Heritage Cultural Genetic Traits Found in Human Beings by Jiya Divyanshi Pandita

Historical Aspect of Dominant and Recessive Traits

Introduction

Human genetics is the study of the human genome and the transmission of genes from one generation to the next. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genes are the common factor of the qualities of most human-inherited traits. Study of human genetics can answer questions about human nature, it can help us understand diseases and the development of effective treatment and help us to understand the genetics of human life.

Different Types of Traits Found in Human Beings

Human Beings are unique creatures with varied characteristics and traits. Some of these traits are: -

• Acquired over the lifetime of an individual due to certain external factors or his/her activities.

• Inherited from the previous generations which can be gotten from either parent. (This is governed by Mendelian Inheritance)  

Furthermore, these traits can be divided into Dominant and Recessive.

Trend of Inheritance:-

1. A progeny receiving a dominant allele from either parent will have the dominant form of the phenotypic trait or characteristic.
2. The progeny that receives the recessive allele from both the parents, known as zygosity, will have the recessive phenotype.
3. The progeny that receives a dominant allele from one parent and a recessive allele from the other parent will have the dominant form of the trait.

Examples of Traits:-

1. Dimples:- Click Here To Know More
2. Earlobe Attachment:- Click Here To Know More
3. Hairline Shape:- Click Here To Know more
4. Handedness:- Click Here To Know More
5. Hitchhiker's Thumb:- Click Here To Know More
6. PTC Tasting:- Click Here To Know More
7. Tongue Rolling:- Click Here To Know More

Genetic Differences & Inheritance Patterns

Across the generations traits are found to be common in the family, this is due to Inheritance of Traits:-

Inheritance of traits for humans are based upon Gregor Mendel's model of inheritance. Mendel deduced that inheritance depends upon discrete units of inheritance, called factors or genes. There are two kinds of genetic inheritance:-

Autosomal dominant traits are associated with a single gene on an autosome (non-sex chromosome)—they are called "dominant" because a single copy—inherited from either parent—is enough to cause this trait to appear. This often means that one of the parents must also have the same trait, unless it has arisen due to an unlikely new mutation. Examples of autosomal dominant traits and disorders are Huntington's disease and achondroplasia.

(Brown eyes are Dominant and Blue eyes are Recessive)

Autosomal recessive traits is one pattern of inheritance for a trait, disease, or disorder to be passed on through families. For a recessive trait or disease to be displayed two copies of the trait or disorder needs to be presented. The trait or gene will be located on a non-sex chromosome. Because it takes two copies of a trait to display a trait, many people can unknowingly be carriers of a disease. 

Mendel's Study

Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent.

(Gregor Mendel)

Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel's Laws of Heredity are usually stated as:-

1. The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.
2. The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.
3. The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. 

Transfer Of Traits

The Law of Inheritance – Mendel’s Law, is significant in comprehending how characteristics or traits are genetically passed from one generation to the next.

(Parental DNA Transfer)

• Every individual has 22 pairs of chromosomes, each of which comes from the father and the mother. As genes are present on chromosomes, we receive two copies of each gene from paternal and maternal side respectively and one pair of sex chromosomes from each parent to form 46 chromosomes on the whole.
  
• Traits acquired through inheritance is determined by rules of heredity. These traits are coded in our DNA and hence can be passed to the offspring(eye color, hair color, height etc.) Thus for each trait, there are two versions in a child. 
• During the cell division process, genetic information(DNA structure) containing chromosomes are transferred into the cell of the new individual, therefore, passing traits to the next generation.

Gender Based Traits

In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes—one pair of non-homologous chromosomes. Until now, we have only considered inheritance patterns among non-sex chromosomes, or autosomes. 

(Chromosome Pairs Determine the Gender)

• In addition to 22 homologous pairs of autosomes, human females have a homologous pair of X chromosomes, whereas human males have an XY chromosome pair. 
• Although the Y chromosome contains a small region of similarity to the X chromosome so that they can pair during meiosis, the Y chromosome is much shorter and contains fewer genes. When a gene being examined is present on the X, but not the Y, chromosome, it is X-linked.

Genetic Variation

Genetic variation is a measure of the genetic differences that exist within a population. The genetic variation of an entire species is often called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele.

(Different Skin Tones due to Gene Variation)

• For example, a population with many different alleles at a single chromosome locus has a high amount of genetic variation. Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population.

Genetic variation is caused by:-

1. Mutation
2. Random mating between organisms
3. Random fertilization
4. Crossing over (or recombination) between chromatids of homologous chromosomes during meiosis