## shreehari499 one year ago **Genetics**Session 2** Before I continue with session 2 , I would highly recommend the users to go through the Session 1 that I had posted a few days back. Here’s the link http://openstudy.com/study#/updates/55cd7ee7e4b0016bb016b439

1. shreehari499

$$\color{red}{\Huge\text{SESSION 2}}$$

2. shreehari499

So as the story goes, Mendel’s work was either not known or completely appreciated that that time: • Some said that he had used up a lot of Mathematics in his work which many scientists did not like at that time..:p • His idea of genetics had also not reached different places as the communication system was not well developed at that time. • Also there were certain exceptions to Mendel’s laws which were given in the first session. • His concept of Factors as the base of characteristics, were not accepted by the scientists

3. shreehari499

In 1900 Scientists 3) $$\color{blue}{\\{de Vries}}$$ $$\color{red}{\\{ von Tschermark }}$$ and $$\color{green}{\\{ Correns }}$$ independently rediscovered Mendel’s results on the inheritance of characters. Also, by this time due to advancements in microscopy that were taking place, scientists were able to carefully observe cell division. This led to the discovery of structures in the nucleus that appeared to double and divide just before each cell division. These were called chromosomes

4. shreehari499

• The stable movement of chromosomes was discovered by Sutton and Boveri and used it to explain Mendel’s Laws. The important things to remember are that chromosomes as well as genes occur in pairs. The two alleles of a gene pair are located on $$\color{black}{\\{homologous }}$$ $$\color{black}{\\{sites }}$$ on homologous chromosomes. • They argued that the pairing and separation of a pair of chromosomes would lead to the segregation of a pair of factors they carried. Sutton united the knowledge of chromosomal segregation with Mendelian principles and called it the $$\color{blue}{\\{ chromosomal }}$$ $$\color{blue}{\\{theory}}$$ $$\color{blue}{\\{of}}$$ $$\color{blue}{\\{inheritance}}$$

5. shreehari499

Some important points related to CTH: 1. Chromosomes are vehicles of heredity. They are transmitted from parents to offspring, i.e. they are immortal. 2. Two identical chromosomes form a homologous pair. 3. They segregate at the time of gamete formation. 4. Independent pairs segregate independently of each other $$\color{blue}{\small\text{ Thomas Hunt Morgan }}$$ proved chromosomal theory of inheritance using fruit flies (Drosophila melanogaster).

6. shreehari499

$$\color{black}{\Large\text{Pedigree Analysis and Some Genetic Disorders}}$$

7. shreehari499

This is the last topic that I would like to present here in the basics of genetics. In human, control crosses are not possible. So the study of family history about inheritance is used. Such an analysis of traits in several generations of a family is called pedigree analysis. The representation or chart showing family history is called family tree (pedigree). Genetic Disorders: They are basically divided into 2 i.e, Mendelian and Chromosomal Disorders

8. shreehari499

$$\color{red}{\Large\text{Mendelian Disorders}}$$ Some important points: • Caused by alteration or mutation in the single gene. • The pattern of inheritance of Mendelian disorders can be traced in a family by the pedigree analysis. • E.g. Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalesemia, etc. • Mendelian disorders may be dominant or recessive. • By pedigree analysis one can easily understand whether the trait is dominant or recessive.

9. shreehari499

$$\color{green}{\Large\text{Chromosomal Disorders}}$$ They are caused due to absence or excess or abnormal arrangement of one or more chromosomes. They are 2 types namely aneuploidy and polyploidy. 1. Aneuploidy: The gain or loss of chromosomes due to failure of segregation of chromatids during cell division 2. Polyploidy (Euploidy): It is an increase in a whole set of chromosomes due to failure of cytokinesis after telophase stage of cell division. This is often seen in plants. Some examples of chromosomal disorders are Down’s Syndrome, Klinefelter’s Syndrome, Turner’s Syndrome etc. Since this is only the basics of genetics, I would not like to expand these disorders

10. shreehari499

So this concludes the tutorial on ‘The Basics of Genetics’. But keep this in mind friends, this is never the end. Genetics is a very vast topic and a lot of problem arise from these ratios, disorders etc. I do suggest you read some books on genetics as one given by @nincompoop in the 1st session. I’ll try to solve some problems on this topic in the 3rd session. Hoping that this tutorial could be useful to at least some people on OS, I conclude this session. Thanks again!