Genetics, populations, evolution, and ecosystems

Question 1

Allele

Answer 1

A version of a gene.

Question 2

Dominant

Answer 2

Describes an allele that is always expressed. Represented by a capital letter

Question 3

Diploid

Answer 3

Describes a cell with a nucleus containing two sets of chromosomes.

Question 4

Gene

Answer 4

A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA.

Question 5

Genotype

Answer 5

An organism’s genetic composition. Describes all alleles.

Question 6

Heterozygous

Answer 6

When someone has two different alleles of a gene e.g. Ff.

Question 7

Homozygous

Answer 7

When someone has two identical alleles of a gene e.g. ff.

Question 8

Locus

Answer 8

The position of a gene on a chromosome.

Question 9

Phenotype

Answer 9

An organism’s observable characteristics. Due to interactions of the genotype and the environment.

Question 10

Recessive

Answer 10

An allele that is only expressed in the absence of a dominant allele.

Question 11

Codominant

Answer 11

When both alleles for a gene in a heterozygous organism equally contribute to the phenotype.

Question 12

Dihybrid inheritance

Answer 12

The inheritance of two different genes, that determine two

phenotypes, on two different chromosomes.

Question 13

Monohybrid inheritance

Answer 13

When a phenotype or trait is controlled by a single gene.

Question 14

Example of codominance

Answer 14

shown in human ABO blood groups. There are three
alleles that are associated with the immunoglobulin gene (gene I). These lead to different
antigens on their surface, these are:
1. Allele IA - leads to the production of antigen A
2. Allele IB - leads to the production of antigen B
3. Allele Io - leads to the production of neither antigen A or B

Question 15

Sex linkage

Answer 15

the expression of an allele dependent on the gender of the individual as the gene is located on a sex chromosome.

Question 16

How many pairs of autosomal chromosomes do humans have?

Answer 16

22 pairs

Question 17

Example of sex linkage diseases

Answer 17

Haemophilia which is a disease in which the blood clots slowly and there may be slow and persistent internal bleeding, especially around
the joints. It is caused by a change to the DNA sequence resulting in a faulty protein being created.

Question 18

Why is the the haemophilia only inherited by the mother?

Answer 18

As a male can only obtain the Y chromosome
from his father, it means that the X chromosome
must come from his mother.

As this disease is not found on the Y chromosome it means that this disease is always inherited from the mother in
males. If the mother doesn’t suffer from the disease but is heterozygous with the alleles then she is a carrier.

Question 19

Autosomal linkage

Answer 19

Two or more genes are positioned on the same autosome. They

are unlikely to be separated by crossing over during meiosis so are often inherited together

Question 20

Epistasis

Answer 20

Describes a relationship between genes where the allele of one gene affects the expression of a different gene.

Question 21

Recessive epistasis

Answer 21

occurs when the presence of a recessive allele prevents the expression of another allele at a second locus.

Question 22

Dominant epistasis

Answer 22

Is when a dominant allele at one locus completely masks the alleles at a second locus.

Question 23

What is the ratio of Recessive epistasis?

Answer 23

9:3:4.

Question 24

What ratio does Dominant epistasis gives a ratio of?

Answer 24

12:3:1

Question 25

Chi-squared

Answer 25

is a statistical test which can be used to establish whether the difference
between observed and expected results is small enough to occur purely due to chance. It can be used to test the null hypothesis.

Question 26

Criteria of a null hypothesis

Answer 26

• The sample size must be sufficiently large enough, that is over 20.
• Used only for data that falls into discrete categories.
• Only raw counts and not percentages, rates, etc can be used

Question 27

Formula for chi-squared

Answer 27

x squared = sum of all (observed - expected)2 / expected

Question 28

What is the critical value

Answer 28

p=0.05
Where the value obtained is equal to or greater than the critical value, the null hypothesis is accepted as the difference due to chance is not significant. To read off the value though the degrees of freedom need to be known. These are simply the number of categories minus one.

Question 29

What happens if the value is less then the critical value?

Answer 29

The null hypothesis is rejected

Question 30

What happens if the value is equal or greater than the critical value

Answer 30

The null hypotheis is accepted

Question 31

Population

Answer 31

Is a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Question 32

Gene pool

Answer 32

The total number of alleles that are present in a population

Question 33

allelic frequency

Answer 33

Expresses as a decimal or percentage the proportion of a certain allele in a gene pool.

Question 34

Hardy-Weinberg Equation

Answer 34

Can be used to estimate the frequency of alleles in a population and to see whether a change in allele frequency is occurring in a population over
time.

Question 35

What are the 5 conditons for the proportion of dominant and recessive alleles of any gene is a population remains the same from one generation to the next?

