Key Principles of Genetics and Evolution for Students
Genetics is a branch of science which deals with the study of genes, genetic variations, and heredity in organisms. Genes are made up of DNA and are a kind of genetic guidance. These instructions are used to make molecules and to regulate the chemical reactions of life. We are transferred from parent to offspring.
What is Genetics ?
We have studied in earlier classes about the DNA present inside the nucleus of the cell. DNA of male and female gametes combine and form a new DNA during the fertilization and gamete formation. This DNA gets transferred in the cells of the offspring and is responsible for the transfer of biological information required for the growth of the organism. This particular substance is known as gene in the common language and Biology as well. Gene is formed out of DNA molecules arranged in a helical structure. The study of all these genes is known as Genetics. Though the term is a very recent development, as a concept it has been used by mankind since prehistoric times for breeding and developing crop species.
Evolution
It is a process of hereditary changes in the population of organisms over several generations. The inherited traits are the expression of genes that are copied and transmitted to the offspring during reproduction. Heritable traits that are useful for survival and reproduction become more common, while harmful traits are uncommon.
What is Evolution ?
It is said that life originated 3.6 billion years ago. It started with unicellular organisms or prokaryotic bacteria. Later it developed into more structured cellular organisms called eukaryotic organisms. These eukaryotic organisms in turn developed into multicellular organisms and gradually into more bigger and complex organisms. But the diversity we see today resembles nothing like those during the origin of life on the history of earth. plants and animals have changed substantially over their ancient predators with time. This phenomenon is known as evolution.
The evolutionary biology describes how the organisms get adapted to the ever changing natural environment by the process of natural selection. Charles Darwin was the pioneer of this theory. He drew this conclusion by observing the similarity between two or more distant species of animals or birds of the same family. He also discovered the modification of body parts of the same species living in different environments or habitats.
Evolutionary Genetics
Evolutionary genetics is a study of how genetics leads to evolutionary changes. It involves studying the evolution of the structure of the genome. This is the sum of population genetics and evolution. Genome evolution is the process by which the size and structure of the genome change over time. The prokaryote genome develops through mutation, transduction, and horizontal gene transfer.
What is Evolutionary Genetics?
Evolutionary genetics is known as how genetic variation contributes to evolutionary changes. This includes the evolution of the genome structure, the genetic basis of adaptation and specification, and genetic changes in response to population selection. Evolutionary genetics is the sum of the genetics and evolution of the population.
Evolution of Structure of Genome
Genome evolution is defined as the process by which the genome changes its structure and size over time. The evolution of the prokaryotic genome happens by a number of methods-mutation, horizontal gene transfer, and transduction. The mutation is any permanent change in the body's nucleotide sequence. Horizontal gene transfer is a method of transferring genetic material from donor to recipient that is different from the vertical transfer (from parent to offspring).
Example of Genome Evolution - Bacteria
Transduction is another mode that takes evolution into the structure of the genome. It is defined as the transfer of genetic material via the virus to the cell. Figure 2 below: shows the evolutionary methods of prokaryotes. The eukaryotic genome is larger and more complex than the procaryotes. They 're evolving through sexual reproduction. This introduces a wide genetic diversity in eukaryotes compared to prokaryotes.
Mechanism of Genome Evolution
1.Duplication of Gene
This is the duplication of a particular DNA region. It occurs by recombination, aneuploidy, transposition, polyploidy, and error in DNA replication.
2.Transposable Components
This refers to a DNA region that can be inserted anywhere in the genome. Ty elements in Drosophila, for example. Sequence Alu is the most common transposable element found in humans.
3.Mutation
Spontaneous mutations are responsible for genome changes. The nucleotide sequence changes resulting in a frameshift mutation that alters the genome. This is most common in prokaryotes.
4.Exon's Shuffling
During this time, two exons from different genes come together. This process is created by new genes. As a result, a new gene is inserted in the genome.
What are the Different Mechanisms of Genome Evolution?
Gene Duplication- When a particular DNA region is duplicated. Gene duplication can occur through recombination, transposal, aneuploidy, polyploidy, and replication of the slippage (DNA replication error). Gene replication via recombination occurs when there is an irregular crossing at the time of meiosis.
Transposable Elements – A region of DNA that can be inserted anywhere in the genome either by "cutting and paste mechanism" or by "copy and paste mechanism." For example, "Ty elements in Drosophila." The most common transposable element found in humans is the Alu sequence.
Mutation - Spontaneous mutations often cause changes in the genome. Mutations induce changes in the nucleotide sequence that induce the mutation of the frameshift, thereby altering the genome. It is also one of the processes of adaptation of the genome. Most common in prokaryotes.
Exon Shuffling - During exon shuffling, two exons of two different genes come together to form exon or repeat the same exon. This is the process by which new genes are being created. This adds a new gene to the genome. This plays an important function in the evolution of the genome.
