9.3 and 18.3 Genetic diversity and adaptation

Question 1

What is the main cause of variation

Answer 1

DNA
It determines many proteins that make up each organism
So similarities and differences between organisms are defined in terms of variation in DNA

Question 2

What is a gene

Answer 2

A section of DNA that codes for a specific polypeptide

Question 3

What do all members of the same species have in common

Answer 3

They have the same genes

Eg a gene for blood group, petal colour etc

It is the alleles of a gene that cause variation, so humans may have different alleles of blood group.

Question 4

What is genetic diversity

Answer 4

The total number of different alleles in a population

Question 5

What is a population

What is the difference between a species and a population

Answer 5

A group of individuals of the same species that live in the same place and can interbreed

A species consists of multiple populations

Question 6

What increases genetic diversity

Answer 6

The more alleles that all members of the species possess, the greater the genetic diversity of that species

So genetic diversity is reduced when a species have fewer different alleles

Question 7

Why is increased genetic diversity good

Answer 7

. More genetic diversity leads to more variation
. So it is more likely that the species will survive an environmental change (selection pressure)
. Because a wider range of alleles leads to a wider range of phenotypes/ characteristics
. So there is a greater probability that an individual will possess a characteristic that suits it to the new environmental conditions

Question 8

What does the process of evolution by means of natural selection depend on

Answer 8

. Depends on variety of phenotypes that selection operates against

. Genetic variety within the populations of all species

. Organisms producing more offspring than they can support with food etc so only the most well adapted ones survive and reproduce

Question 9

What are selection pressures

Answer 9

The environmental factors that limit a population of a species

Eg predation, disease, and competition

Question 10

How many alleles are there per gene

Answer 10

There are 2 alleles per gene
One from each parent

So both alleles together form the genotype for that specific gene

As they is an alternative forms of it

Question 11

What is natural selection

Answer 11

Not all alleles are passed down to the next generation, as not all the individuals that carry those alleles will reproduce successfully to pass the allele down.

So natural selection is a mechanism of evolution, where organisms more adapted to the environment are more likely to survive and reproduce to pass their alleles down

Question 12

Describe process of natural selection

Answer 12

. Within any species there is a gene pool which contains a wide variety of alleles

. Random mutation of alleles within this gene pool result in a new allele of a gene which is usually harmful

. But in certain environments, this new allele of a gene may give the individual that possesses it a selective advantage over others in the population

. These individuals have characteristics that are more adapted to the environment
so they will survive more due to obtaining all available resources etc

. They have a better chance of reproducing successfully to give this allele to the offspring, than other individuals who don’t have it

. As these new offspring have the advantageous allele they will survive and reproduce more successfully

. Over many generations, the number of individuals with this allele will increase at the expense of those without it

. So allele frequency of that advantageous one increases, whilst that of other non-advantageous one decreases

Question 13

What is a gene pool

Answer 13

The total number of alleles in a specific population at the same time

Question 14

What is allele frequency

Answer 14

How many of a specific allele there is in a gene pool

Question 15

What shape graph would there be if a species reproduced exponentially, so if there were no environmental selection pressures stopping it

Answer 15

It would be shaped like an exponential graph, so e^x in maths
Going through (0,1)

However in reality this isn’t the case as death rate must be extremely high for the populations to not grow by that much

This is why there are high reproductive rates in most species, so there are enough offspring to be the next generation, and this compensates for high death rates from predation, water, food, territory etc

However some species produce less offspring, but have lots of parental care and attention now so lower death rates help maintain their population size

Question 16

What is intraspecific competition

Answer 16

There are too many offspring for the available resources, so there is competition between the individuals for these limited resources

The greater the numbers, the greater this competition so more individuals die as they struggle to survive
So those who are better suited to conditions eg thick fur in the cold will be more likely to survive and breed, passing on their favourable alleles to next generation

Question 17

Why does allele frequency change between generations

Answer 17

Because selection pressures change between generations, so those with alleles that are more adapted to the environment will survive more and pass down these alleles

So the new generation contains alleles more adapted to the current conditions

Question 18

Why is variation important in natural selection

Answer 18

Variation provides the potential for a population to evolve and adapt to new circumstances

If there are any environment changes and selective pressures, if there are many genetically different individuals in the species…

There will always be a combination of genes (so phenotypes) to survive in a new set of circumstances

The larger a population, and more genetically varied it is , there is a higher chance of an individual who will have a combination of alleles that lead to a phenotype which is advantageous.

Populations with less variation are more vulnerable to new disease and climate changes.