Day 5) Factors that affect evolution & Evidence for evolution - Life Science 11 - Joanna Peng

Evolution

Change in the relative frequency of alleles in a population’s gene pool.

Allele

Alleles is a variations of gene.

A gene for eye colour would have brown, blue, and green alleles.

Inheritable mutations

Inheritable mutations are changes in DNA that can be passed from parents to children. An inheritable change to DNA occurs in germ cells (eggs & sperm). Mutations create new versions of genes, and those new versions add more differences among individuals in a population.

New ways inheritable mutations can occur:

1) Radiation - X-rays or UV exposure

2) Chemicals - Pesticides, herbicides, nicotine

3) During DNA replication

Beneficial mutations

Positively impacts the organism’s ability to survive in its environment. Mutations can be beneficial depending on the environment.

Harmful mutations

Negatively impacts the organism’s ability to survive in its environment. Mutations can be harmful depending on the environment.

Neutral mutations

Neutral mutations doesn’t impact the organism’s ability to survive or reproduce in its mutations.

Ex. Birth marks, type of thumbs, eye colour, etc.

Gene pool

A gene pool is all the alleles in a population.

Ex. In a population of rabbits, there may be alleles for: brown fur, white fur, black fur, long ears, short ears.

Which factors will change the frequency of certain alleles?

1) Natural selection

2) Gene flow

3) Genetic flow

4) Genetic drift (genetic bottleneck & founder effect)

5) Inbreeding

How does natural selection change the frequency of alleles?

Natural selection changes the frequency of alleles by increasing the number of helpful alleles in a population and decreasing the number of harmful alleles over many generations, because organisms with helpful traits are more likely to survive, reproduce, and pass those alleles to their offspring.

Gene flow

Gene flow is the exchange of alleles between two populations of the same species when individuals move and reproduce. More genetic variation can help a population survive changes.

Ex. Maybe western deer have more alleles for thicker fur, and eastern deer have more alleles for faster running. If some western deer move east and mate with eastern deer, their alleles enter the eastern deer population. That is gene flow.

Genetic drift

A change in a population’s gene pool due to random change. Genetic drift has a MAJOR impact on SMALL populations.

2 types: genetic bottleneck & founder effect.

Genetic bottleneck

A genetic bottleneck happens when a natural disaster, disease, or another sudden event greatly reduces the size of a population and gene pool, causing many alleles to be lost and lowering the population’s genetic variation.

By chance, the survivors will have certain alleles, which will change the gene pool.

Founder effect

The founder effect happens when a small group leaves a larger population and starts a new population, but the new group only carries a small part of the original gene pool. The small group are known as the founder population.

Founder population

A founder population is the new population started by a small group of individuals from a larger original population.

Inbreeding

Reproduction of closely related animals over multiple generations. Inbreeding matters because closely related parents are more likely to carry the same deleterious allele.

Ex. The House of Habsburg had Habsburg jaw.

Deleterious alleles

Deleterious alleles are alleles that can cause harmful effects, like disease, weakness, lower survival, or lower reproduction. Many deleterious alleles are recessive, which means they only show their harmful effect if an offspring gets two copies of that allele: one from each parent.

Artificial selection/Selective breeding

Happens when humans, rather than the environment, decide which traits are useful.

It works like this: individuals have different traits, then humans decide which trait they want more and selectively breed individuals with that trait. Then humans repeat the process until we get the traits that we desire.

Ex. Vegetables, pugs, etc.

Advantages of selective breeding

Selective breeding tries to establish certain traits that animals will pass to the next generation. These are traits that humans find desirable in domesticated species such as disease resistance, strength, calmness, more lean meat, endurance, etc.

Disadvantages of selective breeding

Selective breeding results in decreased genetic diversity found in the population. Undesirable traits from parents may appear in the offspring.

Ex. Diseases and health problems can accumulate in the population (deaf Dalmatians, bowers with heart disease, labs with hip problems, etc)

What are the 5 types of evidence for evolution?

1) Homologous structure

2) Vestigial structures

3) DNA evidence

4) Embryological development

5) Fossil record

Homologous structure

Parts of body that are similar in structure (same origin) but have different functions. This occurs because of divergent evolution.

Vestigial structure

A structure that has been reduced in size and function, but may once have been complete and functional.

Ex. Human’s tailbone, wisdom teeth, whale’s leg bones, emus wings, etc.

DNA evidence

Species that share a closer evolutionary relationship will exhibit a higher degree of similarity in their DNA.

Ex. Human & gorilla hemoglobin differs by 1 amino acid; Human & frog hemoglobin differs by 67 amino acid.

Embryological development

When embryos of different species develop in very similar ways, it suggests that they have a common ancestor.

Ex. Humans, birds, reptiles, and fish embryos look similar, suggesting that we all came from a common ancestor.

Fossil record

Fossils are preserved remains of organisms. Fossil record gives us a time scale of how long evolution takes (however there are many gaps in the record). It helps show similarities between extinct animals and animals alive today.

Gradualism

Changes happen slowly and gradually over a long period of time, rather than suddenly or in large leaps.

Punctuated equilibrium

Punctuated equilibrium suggests that species often experience long periods of little or no significant change (equilibrium), punctuated by relatively short periods of rapid and substantial change.

Long stable period → sudden faster change → long stable period again.

Occurs when there’s a big change in environment, for example: mass extinction events, migration into new environments, isolation of small populations.