typhoon , population reduced to 20. One individual was heterozygous for achromatopsia. Due to isolated breeding, 5% population shares similar trait while surrounding society only 0.0033%

Question 35

What causes changes to allele frequencies

Answer 35

Selection pressures, random assortment, non-disjunction, crossing over, random fertilisation, mutation

Question 36

Define selection pressures

Answer 36

Factors that affect an organisms ability to survive within the environment

Question 37

Using Tay-Sachs disease as an example, outline what a lethal recessive is

Answer 37

fatal, inherant condition lethal if not masked by dominant allele. Death in early childhood due to disorder of lipid metabolism

Question 38

Describe Thalassemia and it’s population frequency

Answer 38

an autosomal recessive gene mutation (inherited disorder) caused when the body doesn’t make enough of a protein called hemoglobin
-mediterranean coast and S.E. africa