EVOLUTION AT THE POPULATION LEVEL
Understanding genetics at the population level is fundamental to studying evolution. Let's look at an example of how wing color in moths has been affected by industrialization. This example illustrates evolutionary processes and Darwin’stheory of natural selection.
Biston betularia is a moth that has light-colored wings with black speckles (hence its name "peppered moth") and is commonly found in Great Britain, In the late 19th century, during the industrial revolution in the U.K., trees near cities became blackened from pollution. Coincidently, biologists noticed the increasing presence of a dark-winged form of B. betularia in these regions. Dark-winged moths produce more melanin, orpigment, than light-winged moths. How did the dark wings evolve?
Initially, among B. betularia populations, both light-winged as well as dark-wingedindividuals were present. This is an example of VARIATION in a population.
As the industrial revolution progressed, and the bark of trees became darkened by pollution, the dark-winged moths had a higher survivorship and more reproductivesuccess than light-winged individuals, which were eaten. This resulted in DIFFERENTIAL FITNESS betweenthe two forms. This is because the dark color worked as a camouflage againstthe dark tree bark, thereby protecting them from predators (birds). The dark-winged moths were "naturally selected” for , and light-winged moths were “naturally selected” against, because of particular environmental conditions.
Finally, these variations were HERITABLE and therefore were passed on to offspring. More dark-winged parents survived to produced more offspring, and those offspring had dark wings. In contrast, fewer light-winged individuals survived to reproduce. This is how a population of mostly light-winged moths gradually gave rise to a populationof mostly dark-winged moths.
In recent years, the sootiness that prevailed during the 19th century has gone, even from the urban cities of England. In parallel, the dark-winged form of the moth has declined dramatically in frequency since then. This shows how a particular trait might only be favorable under specific environmentalconditions.
FAQs
Meiosis II is very similar to mitosis, in the sense of sister chromatid separation. Meiosis II involves 4 steps: prophase II, metaphase II, anaphase II, and telophase II.
How many daughter cells are there in meiosis 2? ›
Meiosis I is followed by meiosis II, which resembles mitosis in that the sister chromatids separate and segregate to different daughter cells. Completion of meiosis II thus results in the production of four haploid daughter cells, each of which contains only one copy of each chromosome.
What happened in prophase 2? ›
During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells.
What happens in telophase 2 of meiosis 2? ›
Telophase II: The chromosomes gather at the 2 poles of the cell and the cell divides via cytokinesis forming 2 daughter cells (1n 1c) from each of the two cells from meiosis I. The nuclear envelope reappears, the spindle apparatus disappears and the chromosomes de-condense back into chromatin.
What are the different stages of meiosis 1 2 3 and 4 in sequence? ›
The correct sequence is: Synapsis → Crossing over → Disjunction of genomes → Terminalization. Q. Arrange the following events of meiosis in a correct sequence.
What is meiosis 2 also known as? ›
Meiosis II is termed as Equational Division because the Chromosome number at the end of meiosis II, remains the same as at the end of meiosis I, in daughter cells. To further clarify, at the end of meiosis I, there are two daughter cells with 1n chromosomes each.
How many pieces of DNA are found after meiosis 2? ›
After meiosis II, when each parent cell gets divided into two gametes each gamete cell contains 23 chromosomes. In this phase, each gamete remains haploid in nature. At the end of meiosis II, each cell will have the half number of the actual chromosome i.e. 23 chromosomes.
What is meiosis 2 similar to? ›
Meiosis II is the second division of meiosis. It occurs in both of the newly formed daughter cells simultaneously. Meiosis II is similar to Mitosis in that the sister chromatids are separated.
What separates during meiosis II? ›
Subsequently, during meiosis II, the sister chromatids separate to produce a total of four products, each with half the number of chromosomes as the original cell. The separation of hom*ologous chromosomes or sister chromatids relies on them being pulled apart by microtubules.
Is meiosis asexual? ›
Meiosis does not occur during asexual reproduction. Meiosis is the process of producing gametes (eggs and sperm).
In anaphase II, chromosomes divide at the centromeres (like in mitosis) and the resulting chromosomes, each with one chromatid, move toward opposite poles of the cell. Four haploid nuclei (containing chromosomes with single chromatids) are formed in telophase II.
What is the second meiotic division? ›
The second meiotic division then separates the two sister chromatids from each other. Consequently, each of the four cells produced by meiosis has a single (haploid) copy of each chromosome.
Is mitosis asexual? ›
Mitosis is a phase of the cell cycle in which a cell's nucleus is divided into two nuclei, each with an equal quantity of genetic material. It is an asexual reproductive process that occurs in unicellular organisms. Thus, mitosis is a type of cell division that occurs during the asexual reproduction process.
Are haploid gametes identical? ›
Telophase I: Newly forming cells are haploid, n = 2. Each chromosome still has two sister chromatids, but the chromatids of each chromosome are no longer identical to each other.
Does meiosis 2 have cytokinesis? ›
Telophase II and Cytokinesis
Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid.
What are the four phases of mitosis 2? ›
Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase. Some textbooks list five, breaking prophase into an early phase (called prophase) and a late phase (called prometaphase).
What are the stages of meiosis 2 quizlet? ›
Q-Chat
- meiosis 2. divides sister chromatids. ...
- prophase 2. nuclear membrane breaks down, centrosomes and centrioles move to opposite sides of the cell, spindle fibers start to assemble.
- metaphase 2. spindle fibers align the chromosomes along the cell equator.
- anaphase 2. ...
- telophase 2.
In the final step, called telophase II, two nuclei form and the two cells separate to form four cells, each with a single chromosome. So now that we have the correct sequence for meiosis II, we can see that the best option is given by answer choice (C): prophase II, metaphase II, anaphase II, telophase II.
What are the 4 cells made at the end of meiosis 2? ›
Final answer: The four daughter cells produced at the end of Meiosis II are haploid. This is because the original diploid cell divides into two haploid cells during Meiosis I and these haploid cells divide again during Meiosis II but their chromosome number does not double.
Initially, among B. betularia populations, both light-winged as well as dark-wingedindividuals were present. This is an example of VARIATION in a population.
