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19.2 Population Genetics
The calculator can be used to determine a population's genetic structure.
Scientists refer to individuals in a population as polymorphisms, because they display different phenotypes or alleles of a particular gene.
Populations are called if they have two or more variations of the same characteristics.
Understanding the sources of variation in a population is important for determining how a population will evolve.
Population variation is shown by the distribution of phenotypes in this litter of kittens.
Natural selection and some of the other evolutionary forces can only act on an organisms genetic code.
Because alleles are passed from parent to offspring, those that confer beneficial traits or behaviors may be selected, while those that do not may not.
Most of the acquired traits are not heritable.
If an athlete works out in the gym every day and builds up their muscles, their offspring may not grow up to be a body builder.
A child may be given the ability to run fast if there is a genetic basis for it.
Jean-Baptiste Lamarck believed that organisms could inherit trait from one another.
Some scientists have recently begun to realize that Lamarck was not completely wrong, despite the fact that the majority of scientists have not supported this hypothesis.
To learn more, visit this site.
The evolutionary forces that act on heritable variation are more susceptible to heritability.
When scientists are involved in the breeding of animals in zoos and nature preserves, they try to increase the population's genetic variation to preserve as much of the diversity as possible.
A disease that is caused by a rare, recessive allele might exist in a population, but only if an individual carries two copies of it.
Only 25 percent of offspring of two carriers will inherit the disease from both parents, because the chance that two carriers will mate is low.
Natural selection won't be able to eliminate the allele from the population quickly because it won't happen frequently.
Changes in allele frequencies can shed light on how a population is evolving.
There are other evolutionary forces that could be involved in natural selection.
Natural selection is based on the idea that some people in a population are more likely to live longer and have more children than others.
A big, powerful male gorilla is more likely to become the silverback, the leader of the group, than a smaller, weaker one.
Half of the pack leader's genes will be passed on to his offspring, who are likely to be bigger and stronger than their father.
The population will grow larger on average as the population's genes for bigger size increase in frequency.
The selection pressure might be caused by better camouflage or a stronger resistance to drought.
By chance, some individuals will have more offspring than others, just because one male was in the right place at the right time, or the other one was in the wrong place.
It is possible to eliminate an allele from a population by chance.
rabbits with the brown coat color allele are more dominant over rabbits with the white coat color allele.
In the first generation, the two alleles occur with equal frequencies, resulting in p and q values.
A second generation with p and q values of.7 and.3 was created by only half of the individuals.
Two individuals in the second generation are dominant for brown coat color.
The b allele is lost in the third generation.
Small populations are more vulnerable to genetic drift.
Large populations are not affected by chance.
All of the population's genes will be lost if one of the 10 individuals dies before the next generation is born.
You can watch an animation of random sampling and genetic drift on this site.
A large portion of the population can be affected by a natural disaster.
The survivors' genetic structure becomes the entire population's genetic structure at once, which may be very different from the pre-disaster population.
The genetic variability within a population can be reduced by a chance event.
If a portion of the population leaves to start a new population in a new location or if a physical barrier divides the population, there is a chance of a strong influence of genetic drift.
The founder effect occurs when those individuals are an unlikely representation of the entire population.
The founder effect occurs when the genetics of the new population match those of the founding fathers and mothers.
The founder effect is believed to be a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa.
A higher proportion of the founding colonists carried these genes.
There is a short video to learn more about the founder and bottleneck effects.
The Fanconi Anemia Families of the Afrikaner Population of South Africa have evidence of a founder effect.
When a big earthquake or storm wipes out a lot of people, the survivors are usually a random sample of the original group.
The population's genetic makeup can change a lot.
The phenomenon is called the bottleneck effect.
Each time one runs this experiment, the results will vary.
Use different colored beads to count out the original population.
There are red, blue, and yellow beads.
After recording the number of each individual in the original population, place them all in a bottle with a narrow neck that will only allow a few beads out at a time.
Put 1/3 of the bottle's contents in a bowl.
A majority of the population is killed by a natural disaster.
Place all of the beads back in the bottle and repeat the experiment four more times.
The populations resulted from the experiment.
The populations all came from the same parent.
The five resulting populations are likely to differ a lot.
Natural disasters kill and spare people at random.
Think about how this might affect a population.
Some populations are stable.
Many plants send their pollen far and wide, by wind or bird, to other populations of the same species some distance away.
A pride of lions can experience immigration and emigration as developing males leave their mothers to seek out a new pride with genetically unrelated females.
Variable flow of individuals in and out of the group can change the population's gene structure and introduce new genetic variation to populations in different geological locations and habitats.
Gene flow occurs when an individual travels from one location to another.
Diversity in populations is influenced by changes to an organisms' genes.
Over time, the species evolve.
Novel genotypic and phenotypic variance can be introduced by the appearance of new genes.
Natural selection eliminates unfavorable or harmful genes from the population.
Others will spread through the population.
Whether or not a genetic change is beneficial or harmful depends on whether the change helps the organisms survive to sexual maturity and reproduce.
Natural selection can cause some genes to linger unaffected in the genome.
There are some genes that can have a dramatic effect.
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