Genetic Variation Overview
The goal of this standard is to understand how and why genetic variation develop in populations. The key concept is that diversity enables organisms to adapt to changing environments. As a consequence, DNA replication and activities during meiosis often result in DNA code alterations. Mutations may be advantageous or harmful, resulting in a gain in fitness or a loss in fitness.
Recombination during Meiosis
During meiosis, the process of genetic combining occurs in two ways. First, according to the Law of Segregation, diploid chromosomes are segregated into distinct haploid gametes. In essence, this divides your mother’s and father’s homologous chromosomes into distinct reproductive cells. This permits novel allele combinations to emerge in future generations, as well as the ability to conceal recessive alleles across generations.
Second, according to the Law of Independent Assortment, chromosomal separation does not occur along maternal and paternal lineages. In other words, each gamete is randomly given alleles for various qualities, and they do not necessarily follow the pattern found in parents. You may, for example, have any combination of your mother’s green eyes and black hair and your father’s blue eyes and blonde hair. (When genes are present on the same chromosome, they might indicate linkage, which lessens the chances of their being inherited independently.)
Finally, during meiosis, your maternal and paternal chromosomes are mixed together, guaranteeing that the collection of alleles you inherit is unlikely to include just your mother’s or father’s DNA. The Law of Independent Assortment is also aided by this.
Errors during Replication
Although DNA replication is a fairly precise process, minor mistakes sometimes occur. Though some mutations are not repaired or recognised by these systems, there is a vast cellular machinery made of many different proteins and chemicals that seeks to locate and rectify mutations.
Deletions, insertions, and point mutations are all examples of these mistakes. However, in order to be handed down to the next generation, these alterations must be present in gamete-producing cell lines.
Some mutations are generated by mutagens, which are substances in the environment that may modify or damage DNA outside of regular replication processes, such as those present in tobacco and vaping products. Mutagens may cause DNA damage in a variety of ways. Despite the fact that the cellular machinery is continually searching for and correcting mutations, some mutations unavoidably get through the cracks.
Germ-line cell mutations may be passed down to future generations, but somatic cell mutations are most typically displayed in cancer. Most cancers begin with small cell abnormalities that promote an increase in cellular division, resulting in tumour development. These malignancies may accumulate additional mutations over time, leading to metastasis, or the spread of cancer throughout the body.
A little clarification
This clarification statement is in the standard:
The emphasis is on utilising statistics to back up claims about how variation arises.
Let’s take a deeper look at this clarification to see what’s not included:
Supporting Arguments for the Origins of Variation
Gregor Mendel’s renowned “Pea Plant” experiments provided the first arguments in favour of the techniques of variation. Mendel demonstrated scientifically that kids inherit different combinations of features than their parents did throughout the tests. This resulted in the Laws of Segregation and Independent Assortment, which explain why kids show variance in qualities not found in their parents’ generation.
Other plainly visible human characteristics, such as eye and hair colour, may be used as basic arguments. In a class of 30, there should be at least one kid with a different eye colour/hair colour combination than either of their parents. This demonstrates that characteristics may be passed down maternal and paternal lineages and investigates the same fundamental principles that Mendel studied in pea plants.
What to Avoid
The following Assessment Boundary is also included in this NGSS standard:
The stages of meiosis and the biochemical mechanisms of individual steps in the process are not included in the evaluation.
Here’s a more detailed explanation of what it means:
Biochemical Mechanisms of Variation:
Other NGSS standards go into further detail on meiosis. The outcomes of meiosis, rather than the biochemical mechanisms that allow for recombination and diversity, should be the emphasis here. Students, for example, are not required to understand the individual proteins and mechanisms involved in DNA repair. They just need to know that the process is flawed, which adds variety (both good and negative) into the population for the purposes of this criteria.