Dr Praveen Kumar Agrawal is teaching live on Unacademy Plus
COURSE Principles of inheritance and variations Lesson 21 Sex Chromosomes Dr. Praveen Kumar Agrawal M.Sc., Ph.D., CSIR NET (JRF). SRF, GATE 21Years of Pre-medical teaching experience
UNACADEMY LIVE NOW SUBSCRIBE FOR ALL LIVE/PLUS COURSES Of ALL EDUCATORS IN PRE MED CATEGORY ONLY FOR A NOMINAL FEE Use following referral code for EXTRA 10% REBATE biologybypkagrawal-6909
SEX CHROMOSOMES AND AUTOSOMES In diploid and unisexual organisms a particular chromosome or a pair of chromosomes is associated with * These chromosomes carry certain genes, which are responsible for the formation of a particular kind of sex Remaining other chromosomes of the individual (i.e., chromosomes, other than sex chromosomes) are In man, there are 23 pairs of chromosomes. Of these, the chromosomes of 23rd pair are called sex the determination of sex. Such chromosomes are called sex chromosomes or allosomes. organs. called autosomes. chromosomes or allosomes. The X chromosome in humans contains about 153 million base pairs (the building material of DNA). It represents about 800 protein-coding genes compared to the Y chromosome, which contains just 70 genes. Y is the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction The Y chromosome contains the gene SRY (sex determining region of Y), which triggers testis development. It is also called TDF (Testes determining factor). The DNA in the human Y chromosome is composed of about 59 million base pairs. The Y chromosome is passed only from father to son.
Sex Chromatin and Barr Body In 1949, Barr, found that in the interphase nucleus of mammalian females, there is a small chromatin body (that takes a deep Feulgen stain), which is absent in males. He called this body as sex chromatin or Barr body. Later on it was found to be consisted of the chromatin of the X-chromosome. Lyonisation In woman there are two X-chromosome while in man there is only one X-chromosome. Thus there is a double dose of X-chromosomes in females. To compensate this dose, in mammalian females, the chromatin of one of the X-chromosomes becomes randomly inactivated and changed into heterochromatin. This hypothesis was proposed by Lyon, therefore it is known as Lyon hypothesis or Lyonisation. It is also called 'dosage compensation'. The inactivated hetero-chromatinised X-chromosome is called Barr body or sex chromatin. Thus, Barr body is found only in female or in individual which have at least 2 or more than two X-chromosomes. Number of Barr body in a cell is equal to one less than the number of X chromosomes.
WATCH MY LIVE Course Watch my live course in Unacademy Plus section. Actual classroom feel at your home and live doubt removal .Go to www.unacademy.com/plus. Search for my live course and get yourself registered. ALL THE BEST