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Biology IGCSE CIE Extended > Variation and Selection > Flashcards

Variation and Selection Flashcards

1
Q

What is variation?

A

Variation is defined as differences between individuals of the same species

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2
Q

What is phenotypic variation?

A

Phenotypic variation is the difference in features between individuals of the same species

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3
Q

What is genetic variation?

A

Some of these differences are caused by differences in genes, which is genetic variation

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4
Q

What two types of phenotypic variation are there and how are they divided?

A

Phenotypic variation can be divided into two types depending on how you are able to group the measurements:
continuous and discontinuous variation

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5
Q

What is continuous variation?

A

Continuous Variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale

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6
Q

What are examples of continuous variation?

A

Examples include height, mass, finger length etc. where there can be many ‘inbetween’ groups

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7
Q

What is discontinuous variation?

A

Discontinuous Variation is when there are distinct differences for a characteristic

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8
Q

What are examples of discontinuous variation?

A

For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not – there are no ‘inbetweens’

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9
Q

What two things can cause phenotypic variation?

A

Phenotypic variation can be caused in two main ways:
It can be genetic – controlled entirely by genes
Or it can be environmental – caused entirely by the environment in which the organism lives

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10
Q

What are examples of genetic variation in humans?

A 
blood group
eye colour
gender
ability to roll tongue
whether ear lobes are free or fixed
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11
Q

What are examples of environmental variation?

A

Examples include:

  • An accident may lead to scarring on the body
  • Eating too much and not leading an active lifestyle will cause weight gain
  • Being raised in a certain country will cause you to speak a certain language with a certain accent
  • A plant in the shade of a big tree will grow taller to reach more light
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12
Q

What environmental factors may affect variation?

A

Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle

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13
Q

What type of variation is discontinuous variation caused by?

A

Discontinuous variation is usually caused by genetic variation alone

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14
Q

What types of variation cause continuous features?

A

Continuous features often vary because of a combination of genetic and environmental causes

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15
Q

What is an example of a combination of genetic and environmental variation which leads to continuous variation?

A
  • tall parents will pass genes to their children for height
  • their children have the genetic potential to also be tall
  • however if their diet is poor then they will not grow very well
  • therefore their environment also has an impact on their height
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16
Q

What are mutations?

A

Mutations are random genetic changes

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17
Q

Do mutations affect the phenotype?

A

Most mutations have no effect on the phenotype as the protein that a mutated gene produces may work just as well as the protein from the non – mutated gene

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18
Q

Can mutations lead to development of new alleles? What effect do they have?

A

Rarely, mutations lead to the development of new alleles and so new phenotypes and if they do, most have a small effect on the organism

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19
Q

Can mutations be useful? How?

A

Occasionally, the new allele gives the individual a survival advantage over other members of the species
For example:
A bird develops a mutation leading to a change in feather colours
This makes it more attractive to birds of the opposite sex
Which causes the bird to breed more frequently and have more chances of passing on the mutated phenotype to the next generation

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20
Q

Can mutations be harmful? How?

A

Mutations can also lead to harmful changes that can have dramatic effects on the body – for example, sickle cell anaemia in human

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21
Q

What two words can describe mutations?

A

Mutations happen spontaneously and continuously

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22
Q

What can increase the frequency of mutations?

A

their frequency can be increased by exposure to the following:
Gamma rays, x – rays and ultraviolet rays – all types of ionising radiation which can damage bonds and cause changes in base sequences
Certain types of chemicals – for example chemicals such as tar in tobacco

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23
Q

Why are increased rate of mutations bad?

A

Increased rates of mutation can cause cells to become cancerous, which is why the above are linked to increased incidence of different types of cancer

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24
Q

What type of mutation results in sickle cell anaemia?

A

Sickle cell anaemia was the first genetic disease to be described in terms of a gene mutation

