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Changes in allele frequencies that are identified in a population can shed light on how it is evolving. In addition to natural selection, there are other evolutionary forces that could be in play: genetic drift, gene flow, mutation, nonrandom mating, and environmental variances.

Genetic drift

The theory of natural selection stems from the observation that some individuals in a population are more likely to survive longer and have more offspring than others; thus, they will pass on more of their genes to the next generation. A big, powerful male gorilla, for example, is much more likely than a smaller, weaker one to become the population’s silverback, the pack’s leader who mates far more than the other males of the group. The pack leader will father more offspring, who share half of his genes, and are likely to also grow bigger and stronger like their father. Over time, the genes for bigger size will increase in frequency in the population, and the population will, as a result, grow larger on average. That is, this would occur if this particular selection pressure , or driving selective force, were the only one acting on the population. In other examples, better camouflage or a stronger resistance to drought might pose a selection pressure.

Another way a population’s allele and genotype frequencies can change is genetic drift    ( [link] ), which is simply the effect of chance. By chance, some individuals will have more offspring than others—not due to an advantage conferred by some genetically-encoded trait, but just because one male happened to be in the right place at the right time (when the receptive female walked by) or because the other one happened to be in the wrong place at the wrong time (when a fox was hunting).

Art connection

 A population has 10 rabbits. 2 of these rabbits are homozygous dominant for the B allele and have brown coat color. 6 are heterozygous and also have brown coat color. Two are homozygous recessive and have white coat color. The frequency of the capital B allele, p, is .5 and the frequency of the small b allele, q, is also .5.Only 5 of the rabbits, including 2 homozygous dominant and 3 heterozygous individuals, produce offspring. 5 of the resulting offspring are homozygous dominant, 4 are heterozygous, and 1 is homozygous recessive. The frequency of alleles in the second generation is p=.7 and q=.3. Only 2 rabbits in the second generation produce offspring, and both of these are homozygous dominant. As a result, the recessive small b allele is lost in the third generation, and all of the rabbits are heterozygous dominant with brown coat color.
Genetic drift in a population can lead to the elimination of an allele from a population by chance. In this example, rabbits with the brown coat color allele ( B ) are dominant over rabbits with the white coat color allele ( b ). In the first generation, the two alleles occur with equal frequency in the population, resulting in p and q values of .5. Only half of the individuals reproduce, resulting in a second generation with p and q values of .7 and .3, respectively. Only two individuals in the second generation reproduce, and by chance these individuals are homozygous dominant for brown coat color. As a result, in the third generation the recessive b allele is lost.

Do you think genetic drift would happen more quickly on an island or on the mainland?

Small populations are more susceptible to the forces of genetic drift. Large populations, on the other hand, are buffered against the effects of chance. If one individual of a population of 10 individuals happens to die at a young age before it leaves any offspring to the next generation, all of its genes—1/10 of the population’s gene pool—will be suddenly lost. In a population of 100, that’s only 1 percent of the overall gene pool; therefore, it is much less impactful on the population’s genetic structure.

Questions & Answers

explain cell biology
Grace Reply
what are endotherms
angelina Reply
pls can someone elaborate more on biomagnification
angelina
Hey,what?
Peter
Biomagnification, also known as bioamplification or biological magnification, is any concentration of a toxin, such as pesticides, in the tissues of tolerant organisms at successively higher levels in a food chain.
chance
An endotherm (from Greek ἔνδον endon "within" and θέρμη thermē "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat.
chance
What diffusion
Oseres Reply
it is the movement of water molecules from the region of higher concentretion to a region of lower concentration
Lukas
is the movement of anything from region of higher concentration to a region of lower concentration.
chance
pls I don't know how to read very well so how can I understand all this
Mercy Reply
What's succession
Talabi Reply
an acid is a substance that produces hydrogen ions in an aqueous solution
angelina Reply
what is acid
asaa Reply
An acid is a substance which gives Hydrogen ions in aqueous solutions.
Ahsan
food poison
asaa
the difference between prokaryotic cells and Eukaryotic cells
Itz Reply
karyon is nucles eukaryotes have intact membrane around its nucleus, whereas prokaryotes don't have nuclear membrane and other membrane bounded organelles
Ishitha
what is the function of chyme
Divine Reply
what makes a tissue
Divine
cells
Yazi
tell me
Betty
chyme where digested food passes from e stomach through e pyloric sphincter in 2 e duodenum.
Mary
what is an osmosis
SSEJJO Reply
tell me the answer
Betty
Osmosis is the movement of the water molecules through a semipermiable membrane from lower to higher concentrated solution.
Ahsan
is the movement of water molecules from the area of high concentration to the area of low concentration through a semi permeable membrane.
SSEJJO
what is hypertonic solution
SSEJJO
A solution having more solute concentration as compared to a cell which is in place, results shrinkage of cell.
Ahsan
what is water potential
SSEJJO
uses of Osmosis
SSEJJO
what is the meaning of hypothesis
Memory Reply
what is the function of chyme
Jack Reply
what is meiosis,and does it work
Chisom Reply
it's a reduction of chromosomes it is caried by haploid in which it divides the chromosomes by 2 this means by 23n -23n
Mwansa
what is biology
WESINA Reply
is a branch of science that deals with the environment
Ali
The term biology is a combination of two things I .e bio mean life and logy mean study ; And all the study is about life .
Bangura
biology is a branch of science which deal with the study of living organisms and their vital processes .
Sky
biology is the branch of science that deal with the combination of living things and non living things i.e plant and animal
Ezenwa
what is genetic
Mumbere Reply
what is reproduction
Mumbere

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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