Variation and Selection Flashcards
What is variation?
Variation is defined as differences between individuals of the same species
What is phenotypic variation?
Phenotypic variation is the difference in features between individuals of the same species
What is genetic variation?
Some of these differences are caused by differences in genes, which is genetic variation
What two types of phenotypic variation are there and how are they divided?
Phenotypic variation can be divided into two types depending on how you are able to group the measurements:
continuous and discontinuous variation
What is continuous variation?
Continuous Variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
What are examples of continuous variation?
Examples include height, mass, finger length etc. where there can be many ‘inbetween’ groups
What is discontinuous variation?
Discontinuous Variation is when there are distinct differences for a characteristic
What are examples of discontinuous variation?
For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not – there are no ‘inbetweens’
What two things can cause phenotypic variation?
Phenotypic variation can be caused in two main ways:
It can be genetic – controlled entirely by genes
Or it can be environmental – caused entirely by the environment in which the organism lives
What are examples of genetic variation in humans?
blood group eye colour gender ability to roll tongue whether ear lobes are free or fixed
What are examples of environmental variation?
Examples include:
- An accident may lead to scarring on the body
- Eating too much and not leading an active lifestyle will cause weight gain
- Being raised in a certain country will cause you to speak a certain language with a certain accent
- A plant in the shade of a big tree will grow taller to reach more light
What environmental factors may affect variation?
Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle
What type of variation is discontinuous variation caused by?
Discontinuous variation is usually caused by genetic variation alone
What types of variation cause continuous features?
Continuous features often vary because of a combination of genetic and environmental causes
What is an example of a combination of genetic and environmental variation which leads to continuous variation?
- tall parents will pass genes to their children for height
- their children have the genetic potential to also be tall
- however if their diet is poor then they will not grow very well
- therefore their environment also has an impact on their height
What are mutations?
Mutations are random genetic changes
Do mutations affect the phenotype?
Most mutations have no effect on the phenotype as the protein that a mutated gene produces may work just as well as the protein from the non – mutated gene
Can mutations lead to development of new alleles? What effect do they have?
Rarely, mutations lead to the development of new alleles and so new phenotypes and if they do, most have a small effect on the organism
Can mutations be useful? How?
Occasionally, the new allele gives the individual a survival advantage over other members of the species
For example:
A bird develops a mutation leading to a change in feather colours
This makes it more attractive to birds of the opposite sex
Which causes the bird to breed more frequently and have more chances of passing on the mutated phenotype to the next generation
Can mutations be harmful? How?
Mutations can also lead to harmful changes that can have dramatic effects on the body – for example, sickle cell anaemia in human
What two words can describe mutations?
Mutations happen spontaneously and continuously
What can increase the frequency of mutations?
their frequency can be increased by exposure to the following:
Gamma rays, x – rays and ultraviolet rays – all types of ionising radiation which can damage bonds and cause changes in base sequences
Certain types of chemicals – for example chemicals such as tar in tobacco
Why are increased rate of mutations bad?
Increased rates of mutation can cause cells to become cancerous, which is why the above are linked to increased incidence of different types of cancer
What type of mutation results in sickle cell anaemia?
Sickle cell anaemia was the first genetic disease to be described in terms of a gene mutation
What is a gene mutation?
A gene mutation is a change in the base sequence of DNA
How does the mutation change cells in sickle cell anaemia?
The mutation changes the molecule haemoglobin
What effects do the mutations have on the red blood cells?
causing the red blood cells (RBC’s) to become stiff and sometimes sickle-shaped when they release oxygen to the body tissues
What can happen to the red blood cells due to their shape?
The sickled cells tend to get stuck in narrow blood vessels, blocking the flow of blood
As a result, those with sickle cell disease suffer painful “crises” in their joints and bones
What things may people with SCA suffer from?
They may suffer strokes, blindness, or damage to the lungs, kidneys, or heart. They must often be hospitalized for blood transfusions and are at risk for a life-threatening complication called acute chest syndrome
How long do people with SCA live with?
Although many sufferers of sickle cell disease die before the age of 20, modern medical treatments can sometimes prolong these individuals’ lives into their 40s and 50s
What two versions of the gene are important for sickle cell anaemia?
There are two versions or alleles of the gene important for the inheritance of sickle cell anaemia : A and S
Are the A and S alleles codominant?
The two alleles are codominant, meaning there is no ‘dominant’ or ‘recessive’ version of the gene
How would you represent someone having normal haemoglobin?
Individuals with two A alleles (HbAHbA) have normal haemoglobin, and therefore normal RBCs
How would you represent someone having SCA?
Those with two S alleles (HbSHbS) develop sickle cell anaemia
How would you represent someone being heterozygous for SCA?
Those who are heterozygous for sickle cell (HbAHbS)
What type of RBC’s do people who are heterozygous for SCA have?
produce both normal and abnormal haemoglobin (as the alleles are codominant)
What symptoms do people who are heterozygous for SCA have?
Heterozygous individuals are usually healthy, but they may suffer some symptoms of sickle cell anaemia under conditions of low blood oxygen, such as high altitudes or during exercise
What are people who are heterozygous for SCA called?
Heterozygous individuals are said to be ‘carriers’ of the sickle cell gene and are said to have ‘sickle cell trait’
What other illness is SCA related with?
malaria
How many people in USA are affected by SCA?
In the United States, about 1 in 500 African-Americans develops sickle cell anaemia
How many people in Africa are affected by SCA?
In Africa, about 1 in 100 individuals develops the disease
What is malaria?
Malaria is a disease spread by mosquitoes that are endemic in many areas of Africa
