Selection and Evolution
202 questions· page 1 of 21
When organisms reproduce, they pass on their alleles to the next generation. There are many factors that can affect how allele frequencies change over time in a population.
Explain how genetic drift and the founder effect may affect allele frequencies in populations.
A mutation in a bacterial gene can give resistance to an antibiotic. Directional selection can occur when the antibiotic is present in the environment.
A bacterium can also gain resistance when it receives genetic material from another bacterium in a process known as horizontal gene transfer.
Outline how directional selection and horizontal gene transfer result in a new population of bacteria that is resistant to an antibiotic.
Some bacterial diseases can be treated only with one antibiotic, because the bacterial pathogens are resistant to all other antibiotics.
A drug is being developed to help treatment.
- The drug is a small polynucleotide.
- The drug inhibits translation of the messenger RNA (mRNA) produced by transcription of the gene associated with antibiotic resistance.
- The bacteria are then susceptible to more antibiotics.
Suggest and explain how the drug could cause bacteria to become susceptible to more antibiotics.
Selective breeding is used to produce uniform varieties of maize. The maize plants in a crop ripen at the same time and are the same height. The advantage of this is that harvesting is easy and quick. The disadvantage is that farmers must buy new seeds each year.
Explain why farmers must buy new seeds each year.
Scientists investigated the evolutionary relationships of the squirrel family, Sciuridae. The scientists took samples from the current species in the family and carried out DNA sequencing and morphological analysis.
To compare current species with species from the past:
- specimens from museums were used to provide the tissue for DNA sequencing
- teeth and skulls from fossils were compared as part of the morphological analysis.
Describe the advantages of using DNA sequencing rather than morphological analysis to find out more about the evolutionary relationships of the squirrel family.
The estimate for the date that an ancestral species diverged into A. harrisii and A. leucurus is 3.58 million years ago. This estimate has a large uncertainty.
DNA sequencing, including DNA from fossils, was used to estimate this date of divergence.
Suggest a reason why there is such a large uncertainty for this date estimate.
The World Health Organisation regularly analyses bacterial DNA sequence data.
Suggest one way in which this contributes to solving the problem of antibiotic resistance in bacteria.
Some infectious bacterial diseases are treated with the antibiotic streptomycin.
If a person does not finish the prescribed course of streptomycin, bacteria are more likely to become resistant to the antibiotic.
Explain why a streptomycin-resistant strain of bacteria is more likely to develop as a result of natural selection when a person does not complete the prescribed course of antibiotics.
With reference to Fig. 4.1, state the relative frequency of the t allele after 20 generations.
Suggest possible explanations for the change in the relative frequency of the T allele between generation 0 and generation 13.
The relative frequency of the T allele in a population of only 10 individuals was determined over 20 generations. The environmental conditions remained the same throughout the experiment.
Fig. 4.2 shows the results.
Explain why Fig. 4.2 shows a different result from Fig. 4.1.
State the name of the principle that can be used to calculate relative frequencies of two alleles by counting the numbers of organisms in the population showing dominant and recessive phenotypes.
With reference to Fig. 4.2, describe the trends in air temperature and milk yield from April to August.
Many dairy farmers in tropical regions use cattle breeds that are tolerant to heat stress (heat-tolerant cattle). These heat-tolerant cattle:
• can tolerate higher air temperatures than Holstein Friesian cattle before heat stress occurs
• have milder symptoms of heat stress than Holstein Friesian cattle for the same high air temperatures.
Where heat stress does not occur, heat-tolerant cattle produce a lower milk yield than Holstein Friesian cattle under the same conditions.
Scientists compared DNA sequences of Holstein Friesian cattle and heat-tolerant cattle for a number of genes known to have an effect on body temperature.
Twenty genes were found that had alleles associated only with heat-tolerant cattle.
With reference to the information provided, including the data in Fig. 4.2:
• state the type (pattern) of phenotypic variation shown by milk yield in cattle
• identify factors that cause phenotypic variation in milk yield in cattle.
