Biology U2

Mutation

A random and spontaneous change in the structure of a gene, chromosome or number of chromosomes. They are often random changes in the genetic material that can be inherited, such as changes in body shape and function of the creature who inherits the mutated DNA. There is extensive genetic variation within a population caused by these.

Causes of mutation

They occur continuously and can be spontaneous. it can also happen:

• when cells are copying themselves during mitosis

• if a person comes into contact with environmental factors such as ionising radiation

• because of chemical mutagens - such as tar from cigarette smoke

What can mutations do?

They may change the activity of a protein, in a coding part of the DNA, or might change how the genes are expressed if the change is in a non-coding section of DNA. These might result in phenotype changes or they might appear hidden, and be unnoticed. Alternatively, they might result in a serious consequence, such as genetic disease such as cystic fibrosis.

Evolution

Any change in the heritable traits (physical traits or instinctive behaviours) within a population across generations.

What does mutation create?

Change in physical traits and instincts. This can include variation in the body shape and function of the creature who inherits the modified DNA.

Individuals in a species show a wide range of variation and this variation is because of…

differences in their genes

What does variation occur as a result as?

A result of mutations that create new forms of genes, known as alleles, which can be inherited by the next generation.

Survival of the fittest

Individuals with characteristics most suited to their environment are more likely to survive and reproduce.

The genes that allow individuals to be successful within their environment are…

Passed on to their offspring, which results in these favourable alleles becoming more common.

Process of natural selection

1. Individuals in a species show variation.

2. Many characteristics are inheritable as they are passed from parents to their offspring.

3. Life in the wild is competitive and more offspring are produced than can adapt.

4. Individuals with the most favourable characteristics will live longer and reproduce more offspring. This is called survival of the fittest.

5. Individuals that do not survive live and die with the features they inherited.

6. Given enough time, a species will gradually evolve and become better adapted to their environment.

Natural selection

The process where organisms better adapted to their environment tend to survive and produce more offspring, passing on their advantageous traits over generations. This mechanism of evolution leads to changes in a population's heritable characteristics, making the population better suited to its environment over time.

Natural selection example - beetles

1. There is variation in the population of beetles (colour) due to mutation.

2. The selection pressure is predation by the birds. Since they prey on green beetles, the brown beetles have a survival advantage.

3. Since the brown beetles have a survival advantage, the allele for brown appearance is favourable, and increases. This is because they are more likely to reach reproductive age and increase, while green beetle’s less favourable alleles decrease.

4. This is called survival of the fittest, where the brown beetle is better suited to the environment because they are better adapted to the selection pressure and therefore survive.

Selection pressures

These are environmental factors which affect reproductive success in a population. They select for favourable alleles, resulting in those allele that provide a survival advantage increasing in the population. Examples include food, predation, mate selection and infectious disease.

Examples of selection pressures

Predators - variants with adaptations allowing them to escape predators have more offspring e.g. speed, defensive weapons, camouflage, mimicry

Prey/Food - variants with adaptations allowing them to obtain food have more offspring e.g. speed, senses for finding prey/food, weapons for killing prey/obtaining food, camouflage for stealth

Climate - those who can survive new climate best have more kids e.g. ice age, change in climate due to migration

Mates - variants with adaptations allowing them to attract a mate to have offspring e.g. strong, attractive, good provider

Species

A group of interbreeding individuals that can produce fertile offspring.

Process of speciation

1. One population has gene flow - reproduction between individuals within a population

2. Reproductive isolation occurs, where the population is split in two and can’t get across due to a barrier, creating two gene pools and two populations. There is no gene flow between the populations (sharing of genes)

3. Random mutations occur over time in the two populations. These mutations are probably not the same due to different selection pressures as climate, environment and predators may be different.

4. If the two new mutated populations somehow meet and can no longer mate, speciation has occurred.

Gene flow

The movement of genetic material throughout a population.

Population

The total number of individuals of a species living in a particular area and capable of interbreeding.

Gene pool

The collection of all the genes and their various alleles found within an interbreeding population of a species at a given time.

VISS for speciation

Variation - Variation exists in a population due to mutations, which occur randomly, specifically in meiosis, when there is an error in copying DNA. The organisms within this population are part of the same species and share a gene pool, and have gene flow.

