4.4 Genetic Diversity & Adaptation

Streptococcus pyogenes is a pathogenic bacterium found on the skin of some people.

A dilution series can be used to calculate the approximate number of these bacterial cells in liquid culture. Describe how a student could use a 10 cm3 culture solution to make a dilution of 1 in 10 000. 

The student using a light microscope recorded that there were 32 Streptococcus pyogenes cells in 0.076 mm³ of the 1 in 10 000 dilution of the culture medium. 

Calculate the number of cells in the original undiluted 10 cm³ culture. Give your answer to three significant figures. 

In parts of Europe, national campaigns were used to reduce usage of the antibiotic erythromycin against Streptococcus pyogenes. 

Figure 1 shows the number of doses of erythromycin prescribed per month over an eight year period between 2001-2009. The data also shows the percentage of infections each year caused by Streptococcus pyogenes that were resistant to erythromycin. 

Figure 1

Describe and explain the results seen in Figure 1.

Suggest why there is a time delay between the use of erythromycin and the appearance of erythromycin resistant strains of Streptococcus pyogenes. 

Lactose is a sugar that is found in milk and dairy products. The enzyme lactase hyrdolyses this sugar in the ileum, making it an important enzyme to newborn mammals who rely entirely on lactose based food sources. Most mammals stop producing lactase as they get older as their diet becomes more varied. An exception to this are humans, they are able to produce lactase as adults, known as lactase persistence. This ability to produce lactase is controlled by a dominant allele.  

It is thought that the farming of cattle by early humans could have led to a rapid increase in the frequency of the allele for lactose persistence. Describe how this could have occurred.

Suggest why the frequency of lactose persistence in individuals can increase at such a rapid rate within a population. 

Different mutations within the lactase gene can produce the same phenotype. Scientists have identified distinct mutations among northern Europeans and the Maasai people of eastern Africa that resulted in lactase persistence. Suggest how humans from different regions may have different favourable lactase mutations. 

Lactose intolerance is often mistaken for a milk allergy. Globally, 2% to 6% of infants and 0.1% to 0.5% of adults suffer from cow’s milk allergy. Milk allergy is a potentially much more serious condition involving an inflammatory immune response to some of the proteins in cow’s milk that are not found in human milk. Lactose intolerance does not involve the immune system but rather results from having a low concentration of the enzyme needed to digest lactose which is very common within most human populations. 

Explain why so few infants and adults suffer from cow’s milk allergy but many more people are likely to be lactose intolerant.

Mildew is a disease caused by a type of flowering and fruit plants. It is characterised by white powdery patches on the upper and lower side of leaves. It can cause tissues to become stunted or distorted. There are some types of cucumber plants that show resistance to the mildew, however, the yield from these plants is low. 

Scientists carried out an investigation on mildew resistant cucumber plants. Figure 1 shows their results. 

Figure 1

State and explain the type of variation shown by the cucumber plants. 

Some plants can be genetically engineered to have resistance to mildew, for example by introducing genes that produce a chemical that can destroy the mildew fungus. However, mildew can overcome this resistance over time. Explain how the mildew fungus adapts to overcome this chemical resistance.

Scientists found that over several generations, that there was a very low frequency of cucumber plants that possessed a high level of resistance to mildew despite it being highly advantageous. Use the information provided in part a) to suggest why. 

State the type of selection experienced by cucumber plants and explain your answer. 

Cod has been harvested heavily for around 50 years with roughly 60% of the total the (reproductively active) cod population being harvested annually. The Grand Banks is an area of sea off the coast of Canada where cod fishing was common.

Cod fishing in the Grand Banks stopped in 1992 but by then the population was less than 1% of its original size. Cod grow until maturation. Figure 1 shows the changes in the cod population that occurred during the years of heavy fishing.

Figure 1

Describe and explain the results seen in Figure 1.

Use Figure 1 to calculate the percentage change in the median age of maturity of male cod fish in 1961 compared to 1978.

State and explain the type of selection that is shown in Figure 1.

Although the cod fisheries have been closed for over 20 years, there has been little population recovery and almost no change in the median age of maturity for both male and female codfish. Suggest two reasons why.  

Define the term genetic diversity.

A researcher was investigating the genetic diversity in four different breeds of cat. 

They calculated the mean genetic diversity for each breed. The value of this mean fell somewhere between 0 and 1. A mean value of 1 indicated maximum genetic diversity while a mean value of 0 indicated no genetic diversity.

The results are shown in Table 1 below.

 Table 1

Describe what the data in Table 1 says about the differences in genetic diversity between these breeds of cat?

Oriental shorthairs were first bred in England in the early 1900s.

Suggest one explanation for the observed difference in genetic diversity between Oriental shorthairs and British shorthairs.

Suggest a method for how the scientist calculated the mean genetic diversity for the different breeds of cat.

Carrots are root vegetables characterised by their shape and vibrant colour (usually orange). The carrots sold in shops today are a domesticated form of the wild carrot, Daucus carota. The roots of carrot plants contain a high amount of vitamin A.

Plant breeders selected high-yielding wild carrot plants and used them to produce a strain of domestic carrots to grow as a crop.

Figure 1 shows a wild carrot plant and a domestic carrot plant. The drawings are to the same scale.

Figure 1

Use Figure 1 to describe two ways in which a wild carrot plant differs from a domestic carrot plant. Explain how these differences allow it to grow in conditions with poor soil and sunlight.

Some domestic carrot plants have been selected for disease resistance. Suggest how disease resistance may benefit a farmer.

Describe and explain how artificial selection will have impacted the genetic diversity of the domestic carrot plant.

Some seed banks contain the seeds of the ancestors of the modern domestic carrot plant. Suggest how they can be used to help farmers growing domestic carrot plants.

An IQ test measures conventional intelligence through pattern recognition, logic and problem solving. An EQ test measures emotional intelligence. 

In a study of families with children produced via egg and sperm donation, the mean EQ scores of the children was closer to the mean EQ scores of the two biological parents than to that of the two legal parents.

Explain the results of this study.

Explain how information from the studies of identical and non-identical twins could help scientists further understand the genetic control of emotional intelligence.

In an experiment, two sterile agar plates were inoculated with bacteria from the same culture. 3 cm3 of an antibiotic solution was added to plate A and 3 cm3 of sterile water was added to plate B. Figure 1 shows the plates after 36 hours.

Figure 1

Suggest how and why the agar was sterilised.

Explain the results of plate A.

Researchers collected fish from a water source inside a cave and from the same water source in the open.

They measured the maximum diameter of each fish’s eye and the length of its body. From these measurements they calculated the mean values for each site. Table 1 shows their results.

Table 1

An article published by a researcher several years before this study suggested that animals living in caves had similar adaptations; smaller eyes and a smaller body for decreased energy expenditure.

Does the data in Table 1 support this researcher’s suggestion? Justify your answer.

The researcher decided to continue their investigation and calculate the genetic diversity
of the fish. Table 2 shows the data they collected.

Table 2

The researcher concluded that the fish in the open exhibited a higher level of genetic diversity than the fish in the cave. Does Table 2 support this conclusion?

The percentage of fish with allele C in the open is different from the percentage of fish with allele C in the cave. Suggest a reason for this difference.

Suggest how the researcher could find out if the fish living in the open are still the same species as those living in the cave.