Write notes on Thalassemia.

Haemoglobin is the protein molecule in red blood cells that carries oxygen. Thalassaemia is an inherited blood disorder in which the body makes an abnormal form of haemoglobin. It occurs due to mutation in one of the gene encoding for haemoglobin. It results in excessive destruction of erythrocytes. This leads to anaemia. There are three types of it, namely beta thalassaemia, alpha thalassaemia and thalassaemia minor. The symptoms include pale skin, dark urine, bone deformities, excessive tiredness and fatigue. Treatment includes blood transfusions, bone marrow transplant, medications and supplements.

Write notes on Down's syndrome.

Down's syndrome is a chromosomal disorder, wherein, an error in cell division leads to an extra copy of chromosomes in the body. This extra chromosome 21 tends to affect the physical and cognitive abilities of affected individuals. The karyotype of a person with Down's syndrome is (47, XY+21). It is a condition in which the person shows delay in physical and intellectual growth, short stature, small round neck, partially open mouth with furrowed tongue . Down's syndrome is typically called Trisomy 21. It is mostly caused by the irregular separation of chromosome 21 during meiosis either in egg cells or sperm. When the fertilized egg develops, it transfers an extra copy of this chromosome to each cell in the body.

Describe the chromosomal basis of sex determination in humans, honeybees and birds.

Sex determination is the establishment of sex through differential development in an organism or offspring. It determines whether it will be male or female. Sex of human being and insects like grasshopper, Firefly, Drosophila etc. is determined genetically. Some organisms like turtles rely entirely on environmental factors such as temperature for sex determination. It can be done by finding the number of chromosomes or type of chromosomes present in the organisms. The organisms which contain complete sets of chromosomes are diploid while the haploid organisms contain half the number of chromosomes. Chromosomal basis of sex determination in humans: In humans, the male-specific Y chromosome plays a pivotal role in sex determination, and also bears genes that are required for spermatogenesis. However, not all the genes that are needed to make a testis or to make germ cells need to be on the Y chromosome, and many are known to be located on the X chromosome or on the autosome. Human females have two X chromosomes (XX) and males have a single X and a single Y chromosome (XY). Chromosomal basis of sex determination in Honeybees: The sex determination in the honey bees is mainly understood by the fertilization and non-fertilization of eggs. An offspring formed of the union of a sperm and an egg develops as a female (queen or worker), and an unfertilized egg develops as a male (drone) by means of parthenogenesis. It is called Haplo-diploid system. Chromosomal basis of sex determination in Birds: The ZZ and ZW type of sex determination occurs in the birds in which females are heterozygous (ZW) and males are homozygous (ZZ). The sex chromosomes in birds are designated Z and W, and the male is the homomorphic sex (ZZ) while the female is heteromorphic (ZW).