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IGCSE Biology > B11.4 : Variation and Selection > Flashcards

B11.4 : Variation and Selection Flashcards

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1
Q

Phenotypic variation

A
  1. People vary in many things including intelligence, hair, blood type, etc
  2. Differences between the features of different individuals are called phenotypic variation
  3. Phenotypic variation is variation from both genetics and the environment
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2
Q

Types of variation

A
  1. Discontinuous variation

2. continuous variation

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3
Q

Variation

A

Within a species, variation describes differences in the characteristics of individuals.

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4
Q

Genetic variation

A
  1. Genetics (inherited genes).
  2. Most genetic variation is the result of mutations, some of which are then inherited and passed onto the next generation.
  3. Humans are different because their genotypes are different. That difference is known as genetic variation
  4. e.g. blood type, gender
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5
Q

Things variation can be a result of

A
  1. Genetics

2. Environment

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6
Q

Environmental variation

A
  1. The conditions in which the organism developed.
  2. Variation occurs because of the difference between the environments of individuals
  3. e.g. pine trees possess genes that enable them to grow to about 30m but if it is in a small pot, their genes are pruned so they are permanently stunted making it not grow till 30m
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7
Q

Discontinuous variation

A
  1. Discontinuous variation results in a limited number of phenotypes with no intermediates.
  2. E.g tongue rolling is either an ability you have, or not.
  3. Discontinuous variation is mostly caused by genes alone.
  4. E.g. A, B, AB, and O blood groups in humans. There are no in-between categories
  5. Often caused by genes along
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8
Q

Continuous variation

A
  1. Continuous variation results in a range of phenotypes between two extremes.
  2. E.g. height in humans as there is no definite height that a person must be. People vary in height
  3. Variation is often caused by both genes and environment
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9
Q

Mutations

A
  1. In sexually reproducing populations, many different combinations of alleles are present, meaning that variation is high.
  2. Whilst sexual reproduction is capable of shuffling pre-existing alleles, only mutations (genetic changes) can generate new alleles.
  3. They happen very rarely but often for no reason
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10
Q

Do mutations always affect the phenotype?

A
  1. Most mutations do not affect the phenotype.
  2. Of the small number that do affect the phenotype, it is rare that the phenotypic change will give a significant survival advantage.
  3. If a new mutation generates a new phenotype that’s more adapted to a recent environmental change than the rest of the population, the mutation will likely spread throughout the population over a small number of generations.
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11
Q

What rate do mutations happen at?

A
  1. Mutations are rare.
  2. The rate of mutations can be increased by ionising radiation and some chemicals.
  3. Ionising radiation can increase mutation because radiation can damage the bases in DNA molecules. If this happens in the testes or ovaries, then the altered DNA may be passed on to the offspring
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12
Q

How can mutations lead to human evolution?

A
  1. Most mutations (permanent changes in nucleotide sequences of DNA) do not affect the phenotype.
  2. But if a mutation creates a new phenotype that is better adapted to environmental changes (than the rest of the population), the mutation is likely to spread throughout the population over a small number of generations.
  3. For example, over time the size of the human brain has increased, as those born with a bigger brain were found to be at a survival advantage.
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13
Q

Natural Selection

A
  1. Charles Darwin’s theory of natural selection proposed that all species have evolved from simple life forms that first appeared on Earth more than three billion years ago.
  2. It suggests that the best-adapted organisms are selected to pass on their characteristics to the next generation
  3. This process continues over time, generation after generation, gradually, the individuals in successive generations of a species gain more and more advantageous features - that is, features that adapt them to their environment
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14
Q

Genetic variation in natural selection

A

Different individual animals in a population (or species) have different combinations of genes (show genetic variation).

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15
Q

Survival of the fittest

A

Individuals that are best adapted to the environment will have a greater chance of survival.

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16
Q

Successful breeding

A

Individuals with the best chances of survival are the most likely to breed successfully (because they survive).

17
Q

Characteristics in natural selection

A

The characteristics responsible for the greater chance of survival are more likely to be passed on to the next generation.