Isolation - Isolation forms a barrier, turning the one population into two. This means there are two gene pools as there is no longer gene flow between these populations.

Selection - Selection pressures in the two environments of the populations differ. This means that different mutations (which occur randomly) are favourable in each environment. Over time, the favourable organisms pass the favourable allele to offspring when interbreeding with other organisms in the same population. This is because a higher proportion of the organisms with the favourable allele and favourable phenotype reach reproductive age and reproduce, while those that do not possess the trait do not.

Species - Speciation occurs when the two populations have evolved so much that if reunited, they are no longer able to interbreed to create viable and fertile offspring. Therefore, the two populations are different species.

Evidence for evolution

All living things are related and share a common ancestor. This can include:

• comparative anatomy

• embryology

• fossil record

• dna

^{Comparative anatomy}

The study of differences and similarities between living things. For example, both dolphins and humans are warm blooded, have lungs and give birth to live young. It also includes vestigial structures.

Vestigial structure

A bodily feature that has lost its original function through evolution and may be reduced in size or may even have a different, minor function. These structures serve as evolutionary remnants, providing evidence of common ancestry and demonstrating how species have adapted over time to different environments. Examples in humans include the appendix, wisdom teeth, and the coccyx (tailbone), while other examples include the leg bones of whales and the wings of flightless birds.

Embryology

The study of how creatures develop before being born or hatching from an egg. For example, all vertebrates have similar embryos, like gills and having arms and legs.

Fossil record

A record within the ground that discusses transitional forms and evidence for evolution. The further down, the older it is, where scientists can use comparative anatomy. For example, there are intermediate species in between two distinct species, blurring the line between aquatic and terrestrial over time.

DNA as evidence for evolution

Scientists compare DNA code of different animals. Seeing who has the most genetic information similar to each other are the most related.

How does fossil record provide evidence for evolution?

Fossils can show the bone structure of organisms from a certain time period. Seeing fossils from different periods can reveal a pattern of how an organism evolved, demonstrating the emergence of new species and a trend towards increasing biological complexity.

Simpler organisms appear in older rocks due to the theory of evolution, and more complex ones in newer rocks.

How do transitional forms provide evidence for evolution?

Transitional forms demonstrate how one organism evolved into another. They could have traits that are in between the two organisms, such as a blowhole in the middle of the head, rather than the top of the head or on a snout.

How does a sequence of change provide evidence for evolution?

Involves a whole lot of transitional forms, showing a progression from simpler to more complex organisms, documented in different geographical layers (older is further down, newer is closer to the surface), allowing scientists to establish a chronology of evolutionary events.

Older fossils are less complex than younger fossils

The simplest organisms are found in the oldest rocks, with complexity increasing in rock layers closer to the surface. It supports the theory of evolution, which states that simple life forms evolve into more complex ones

Antibiotic

Substances that kill bacteria or prevent their growth. They do not work against viruses. It is difficult to develop drugs that kill viruses without damaging the body’s tissues as viruses live inside the cells of the infected person.

Antibiotic resistance

Over time, bacteria can become resistant to certain antibiotics. This is an example of natural selection. In a large population of bacteria, there may be some that are not affected by the antibiotic, an example of variation. These survive and reproduce, creating more bacteria that are not affected by the antibiotic.

Process of antibiotic resistance

There is variation in a population of bacteria. This means that some bacteria is resistant to a particular antibiotic, while others aren't, due to mutations. When an antibiotic is used, it becomes a selection pressure for the bacteria. Those that aren't resistant die, and the ones that are thrive. They reproduce and pass their genes on to their offspring, increasing the allele frequency of drug resistance.

Phylogenetic tree information

• A phylogenetic tree is a diagram that represents evolutionary relationships among organisms. Phylogenetic trees are hypotheses, not definitive facts.

• The pattern of branching in a phylogenetic tree reflects how species or other groups evolved from a series of common ancestors.

• In trees, two species are more related if they have a more recent common ancestor and less related if they have a less recent common ancestor.

• Phylogenetic trees can be drawn in various equivalent styles. Rotating a tree about its branch points doesn’t change the information it carries.