10.3 Gene pools and speciation Flashcards
(123 cards)
What is a species?
A group of organisms that can interbreed to produce fertile offspring (this definition can only be used with sexually reproducing species).
What is the ability of species to evolve limited by?
The genetic variations that exist.
What is a population?
This refers to individuals of the same species living in the same place and time.
What is a gene pool?
- The set of all the variations of all genes in any population.
- A gene pool is similar to the genome of an individual, but includes the alleles of all individuals in the population.
Alleles in gene pools
- Some alleles will be common in the gene pool, and others will be rare.
- All members of a population share a gene pool.
- When they reproduce, their alleles may combine with any of the alleles found in the gene pool depending on the choice of partner.
Define gene pool
A gene pool consists of all the genes and their different alleles present in an interbreeding population.
What is allele frequency?
The allele frequency, usually expressed as a percentage or proportion, measures how common an allele is in a population.
What is the depth, or richness, of a gene pool measured by?
By the number of alleles and their relative frequencies.
Diagram showing a simplified version of the gene pool of dogs
Characteristic alleles in dog breeds
- Dog breeds have particular characteristic alleles that confer their distinctive body shape and size, their fur color and length, and their personality traits.
- In similar breeds, such as different types of collies or terriers, many of the same alleles are common.
- In breeds that are very different, there will be numerous alleles that are common in one breed but rare in the other.
- However, dogs are a single species.
- Through sexual reproduction between breeds, every possible combination of alleles in the gene pool could exist in individual dogs.
Whenever genetic variation exists, so does ___
The potential for genetic change.
What is genetic drift?
Random fluctuations in allele frequency
In what situations is there little genetic change in a population?
If the population has allele frequencies that are already well adapted to the environment, there is often little genetic change because natural selection acts to maintain the status quo.
What is a prerequisite for evolution?
Genetic variation
What is the original source of all genetic variations?
Mutation in DNA
What is the significance of mutations in DNA
- The original source of all genetic variations is mutation in DNA.
- These mutations are often harmful, sometimes neutral, and occasionally beneficial.
- Though each mutation is a random event, mutations do occur in all living things.
- Mutations form alleles, and evolution occurs whenever there is a change in allele frequencies.
Why does natural selection act on the entire collection of alleles that constitute the individual?
How do new allele combinations in individuals occur?
- Through crossing over and random orientation of homologous chromosomes in meiosis and the fusion of genetic material from two parents.
- Thus, given enough time and a large enough population, alleles that are helpful become more common in the population, even though every individual contains a combination of beneficial and harmful alleles.
Evolution requires that allele frequencies ___
Change with time in populations.
Overview of natural selection and selective pressure
- In a population, individuals with different combinations of alleles may show differential survival and reproductive success because of natural selection.
- Selective pressure leads to the evolution of the population.
What happens when populations are isolated from each other?
- Genetic drift and different selective pressures can cause the populations to evolve differently.
- Over time, when enough differences accumulate, the populations may speciate.
What is selective pressure?
- Environmental factors can affect the rates of survival and reproduction of certain phenotypes (which are determined by alleles).
- This influence of natural selection is called selective pressure.
What is selective pressure caused by?
By both biotic and abiotic factors that change the rate of survival and reproduction of a segment of a population.
Selective pressure can be ___ or ___.
Weak
Strong