CONTENTS OF HUMAN GENETICS :
1) CHROMOSOMAL INHERITANCE.
1.1) AUTOSOMAL INHERITANCE .
1.1.A) AUTOSOMAL DOMINANT INHERITANCE .
1.1.B) AUTOSOMAL RECESSIVE INHERITANCE .
1.2) SEX CHROMOSOMES INHRITANCE .
1.3) THE HUMAN KARYOTYPE .
1.4) MENDELIAN INHERITANCE .
1.4.A) PEDIGREES .
CHROMOSOMAL INHERITANCE :
AUTOSOMAL DOMINANT INHERITANCE :
The inheritance produced is called “DOMINANT ” because AUTOSOMAL TRAITS are associated with a single copy of autosome which can be inherited from either parent for the cause of appearence of trait .Now due to this inheritance the offspring produced should have the traits of either parents but sometime it is not observed due to the new mutation which changes the traits.The example of Autosomal Dominant Inheritance is Achondroplasia and example of disease is huntington’s disease .
AUTOSOMAL RECESSIVE INHERITANCE :
If one pattern of inheritance for a disease ,disorder or trait is passed through families than it is known as Autosomal Recessive Inheritance .As the trait is present on a non-sex chromosome so two copies of trait or disorder are presented on non sex chromosome to display a recessive trait .One more important factor is that it can remain hidden for various generations that’s why many people don’t know that they are the carrier of disease for example : albinism, Cystic Fibrosis, Tay-Sachs disease .
SEX CHROMOSOME LINKED INHERITANCE :
As we know that their are two sex chromosomes are of two types X and Y .
1. X LINKED INHERITANCE :
X-linked chromosomes have X-linked genes .As we see that X-linked disorders are seen very few in females .WHY ??? Because X-chromosomes are inherited by males only .DOMINANT and RECESSIVE these both types are shown by X-linked chromosomes .Father will never pass X-linked traits to his son because during this process male pass only Y-chromosome .The X-linked disorders are shown by female when they are Homozygous and they carry this disorder when they are Heterozygote .
2.) Y LINKED INHERITANCE :
It is observed when a trait or disorder appears due to Y-chromosome .The y-chromosomes are found in male only thus they are transferred only from a father to his son .This is used to only test the maleness and their no other characteristic found linked to Y-chromosome .
THE HUMAN KARYOTYPE :
In early times we were not able to properly visualize the chromosomes and we do not know about their number but in 1956 TJIO and LEVAN had produced the method to know the exact number of chromosomes and to find the error from their seven groups. Chromosomes are identified during MITOSISin the late prophase and early metaphase because during this stage they have two chromatids with each chromosome .
A karyotype is the proper arrangement of chromosomes after their staining and photography from larger to smaller .A normal human karyotype is as shown below .
The grouping is done by taking into account the position of centromere .Chromosomes consist of histones ,protiens and a double strand DNA.Chromatin loops contains the arrangement of DNA .
The most important part of chromosomes are CENTROMERE and TELOMERE . Role of centromere and telomere .
1) CENTROMERE :
a) Join spindle fibre .
b) Without it mitosis and meiosis is not possible and chromosome will be decomposed in cytoplasmic fluid .
2) TELOMERE :
a) It is responsible to give structural integrity to chromosomal DNA .
b) It prevents joining of two chromosomes and prevents forming of abnormal chromosomal structure .
MENDELLIAN INHERITANCE :
pedigrees:
These are just a kind of diagrams which shows the relationship and relationship of traits with our ancestors .
These diagrams are used to find the disease or a trait .By using these diagrams we can forecast the traits of the offsprings .these are also used to show and calculate partial penetrance .now a days couples go to genetic councilors to find that whether they will be having a healthy child or not and this is defined by taking the help of PEDIGREES .
