Evolution: Variation, Infertile Species

SACE Stage 2 O8 – O9

Evolution – includes all of the changes in the characteristics and diversity of life that occur throughout time.Evolution can occur on both large and small

scales.MicroevolutionMacroevolution

The concept of evolution, that organisms may change over time, was not new in Darwin’s time.However, it was not a widely accepted

concept because no one understood how it could work.

A mechanism was missing.

Natural Selection

Darwin provided that mechanism with his theory of Natural Selection.

Natural Selection

In any population of organisms there is natural variation.

Some of these variations will allow the organisms possessing them to survive and reproduce better than those without these particular traits.

Natural SelectionThe successful traits will spread through the

population.This change in the frequency of alleles in the

population is evolution.

Natural Selection – High Reproductive Potential

Darwin observed that organisms

have the potential for very high fertility. Organisms have the potential to

produce, and often do produce large

numbers of offspring. Population size would quickly become

unmanageable if all of the offspring survived.

Natural Selection – Population Size Remains Constant Despite this high potential fertility, natural

populations usually remain constant in size, except for small fluctuations.Not all of the potential offspring survive.

Natural Selection – Limited Resources Resources that organisms need to survive are

limited.Food, water, shelter, nesting sites, etc.

Natural Selection – Competition If there are not enough resources for all of the

individuals, there will be competition for those resources.Survivors represent a small part of the

individuals produced each generation.

Variation

Variation: observable differences within a species (changes that are visual within a species).

Variation that can be inherited is called genetic or heritable variation

Acquired characteristics - dependent on nature or environmental factors are called acquired variations

For example: dark skin vs. suntan

Heritable variations occur due to new combination of genes which can be caused due to independent assortment of chromosomes during meiosis or crossing over.

Independent Assortment: Refer to Meiosis PowerPoint

Crossing Over: Refer to Meiosis PowerPoint https://

www.youtube.com/watch?v=pdJUvagZjYA https://

www.youtube.com/watch?v=BcW0o9IeYGM

Natural Selection – Some traits Enhance Survival Some of the traits found in the population

enhance the survival and reproduction of the organisms possessing them.

Natural Selection – AdaptationThe favored traits will spread through the

population.Over many generations, the species will

become adapted to its environment.Over time, these changes can lead to the

formation of a new species.

AdaptationA species may become adapted to its

environment in response to environmental pressures.

A trait may be favored due to enhanced survival or reproduction when faced with a particular aspect of the environment.

When an environment changes, or when individuals move to a new environment, natural selection may result in adaptation to the new conditions.

Sometimes this results in a new species.

Populations Evolve Individuals do not evolve; populations evolve. Evolution is measured as changes in relative

proportions of heritable variations in a population over several generations.

Natural Selection – Important Points

Natural selection can only work on heritable traits.

Acquired traits are not heritable and are not subject to natural selection.

Environmental factors are variable. A trait that is beneficial in one place or time

may be detrimental in another place or time. Natural selection is not random. It occurs in

response to environmental pressures and results in adaptation.

Natural Selection – Important Points When natural selection is occurring, some

individuals are having better reproductive success than others.

Alleles are being passed to the next generation in frequencies that are different from the current generation.

See the Tutorial on Microevolution!

Upsetting Genetic EquilibriumNatural selection is not the only way that

allele frequencies can change from one generation to the next.

Genetic Drift – a random loss of alleles.Mutation – a new mutation can add alleles.Nonrandom mating – inbreeding increases the

number of homozygous traits.Migration – shuffles alleles between

populations; can prevent speciation.

Genetic DriftThe smaller the sample, the greater the

chance of deviation from expected results.These random deviations from expected

frequencies are called genetic drift.Allele frequencies are more likely to deviate

from the expected in small populations.

Genetic Drift Which allele gets lost is

due to random chance. Over time, drift tends to

reduce genetic variation through random loss of alleles.

CRCR = red

CRCW = pink

CWCW = white

Frequency CR = 0.5Frequency CW = 0.5

Frequency CR = 0.7Frequency CW = 0.3

Frequency CR = 1.0Frequency CW = 0

The Bottleneck EffectSometimes a catastrophic

event can severely reduce the size of a population.

The random assortment of survivors may have different allele frequencies.

