NARAYANKAR NOTES

The H-Y antigen gene is found only on the Y chromosome , so it is present only in males . This gene controls the production of a protein called H-Y antigen . The H-Y antigen is a type of minor histocompatibility antigen , which means it plays a role in how the immune system recognises tissues . It is found on the surface of male body cells , including cells in the testes . Since only males have the Y chromosome , only male cells produce H-Y antigen . Function of H-Y Antigen: One of the most important roles of H-Y antigen is in sexual development . During the early development of a male embryo, the presence of the H-Y antigen helps trigger the development of the testes . The testes then start producing testosterone , which helps in forming the male body structure. So, the H-Y antigen is one of the early signals for the body to develop as male . Without this antigen, even if the child has an XY pair, male development might not occur properly . H-Y ...

Important Genes Found Only on the Y Chromosome and Their Functions The Y chromosome is much smaller than the X chromosome and contains fewer genes . These genes are only found in males , because only males have a Y chromosome . The genes on the Y chromosome are mainly responsible for male development, sex determination, and sperm production . Below are some important Y-linked genes and their functions: 1. SRY Gene (Sex-determining Region Y) This is the most important gene on the Y chromosome. It tells the body to develop as a male during early development in the womb. The SRY gene starts the process of forming testes , which then produce male hormones (like testosterone) . Without this gene, even an XY individual would develop as a female . 2. TSPY Gene (Testis-Specific Protein Y-encoded) This gene is active only in the testes . It helps in the growth and division of cells in the testis. It may also be involved in sperm production and male ...

  The X chromosome is larger than the Y chromosome and contains more than 1,000 genes . Many of these genes are not found on the Y chromosome at all, and they are known as X-linked genes . These genes play important roles in vision, blood clotting, muscle strength, brain development, and immunity . Below are some well-known X-linked genes and the functions they perform: 1. OPN1LW and OPN1MW Genes These genes are responsible for red and green colour vision . When these genes are faulty or missing, the person may suffer from red-green colour blindness . This condition is more common in males because they have only one X chromosome. 2. DMD Gene (Dystrophin Gene) This gene helps in the production of dystrophin , a protein that protects muscle cells . Mutation in this gene causes Duchenne muscular dystrophy , a severe muscle-wasting disease. It affects boys mainly and leads to muscle weakness and difficulty in walking . 3. F8 Gene (Factor VIII Ge...

Explanation of X and Y Chromosomes and Their Regions In human beings, there are two types of sex chromosomes – X and Y. These chromosomes decide whether a person is male or female. A female has two X chromosomes (XX), and a male has one X and one Y chromosome (XY). The X and Y chromosomes are not exactly the same, but they do have some parts that are similar and some parts that are different . The similar parts are called homologous regions . The different parts are called non-homologous regions . Homologous regions of X and Y chromosomes contain similar genes . These similar genes help the X and Y chromosomes to pair up during cell division in males. Crossing over is a process where chromosomes exchange pieces of their genetic material. This crossing over happens only in the homologous regions of the X and Y chromosomes. This means only the similar parts of the X and Y chromosomes take part in the exchange. The non-homologous region of the X c...

These are two types of genetic interactions that affect how traits (like eye colour or height) are shown in a living thing. 🌱 What is a Genetic Interaction? Sometimes, how a trait appears depends on how genes work together . When two or more genes affect each other’s activity , we call that a genetic interaction . 🔍 Let's see the two main types: 🌿 1. Intragenic Interactions (Within One Gene) Intra means inside or within . So, intragenic interaction happens within a single gene . It involves two or more alleles (versions of the same gene). 👇 Example: Let’s say there is a gene that controls flower colour. It has 3 versions (alleles): R (makes red flower), r' (makes pale pink), r (no colour, white). Now, if a plant has the combination Rr' , it may show a different colour than just red or white, like pink. This kind of effect is due to how alleles of one gene interact with each other . That’s intragenic . 🧠 Some types of intrageni...

3.1 Chromosomes and Mechanism of Inheritance Heredity (inheritance) is the transmission of genetic information from parents to offspring. Gregor Mendel used hybridisation on pea plants to propose the mechanism of inheritance before genes and chromosomes were discovered. He studied 7 traits in pea plants (e.g. seed shape, colour, etc.), observing them individually and in combinations. Mendel proposed that "factors" (now known as genes ) are responsible for traits and occur in pairs. They segregate during gamete formation without blending. His success was due to large sample size, precise planning, and mathematical analysis. The concept of dominance and recessiveness emerged from his work. 3.2 Genetic Terminology Character : A specific feature, e.g. plant height. Trait : A variant of a character (e.g. tall or dwarf). Gene/Factor : Unit of heredity. Alleles : Alternative forms of a gene. Dominant/Recessive : Alleles that express in F1 gener...