Answer 35

• No mutations occur to create new alleles.
• There is no movement of alleles into or
  out of the population by migration.
• Population is large.
• No selection, so every allele has an equal chance of being passed to the
  next generation.
• Mating is random.

Question 36

What is the The formulae for Hardy-Weinberge?

Answer 36

p + q = 1.0 AND p² + 2pq + q² = 1

Question 37

What does the P stand for in the p+q=1.0 formulae

Answer 37

p = the frequency of the dominant allele (represented by A)

Question 38

What does the q stand for in the p+q=1.0 formulae?

Answer 38

q = the frequency of the recessive allele (represented by a)

Question 39

What does p² stand for in the 2pq + q² = 1 formulae?

Answer 39

q2 = frequency of aa (homozygous recessive)

Question 40

What does 2pq stand for in 2pq + q² = 1 formulae?

Answer 40

Frequency of Aa (heterozygous)

Question 41

There are variations in the alleles of genes for members of the same species due to a number of factors such as:

Answer 41

1. Random fertilisation - the gametes that are carrying different alleles will join together
   randomly.
2. Meiosis - meiosis is the nuclear division that creates gametes and means that the alleles will
   be assorted in the gametes at random.
3. Mutation - the mutation of an allele can go on to lead to the creation of another new allele
   which can then be passed to the next generation

Question 42

Niche

Answer 42

Describes how an organism ‘fits’ into an ecosystem and its role in that environment

Question 43

Intraspecific competition

Answer 43

A type of competition that takes place between members of the
same species.

Question 44

Interspecific competition

Answer 44

A type of competition that takes place between members of

different species.

Question 45

Selection

Answer 45

is the process by which individuals that are better adapted to their environment are more likely to survive and breed.

Question 46

Directional Selection

Answer 46

occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive

Question 47

Stabilising Selection

Answer 47

In stabilising selection the phenotypes with successful characteristics
are preserved and those of greater diversity are reduced.

Question 48

Disruptive Selection

Answer 48

A type of selection that favours individuals with extreme phenotypes
and selects against those with phenotypes close to the mean

Question 49

Speciation

Answer 49

the process by which new species arise after a population becomes separated and cannot interbreed.

Question 50

Allopatric speciation

Answer 50

A form of speciation that occurs when two populations become

geographically isolated. Results in the gene flow being reduced

Question 51

sympatric speciation

Answer 51

A form of speciation that occurs when two populations within the
same area become reproductively isolated.

Question 52

Ecosystem

Answer 52

The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions. It is a dynamic system.

Question 53

The abiotic factors that affect population growth are:

Answer 53

1. Temperature
2. Light
3. pH
4. Water and humidity

Question 54

Predator

Answer 54

An organism that eats other organisms.

Question 55

Prey

Answer 55

An organism that is eaten by predators.

Question 56

Predatorprey relationship and occurs as follows:

Answer 56

1. When the prey is eaten by the predator the population of the prey falls.
2. This results in the predator population growing, however means that more prey is consumed.
3. Therefore the population of prey reduces and there is increased competition for the the prey
   between the predators.
4. The lack of food for the predators means that the population falls meaning that less prey is
   eaten.
5. This allows the population of the prey to recover and therefore the cycle occurs over in a
   oscillating manner.

Question 57

The abundance of different species

can be measured in two main ways these are:

Answer 57

Percentage cover

Frequency

Question 58

Percentage cover

Answer 58

suitable for plants or algae whose individuals numbers are difficult to
count.

Question 59

Frequency

Answer 59

expressed as a decimal or percentage, and is the number of times an organism
appears in the sampling area

Question 60

mark-release-recapture

Answer 60

1. Known number of species is captured and marked in a way that doesn’t reduce their chance of survival.
2. These marked organisms are then released again into the same area they were caught.
3. After a suitable length of time another known number of organisms are captured, with the number of these that are marked being recored

Question 61

Population can be estimated using the following equation:

Answer 61

Estimated population size = Total number of individuals in the first sample X Total number of individuals in the second sample/ Number of marked individuals recaptured

Question 61

Population can be estimated using the following equation:

Answer 61

Estimated population size = Total number of individuals in the first sample X Total number of individuals in the second sample/ Number of marked individuals recaptured

Question 62

Succession

Answer 62

Describes changes in the community of organisms occupying a certain area over time.

Question 63

Primary succession

Answer 63

occurs when area previously devoid of life is colonised by communities of organisms. E.g after the eruption of a volcano which lead
to formation of a rock surface.

Question 64

Secondary succession

Answer 64

occurs in a previously colonised area in which an existing community has
been cleared. This type of succession can occur after events such as forest fires.

Question 65

Conservation

Answer 65

The human management of the Earth’s resources and typically involves the managing of succession. E.g the controlled burning of land is done in order to stop the formation of a climax community.