B11.4 : Variation and Selection

Question 1

Phenotypic variation

Answer 1

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

Question 2

Types of variation

Answer 2

1. Discontinuous variation

2. continuous variation

Question 3

Variation

Answer 3

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

Question 4

Genetic variation

Answer 4

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

Question 5

Things variation can be a result of

Answer 5

1. Genetics

2. Environment

Question 6

Environmental variation

Answer 6

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

Question 7

Discontinuous variation

Answer 7

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

Question 8

Continuous variation

Answer 8

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

Question 9

Mutations

Answer 9

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

Question 10

Do mutations always affect the phenotype?

Answer 10

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.

Question 11

What rate do mutations happen at?

Answer 11

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

Question 12

How can mutations lead to human evolution?

Answer 12

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.

Question 13

Natural Selection

Answer 13

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

Question 14

Genetic variation in natural selection

Answer 14

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

Question 15

Survival of the fittest

Answer 15

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

Question 16

Successful breeding

Answer 16

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

Question 17

Characteristics in natural selection

Answer 17

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

Question 18

Evolution

Answer 18

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

Question 19

Antibiotic Resistance

Answer 19

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.

Question 20

Artificial selection

Answer 20

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

Question 21

Why selective breeding?

Answer 21

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

Question 22

History of selective breeding

Answer 22

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.

Question 23

Organisms used in selective breeding

Answer 23

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

Question 24

Selective Breeding process

Answer 24

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)

Question 25

Uses of selective breeding

Answer 25

1. In animals 2. For crops 3. For dogs 4. For flowers

Question 26

Selective breeding for animals

Answer 26

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

Question 27

Selective breeding for dogs

Answer 27

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.

Question 28

Selective breeding for crops

Answer 28

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

Question 29

Selective breeding for animals

Answer 29

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

Question 30

Normal distribution curve

Answer 30

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

Question 31

Causes of genetic variation

Answer 31

1. Mutation 2. Meiosis 3. Fertilisation

Question 32

Mutagens

Answer 32

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

Question 33

Meiosis leading to genetic variation

Answer 33

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

Question 34

Fertilisation leading to genetic variation

Answer 34

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

Question 35

Over-production

Answer 35

Most organisms produce more young than will survive to adulthood

Question 36

Natural selection Requirements

Answer 36

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

Question 37

Struggle for existence

Answer 37

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

Question 38

Gradual change

Answer 38

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

Question 39

Differences and similarities between selective breeding and natural selection

Answer 39

1. Similarity: features are inherited | 2. Difference: humans select the feature vs environment selecting the feature