3) SEX CHROMOSOMES DISORDERS/ABNORMALITY

Aneuploidy is a chromosome abnormality that causes individuals to have an abnormal number of chromosomes. If the zygote (fertilised ovum) has three chromosomes instead of the usual pairs, it is trisomic. If the zygote has an unpaired chromosome, it is monosomic. Aneuploid cells occur as a result of chromosome breakage or non-disjunction errors that happen during meiosis (cell division in organisms that reproduce sexually). Two types of errors occur during non-disjunction: homologous chromosomes or sister chromatids.

In sex chromosomes, non-disjunction results in a number of abnormalities .The Klinefelter syndrome is such a disorder in which males have an extra X chromosome. The genotype for males with this disorder is XXY. People with Klinefelter syndrome may also have more than one extra chromosome resulting in genotypes which include XXYY, XXXY, and XXXXY. Other mutations result in males who have an extra Y chromosome and a genotype of XYY.

 (left diagram. trisomic embryo)

 Based on prison studies, these males were once thought to be taller than average males and overly aggressive. Additional studies however, have found XYY males to be normal. Next, Turner syndrome is a condition that affects females. Females with this syndrome, also called monosomy X, have a genotype of only one X chromosome (XO). Trisomy X females have an additional X chromosome and are also referred to as metafemales (XXX). 

 (left diagram. the chromosomes

and the difference in the body structures between people with and without sex chromosomes look like)

Non-disjunction can occur in autosomal cells as well. Down syndrome is most commonly the result of non-disjunction affecting autosomal chromosome 21. Down syndrome is also referred to as trisomy 21 because of the extra chromosome.

2) CHROMOSOMES

Chromosomes are threads composed of chromatin-a combination of DNA and protein-that sit in the cell’s nucleus and hold the vast majority of its genetic information.

They are usually depicted as sticks that are pinched in the middle, but they actually take on this form during cell division. For most of the time, the chromosomes are long, loose strings, like fabric necklaces, and the genes are like patches of colour woven into the design.

 (left diagram. human chromosome)

                                                                               

The number of chromosomes differs from organism to organism, and they almost invariably come in pairs: individuals inherit one copy from their mother and one from their father. Only in reproductive cells called gametes(in animals, the eggs and sperms) is just a single set present.

Ordinary paired chromosomes are known as autosomes, of which humans have 22 pairs, and most animals also have sex chromosomes that can differ between males and females. In humans, people who inherit two X chromosomes are female, while those who have one X and one Y chromosome are male.  

 (right diagram. structure of human chromosome)

1) INHERITANCE

Inheritance is the transmission of genetically controlled characteristics or qualities from parent to offspring. It is a type of relationship among generations, in which one generation shares the structure or behaviour defined in one (single inheritance) or more (multiple inheritance) other generations. Inheritance defines a "kind of" hierarchy among classes in which a sub class inherits from one or more super-classes; a sub-class typically improves or redefines the existing structure and behaviour of its super-classes. 

A sub-class is a specialization of its parent class. All sub-classes inherit the super-class traits & operations. Each sub-class has unique traits and operations. A sub-class may override features of a parent class by defining one with the same name.

The concept of inheritance is used in the context of object oriented modelling. Its key objective is to reduce the redundancy in object models by arranging classes with similar attributes and operations in a hierarchy.

(left picture. A picture of   inheritance/heredity)