- 01. What is the Aim of Learning About Genetics in the Junior Cycle?
- 02. What is Genetics, Inheritance and Variation?
- 03. What is the Difference Between Sexual and Asexual Reproduction?
- 04. What is DNA and What does it do?
- 05. Gregor Mendel and Genetic Discovery
- 06. Keywords in Inheritance and Variations
By the time you study Inheritance and Variation in school, you should have already studied the chapter on Human Reproduction, as having an understanding of the egg and sperm will be useful when studying this section. In fact, there are several topics in Junior Cycle Biology which may interlink.
"Our own genomes carry the story of evolution, written in DNA, the language of molecular genetics, and the narrative is unmistakable."
Kenneth R. Miller
What is the Aim of Learning About Genetics in the Junior Cycle?
By learning the inheritance and variation topic in Junior Cycle Science you will gain the following knowledge:
- You will be able to define key terms such as DNA, variation, asexual reproduction, species, chromosome and gene.
- You will learn how to compare and contrast asexual and sexual reproduction.
- You will learn about the number of chromosomes (and pairs) which are in normal body cells and gametes.
- You will be able to identify, compare and contrast two different types of variation
- You will be able to identify the 3 main scientists and their discoveries regarding DNA and genetics.
As in other topics such as the digestive system and evolution, there are many experiments and activities which will take place both in and out of the classroom. For example, your teacher may show you how to extract DNA from fruit such as a Kiwi.
What is Genetics, Inheritance and Variation?
We are going to look at this topic in more detail, however, first I want to give you the basic definition of each.
- Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.
- Variation is the way members of the same species differ (in DNA)
- Inheritance is the explanation of how genetic material is passed from parent to child.
Now that we can identify each, it's time to take a closer look:
Variation is the degree to which offspring differ from their parents. There are two types of variation, genetic also known as inherited and non-inherited which may be called acquired genetics.
Inherited characteristics are passed down from parents to children and include things such as height, eye colour, eye shape and even sometimes shape your face.
Non-inherited characteristics are things that we learn, they are not controlled by our genetics. An example of non-inherited characteristics could be the ability to be creative with art or writing, the ability to learn a musical instrument or language quickly or even learning to ride a bike.
What is the Difference Between Sexual and Asexual Reproduction?
There are two types of reproduction that you will learn about in Junior Cycle Science, Sexual Reproduction and Asexual Reproduction.
Sexual Reproduction is when two-parent gametes, one male and female, fuse together to form a zygote. Their offspring will contain genetic information from both parents, it will be similar (inherited characteristics) to its parents but will have characteristics that differ from them (variation/non-inherited).
Asexual Reproduction involves only one parent with the offspring having identical genetic information. Some plants such as strawberry plants and potatoes reproduce asexually as well as certain bacteria. There is no variation in asexual reproduction.
"The more that I looked at DNA, the more I realized it was nature and nurture. It's how genes and your environment work together to produce the person you are."
What is DNA and What does it do?
DNA is an abbreviation for Deoxyribo-Nucleic Acid. DNA is in every single cell of every living thing, it is found in structures of the cell called chromosomes.
When DNA works correctly, it helps keep the body functioning properly it is also what allows living things to reproduce. The genes in DNA pass along physical traits from parents to children. Sometimes there are mistakes in DNA (these are what are know as genetic mutations) which can cause diseases and other problems.
DNA has a unique structure, it is made of chemical substances that are linked together like a chain (strand) shaped like a double helix. Each piece of DNA has two strands that are joined together by links (think of it like a spiral ladder) these links are known as bases. There are four different bases in DNA: adenine, thymine, guanine, and cytosine. These four chemicals are repeated in different orders over and over again in each strand of DNA.
Human DNA contains about 3 billion pairs of these bases.
When the DNA mixes, there will be two of each gene, one from each parent. Depending on the gene, sometimes both can work together or sometimes one gene will control everything itself. We call genes that win out over other genes dominant genes. Genes that lose out to dominant genes are called recessive genes.
Gregor Mendel and Genetic Discovery
Gregor Mendel was a Czech-Austrian monk better known as the "Father of Genetics". Through his work on pea plants, he discovered the fundamental laws of inheritance. He found that the plants' respective offspring retained the essential traits of the parents, and therefore were not influenced by the environment. This simple test gave birth to the idea of heredity.
Some of Mendel's main discoveries include:
- He deduced that genes came in pairs
- He worked out that genes were inherited at units, so one came from each parent
- He introduced the idea of 'dominant' and 'recessive' genes
- He recognised mathematical patterns that occurred in inheritance
- He also introduced 'Mendel's Laws of Heredity"
Mendel introduced some important laws surrounding inheritance. These were:
- The Law of Segregation: Each inherited trait has its own gene pair. These pairs are taken from both parents, and offspring get one gene from each parent.
- The Law of Independent Assortment: Genes inherited for each trait are all separate - so the inheritance of one trait does not affect any of the others.
- The Law of Dominance: The trait or characteristic that the offspring will express will come from whichever gene in the pair is dominant.
Keywords in Inheritance and Variations
Just like all topics in science for Junior Cycle, there are certain words and terms which are worth making a note of, because familiarising yourself with can be helpful in exams or at more advanced levels of the subjects. I have compiled a list of useful terms/words in relation to Genetics below:
- Gametes are the "parents", the male (sperm) and the female (eggs)
- DNA - DeoxyriboNuclleic Acid, discovered by Watson and Crick
- Chromosomes are structures found inside the nucleus of a cell.
- Genes are sections of DNA found in Chromosomes.
There are also some questions worth keeping in mind when it comes to studying this topic, they include:
- What is the difference between sexual and asexual reproduction?
- What are genes?
- Why do offspring resemble both their parents?
If you find Genetics interesting or want to learn more on the topic I recommend checking out National Geographic particularly this cool article on identical twins, it explains how identical twins occur when a single fertilized egg splits into two separate, genetically identical embryos.
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