Variation and selection

Question 1

Variation definition

Answer 1

differences between individuals of the same species

Question 2

Continuous variation

Answer 2

Continuous variation results in a range of phenotypes between two extremes

• Examples include body length and body mass
• Graph is a smooth bell curve
• Caused by both genes and the environment

Question 3

Discontinuous variation

Answer 3

Discontinuous variation results in a limited number of phenotypes with no intermediates

• Examples include ABO blood groups, seed shape in peas and seed colour in peas
• Graph for discontinuous is a bar graph
• Usually caused by genes only

Question 4

What is mutation?

Answer 4

Mutation is genetic change, it is the way in which new alleles are formed

Question 5

What increases the rate of mutation?

Answer 5

Ionising radiation and some chemicals increase the rate of mutation

Question 6

What is gene mutation?

Answer 6

Gene mutation is a random change in the base sequence of DNA

Question 7

What are sources of genetic variation in populations?

Answer 7

Mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations.

Question 8

Adaptive feature definition

Answer 8

Adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment

Question 9

What are hydrophytes and what is an example?

Answer 9

Hydrophytes are plants adapted to live in extremely wet conditions

Examples: Water lilies

Question 10

What are the adaptations of hydrophytes?

Answer 10

• Large air spaces in their leavesfor flotation, to keep the leaves close to the surface of the water where there is more light for photosynthesis
• Small rootsas they can also extract nutrients from the surrounding water through their tissues
• Stomata usually open all the time andmainly found on the upper epidermisof the leaf where they can exchange gases much more easily with the air
• Flat leaves maximise photosynthesis and help them float

Question 11

What are xerophytes and what is an example?

Answer 11

Xerophytes are plants adapted to live in extremelydry conditions

Examples: Cactus

Question 12

Adaptations of xerophytes

Answer 12

• Thick waxy cuticle: the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers the temperature
• Sunken stomata: stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces the evaporation rate
• Leaf rolledwith stomata inside and an inner surfacecovered in hairs: traps moist air and prevents air movement across stomata which reduces transpiration
• Small leaves: many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
• Extensive shallow rootsallow for the quick absorption of large quantities of water when it rains
• Thickened leaves or stemswhich contain cells that store water

Question 13

Adaptation definition

Answer 13

Adaptation is the process, resulting from natural selection, by which populations become more suited to their environment over many generations

Question 14

Process of natural selection

Answer 14

(a) Genetic Variation Within Populations

Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation arises from mutations, genetic recombination during sexual reproduction, and other processes. It is crucial for natural selection because it provides the raw material upon which selection acts. Without genetic variation, all individuals would be genetically identical, and there would be no differential survival or reproduction among individuals.

(b) Production of Many Offspring

Most species produce more offspring than the environment can support. This overproduction leads to a large number of individuals that must compete for limited resources, such as food, space, and mates. Not all offspring will survive to adulthood or reproduce; this sets the stage for natural selection by ensuring that there is always competition among individuals.

(c) Struggle for Survival, Including Competition for Resources

Due to the overproduction of offspring, there is a constant struggle for survival in nature. Individuals must compete with one another for the resources they need to survive and reproduce. This competition can be for food, water, shelter, and other essentials. Those individuals that are better suited to their environment will have a better chance of surviving and obtaining the resources they need.

(d) A Greater Chance of Reproduction by Individuals that Are Better Adapted to the Environment Than Others

Natural selection favors individuals that have advantageous traits or adaptations that improve their chances of survival and reproduction in a given environment. These individuals are more likely to survive the struggle for existence and more likely to reproduce. As a result, they have a greater chance of passing on their advantageous traits to their offspring.

(e) These Individuals Pass on Their Alleles to the Next Generation

Individuals that survive and reproduce pass their alleles (versions of genes) to their offspring. If these alleles contribute to advantageous traits, they will become more common in the population over generations. Over time, this process can lead to the evolution of populations, as advantageous traits become more widespread and individuals become better adapted to their environments
- Over time, this will bring about achange in the characteristics of the species- it will produceevolution

Question 15

What is evolution?

Answer 15

Evolution is defined as thechange in adaptive features of a population over time as a result of natural selection

Question 16

Natural selection in developing strains of antibiotic resistant bacteria

Answer 16

1. Genetic Variation Within Bacterial Populations

Within any bacterial population, there is genetic variation due to mutations, which are changes in the DNA sequence. Some of these mutations may randomly provide a bacterial cell with resistance to a particular antibiotic.

2. Struggle for Survival

When a population of bacteria is exposed to an antibiotic, the antibiotic works to kill the bacteria or inhibit their growth. However, bacteria with a mutation that gives them resistance to the antibiotic have a survival advantage. The presence of the antibiotic creates a selective pressure in the environment. Bacteria that are susceptible to the antibiotic are more likely to be killed or inhibited, while resistant bacteria are more likely to survive.

3. Reproduction of Resistant Bacteria

Bacteria that survive the antibiotic exposure due to their resistance have the opportunity to reproduce. They replicate rapidly, producing many offspring, these offspring will inherit the resistance genes. As a result, the proportion of antibiotic-resistant bacteria in the population increases over time.

4. Passing on of Resistance Alleles to the Next Generation

As resistant bacteria reproduce, they pass on the alleles that cause resistance to their offspring. Over time, these alleles become more common in the bacterial population. If antibiotic use continues, the population will increasingly be dominated by resistant bacteria, making the antibiotic less effective against the infection.

Question 17

What is selective breeding?

Answer 17

Selective breeding means toselect individuals with desirable characteristics and breed them together.

Question 18

Process of selective breeding

Answer 18

(a) Selection by Humans of Individuals with Desirable Features

The first step in selective breeding involves identifying and selecting individuals within a population that exhibit desirable traits. These traits can vary widely depending on the goals of the breeding program. Humans play a crucial role in this process by choosing which individuals possess the most desirable features to pass on to future generations.

(b) Crossing These Individuals to Produce the Next Generation

Once the individuals with desirable traits have been selected, they are bred together to produce the next generation. This process is called crossing. The goal of this step is to combine the genetic material of two individuals with desirable traits, increasing the likelihood that their offspring will also exhibit these traits. This step may be repeated multiple times across several generations to enhance the desired features in the population.

(c) Selection of Offspring Showing the Desirable Features

After crossing, the offspring produced are evaluated for the presence of the desired traits. Not all offspring will necessarily display these traits due to genetic variation and inheritance patterns. Therefore, only those offspring that show the desirable characteristics are selected for further breeding. This selection process ensures that the desirable traits are concentrated and maintained in the population. Over successive generations, through repeated selection and breeding, these traits can become more pronounced and widespread within the population.

🌟 Selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals

Question 19

Differences between natural and artificial selection

Answer 19

• Natural selection occurs naturally while artificial selection occurs through human intervention
• Natural selection populations have features that are better adapted to suit their environment and survival. Artificial selection have features that are useful to humans not necessarily to the survival of the individual
• Natural selection takes a long time to occur while artificial selection takes less time as only individuals with the desired trait are allowed to reproduce