Gynaecomastia, high pitched voice, under developed genetalia and tall with long limbs.

Huntington's chorea is inherited as an autosomal dominant lethal gene in man. It is characterized by involuntary jerking of the body and progressive degeneration of the nervous system, accompanied by gradual mental and physical deterioration. The patients with this disease usually die between the age of 35 and 40.

(a) I^Al^O - A blood group person
(b) 1^O1^O - O blood group person

(a) Thalassemia
(b) Albinism
(c) sickle cell anaemia
(d) Huntington's chorea

Red-green colour blindness or daltonism, haemophilia and Duchenne's muscular dystrophy

The I gene exists in three forms: l^A, I^B and 1^O. The alleles are located on chromosome 9.

When three or more alleles of a gene that control a particular trait occupy the same locus on the homologous chromosome of an organism, they are called multiple alleles and their inheritance is called multiple allelism.

Group of signs and symptoms that occur together and characterize a particular abnormality is called a syndrome. 
Eg : Down's syndrome, Turner's syndrome, Klinefelter's syndrome, Patau's syndrome are some of the examples of chromosomal disorders.

Symptoms:
1. Severe mental retardation (Phenylpyruvic acid which damages the brain).
2. Light pigmentation (reduction of color) of skin and hair.

The genes present in the differential region of Y chromosome are called Y- linked or holandric genes. The Y linked genes have no corresponding allele on X chromosome. The Y linked genes inherit along with Y chromosome and they are phenotypically express only in the male sex.

It is the transmission of a gene from mother to son or father to daughter.
These patterns of inheritance are called criss-cross inheritance (or) skip generation inheritance in which a character is inherited to the second generation through the carrier of first-generation.
E.g., Wing color in the magpie moth (Abraxus) feather pattern in chickens

The inactivation of an X chromosome one of the two X chromosomes in every cell in some female mammal is randomly inactivated early in embryonic development and named after geneticist Mary Lyon.
The inactive X chromosome is silenced by it being packaged in such a way that it has a transcriptionally inactive structure called heterochromatin found in nucleoplasm of nucleus.

Heterogametic sex determination	Homogametic sex determination
Produces identical gametes (produces one type of gamete)	Produces two different gametes
Two sex chromosomes of the organism are same (XX) (Females)	Two sex chromosomes of the organism are different (XY) (Males)

Haplodiploidy is a sex determination system in which males develop from unfertilized eggs are haploid, and female develops from fertilized egg and is diploid.
It is sometimes called arrhenotoky.
e.g., Honeybees, ants, and wasps.

1. The X chromosome which is common to male and female carries a number of genes. Such genes are called sex linked genes and the characters controlled by them are termed as sex-linked characters. The inheritance of sex linked genes or traits is known as sex linked inheritance.
2. Sex linked inherited traits are more common in males than females, because males are hemizygous (XY) and therefore express that traits when they inherit one mutant allele.
3. Any male receiving X linked recessive allele from his mother will express the trait as his y  chromosome has no corresponding allele.
4. If a recessive X linked gene causes disorder then more males than females have the disorder because the disorder is caused by a single allele in males. Their y chromosome does not carry any corresponding allele. So that sex linked recessive characters are mole in moles.