18
Q

Evolution

A
  1. Evolution explains the origin of life we see today.
  2. Evolution can be defined as the gradual change in adaptive features of a population over many generations, as a result of natural selection.
  3. The process of adaptation results in populations becoming more suited to their environment over many generations.
  4. Natural selection leads to evolution
19
Q

Antibiotic Resistance

A
  1. Within a population of bacteria, some will have random mutations (random change in DNA).
  2. The mutated bacteria are resistant to antibiotics and so they are able to survive, whilst the non-resistant bacteria die.
  3. The resistant bacteria can reproduce rapidly because their competition (non-resistant bacteria) has been destroyed by the antibiotic.
  4. The bacteria with the resistance survive and they reproduce.breed and the resistant allele is passed onto offspring
  5. they produce genetically-identical copies. These copies will all be resistant to the antibiotics.
20
Q

Artificial selection

A
  1. In artificial selection, a deliberate choice is made by humans as to which individuals reproduce together.
  2. This is why it is also known as selective breeding.
  3. e.g. Getting strong, fast racehorses to reproduce
  4. It is not an example of adaptation as adaptation results from natural selection and not artificial selection
21
Q

Why selective breeding?

A

Selective breeding is carried out to produce desirable characteristics in the offspring.

22
Q

History of selective breeding

A
  1. Humans have done this in farming for thousands of years (with both crops and animals) to promote the genetic characteristics that we view as desirable.
  2. This practice was around even before genetics was understood.
23
Q

Organisms used in selective breeding

A
  1. Dogs/Cats
  2. Farm animals
  3. Crops
  4. Flowers
24
Q

Selective Breeding process

A
  1. Choose parents who most strongly display the desired characteristic.
  2. Breed the chosen parents.
  3. From the resultant offspring (children), choose the offspring that best display the desired characteristic.
  4. Breed these chosen offspring.
  5. Repeat this process of breeding and re-selection over many generations until all the offspring show the desired characteristic. (must be done repeatedly)
25
Q

Uses of selective breeding

A
  1. In animals
  2. For crops
  3. For dogs
  4. For flowers
26
Q

Selective breeding for animals

A

In farming, animals that produce more milk or meat are also useful for yield-related reasons.

27
Q

Selective breeding for dogs

A
  1. Gentle-natured domestic dogs are useful as these animals must co-exist (live with) with humans.
  2. e.g. breeding a labrador and a poodle to create labradoodles.
28
Q

Selective breeding for crops

A

Disease resistance in food crops is a useful characteristic because it improves yield (food production productivity).

29
Q

Selective breeding for animals

A

In farming, animals that produce more milk or meat are also useful for yield-related reasons.

30
Q

Normal distribution curve

A
  1. A graph that measures and records continuous variation

2. Most people will come in the middle of the range, but a few will be at the upper and lower ends

31
Q

Causes of genetic variation

A
  1. Mutation
  2. Meiosis
  3. Fertilisation
32
Q

Mutagens

A
  1. Heavy metals like lead and mercury and their compounds can also interfere with the process in which DNA is copied.
  2. If this process goes wrong, the daughter cells will get faulty DNA when the cell divides
  3. Chemicals that cause mutations are called mutagens
33
Q

Meiosis leading to genetic variation

A
  1. During sexual reproduction, gametes are formed by meiosis
  2. In meiosis, homologous chromosomes exchange genes, and separate from one another so the gametes which are formed are not all exactly the same
  3. The new cells are genetically different from the parent cell leading to genetic variation
34
Q

Fertilisation leading to genetic variation

A
  1. Any two gametes of opposite types can fuse together at fertilisation, so there are many possible combinations of genes which may be produced in the zygote
  2. An organism with a large number of genes, the possibility of two offspring having identical genotypes is so small that i can be considered almost zero
  3. This could possibly lead to genetic variation
35
Q

Over-production

A

Most organisms produce more young than will survive to adulthood

36
Q

Natural selection Requirements

A
  1. Variation within populations
  2. production of many offspring
  3. struggle for survival
  4. competition for resources
  5. Advantageous characteristics passed on to offspring
  6. Gradual change
  7. Passing on of their alleles to the next generation
37
Q

Struggle for existence

A

Most populations do not generally increase rapidly in size, so there must be considerable competition for survival between the organisms

38
Q

Gradual change

A
  1. Over a period of time, the population will lose all the poorly adapted individuals
  2. The population will gradually become better adapted to its environment
39
Q

Differences and similarities between selective breeding and natural selection

A
  1. Similarity: features are inherited

2. Difference: humans select the feature vs environment selecting the feature

IGCSE Biology (31 decks)

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