Biology 2 Y10

Variation definition

Differences between individuals within a population

Mutation definition

Permanent change to genetic material (DNA)

Mutagen definition

Substances that increase the rate of mutations occurring

Examples of biological mutagens

Some viruses

Examples of chemical mutagens

Mustard gas, formaldehyde

Examples of physical mutagens

UV light, x-rays

How can mutations occur without a mutagen being present?

There could be errors in DNA replication which results in changes in the DNA base sequence

Why is it impossible to avoid mutagens?

Mutagens are present almost everywhere in the environment. It is only possible to limit the level of exposure not avoid them. For example mutagens like UV light are difficult to avoid as direct sunlight is necessary to maintain natural vitamin D levels.

Explain the population effect (biodiversity)

Mutations increased genetic variation which increases biodiversity. mutations may help species survive better, be harmful or have no effect

What determines the function of a protein?

The specific order of amino acids

How is a protein created?

The sequences of bases in a DNA strand code for a protein. every three bases in the DNA strand for a code for one amino acid. These amino acids are linked together in a chain to create a protein.

Define gene mutation

A change to a single gene

Define substitution mutation

This is a point mutation so it only affects one amino acid. A single base is swapped for another and this may or may not affect the protein. It could be neutral.

Define insertion mutation

A nitrogen base is added to the sequence. This creates a frame shift. This affects all triplets from the point of mutation.

Define deletion mutation

A nitrogen base is removed from the sequence. This creates a frame shift. This affects all triplets from the point of mutation.

Define frameshift

A large scale movement that completely changes the following amino acids. A shift of the reading frame

Describe the effect of frameshift

Causes triplets to be read incorrectly from the point of mutation.

Structure to a natural selection answer

Variation: There is natural variation between individuals in a population. (Describe the different alleles in the population). Genetic variation arises through mutation.

What causes different alleles in a population/how does genetic variation initially arise?

Mutation

Describe the process of artificial selection

Differences exist between individuals of a population. Humans select individuals with favourable traits to breed, passing on favourable alleles to the next generation. Over time, the frequency of favourable alleles will have increased within the population.

Structure of answer for artificial selection

Within the population of (organism) there was variation in (what differs).

Humans identify the (organisms) with (favourable allele). The (organisms) were chosen to breed with one another. The offspring with the desirable traits were then selected to breed with one another over many generations.

Overtime the frequency of the alleles for (favourable trait) will increase within the population.

Compare natural and artificial selection

Similarities:

• both require variation in original population

• both result in changes to allele frequency within population

• both rely on it being a heritable trait

Differences: natural vs artificial

• favourable traits determined by nature (selective pressure) vs. humans

• change to pop. increase species chance of survival vs don't

• more genetic variation vs. less genetic variation

• occurs over a long period vs a shorter period of time

Define species

A group of organisms capable of breeding and producing fertile offspring

Define speciation

When populations become isolated and become two separate species

Speciation answer structure

There was natural variation as there were differences in (trait).

There was geographic isolation as the (species) were isolated on (where). This prevented interbreeding and gene flow.

There were different (selection pressure) on different (locations). (Location A) had (selection pressure) while (Location B) had (selection pressure). The (species) with (favourable allele A) can (avoid selection pressure) and reproduce and pass those alleles on. The (species) with (bad allele) died.

Several species of (species) evolved, with different (trait) suited to the particular habitat they live in. Over time, each population became so unique that they were not able to reproduce with each other to produce fertile offspring.

Define fossil and provide examples

Preserved traces left behind by organisms that lived long ago e.g bones, footprints, burrows, faeces, shells, teeth

Describe how fossils can be used as evidence of evolution.

Reveal the appearance of past organisms that are now extinct and can compare how organisms have changed over time. Fossils establish evolutionary link between species/show common ancestry. Transitional fossils develop sequence of the evolution of plants or animals.

Describe the conditions required for fossil formation. (5)

Rapid burial: To avoid damage from scavengers and weathering

Lack of oxygen/water in soil: will prevent decomposition by bacteria and fungi as decomposers need oxygen to survive.

Alkaline soil: acidic soils can dissolve bone

Hard body parts: can create an imprint/impression e.g bone, soft body parts can't imprint.

Time: undisturbed for a long period of time (long period of stability)

Describe the process of fossil formation (4)

1. organism dies

2. organism is rapidly buried (by mud, sand or volcanic ash)

3. minerals in sediment leach into organic material and the organic material turns to rock (but detail is preserved)

4. fossil revealed at surface due to Earth movements or digging.

State the principal of superposition.

assumes that in layers of sedimentary rock the layers at the top are younger than the layers at the bottom

Define strata.

layers of rock

Describe how index fossils work.

involves matching layers of rock (strata) from different areas. strata of the same age will contain fossils of the same age

Identify three features necessary for a fossil to be used as an index fossil (match with other strata of smae age).

1. fossils widely distributed around the world e.g found in most dig sites

2. present on earth for a limited period of time e.g will only be found in one strata/a few

3. distinctive (easy to tell)

Define comparative anatomy

The comparison of structures of organisms in both fossils and living species. Includes study of homologous structures, vestigial organs and comparative embryology.

Define homologous structure

Common structure that are found in different species often have a similar pattern but different structure. E.g pentadactyl limb.

Structure of how do homologous structures, such as __, support the Theory of Evolution.

(Animals with this) have the same basic bones in their (body part). So, the (body part) is a homologous structure.

Characteristics are inherited from ancestors. So, these groups of in/vertebrates must be descended from a common ancestor that passed on the genes for these bones to them.

These bones structures have been slightly modified to suit a particular function.

Define vestigial organ

Vestigial structures are functionless structures found in organisms.

Describe how an organ can become vestigial with cocyx as an example.

The coccyx in humans is the remnants of a tail that was used by our ancestors who lived in trees. 

For this ancestor, the tail had an advantageous function.

However, as humans do not live in trees the coccyx is no longer functional.

It suggests humans descended from an ancestor who needed a tail to live in trees.

Examples of vestigial organs

he human appendix, wisdom teeth, and coccyx

Structure of vestigial organ answer

The (body part) in (modern species) is the remnants of a (old body part) that was used by their ancestors who (why they have body part).

For this ancestor, the (old body part) had an advantageous function.

However, as (modern species) do not (why it was useful for ancestors) the (body part) is no longer functional.

It suggests (modern species) descended from an ancestor who (why old body part was useful).

Define comparative embryology

The comparison of embryos of different species.

Why is comparative embryology evidence for evolution

Comparison of vertebrate embryos shows striking resemblance in the early stages of their development

Embryos show many features that may not be present as an adult therefore this can be evidence of common ancestry.

Define genome

The complete DNA sequence of an organism

How is comparative genomics evidence fro evolution

Sciences can compare genes of organisms, looking for differences in base order. The more similar the DNA, the more closely related the species are

Define and explain comparative proteins

Proteins are long chains of amino acids, the sequence of amino acids is determined by sequence of bases in DNA. By comparing type and sequence of amino acids from different species, degree of similarity can be established.

Less differences = more recent common ancestor

How do comparative proteins provide evidence for evolution

Less differences in amino acid sequence indicates more recent common ancestor (the species is more closely related).