Monday, July 19, 2010

Friday, April 3, 2009

EXERCISE (mutation)

1. Mutation is a change which occur spontaneously in chromosome or gene.

2. Name two types of mutation

a) Chromosome mutation
b) Gene mutation

3. Identify the following disorders that caused by chromosome mutation:

a) A person who has three sex chromosome (XXY) instead of the usual two
sex chromosome (XY)
Klinefelter’s syndrome

b) A female who has only X chromosome (XO)
Turner’s syndrome

c) He/she has an extra chromosome 21. This person has 47 chromosomes
in somatic cell instead of the normal person.
Down’s syndrome

4. Gene mutation is due to chemical changes in individual gene.

5. List the consequences of gene mutation.

a) colour-blindness
b) albinism

6. Complete the schematic diagram of colour-blindness below:

Keys: X : X chromosome which carries the normal gene
X : X chromosome which carries the recessive gene for colour-blindness

Parent : father X mother






  • Mutation is a change which occur spontaneously in chromosome or gene.

  • There are two types of mutation; chromosome mutation and gene mutation

  • Chromosome mutation refer to change in stucture or number of chromosome.
  • The consequences of chromosome mutation includes Down's suyndrome, Klinefelter's syndrome and Turner's syndrome.
Down's syndrome

Turner's syndrome

  • Gene mutations due to chemical changes in individual genes.
  • The consequences of gene mutation are colour-blindness, haemophilia, albinism and thalasseamia. Albino


Friday, March 27, 2009

Identical Vs Non-identical twins

Twins are two offspring resulting from the same pregnancy, usually born in close succession. They can be the same or different sex. Twins can either be monozygotic (MZ, colloquially "identical") or dizygotic (DZ, colloquially "fraternal" or "non-identical").



Sex Determination

Sex-determination system

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals, this is often accompanied by chromosomal differences. In other cases, sex is determined by environmental variables (such as temperature) or social variables (the size of an organism relative to other members of its population). The details of some sex-determination systems are not yet fully understood.

XX/XY sex chromosomes

The XX/XY sex-determination system is one of the most familiar sex-determination systems and is found in human beings and most other mammals, although at least one monotreme, the platypus, presents a particular sex determination scheme that in some ways resembles that of the ZW sex chromosomes of birds, and it also lacks the SRY gene. Several Arvicolinae (voles and lemmings) and some other rodents are also noted for their unusual sex determination systems.
In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY). Some species (including humans) have a gene SRY on the Y chromosome that determines maleness; others (such as the fruit fly) use the presence of two X chromosomes to determine femaleness. The XY sex chromosomes are different in shape and size from each other unlike the autosomes, and are termed allosomes.