variation and selection

Question 1

what is variation (definition)

Answer 1

differences between individuals of the same species

Question 2

what is phenotypic variation

Answer 2

differences in physical characteristics between individuals of the same species

Question 3

what are the 2 types of phenotypic variation

Answer 3

continuous and discontinuous

Question 4

what is continuous variation

Answer 4

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

Question 5

what is a discontinuous variation

Answer 5

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’

Question 6

what would a continuous variation graph look like

Answer 6

smooth bell curve

Question 7

what would a discontinuous variation graph look like

Answer 7

step-shaped bar graph with distinct values

Question 8

what are the 2 causes of continuous variation

Answer 8

genetic and environmental

Question 9

what is the only cause of discontinuous variation

Answer 9

genetic

Question 10

examples of genetic variation

Answer 10

-blood group
-eye colour
-gender
-ability to roll the tongue
-whether ear lobes are free or fixed

Question 11

examples of environmental variation

Answer 11

-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

Question 12

examples of genetic variation

Answer 12

-blood group
-eye colour
-gender
-Ability to roll the tongue
-whether ear lobes are free or fixed

Question 13

how do continuous features vary through a combination of genetic and environmental variation

Answer 13

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

Question 14

what is a mutation (definition)

Answer 14

random genetic change in the base sequence of dna

Question 15

what can mutation create

Answer 15

new alleles

Question 16

what can increase the rate of mutation

Answer 16

ionizing radiation and some chemicals

Question 17

what are the sources of genetic variation in populations

Answer 17

mutation, meiosis, random mating
and random fertilisation

Question 18

which gene is mutated in the body to cause sickle cell anaemia and how is it mutated

Answer 18

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

Question 19

what are the 2 possible genotypes that can cause sickle cell anaemia

Answer 19

HNHn - some abnormal haemoglobin can be carriers of the disease
HnHn - sickle cell anaemia, life threatining

Question 20

symptoms of sickle cell anaemia

Answer 20

strokes, blindness, or damage to the lungs, kidneys, or heart

Question 21

what are the alleles for sickle cell anaemia

Answer 21

codominant

Question 22

what do heterozygous individuals for sickle cell anaemia experience

Answer 22

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

Question 23

what is an adaptive feature

Answer 23

an inherited feature that helps an organism to survive and reproduce

Question 24

what is fitness

Answer 24

probability of an organism surviving and reproducing in the environment in which it is found

Question 25

what are hydrophytes

Answer 25

plants that are adapted to live in extremely wet conditions

Question 26

what are the adaptations of hydrophytes

Answer 26

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

Question 27

what are xerophytes

Answer 27

plants adapted to live in extremely dry conditions

Question 28

what are the adaptations of xerophytes?

Answer 28

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

Question 29

what is natural selection

Answer 29

the individuals that have the best adaptive features are the ones most likely to survive and reproduce

Question 30

how does the survival of the fittest occur

Answer 30

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

Question 31

evolution definition

Answer 31

change in adaptive features of a population over time as a result of natural selection

Question 32

selection pressure definition

Answer 32

something in the environment that affects the chance that individuals with different features will survive and reproduce

Question 33

adaptation definition

Answer 33

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

Question 34

drug definition

Answer 34

any substance taken into the body that modifies or affects chemical reactions in the body

Question 35

antibiotic definition

Answer 35

a substance that is taken into the body and which kills bacteria but does not affect human cells or viruses

Question 36

how do bacteria become antibiotic resistant?

Answer 36

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

Question 37

example of bacteria that are antibiotic resistant

Answer 37

MRSA (methicilin-resistant staphylococcus aureus)

Question 38

selective breeding def

Answer 38

select individuals with desirable characteristics and breed them together

Question 39

natural selection vs selective breeding

Answer 39

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

Question 40

why are plants selectively bred for development by humans

Answer 40

disease resistance in food crops increased crop yield hardiness to weather conditions (e.g. drought tolerance) better tasting fruits large or unusual flowers

Question 41

why are animals selectively bred for development by humans

Answer 41

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

Question 42

Explain why sickle cell anaemia is common in people who live in areas where malaria occurs.

Answer 42

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