Biology - Chapter 18 - Variation and selection

Define variation

differences between individuals of the same species

what does continuous variation result in

a range of phenotypes between two extremes like body length and body mass

how discontinuous and continuous variation is caused

• discon - genes only

• con - both genes and environment

what does discontinuous variation result in

a limited number of phenotypes with no intermediates

Ex of discontinuous variation

ABO blood groups, seed colour in peas and seed shape in peas, male or female, can roll tongues (no in between)

Examples of continuous variation

height,mass, finger length (in betweens)

Define mutation

a genetic change

what is the way in which new alleles are formed

mutation

what increases rate of mutation

ionising radiation and some chemicals

define gene mutation

a random change in base sequence of DNA

Define adaptive feature

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

sources of genetic variation in populations

mutation, meiosis, random mating and random fertilisation

Types of adaptive features of hydrophytes

• live in wet conditions

• large air spaces in leaves for flotation

• close to the surface of water where there is more light for photosynthesis

• small roots they can extract nutrients from surrounding water through their tissues

• stomatas open all the time

• stomata mainly found on the upper epidermis of leaf where gas exchange happens much more easily with air

Types of adaptive features of xerophytes

• dry conditions

• thick waxy cuticle, it cuts down water by acting as a barrier to evaporation and also the shiny surface reflects heat and so lowers temp

• sunken stomata: stomata may be sunk in pits in epidermis. moist air is trapped were lengthens the diffusion pathway and reduces evaporation rate

• leaf rolled with stomata inside and inner surface covered 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 evaporating surface

what do extensive shallow roots allows

for quick absorption of large quantities of water when it rains. thickened leaves or stems which contain cells that store water

describe natural selection

genetic variation within populations. when organisms reproduce more offspring than the environment is able to support and leads to competition for resources and a struggle for survival. there is a greater change for reproduction by individuals that are better adapted to the environment than others. these individuals pass on their alleles to the next generation

describe selective breeding

selection by humans of individuals with desirable features. they cross these individuals to produce the next generation. humans select offspring showing desirable features and breed them together

how selective breeding by artificial selection carried out over many generations to improve crop plants and domesticated animals

for plants and animals farmers select parents with desirable characteristics

Define adaptation

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

example of natural selection

development of strains of antibiotic resistant bacteria

Differences between natural selection and artificial selection

natural selection

• occurs naturally

• results in development of populations with features that are better adapted to their environment and survival

• takes a long time to occur

artificial selection

• occurs when humans intervene

• results in development of population with features that are useful to humans and not necessarily to survival of the individual

• takes less time as only individuals with desired features are allowed to reproduce