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Have you heard of Charles Darwin? He was a naturalist from England who came up with the idea that living things change over time. This idea is called natural selection and survival of the fittest. It's still used today! Darwin's work led to the study of genetics. Genetics is things pass on traits from one generation to the next. It's an important topic to study because it helps us understand how we inherit traits from our parents. In this article, we'll define genetics, talk about why it's important, and introduce some key terms you should know. We'll also briefly talk about the different ways traits can be passed down from parents children. So, let's get started!

What is genetics?

Genetics is all about studying genes and how they're passed down from parents to their offspring. We've known for a long time that children often share traits with their parents, and we've been taking advantage of for thousands of years through selective breeding of crops and animals. This passing of traits from parents to children is called heredity, which is why we often refer to genetics as the study of heredity.

At the core of genetics is DNA, which holds all of an organism's genetic information DNA gives instructions to cells for important processes like growth, survival, and reproduction. Genes are specific sections of DNA that tell a cell what to do. When an organism reproduces, its DNA is copied and passed down to its offspring. In sexual reproduction, each parent provides half of the offspring's DNA, which means the child inherits some genes from each parent. So, genetics is all about understanding how DNA and genes work to create the traits we see in living organisms.


Inheritance of features from the parents
Inheritance of features from the parents

What is the difference between genes and alleles?

packaged into structures called chromosomes. chromosome is formed when a wraps hist. This creates a "atid is one of the identical halves of a replicated chromosome. Two chromatids join together to make a full chromosome. Humans have 46 chromosomes, while some other species can have over 100.

Each chromosome is a long, compressed DNA molecule that contains many genes. A gene is a specific section of DNA that codes for a particular protein, as well as other important molecules. The exact location of a gene on a DNA molecule is called its locus.

Humans have two copies of each gene, one from their mother and one from their father. Genes can exist in different forms, called alleles, which are located at the same locus on a chromosome but have slightly different nucleotide bases. All individuals of a species have the same genes, but they may not have the same alleles. Only one allele can be present at a gene's locus on any chromosome, and we often represent this allele using letters. So, chromosomes, genes, alleles, and loci are all important concepts in the study of genetics.


Representation of a gene
Representation of a gene

DNA from one cell is about 2 metres long! Humans are 99-99.9% identical at the DNA level! Genes make up only 1.5% of DNA.

Gregor Mendel

Our understanding of genetics really took off in the 19th century when Gregor Mendel conducted experiments on pea plants. He found that when he bred red-flowered plants with white-flowered plants, all of the offspring had red flowers, which went against his prediction of pink flowers. This led him to discover the concept of dominant and recessive alleles. Mendel's work was rediscovered in the early 20th century and is considered the basis of modern genetics. He is often called the father of modern genetics.

Mendelian inheritance refers to the way offspring inherit genes from their parents. This includes monohybrid and dihybrid inheritance, where the inheritance of a single gene or two genes respectively, follows the principles proposed by Mendel. However, not all patterns of inheritance follow Mendelian laws. These non-Mendelian patterns of inheritance might occur when genes exhibit linkage or don't follow Mendelian patterns of dominance. Other factors that can affect the resulting phenotype include additional interactions between genes. So, while Mendelian inheritance is an important concept in genetics, it's not the only way that traits are passed down from parent to offspring.


Drawing of Mendel
Drawing of Mendel

Genetics Key Terms

Gregor Mendel's experiments with pea plants helped us understand more about genetics. In genetics, we use some key vocabulary to describe the traits that organisms have.

An individual's genotype refers to the alleles that they possess, which make up their genetic constitution or blueprint for their characteristics. However, environmental factors can also affect an organism's traits, which are referred to as the phenotype. For example, a plant may have alleles that allow it to grow tall, but it may remain small if it is growing in a nutrient-poor or excessively shady environment.

Dominant and recessive alleles are important concepts in genetics. There are usually two alleles present in an individual, and they can either be dominant or recessive. A dominant allele is always expressed, while a recessive allele will not be expressed in the presence of the dominant allele. Recessive genes remain dormant unless they are paired with another recessive gene.