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25
What is a gene mutation?
A gene mutation is a change in the base sequence of DNA
26
How does the mutation change cells in sickle cell anaemia?
The mutation changes the molecule haemoglobin
27
What effects do the mutations have on the red blood cells?
causing the red blood cells (RBC’s) to become stiff and sometimes sickle-shaped when they release oxygen to the body tissues
28
What can happen to the red blood cells due to their shape?
The sickled cells tend to get stuck in narrow blood vessels, blocking the flow of blood As a result, those with sickle cell disease suffer painful “crises” in their joints and bones
29
What things may people with SCA suffer from?
They may suffer strokes, blindness, or damage to the lungs, kidneys, or heart. They must often be hospitalized for blood transfusions and are at risk for a life-threatening complication called acute chest syndrome
30
How long do people with SCA live with?
Although many sufferers of sickle cell disease die before the age of 20, modern medical treatments can sometimes prolong these individuals’ lives into their 40s and 50s
31
What two versions of the gene are important for sickle cell anaemia?
There are two versions or alleles of the gene important for the inheritance of sickle cell anaemia : A and S
32
Are the A and S alleles codominant?
The two alleles are codominant, meaning there is no ‘dominant’ or ‘recessive’ version of the gene
33
How would you represent someone having normal haemoglobin?
Individuals with two A alleles (HbAHbA) have normal haemoglobin, and therefore normal RBCs
34
How would you represent someone having SCA?
Those with two S alleles (HbSHbS) develop sickle cell anaemia
35
How would you represent someone being heterozygous for SCA?
Those who are heterozygous for sickle cell (HbAHbS)
36
What type of RBC's do people who are heterozygous for SCA have?
produce both normal and abnormal haemoglobin (as the alleles are codominant)
37
What symptoms do people who are heterozygous for SCA have?
Heterozygous individuals are usually healthy, but they may suffer some symptoms of sickle cell anaemia under conditions of low blood oxygen, such as high altitudes or during exercise
38
What are people who are heterozygous for SCA called?
Heterozygous individuals are said to be ‘carriers’ of the sickle cell gene and are said to have ‘sickle cell trait’
39
What other illness is SCA related with?
malaria
40
How many people in USA are affected by SCA?
In the United States, about 1 in 500 African-Americans develops sickle cell anaemia
41
How many people in Africa are affected by SCA?
In Africa, about 1 in 100 individuals develops the disease
42
What is malaria?
Malaria is a disease spread by mosquitoes that are endemic in many areas of Africa
43
How many deaths does malaria cause?
causes over 1 million deaths per year
44
What relation is there between malaria and anaemia?
African children who are heterozygous for the sickle cell allele have a ten-fold reduction in their risk of getting malaria This means that there is a strong correlation between the prevalence of sickle cell anaemia in areas of the world where malaria is common
45
What is an adaptive feature?
An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment ( inherited functional features of an organism that increase its fitness)
46
What does fitness mean?
Fitness is the probability of an organism surviving and reproducing in the environment in which it is found
47
What are hydrophytes?
Plants adapted to live in extremely wet conditions
48
What are 3 common adaptations of hydrophytes?
- large air spaces in their leaves - small roots - stomata mainly found in the upper epidermis
49
Why do hydrophytes have large air spaces in their leaves ?
Large air spaces in their leaves to keep them close to the surface of the water where there is more light for photosynthesis
50
Why do hydrophytes have small roots?
Small roots as they can also extract nutrients from the surrounding water through their tissues
51
Why do hydrophytes have stomata mainly found in the upper epidermis ?
Stomata usually open all the time and mainly found on the upper epidermis of the leaf where they can exchange gases much more easily with the air
52
What are xerophytes?
Plant adapted to live in extremely dry conditions
53
What are 6 adaptations of xerophytes?
- thick waxy cuticle - sunken stomata - leaf rolled with stomata inside - small leaves - extensive shallow roots - thickened leaves or stems
54
Why do xerophytes have a thick waxy cuticle ?
the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers temperature
55
Why do xerophytes have sunken stomata ?
stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces evaporation rate
56
Why do xerophytes have leaf rolled with stomata inside ?
Leaf rolled with stomata inside and an inner surface covered in hairs – traps moist air and prevents air movement across stomata which reduces transpiration
57
Why do xerophytes have small leaves ?
many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
58
Why do xerophytes have extensive shallow roots ?
allowing for the quick absorption of large quantities of water when it rains
59
Why do xerophytes have thickened leaves or stems ?
contain cells that store water
60
What does selective breeding mean?
Selective breeding means to select individuals with desirable characteristics and breed them together
61
Why is selective breeding not only done once?
The process doesn’t stop there though because it’s likely that not all of the offspring will show the characteristics you want so offspring that do show the desired characteristics are selected and bred together
62
At what point can one determine that selective breeding is successful?
This process has to be repeated for many successive generations before you can definitely say you have a ‘new breed’ which will reliably show those selected characteristics in all offspring
63
What is the difference between natural and artificial selection relating to how it occurs?
NS - occurs naturally | AS - only occurs when humans intervene
64
What is the difference between natural and artificial selection relating to how it develops populations and their features?
NS - results in development of populations with features that are better adapted to their environment and survival AS - Results in development of populations with features that are useful to humans and not necessarily to survival of the individual
65
What is the difference between natural and artificial selection relating to how long it takes?
NS - takes a long time to occur AS - takes less time as only individuals with the desired features are allowed to reproduce
66
For what reasons may crops be selectively bred? 5
- disease resistance in food crops - increased crop yield - hardiness to weather conditions (e.g. drought tolerance) - better tasting fruits - large or unusual flowers
