3. A species of rats live in a certain type of tree with the branches evenly spaced. Smaller rats could not reach from branch to branch and larger rats would break the branches and fall. Soon, all rats were just the right size for the tree branches. Analyze the given example and evaluate how variation, adaptation and natural selection are major components of evolution.

Different body size of the rat population serves as variations. The smaller and larger rats cannot reach the branches but the rats with average body size are better adapted to reach the tree branches. The change in body size (average) is a result of random mutation. Due to their better fitness to the given habitat, their population size increases resulting in an increased number of rats with average body size in the population.  

Explanation:  

Evolution represents the accumulation of variations in the population of organisms. These variations are imparted by evolutionary agents. Mutation, genetic recombination, gene flow serve to add new genetic variations in the populations. These variations are the raw materials on which evolutionary forces act to bring about changes in the populations.  

Natural selection serves to drive the process of evolution. It requires the presence of genetic variations in the population. The organisms with the genetic traits that allow them to survive well in the given conditions are favoured by natural selection. This results in an increased frequency of the beneficial genetic trait in the population with generations.

In the given example, the rat population exhibits genetic variation for body size. The population has rats of smaller and larger body size. The smaller rats find it difficult to reach the branches of trees. On the other hand, the larger rats can reach the branches but fall off due to breaking of the branches. Random mutations give rise to rats of average size that can reach the branches without breaking them apart. They are adapted to the pattern of the trees grown in the habitat. They survive well and reproduce more to leave more progeny. With time, the number of rats with average body size is increased in the population and the population is said to be adapted to reach the tree branches.  

six grader is what i am ssorry

the african cheetah.

this species has a relatively low level of genetic

variation because the population was reduced to a small size approxi-

mately 10,000 to 12,000 years ago.

chapter   outline

24.1

genes in populations and the hardy-

weinberg equation

24.2

factors that change allele and genotype

frequencies in populations

24.3     sources of new genetic variation

population   genetics

24

until   now,   we   have   primarily   focused   our   attention   on   genes  

within   individuals   and   their   related   family   members.   in   this  

chapter   and   chapters   25   and   26   ,   we   turn   to   the   study   of   genes   in  

a   population   or   species.   the   field   of

population   genetics

  is   con-

cerned   with   changes   in   genetic   variation   within   a   group   of   indi-

viduals   over   time.   population   geneticists   want   to   know   the   extent  

of   genetic   variation   within   populations,   why   it   exists,   and   how   it  

changes   over   the   course   of   many   generations.   the   field   of   popu-

lation   genetics   emerged   as   a   branch   of   genetics   in   the   1920s   and  

1930s.   its   mathematical   foundations   were   developed   by   theoreti-

cians   who   extended   the   principles   of   gregor   mendel   and   charles  

darwin   by   deriving   formulas   to   explain   the   occurrence   of   geno-

types   within   populations.   these   foundations   can   be   largely   attrib-

uted to three scientists: sir ronald fisher, sewall wright, and j. b. s.

haldane.   as   we   will   see,   support   for   their   mathematical   theories  

was provided by several researchers who analyzed the genetic com-

position   of   natural   and   experimental   populations.   more   recently,  

population   geneticists   have   used   techniques   to   probe   genetic  

variation   at   the   molecular   level.   in   addition,   staggering   advances  

in   computer   technology   have   aided   population   geneticists   in   the  

analysis   of   their   genetic   theories   and   data.   in   this   chapter,   we   will  

explore   the   genetic   variation   that   occurs   in   populations   and   con-

sider   the   reasons   why   the   genetic   composition   of   populations   may  

change over the course of several generations