Principles of Inheritance: Mendelian, Genetic Variation, and Chromosomal Inheritance

Inheritance is the transmission of traits from one generation to another. There are several principles associated with this phenomenon, including Mendelian inheritance, genetic variation, and chromosomal inheritance. Here we will discuss each principle in more detail:

Mendelian Inheritance

Mendelian inheritance was first proposed by Gregor Mendel in the mid-19th century based on his experiments with peas. He observed that certain traits were inherited in a predictable manner proportional to their allele frequencies in the population. This means that offspring receive one gene from each parent according to specific rules known as the laws of segregation and independent assortment. According to these rules, every individual has two copies of almost all genes, one inherited from its mother and one from its father. These copies can be different versions of the same gene called alleles. For example, if someone inherits a blue eye color from their mother and brown eyes from their father, they may have both colors in their cells because there are two separate genes controlling eye color. When sexually reproducing organisms produce eggs and sperm, the pairs of alleles separate randomly so that half of the gametes end up having one version of the gene and half have the other version. When a sperm fertilizes an egg, it contributes only one copy of each gene. So, a child will get one copy of each gene from its parents. If a parent has a trait like curly hair, they must have received either one copy of a dominant curl gene from each parent or two recessive straight hair genes from one parent and a dominant curl gene from the other. Likewise, if the child does not have curly hair, he or she cannot have been given two copies of a curse gene from the parents. Instead, the child must have received either two recessive straight hair genes or one recessive straight hair gene from each parent.

Genetic Variation

Genetic variation refers to any difference between individuals in the DNA sequences that make them who they are. Most genome mutations do not affect health, but some of them cause severe diseases such as cystic fibrosis, sickle cell disease, Huntington’s disease, muscular dystrophy, and Tay-Sachs disease. A person's risk of developing a genetic disorder depends on how many harmful changes they carry in their DNA. If you have no healthy copies of some essential genes, your body might not work properly. Some genetic disorders occur when an abnormal set of instructions causes serious illnesses such as hemophilia, which affects blood clotting. Other times people can pass along multiple bad genes without suffering themselves. Each baby gets an entirely new mix of genes from its parents. Many common characteristics—like height, weight, intelligence, personality, and musical ability—are influenced by dozens of genes and can vary widely among family members. Even identical twins, who share exactly the same DNA, can differ markedly due to environmental influences.

Chromosomal Inheritance

The process of chromosomal inheritance deals with the passage of whole segments of DNA instead of single genes. Whole parts of chromosomes containing large numbers of genes are passed down through generations. Humans normally have 46 chromosomes; 23 come from Mom and Dad. Every human is made up of trillions of cells. Inside each cell, in the nucleus, there is a structure that contains all the information needed to keep us alive and healthy, which includes our chromosomes. Chromosomes contain thousands of genes. One of our most important sets of genes controls what type of skin, hair, and eye color we will have. Another important group tells our bodies whether to grow tall or short. And yet others decide things like whether we tend to gain or lose weight easily, and even whether we are likely to develop diabetes later on. Because we inherit so much information about ourselves in chunks, rather than just small bits here and there, some genetic disorders often run in families. They are caused by an accumulation of errors across many related genes.

In summary, understanding the principles of inheritance and variation helps explain why children look somewhat similar to their parents while still being uniquely themselves. By studying patterns of inheritance, researchers can build models to understand biological processes. Furthermore, knowledge about genetic variability allows doctors to identify potential risks for various diseases that people might face throughout life.