Variation

Question 1

Natural selection

Answer 1

the process by which individuals with a particular set of alleles are more likely to survive and reproduce that those with other alleles
reduces allele frequency conferring a disadvantage

Question 2

define Population

Answer 2

group of individuals of the same species living in the same
area that can interbreed

Question 3

Selection pressure

Answer 3

is an environmental factor that affects the chance of survival of an organism

it increases chances of some alleles being passed on to the next generation and decreases chances of others

Question 4

Stabilizing selection

Answer 4

When natural selection keeps things as they are. A common phenotype remains
equally distributed mean

Question 5

Directional selection

Answer 5

If a new environmental factor or a new allele appears then natural selection may cause allele frequency to change over successive generation
one extreme phenotype

Question 6

Disruptive selection

Answer 6

Maintains different phenotypes (polymorphism) in a population

favors 2 extremes

Question 7

variation

Answer 7

presence of different characteristics
phenotypes results from interaction of genotype and environment

Phenotypic variation = Genetic variation + Environmental variation

VP = VG + VE

Question 8

continuous variation

Answer 8

normal distribution and many genes control the phenotype.

Genes have an additive effect of different alleles at a single gene locus

Type of data Quantitative

Range of phenotypes, many
intermediates

Environment has effect
Helps smooth the curve

Examples Height, mass

Question 9

Geographical isolation

Answer 9

Separation by a geographical barrier (Stretch of water or a mountain range)

Question 10

Reproduction isolation

Answer 10

The inability of 2 groups of organisms to breed with one another

Question 11

ecological separation

Answer 11

The separation between 2 populations because they live in different environments of the same and CANNOT breed together

Question 12

Behavioral separation

Answer 12

The separation of 2 populations because they have different behaviors which prevent them from breeding together

Question 13

Allopatric speciation

Answer 13

The development of new species following geographical isolation
(most common)

Question 14

sympatric speciation

Answer 14

the development of new species without any geographical separation

Question 15

biological species

Answer 15

A group of organisms with similar morphology and physiology which can breed together to produce fertile offspring

Question 16

Morphological species

Answer 16

A group of organisms that’s share many physical physical feature that distinguish them from other species

Question 17

ecological species

Answer 17

A population of individuals of the same species living in the same area at the same time

Question 18

discontinuous variation

Answer 18

Discontinuous distribution

controlling phenotype One / few genes (Monogenic) Many genes (Polygenic)

Effect of diff alleles at
single gene locus
Large
Diff genes have diff effects

Discrete categories, no
intermediates

Effect of environment
on phenotype Little or none

Examples Albinism, sickle cell anemia,

hemophilia, Huntington’s disease

Question 19

main source of genetic variation

Answer 19

1) Meiosis and fertilization
* Crossing over @ Prophase I
* Independent assortment @ Metaphase I
* Random fertilization / mating

2) Mutations!
* Primary source of variations
* Results in new alleles

Question 20

How the environment influences phenotype

Answer 20

Phenotype results from interaction of genotype and environment

Environmental factors that can influence phenotypes:
* Nutrients / diet
* Water availability
* Light intensity
* Disease / parasites
* Temperature
* Chemicals / mutagens
* Lifestyle and culture etc.

• Environment effect usually greater on polygenes
  → Polygenes = many genes controlling one trait
  → Phenotypes affected by environment often show continuous variation

Question 21

Bottle neck effect

Answer 21

• Large decrease in genetic diversity
  → Due to large decrease in population numbers

→ Common when natural disasters occur

→ But can occur due to overhunting / human activities too!
* Small group of survivors

→ Gene pool will not be representative
of gene pool of original population

→ Limited gene pool compared to previous
population

Question 22

Genetic drift

Answer 22

• Random process due to chance, unlike natural selection
  → Changes in allele frequencies fluctuate due to random events
  → Cannot be predicted
• Affects small populations more than large populations
  → Higher chance that allele will be lost from population