67
What is an example of a selectively bred plant and what has it produced?
An example of a plant that has been selectively bred in multiple ways is wild brassica, which has given rise to cauliflower, cabbage, broccoli, brussel sprouts, kale and kohlrabi:
68
How is selective breeding of animals carried out?
Individuals with the characteristics you want are bred together Offspring that show the desired characteristics are selected and bred together
69
Why, during selective breeding, are several different parents often bred together?
ften several different parents all with the desired characteristics are chosen so siblings do not have to be bred together in the next generation
70
How may cows be selectively bred?
cows that produce lots of milk or meat
71
How may chickens be selectively bred?
chickens that lay large eggs
72
How may domestic dogs be selectively bred?
domestic dogs that have a gentle nature
73
How may sheep be selectively bred?
sheep with good quality wool
74
How may horses be selectively bred?
horses with fine features and a very fast pace
75
What is an example of a selectively bred animal that has led to many different characteristics?
An example of an animal that has been selectively bred by humans in many ways to produce breeds with many different characteristics is the domestic dog, all breeds of which are descended from wolves
76
1. In any environment, which individuals are likely to survive? What does this result in?
In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce This results in natural selection:
77
2. Are all individuals in a species the same? | What is this caused by?
NO | Individuals in a species show a range of variation caused by differences in genes
78
3. How much offspring do organisms produce?
When organisms reproduce, they produce more offspring than the environment is able to support
79
4. What does organisms having a large number of offspring result in?
This leads to competition for food and other resources which results in a ‘struggle for survival’
80
5. What individual will survive this?
Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
81
6. Which type of individual will increase in number and why?
This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics
82
7. How are these adaptations passed down?
the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
83
8. What is this theory called? (NS)
This theory of natural selection was put forward by Charles Darwin and became known as ‘survival of the fittest’
84
What is chance mutation?
Random mutation that leads to a change in the features of the snail
85
Will selection change if the environment doesn't change?
If the environment does not change, selection does NOT change
86
1. What individuals will be favoured if the environment doesn't change? (evolution)
This will favour individuals with the same characteristics as their parents
87
2. What will happen if the environment changes or a chance mutation occurs? (evolution)
If the environment changes, or a chance mutation produces a new allele, selection might now favour individuals with different characteristics or with the new allele
88
3. What will be passed onto the offspring? | evolution
So the individuals that survive and reproduce will have a different set of alleles that they pass on to their offspring
89
4. What will the offspring having a different set of alleles result in? (evolution)
Over time, this will bring about a change in the characteristics of the species – it will produce evolution
90
What is evolution defined as?
Evolution is defined as the change in adaptive features of a population over time as a result of natural selection
91
What process does natural selection result in and what is it?
Natural selection results in a process of adaptation, which means that, over generations, those features that are better adapted to the environment become more common
92
What does process of adaptation overall do?
This means populations of organisms become better suited to their environment
93
What is an example of natural selection?
A good example of this is the development of antibiotic resistance by bacteria
94
1.What is an antibiotic? | antibiotic resistance
An antibiotic is a chemical that can kill or inhibit the growth and reproduction of bacteria
95
2.Why do we need antibiotics? | antibiotic resistance
They are extremely useful to humans as some bacteria are pathogenic and can cause life-threatening disease
96
3. How often do bacteria reproduce and what does this aid/result in? (antibiotic resistance)
Bacteria reproduce, on average, every 20 minutes and therefore evolution occurs in a much shorter time span
97
4. What process will be found in this population of bacteria? (antibiotic resistance)
Like all other organisms, within a population there will be variation caused by mutation
98
5. What may cause antibiotic resistance? | antibiotic resistance
A chance mutation might cause some bacteria to become resistant to an antibiotic (eg penicillin)
99
6. What happens when a population of bacteria with non/antibiotic-resistant bacteria is treated with an antibiotic? (antibiotic resistance)
When the population is treated with this antibiotic, the resistant bacteria do not die
100
7.What happens as a result of the non-antibiotic-reistant bacteria dying? (antibiotic resistance)
This means they (antibiotic-reistant bacteria) can continue to reproduce with less competition from non-resistant bacteria, which are now dead
101
8. What amount of bacteria in the next generation will be antibiotic-resistant and why? (antibiotic resistance)
Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment
102
9. Why is antibiotic-resistance considered natural selection? (antibiotic resistance)
This is an example of natural selection that humans have helped to develop due to overuse of antibiotics in situations where they were not really necessary
103
10. In what ways have humans helped create antibiotic-resistant bacteria? (antibiotic resistance)
for treatment of non-serious infections routine treatment to animals in agriculture failure to finish prescribed course of antibiotics
104
11. Why is antibiotic resistance a problem? | antibiotic resistance
Increases in the population of antibiotic-resistant bacteria cause infections and diseases which are harder to control as it is difficult to find antibiotics that certain strains of bacteria are not resistant to Adding to these difficulties, the number of new antibiotics discovered has slowed significantly
105
12. What is an example an antibiotic-resistant bacteria? | antibiotic resistance
An example of this is MRSA, a very dangerous bacterial strain that is resistant to most antibiotics If someone gets infected with MRSA they cannot be treated easily

Biology IGCSE CIE Extended (22 decks)

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