Biology - Lesson 3

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What did Gregor Mendel discover?

founder of the modern science of genetics.


define population

collection of interbreeding organisms of a particular species.


define Population genetics

the study of the frequencies of alleles and genotypes in populations and how these are affected by the mechanisms of evolution.


define adaptation

changes organisms go through successive generations to match the demands of their environment


define Microevolution

a change in allele frequencies in a population over generations


what 2 processes are involved in genetic variations?

mutation, and sexual reproduction. These produce variation in gene pools that contributes to differences among individuals in the population


Polymorphism is the........?

coexistence in the same population of two distinct hereditary types based on different alleles


___________ measures the average percent of loci that are heterozygous in a population.

Average heterozygosity


_____________is measured by comparing the DNA sequences of pairs of individuals

Nucleotide variability


Balanced Polymorphism....
This results in....
Give an example

Maintenance of more than one form or maintenance of a given locus of more than one allele
This results in heterozygotes being more fit than either homozygotes.
Example: Sickle cell disease and malaria.


define cline

, which is a graded change in a trait along a geographic axis


A __________ is a change in one base in a gene.

point mutation


Mutations in _________ of DNA are often harmless

noncoding regions


Mutations in a gene might not affect protein production because of _______.

redundancy in the genetic code.


In sexually reproducing organisms, __________________ is more important than mutation in producing the genetic differences that make adaptation possible

recombination of alleles


A ________consists of all the alleles for all loci in a population

gene pool


A ________is fixed if all individuals in a population are homozygous for the same allele



For diploid organisms, the total number of alleles at a locus is ______

the total number of individuals x 2


The total number of dominant alleles at a locus is 2 alleles for each ________ dominant individual plus 1 allele for each __________ individual



The Hardy-Weinberg principle describes a population that is

not evolving


Hardy-Weinberg equilibrium describes _____.

the constant frequency of alleles in such a gene pool.


p2 + 2pq + q2 = 1 explain what means what

Where, p2 and q2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype.


what are the five conditions for non-living poplations?

No mutations
Random mating
No natural selection
Extremely large population size
No gene flow


Three major factors alter allele frequencies and bring about most evolutionary change:

Natural selection
Genetic drift
Gene flow


Genetic drift describes

how allele frequencies fluctuate unpredictably from one generation to the next.


Genetic drift tends to ______ genetic variation through ______ of alleles.

reduce; losses


The founder effect occurs when _____.

a few individuals become isolated from a larger population.


The bottleneck effect is _______________.

a sudden reduction in population size due to a change in the environment.

The resulting gene pool may no longer be reflective of the original population’s gene pool.

If the population remains small, it may be further affected by genetic drift.


effects of genetic drift

Genetic drift is significant in small populations.
Genetic drift causes allele frequencies to change at random.
Genetic drift can lead to a loss of genetic variation within populations.
Genetic drift can cause harmful alleles to become fixed.


Gene flow consists of ___________________
Alleles can be transferred through the movement of _________________.

Gene flow tends to _____ differences between populations over time.

Gene flow is more likely than _______ to alter allele frequencies directly.

the movement of alleles among populations
fertile individuals or gametes (for example, pollen)


Relative fitness is the ______________.

contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals


Three modes of selection:

Directional selection favors individuals at one end of the phenotypic range
Disruptive selection favors individuals at both extremes of the phenotypic range
Stabilizing selection favors intermediate variants and acts against extreme phenotypes


sexual dimorphism

marked differences between the sexes in secondary sexual characteristics


Intrasexual selection is

competition among individuals of one sex (often males) for mates of the opposite sex.


Intersexual selection, often called mate choice,

occurs when individuals of one sex (usually females) are choosy in selecting their mates.


Various mechanisms help

to preserve genetic variation in a population.


Diploidy maintains

genetic variation in the form of hidden recessive alleles.


Balancing selection occurs when

natural selection maintains stable frequencies of two or more phenotypic forms in a population.


Heterozygote advantage occurs when

heterozygotes have a higher fitness than do both homozygotes.


In frequency-dependent selection,

the fitness of a phenotype declines if it becomes too common in the population.


Neutral variation is
Give examples

genetic variation that appears to confer no selective advantage or disadvantage.
1.Variation in noncoding regions of DNA
2.Variation in proteins that have little effect on protein function or reproductive fitness


Why Natural Selection Cannot Fashion Perfect Organisms

Selection can act only on existing variations.

Evolution is limited by historical constraints.

Adaptations are often compromises.

Chance, natural selection, and the environment interact.

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