Migration → Founder effect
Natural disaster → Bottleneck effect

Question 23

founder effect

Answer 23

→ Become geographically isolated from
the larger population
* New population is established by a small number of individuals

→ Only carry a fraction of the alleles of the original population

→ Gene pool may not be representative of gene pool of original population

→ Lower genetic diversity than original population
* Over time, population may become genetically distinct from original
population

→ May develop into separate species = speciation

Question 24

Antibiotic Resistance

Answer 24

When antibiotics are no longer effective against bacteria
* Antibiotic resistance can be spread from bacteria to bacteria

E.g.
* Penicillin inhibits cross-link formation btwn peptidoglycans in
bacteria’s cell wall
* Many bacteria have penicillinase enzymes can break down penicillin
* Become resistant to penicillin

Question 25

Antibiotic Resistance is caused by

Answer 25

1. Spontaneous/random mutation in some bacteria * Mutation cause change in protein/production of new protein that cannot be targeted by antibiotics a) Antibiotic Resistance Chap 10 Recap Natural selection enables resistance genes to spread 2. Antibiotic is the selection pressure * Bacteria with allele coding for penicillinase has selective advantage * Antibiotics only kill bacteria that are non-resistant 3. Resistant bacteria more likely to survive and reproduce * More likely to pass down allele to offspring via binary fission 4. Over time, resistance allele frequency increases

Question 26

Industrial Melanism (key words)

Answer 26

→ Natural selection caused change in allele frequencies 1. Variation present (Black moths and speckled moths) 2. Selection pressure = Predation by birds * Industrial cities’ tree barks has a darker shade due to high pollutants * Black moths have selective advantage as they were more camouflaged * White moths are selected against 3. Black moths more likely to survive and reproduce * More likely to pass down allele to offspring 4. Over time, allele for black colour increased in frequency in industrial cities

Question 27

Sickle Cell Anaemia & Malaria allele

Answer 27

1. HSHS : Homozygous for sickle cell alleles * RBC cannot carry oxygen very well, may die from SCA * SCA selects against HSHS 2. HNHN :Homozygous for normal Hb allele * No SCA * Plasmodium parasite affects RBC * Malaria is lethal, so more likely to die from malaria * Malaria selects against HN HN 3. HNHS : Heterozygous for sickle cell allele * Have sickle cell trait * Do not die from SCA * Less likely to suffer severe effects of malaria * Contains less Plasmodium in their blood * Has selective advantage * More likely to survive and reproduce * More likely to pass on both HN and HS * Sickle cell allele is maintained within population because of sickle cell trait individuals

Question 28

The Hardy-Weinberg Principle and its requirments

Answer 28

Used to calculate allele, genotype and phenotype frequencies in populations 5 requirements of the principle: 1. The population is large 2. There is random mating within a population 3. No immigration or emigration 4. No mutations 5. No selection pressure against one genotype

Question 29

The Hardy-Weinberg Equation for alleles

Answer 29

p+q=1 p- Dominant allele q- recessive allele

Question 30

The Hardy-Weinberg Equation for genotypes

Answer 30

p² + 2pq + q² = 1

Question 31

Examples for evolution by natural selection

Answer 31

a) Antibiotic resistance in bacteria b) Industrial melanism in peppered moth c) Sickle cell anaemia

Question 32

Examples of Artificial Selection

Answer 32

a) Improving the milk yield of dairy cattle b) Disease resistance in varieties of wheat and rice c) The incorporation of mutant alleles for gibberellin synthesis into dwarf varieties d) Inbreeding and hybridization of maize

Question 33

The incorporation of mutant alleles for gibberellin synthesis into dwarf varieties

Answer 33

→ Incorporate mutant alleles for gibberellin synthesis into wheat by crossing shorter plants → Mutant alleles are of the reduced height gene → Mutant alleles code for faulty enzymes in GA synthesis pathway → Inhibit gibberellin synthesis → DELLA protein not broken down and continues to bind to transcription factor PIF → Inhibit transcription of growth genes → Dwarf variety