variation and selection Flashcards
what is variation (definition)
differences between individuals of the same species
what is phenotypic variation
differences in physical characteristics between individuals of the same species
what are the 2 types of phenotypic variation
continuous and discontinuous
what is continuous variation
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.
Results in a range of phenotypes between two extremes
Examples include height, mass, finger length etc. where there can be many ‘in-between’ groups
what is a discontinuous variation
is when there are distinct differences in a characteristic.
results in a limited number of phenotypes with no intermediates
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 would a continuous variation graph look like
smooth bell curve
what would a discontinuous variation graph look like
step-shaped bar graph with distinct values
what are the 2 causes of continuous variation
genetic and environmental
what is the only cause of discontinuous variation
genetic
examples of genetic variation
-blood group
-eye colour
-gender
-ability to roll the tongue
-whether ear lobes are free or fixed
examples of environmental variation
-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
examples of genetic variation
-blood group
-eye colour
-gender
-Ability to roll the tongue
-whether ear lobes are free or fixed
how do continuous features vary through a combination of genetic and environmental variation
although genes decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop
eg:
-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 is a mutation (definition)
random genetic change in the base sequence of dna
what can mutation create
new alleles
what can increase the rate of mutation
ionizing radiation and some chemicals
what are the sources of genetic variation in populations
mutation, meiosis, random mating
and random fertilisation
which gene is mutated in the body to cause sickle cell anaemia and how is it mutated
the gene that codes for haemoglobin
causes the red blood cells to become stiff and sometimes sickle-shaped when they release oxygen to the body tissues
what are the 2 possible genotypes that can cause sickle cell anaemia
HNHn - some abnormal haemoglobin can be carriers of the disease
HnHn - sickle cell anaemia, life threatining
symptoms of sickle cell anaemia
strokes, blindness, or damage to the lungs, kidneys, or heart
what are the alleles for sickle cell anaemia
codominant
what do heterozygous individuals for sickle cell anaemia experience
suffer some symptoms of sickle cell anaemia under conditions of low blood oxygen
and they are said to be carriers of sickle cell anaemia
resistance to malaria
what is an adaptive feature
an inherited feature that helps an organism to survive and reproduce
what is fitness
probability of an organism surviving and reproducing in the environment in which it is found
what are hydrophytes
plants that are adapted to live in extremely wet conditions
what are the adaptations of hydrophytes
large air spaces in their leaves
-to keep them close to the surface of the water where there is more light for photosynthesis
small roots
-as they can also extract nutrients from the surrounding water through their tissues
stomata placed on the upper epidermis rather than the lower and is open all the time
-they can exchange gasses much easier
what are xerophytes
plants adapted to live in extremely dry conditions
what are the adaptations of xerophytes?
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 (essentially helps to reduce water loss from the surface of the leaf)
Sunken stomata
-stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces the evaporation rate
Small leaves
-many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface
what is natural selection
the individuals that have the best adaptive features are the ones most likely to survive and reproduce
how does the survival of the fittest occur
individuals with adaptive features reproduce, this will cause there too be too many individuals and there will be a competition for resources (food etc.)
due to this only the strongest individuals or individuals best suited for the environment will get the resources and survive
evolution definition
change in adaptive features of a population over time as a result of natural selection
selection pressure definition
something in the environment that affects the chance that individuals with different features will survive and reproduce
adaptation definition
the process resulting from natural selection by which populations become more suited to their environment over many generations
drug definition
any substance taken into the body that modifies or affects chemical reactions in the body
antibiotic definition
a substance that is taken into the body and which kills bacteria but does not affect human cells or viruses
how do bacteria become antibiotic resistant?
bacteria reproduce every 20 minutes
this increases the chance of chance mutation as they reproduce so often
a mutation can cause them to be resistant to antibiotics
the resistant bacteria do not die
they can continue to reproduce with less competition
hence the genes for antibiotic resistance are passed on with much higher frequency
example of bacteria that are antibiotic resistant
MRSA (methicilin-resistant staphylococcus aureus)
selective breeding def
select individuals with desirable characteristics and breed them together
natural selection vs selective breeding
natural selection:
occurs naturally
results in the development of populations with features that are better adapted to their environment and survival
usually takes a long time to occur
selective breeding:
only occurs when humans intervene
results in the development of populations with features that are better adapted to humans and not necessarily to the survival of the species
takes less time to occur as only individuals with the desired features are allowed to reproduce
why are plants selectively bred for development by humans
disease resistance in food crops
increased crop yield
hardiness to weather conditions (e.g. drought tolerance)
better tasting fruits
large or unusual flowers
why are animals selectively bred for development by humans
cows, goats and sheep that produce lots of milk or meat
chickens that lay large eggs
domestic dogs that have a gentle nature
sheep with good quality wool
horses with fine features and a very fast pace
Explain why sickle cell anaemia is common in people who live in areas where malaria occurs.
malaria is a severe disease that can be fatal
patients with sickle cell anaemia are resistant to malaria
homozygous dominant susceptible to malaria (hAhA)
heterzygous are resistant (hAhS)
they are more likely to survive and reproduce hence passing on the allele for resistance to malaria