Are Chimps Closer to Humans than Gorillas?
Earlier human species have been kept in the Hominidae family and apes have been kept in Pongidae. This separation was based on certain features, such as the more advanced human brain and bipedal locomotion. Yet recent work has indicated that chimpanzees are nearest to the man followed by gorillas. The genetic material of primates and humans is closely linked to each other. The genetic material of chimpanzees and man differ by 1.2 percent, while the difference between gorillas and man is about 1.6 percent. This difference in genetic material confirms that chimpanzees are closer to humans than gorillas.
Terms to Remember
Exon is the coding part of the gene, i.e. exon is a part of gene expression. The mature RNA messenger consists only of exons, which are later translated into protein.
Aneuploidy is a deletion or addition of chromosome number, which in normal humans contains 46 chromosomes, but aneuploidy results in either 45 or 47 chromosomes.
Polyploidy consists of more than two sets of chromosomes.
Transposition is a process in which the segment of the chromosome is transferred to a new position.
FAQs on Genetics and Evolution Explained Simply
1. What is the fundamental relationship between genetics and evolution?
Genetics and evolution are intrinsically linked. Genetics is the study of heredity and the variation of inherited characteristics. It provides the raw material for evolution. Evolution is the process by which these heritable variations change in frequency over generations, driven by mechanisms like natural selection. In simple terms, genetics explains how traits are passed on and varied, while evolution explains how these changes lead to the diversification of life over time.
2. What are Mendel's Laws of Inheritance and why are they significant in biology?
Gregor Mendel proposed three fundamental laws of inheritance which form the basis of classical genetics. Their significance lies in demonstrating that traits are passed down as discrete units (genes). The laws are:
- Law of Dominance: In a heterozygous individual, one allele (the dominant one) will mask the expression of the other allele (the recessive one).
- Law of Segregation: During gamete formation, the two alleles for a character separate (segregate) from each other, so that each gamete ends up with only one allele.
- Law of Independent Assortment: Alleles for different traits are inherited independently of one another, provided they are on different chromosomes.
3. How do concepts like incomplete dominance and codominance differ from Mendel's original Law of Dominance?
Incomplete dominance and codominance are non-Mendelian inheritance patterns that show variations from simple dominance.
- In incomplete dominance, the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. For example, crossing a red-flowered snapdragon with a white-flowered one results in pink-flowered offspring.
- In codominance, both alleles in the heterozygote are fully and simultaneously expressed. A classic example is the human ABO blood group system, where an individual with alleles for both A and B antigens has the AB blood type.
4. What is the theory of evolution by natural selection as proposed by Charles Darwin?
The theory of evolution by natural selection, proposed by Charles Darwin, is a primary mechanism for how evolution occurs. It is based on several key principles:
- Variation: Individuals within a population exhibit a range of heritable traits.
- Inheritance: These traits are passed from parents to offspring.
- Differential Survival and Reproduction: Individuals with traits better suited to their environment are more likely to survive, reproduce, and pass those advantageous traits to the next generation.
5. How does comparing the DNA of humans and chimpanzees provide evidence for evolution?
Comparing the DNA of different species is a powerful piece of molecular evidence for evolution. Humans and chimpanzees share approximately 99% of their DNA. This high degree of genetic similarity strongly suggests that both species diverged from a common ancestor relatively recently in evolutionary time. The small differences in their DNA sequences represent the genetic changes that have accumulated in each lineage since they separated, providing a molecular record of their evolutionary history.
6. What are mutations, and what is their role in creating genetic variation?
A mutation is a permanent alteration in the nucleotide sequence of an organism's DNA. Mutations are the ultimate source of all new genetic variation. They can arise spontaneously from errors during DNA replication or be induced by environmental factors called mutagens (e.g., UV radiation). While many mutations are neutral or harmful, some can create new alleles that may be beneficial. This new genetic information provides the raw material upon which natural selection and other evolutionary forces act.
7. Why is gene duplication considered a major force in the evolution of new biological functions?
Gene duplication is an important evolutionary mechanism where a segment of DNA containing a gene is copied, resulting in two identical genes in the genome. Following duplication, one copy can continue to perform its original, essential function. The second, redundant copy is then free from the same selective pressures. This allows it to accumulate mutations over time, which can potentially lead it to acquire a completely new function. This process is a key pathway for the evolution of novel traits and increased biological complexity.
8. What is the Hardy-Weinberg principle and what does it describe?
The Hardy-Weinberg principle is a foundational concept in population genetics. It states that in a large, randomly mating population, the allele and genotype frequencies will remain constant from generation to generation, provided that other evolutionary influences are not acting. These influences include mutation, gene flow, genetic drift, and natural selection. The principle describes a hypothetical, non-evolving population and serves as a crucial baseline (a null hypothesis) to measure and detect if evolution is occurring in a real population.
