Biology 3.7– Genetics, populations, evolution and ecosystems

What is a phenotype?

The set of observable characteristics of an individual, resulting from the interaction of its genotype with the environment.

What is a gene?

A sequence of nucleotide basis that normally codes for a specific polypeptide.

Define codominant.

Both alleles contribute to the phenotype.

Define multiple alleles.

When a gene has more than two allele forms.

In a dihybrid cross with two heterozygous parents, what ratio will you get?

9:3:3:1

Describe how you draw a dihybrid cross.

1. Show the parental phenotypes

2. Show the parental genotypes

3. Show the gametes that can be produced

4. Use a Punnet square to show the possible combinations of gametes with the resulting genotypes of each offfspring

5. Indicate the phenotypes of each offspring

6. Work out the phenotype ratios

What is sex linkage?

Inheritance of a trait that’s determined by a gene carried on a sex chromosome.

What is autosomal linkage?

Inheritance of a trait that is determined by a gene carried on an autosome (body chromosome).

Explain X-linked recessive gene inheritance.

If a trait (e.g. colourblindness) is an X-linked trait, then two copies of the recessive allele are required to confer colourblindness in females (XX), whereas, in males (XY), only one recessive allele is required due to the absence of the non-homologous region on the Y chromosome.

Outline the process of meiosis.

1. Chromosomes replicate— interphase.

2. Chromosomes condense.

3. Chromosomes lineup on the equator in homologous pairs and form bivalents.

4. Crossing over occurs, producing new combinations of alleles.

5. Spindles attach to the centromere.

6. Spindle contract and pull homologous chromosomes to opposite poles.

7. Independent segregation occurs, producing different combinations of maternal and paternal alleles.

8. Cytoplasm and cell membrane divide, producing two daughter cells.

9. Chromosomes lineup along the equator.

10. Spindles attached to the centromere.

11. Spindles contract and pull homologous chromosomes to opposite poles.

12. Cytoplasm and cell membrane divide producing four non-genetically identical daughter cells.

What is genetic diversity?

The number of different alleles of genes in a population.

What are the two steps in meiosis that lead to genetic variation?

1. Crossing over: produces new combinations of alleles.

2. Independent segregation: produces different combinations of maternal and paternal alleles.

What is the gene pool?

All of the alleles of all of the genes within a population.

What are selection pressures?

Changes in the environment that can affect an organisms chance of survival.

What is an advantageous allele?

An allele which gives a survival advantage if inherited.

What is a random mutation?

A random change in DNA that can be beneficial harmful or have no effect.

What is allelic frequency?

The frequency of an allele occurring within a population.

Outline the process of natural selection.

1. Within a population, there is genetic variation caused by random mutations resulting in new alleles.

2. If selection pressures change, certain alleles may become advantageous.

3. Individuals that possess the advantageous alleles will survive, reproduce and pass the allele on to their offspring.

4. Over several generations, there’s an increase in allelic frequency.

What is stabilising selection?

• Occurs when the environment stays stable.

• The same alleles are selected for in successive generations.

• The average phenotype is selected for and both extreme phenotypes are selected against.

What is directional selection?

• A change in the environment results in the change in the selection pressures on the population.

• Previously disadvantageous alleles may be selected for.

• Selects for one extreme phenotype selecting against the other extreme and the average phenotypes.

• This is the evolutionary force of natural selection.

What is disruptive selection?

• It selects for both the extreme phenotypes and selects against the average phenotype.

• It leads to distinct sub populations of a species being formed.

What are the features of a pioneer species?

• Photosynthetic

• Asexual reproducers

• Produce many seeds/spores

• Can fix nitrogen from the atmosphere

• Tolerant to extreme conditions

Outline the process of succession.

1. Colonisation by the pioneer species.

2. This species changes the environment making it less hostile for the next species.

3. The pioneer species die and are decompose by saprobionts to release organic compounds to form soil.

4. The next species outcome the previous species.

5. All the time, a climax community forms.

6. The climax community stabilises over the time and shows increased biodiversity.

Define habitat.

The place where an organism usually lives.

Define ecosystem.

All the living and nonliving factors in an area and their interactions.

What are biotic factors?

Living things affecting organisms.

1. Intraspecific— prediction or competition between members of a species.

2. Interspecific— prediction or competition between species.

What are abiotic factors?

Nonliving factors affecting organisms, e.g. water, pH, humidity, light.

Define carrying capacity.

The maximum number of organisms an area can support.

Define species diversity.

The number of different species and the number of individuals of each species within any one community.

Define population.

A group of individuals of one species which occupy the same habitat at the same time and can interbreed.

Define community.

Several species which occupy the same habitat at the same time.

Define niche.

The role of an organism, and the biotic and abiotic factors that affect it.

Define ecosystem diversity.

The range of different habitats within a particular area and all the interactions between the biotic and abiotic factors.

Define biodiversity.

The range and variety of genes, species and habitats within a particular region.

Define species richness.

The number of different species that occupy an area.

How do you calculate species diversity?

d=\frac{N(N-1)}{\Sigma n(n-1)}

• d: Species diversity index

• N: Total number of all species

• n: Total number of each individual species

What are some direct effects of agriculture that result in reduced species diversity?

• Removal of hedgerows

• Creating monocultures

• Filling in ponds, draining marsh and wetlands

• Over-grazing, preventing regeneration of woodland

What are some indirect effects of agriculture that result in reduced species diversity?

• Use of chemical pesticides and fertilisers

• Escape of affluent into water courses

• No crop rotation

How can you estimate the size of a non-motile population?

1. Set out a grid.

2. Use a random number generator to give coordinates.

3. Place a quadrat at the coordinate.

4. Count to the number of individuals of the species.

5. Repeat 50 times.

6. Calculate the mean and standard deviation.

How can you estimate the size of a motile population?

1. Capture a sample.

2. Mark them in a non-harmful and non-visible way and release them.

3. After enough time has passed for them to disperse back into their habitats, take another sample.

4. Count how many of the new sample are marked.

5. Calculate the population by multiplying the number in the first sample by the total number in the second sample and divide this by the number that were marked in the second sample.

6. Repeat this 50 times.

7. Calculate the mean and standard deviation.

How do you calculate population?

population=\frac{(no.1stsample)(no.2ndsample)}{no.markedin2ndsample}