Sources of Genetic Variation in Cells

Independent assortment

Recombinant chromosomes

Chromosomal mutation

Transposition

Plants

8.4 million (2^23)

a set of organisms that interbreed among themselves but not with other species

a set of organisms that are sufficiently similar to one another and sufficiently different from members of other species

It occurs when gene flow is interrupted due to geographical separation of populations.

Polyploidy, habitat differentiation, and sexual selection

An individual with more than two chromosome sets derived from a single species

They are more likely to become a new species but are also often likely to perish.

The drug 3TC replaced Cytosine in normal DNA, making reverse transcriptase enzyme more discriminating and leading to the emergence of 3TC-resistant HIV strains.

The pea comb mutation, being small-sized, dissipates less heat and offers less area for injury, making it advantageous for cock-fighting in cold environments.

The mutation involved a massive amplification of a duplicated sequence in intron 1 of the gene for SOX5 transcription factor, leading to the development of the pea comb.

Characteristic traits pass on due to heritable variations with alternative forms of genes (alleles), following Mendel's laws of segregation and independent assortment.

Each gene has two alleles, one inherited from each parent, which can have distinct states and may differ in nucleotide sequence at the same locus.

A difference in nucleotide sequence in one place of a gene can alter the protein structure produced, affecting the gene's function and potentially resulting in observable phenotypic changes.

Dominant alleles are phenotypically expressed for homozygous or heterozygous conditions, while recessive alleles are only expressed phenotypically for homozygous condition.

Human blood type A, B, AB, and O are examples of multiple alleles. The varied combinations of two alleles result in the expression of three or more discrete states.

Pleiotropy is when a single gene has multiple phenotypic effects. An example is sickle cell anemia, which shows multiple symptoms associated with the disease.

Epistasis occurs when a gene at one locus alters the phenotypic expression of a gene at a second locus. An example is the gene E controlling the expression of dark pigment in certain organisms.

Polygenic inheritance refers to differences in appearance or function shown in small, incremental ways, involving multiple genes. An example is human skin color, which is controlled by multiple genes.

Sex cells undergo two consecutive cell divisions that reduce the chromosome number from diploid to haploid, resulting in the formation of gametes.

The Founder Effect occurs when few individuals from a large population migrate to an isolated area, leading to a small genetic composition of the colonists compared to the original population. An example is when a few birds from a mainland population colonize a remote island.

The main outcome of Natural Selection is the differential success in reproduction, leading to the selection of alleles that are passed on to the next generation in proportions disproportionate to their frequencies in the present generation.

Gene Flow tends to reduce genetic differences between populations as it involves the exchange of alleles through migration, which can lead to the fusion of populations into a single one.

A Mutation is a change in the sequence of nucleotides in an organism's DNA. It is the source of new alleles and can give rise to structural, functional, or behavioral alterations that impact an individual's chances of survival and reproduction.

Lethal mutations result in a drastic change in phenotype that leads to the death of the organism, while Neutral mutations are changes in the base sequence that have no effect on survival or reproduction.

Natural Selection results in differential reproductive success based on genetic variations, allowing individuals with advantageous traits to survive and pass on their alleles to the next generation, thus adapting the population to its environment.