In each case, give a reason for your choice.
type (pattern) of phenotypic variation and reason for choice ______
factors that cause phenotypic variation and reason for each choice ______
The scientists found that one of the genes studied, PRLR, has a dominant allele known as SLICK. The SLICK allele was identified in Senepol cattle, a heat-tolerant breed, and is not found in Holstein Friesian cattle.
Cattle with the SLICK allele have short hair due to reduced hair growth.
Scientists have used selective breeding to introduce the SLICK allele into Holstein Friesian cattle. The milk yields of normal Holstein Friesian cattle and Holstein Friesian cattle with the SLICK allele are shown in Fig. 4.3, during:
• March, when the mean daily air temperature is .
• September, when the mean daily air temperature is .
With reference to Fig. 4.3, describe the effect of the SLICK allele on milk yield in Holstein Friesian cattle.
The SLICK allele differs from the recessive allele by a single nucleotide deletion. This results in a frameshift mutation and introduces a premature stop codon in the PRLR gene.
Scientists can use gene editing to replicate this mutation in Holstein Friesian cattle. This provides a way to introduce the SLICK allele into Holstein Friesian cattle without selective breeding.
Compare gene editing and selective breeding for introducing the SLICK allele into Holstein Friesian cattle.
Include similarities and differences in your answer.
Complete the following paragraphs using the most appropriate word or words.
The theory of evolution describes a process that can lead to the formation of new species from pre-existing species over ______ .
DNA sequence data of different species can be compared to show evolutionary relationships. Two species that have a more recent common ancestor share more ______ in the DNA nucleotide sequences of their genomes than two species that are more distantly related.
Mitochondrial DNA can also be used in the study of evolutionary relationships. Mitochondrial DNA is inherited only from the female gamete, and its nucleotide sequence is unaffected by ______ during the production of gametes.
DNA sequence data can be stored in large biological ______ , allowing faster comparison of the nucleotide sequences of genomes using computer software. DNA sequence data can also be used to predict the ______ sequences of proteins produced by a species.
A ______ can be used to detect many different mRNA molecules at the same time in studies that compare gene expression between different species.
Within a species, the variation that is observed for a particular characteristic can be described as discontinuous or continuous.
Discontinuous variation has a different genetic basis from continuous variation.
State two differences between discontinuous variation and continuous variation, other than having a different genetic basis.
Fig. 9.1 shows three of the colour patterns seen in H. axyridis and the percentage of each in a population.
Suggest the genetic basis of the variation in colour pattern in H. axyridis.
The body size of adult H. axyridis varies from 5 mm to 8 mm. Adult ladybirds do not grow or change size. Adults develop from larvae that hatch from eggs.
State two environmental factors that may affect adult body size in H. axyridis.
Phenotypic variation exists in many forms and has a number of possible causes.
Describe the main factors that are the cause of phenotypic variation.
The theory of evolution is supported by DNA sequence data.
Explain how DNA sequences are used to show evolutionary relationships between species.
In pond 1, the scientists observed:
• a high density of tadpoles
• a low abundance of food
• that most of the tadpoles they counted were either detritus feeders or carnivores, with very few intermediates present.
Describe and suggest explanations for the type of natural selection that appears to be acting in pond 1.
In pond 2, the scientists observed:
• a low density of tadpoles
• sufficient food availability for all tadpoles
• that most of the tadpoles they counted were intermediates, with fewer detritus feeders or carnivores.
Describe and suggest explanations for the type of natural selection that appears to be acting in pond 2.
The intestine length of S. multiplicata tadpoles shows continuous variation.
Sketch a curve on Fig. 7.2 to show how intestine length varies in the tadpole population in pond 2.
A student suggested that the variation in S. multiplicata tadpoles could lead to sympatric speciation in some populations.
Outline the features of sympatric speciation.
Fig. 7.3 shows the evolutionary relationships between three species of American spadefoot toad.
Explain how analysis of DNA allowed the evolutionary relationships shown in Fig. 7.3 to be determined.