In diploid organisms, which are organisms that contain a complete set of chromosomes, chromosomes occur in homologous pairs. This means that cells of diploid organisms contain two copies of every chromosome, and an individual carries two loci with each having one allele of a gene. These concepts are fundamental to understanding genetics and how traits are inherited.


Heterozygous and homozygous alleles
Heterozygous and homozygous alleles

In genetics there can be different combinations of alleles in an individual's genotype. When an individual has two of the same alleles on a locus, they are homozygous for that trait. When the individual has two different alleles on a locus, they are heterozygous for that trait.

For example, a plant with two T alleles has the genotype TT, while a plant with two t alleles has the genotype tt. Both of these plants are homozygous for that trait. In contrast, a plant with one T and one t allele would have the heterozygous genotype Tt.

Some genes have different dominant traits, and sometimes two dominant genes can be expressed at the same time. This is called codominance, where both alleles are expressed equally. These concepts are essential to understanding genetics and inheritance.

Codominance in coat colours of the cows

Phenotype does not always clearly reflect the genotype of an individual. For instance, if the short phenotype in a plant can only be expressed if the individual is homozygous recessive, one can assume that its genotype is tt. However, if the plant's phenotype is tall, it may still be either homozygous dominant (TT) or heterozygous (Tt). A test cross is a method used to deduce the unknown genotype of an individual expressing the dominant phenotype. The unknown individual is crossed with a homozygous recessive individual. If the resulting offspring all express the dominant phenotype, then the unknown parent is homozygous dominant. If some offspring express the recessive phenotype, the unknown parent is heterozygous. For more in-depth explanation, see our Inheritance and Linkage articles.

Test cross example

Through observations of crosses, scientists developed the law of segregation, which states that in diploid organisms, characteristics are determined by alleles that occur in pairs. Only one allele of each pair can be present in a single gamete.

Autosomal linkage occurs when two or more genes on the same autosome, or non-sex chromosome, do not assort independently during meiosis. When two genes are autosomally linked, they stay together in the original combination inherited from parents.

Sex linkage, on the other hand, occurs when genes are found on a region of a sex chromosome that is not present on the other sex chromosome. The inheritance of these genes is dependent on the sex of the individual. These concepts are important in understanding how traits are inherited and passed down through generations.

Why is genetics important?

As the basis of all life, genetics is important for many reasons. It has many significant applications.

It allows us to study:

Hereditary diseases Pathogens Cancers Crime scenes

It allows us to create:

Vaccines Antibiotics Genetically modified organisms Large quantities of organic molecules

Genetics - Key takeaways Genetics refers to the study of genes, their variation in a population, and their inheritance. Gregor Mendel performed experiments on pea plants and discovered how traits are passed on from parent to offspring. In Mendelian inheritance, offspring inherit genes from their parents in a way that follows the principles initially proposed by Gregor Mendel. This includes monohybrid and dihybrid inheritance. Non-Mendelian inheritance is any pattern of inheritance that does not occur as predicted by Mendel’s laws. When the two alleles on each locus are the same, the individual is homozygous for a particular trait. When the two alleles are different, the individual is heterozygous for that trait. The dominant allele is always expressed in the phenotype, whereas the recessive allele can only be expressed when the dominant allele is absent. The law of segregation states that in diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.


What is genetics?

The study of DNA and hereditary changes in living organisms.

What is a gene?

A section of DNA.

What is an allele?

Alternative forms of a gene occupying a position on a chromosome.

What is a chromosome?

A package of DNA found in the nucleus of the cell.

Who was Gregor Mendel?

A monk who performed experiments on pea plants and discovered how traits are passed on from parent to offspring.

Is depression genetic?

No one single gene causes depression. People inherit a combination of genes from their parents, and certain gene combinations can make it more likely for someone to develop depression.

Is diabetes genetic?

Genetics play a strong role in the chances of developing both type 1 and type 2 diabetes but other factors include environment and lifestyle.

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