Gregor Johann Mendel worked on pea plants to understand inheritance. He is known as the father of genetics. He gave laws of inheritance. To understand the inheritance of two different traits present on different chromosomes, we will perform Mendel’s experiment in which inheritance of two characters is used. In human beings, the genes inherited from the parents decide whether the baby will be a boy or girl. Further in the chapter, we will also find out evolutionary relationships with the help of homologous characters and how Evolutionary relationships of extinct species can be studied with the help of fossils.

Human beings have similar basic body designs but also they have variations in some characteristics based on DNA. The DNA is present in chromosomes inside the nucleus of the cell. DNA is the hereditary material that plays an important role in heredity. 

In this virtual tour, we will learn about Mendel’s law of segregation and the law of dominance. The Law of segregation states that paired chromosomes segregate at the time of gamete formation and gamete contains only one chromosome of pair. The law of dominance states that if both traits and one of the traits in a genotype is a dominant trait then the dominant trait expresses itself.

Mendel’s law of independent assortment states that at the time of gamete formation different traits separate or segregate independently of each other. We will understand through Mendel’s experiment in which inheritance of two characters is used. Shape and color of seeds in pea plants.

Children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus, the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from the father will be a boy.

Natural selection can direct evolution in the population and result in adaptation. Accidents in small populations can change the frequency of some genes, even if they give no survival advantage. This is called genetic drift. Some environmental factors like scarcity may cause low weight but here it’s not a genetic change. So, this is not an example of evolution and thus it cannot direct evolution.

We classify organisms on the basis of common and different characters. For example vertebrates and invertebrates depending upon the presence of a vertebral column. We will then find out evolutionary relationships with the help of homologous characters. It is possible if two species have more common characteristics then that two species might have a common ancestor. 

Evolutionary relationships of extinct species can be studied with the help of fossils. Preserved traces of living organisms are called fossils. Fossils we find closer to the surface are more recent than the fossils we find in deeper layers. The second way of dating fossils is by detecting the ratios of different isotopes of the same element in the fossil material.

We will learn in this virtual tour about the evolution of wild cabbage. Different plants like broccoli, cabbage, cauliflower, kohlrabi, and kale evolved from one wild cabbage.

We will understand evolution in humans. The monkeys migrated in grassland so there was no use of tail and thus over generations it disappeared. They were also stumbling while escaping. They began to adapt and their arms became lighter, shorter and their legs became long. This is the first pre-human species. Over generations they started hunting animals and humans came into existence who migrated all over the planet.

Females have two X chromosomes and males have one X and one Y chromosome. The gametes contain only one set of chromosomes that is either an X or a Y. The ovum cell has an X chromosome and the sperm cell has a Y chromosome. Both attract each other and make a zygote cell. Here, the newly made zygote cell has X and Y as sex chromosomes, X, and Y as sex chromosomes. This zygote will develop into a male.