Yogy's biology

03 Inheritance and Variation - part 12 - Genetic Disorders Genetic Disorders :  Genetic Disorders are broadly grouped into two categories as - Mendelian disorders and  Chromosomal disorders Mendelian discorders  : Mainly caused due to  alteration or mutation in the gene .  e.g.  thalassemia, sicklecell anaemia, colourblindness, haemophilia, phenylketonuria,  etc. Chromosomal disorders : Caused due to  absence or excess of one or more chromosomes  or their abnormal arrangment.  For eg,  Down's syndrome, Turner's syndrome, Klinefelter's syndrome  etc. Thalassemia :  Thalassemia is an  autosomal, inherited recessive  disease.  Haemoglobin molecule is made of four polypeptide chains-  2 alpha (a) and 2 beta (b) chains.  The synthesis of alpha chains are controlled by two closely linked genes  (HBA1 and HBA2) on chromosome 16. Synthesis of beta chain is controlled by a  single gene (HBB) ...

03 Inheritance and Variation - part 11 - Sex Determination Sex Determination :  The mechanism by which sex is established is termed as sex determination. The term sex refers to  sexual phenotype.   In some species, both male and female reproductive organs are present in same organism. It is discribed as  bisexual or hermaphrodite or monoecious. On the other hand, some species in which the organism has either male or female reproductive organs, is said to be  dioecious or unisexual .  Humans are dioecious.  German biologist,  Henking  in 1891, while studying spermatogenesis of the  squash bug (Anasa tristis), noted that 50% of sperms receive the unpaired chromosomes while other 50% sperm do not receive it.  Henking gave a name to this structure as the  x-body  but he could not explain its role in sex determination.  Further investigations by other scientists led to conclusion that the "x-body" of Henking was infact a c...

03 Inheritance and Variation - part 10 - Sex Linked Inheritance Sex Linked Inheritance :  Genes located on non-homologous region of sex chromosomes, are called  sex-linked genes.  The traits that are determined by sex linked genes, are called  sex-linked traits.  The inheritance of sex linked genes from parents to their offsprings, is called  sex linked inheritance.  There are two types of sex-linked genes as -  X-linked genes and  Y-linked genes.  a. X-linked (sex linked) genes :  The X linked genes are located on  non homologous region of X chromosome  and these gene do not have corresponding alleles on Y chromosome.  Female has two X chromosomes.  In female two recessive sex linked genes are required for expression of sex linked traits.  If one X chromosome carries a recessive gene for sex linked trait (defect) its effect is suppressed by the dominant gene present on other X chromosome.  The females ...

03 Inheritance and Variation - part 09 - Autosomal Inheritance Autosomal Inheritance :  Human  somatic (2n) cell  contains  23 pairs  of chromosomes.  They can be divided functionally as  autosomes and sex chromosomes.  A single pair of chromosomes is involved in sex determination and remaining 22 pairs are called autosomes.  Autosomes control a variety of traits other than sex. These traits are called  autosome linked traits.  Transmission of body characters other than the sex linked traits from parents to their offsprings through autosomes, is called  autosomal inheritance. Some characters are influenced by dominant genes while some other are by recessive genes, present on autosomes.  For example,  Autosomal dominant traits like  Widow's peak and Huntington's disease , etc. Autosomal recessive traits like  Phenyl ketonuria (PKU), Cystic fibrosis and Sickle cell anaemia.  a. Widow's peak :  A prom...

03 Inheritance and Variation - part 08 - Linkage and Crossing Over Linkage and Crossing Over :  Linkage :  It is a known fact that  several genes are present on the chromosome.  As chromosomes are carriers of heredity, these genes have tendency to be  inherited together. Such genes are called  linked genes.   This tendency of two or more genes present on the same chromosomes that are inherited together is known as  linkage.  Linkage was discovered  in plants  by  Bateson and Punnett  and  in animals  by  T. H. Morgan.  Linkage is of two kinds -  Complete linkage and  Incomplete linkage I. Complete linkage :  The linked genes which are closely located on the chromosome  do not separate  (no crossing over) and inherit together. They are called  completely linked (strongly linked) genes  and the phenomenon of their inheritance is called  complete linkage .  Thus...

03 Inheritance and Variation - part 07 - Chromosomes Chromosomes :  Chromosomes are  filamentous bodies  present in the eukaryotic nucleus.  The term chromosomes (Gr., Chromo = colour, soma = body) was coined by  W. Waldeyer (1888).  The size of chromosome varies from species to species.  Each metaphase chromosome varies from  0.1 to 33 mm  in length and  0.2 to 2 mm  in thickness.  Visible  during  cell division.  Capable of  self replication. Play vital role in heredity, mutation, variation, and evolutionary devlopment of eukaryotic species.  Chemically eukaryotic chromosomes are made of  DNA, histone and non-histone proteins . Function :   Chromosomes are carriers of  heredity.  Number of chromosomes :  The number of chromosomes is  specific and constant  for a particular species.  Therefore it is of great importance in the study of phylogeny and taxonomy ...