This is a type of genetic drift called the bottleneck effect.

The Bottleneck Effect

The actions of people sometimes cause bottlenecks in other species.

N. California elephant seal population reduced to 20-100 individuals in the 1890s.

Current population > 30,000.Variation drastically reduced –

24 genes with 1 allele.

The Founder Effect Founder effect – Another type of genetic drift

occurs when a small group of individuals becomes separated from the population and form a new population. The allele frequencies in their gene pool may be different than the original population.

Mutations

Definition: A mutation is…

A change in the arrangement of bases in an individual gene or in the structure of the chromosome (which changes the arrangement of genes).

Frequency and repair of mutations

Mutations can occur in gametes and somatic cells.

Chance of mutation is between 2-30 x 10-7

Faulty DNA can be repaired by specific enzymes.

Unrepaired mutations will affect the new proteins being synthesised

Val

Point mutations are caused by:

Changes in an individual gene due to miscopying of one or more nucleotides.

Deletion or insertion of a nucleotide results in a frameshift:

C A T G C G T C A G A TA

Codon 1 Codon 2 Codon 3 Codon 4

Tyr Ala Ser LeuArg

Point mutations

Substitution mutations result in a change of one base:

T A C G T G A AAC G G C A T

Met His Phe Ala Val

T

Leu

The effect of mutations

Production of new/superior protein:Results: gain of reproductive advantage

Neutral mutation:Result: No change

Production of inferior or no protein:Result: Fatal and/or disease causing.

Causes of mutations

Mutagens such as:

X-rays

ionising radiation

chemicals

Summary Define the term:

somatic

mutation

deletion

addition

substitution

chromatid

evolution

variation

mutagen

www.clickbiology.com

13/04/2023

Reproduction between species

Liger

GeepZebroid

Mule

A “species” is defined as when organisms reproduce with each other to produce fertile offspring. Different species can sometimes mate and have offspring but they would be infertile. Some examples:

https://www.youtube.com/watch?v=gEXZzUeD90U

https://www.youtube.com/watch?v=8osbD1jtAmI

https://www.youtube.com/watch?v=zhXvFr1ZIyE

Compare the processes of sexual and asexual reproduction ■ sexual reproduction – the joining (fusion) of male and female gametes. The mixture of the genetic information from two parents leads to variety in the offspring.■ asexual reproduction – no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones.

Describe the process of taking a cutting.Take a piece from an old parent plant.Dip into hormone rooting powder and pot in compost.

Advantages: quick and cheap

Evaluate the economic, social and ethical issues concerning GM crops.- Increased yields, more profit and

cheaper produce.- Environmental activists - concerns about

GM crops include the effect on populations of wild flowers and insects.

- uncertainty about the effects of eating GM crops on human health.

- Is it right to try an influence the evolution direction of plants?

- Reduced gene pool

Define the terms: chromosome, gene, a short sequence of DNA to code for one characteristicgamete, a sex cell – sperm, ovum, pollen, ovuleClone, a genetically identical copy

Describe the process of making a tissue culture.Take a few cells from a plant and place on a petri dish with agar

Advantages: make thousands of copies

Describe the process of developing embryos for transplants Splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers

AdvantagesAnimals will all grow to a similar size and produce similar yields of milk / meat

DisadvantageMore likely to wiped out by a disease

Identify features that are inherited and those that are acquired in your lifetime.Inherited: eye colour, hair colour, attached ear lobes, tongue rolling, migraines

Acquired: piercings, scars, tattoos, dyed hair, suntan, learning a foreign language

Identify methods plants adopt to reproduce asexually.Bulbs in daffodils, runners in strawberries, tubers in potatoes, rhizomes in iris’,

Describe how a Bt plant has been genetically modified.Gene from the DNA of bacteria cell that produces toxin is cut out using enzymes. Length of DNA of same length cut out of chromosome in plant using enzymes.The cut out gene from the bacteria cell is inserted into plant cell using enzymes.

Describe the process of adult cell cloning:■ the nucleus is removed from an unfertilised egg cell. The nucleus from an adult body cell, eg a skin cell, is then inserted into the egg cell. An electric shock then causes the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.

Where might it be used?Clone a favourite pet.Grow tissues / organs for a patient