Chromosomes and sex determination | SEE Notes

chromosomes and sex determination


Definition: The chromosome is a thread like structure composed by protein and DNA, and present inside the nucleus.

a) It caries hereditary character generation to generation.
b) It has two arms called chromatid, and both the chromatids are joined at the centromere, etc.


Types of chromosome:
a) Sex chromosome.
b) Autosomes, etc.

Sex chromosomes: These chromosomes are used in sex determination. It is in pair.
Examples: In a human being, XY is sex-chromosomes where ‘X’ determines a female baby and ‘Y’ determines a male baby.

Autosome: These chromosomes don’t take part in sex determination. In a human being, 44 autosomes and 2 sex chromosomes and 2 sex chromosomes in each cell.

Types as a position of centromere:

metacentric-centromerea) Meta: Middle
b) The centromere is present at centric chromosome.
sub-metacentric-grade-xa) Sub-meta: Up or down to the middle point.
b) The chromosome which centromere is slightly up or down to the middle point is called- Sub-metacentric.
c) Chromatids are unequally divided.
chromosome-notes-grade-xa) The centromere nearly to the endpoint of the chromosome.
b) In this chromosomes, one arm is very short and another is very long.
biology-grade-xa) The centromere is present at top chromatids (Chromosomes), etc.

Haploid and diploid cell:

Haploid cellDiploid cell
A cell which contains only one chromosome of each pair is called Haploid.A cell which contains a pair of a chromosome is called the diploid cell.
It contains only one chromosome.It contains a pair of chromosomes.

Somatic cell: Any cells forming the body of an organism is called Somatic cell.
They are divide only by mitosis.

Germ cell: The specialized haploid cells which are involved in reproduction is called Germ cell.

Deoxyribonucleic acid (DNA):

Definition: DNA is a type of nucleic acid which is present in the gene.

a) It carries hereditary characters from one generation to the next generation.
b) It helps to control the metabolic activities of cells.
c) DNA give rise to RNA by the process of transcription, etc.


Ribonucleic acid (RNA):

Definition: RNA is a type of nucleic acid which acts as genetic material in lower.

a) It acts as genetic material in lower organisms.
b) It is responsible for protein synthesis in higher organisms, etc.

a) Ribosomal RNA: rRNA takes part in protein synthesis.
b) Transfer RNA (tRNA): tRNA activities amino acids.
c) Messenger RNA (mRNA): It carries amino acid molecules for protein synthesis, etc.

Sex-linked diseases (Hereditary diseases):

Definition: The disease linked with sex and expressed in male or female is called sex-linked diseases. Generally, it is related to sex-chromosomes
a) Bleeder diseases (Hemophilia),
b) Colorblindness, etc.

Chromosomal disorder:

Definition: The change in composition and number of chromosomes is called Chromosomal disorder.

Down’s syndrome: First time it was explained by Langdon Down. It is caused by an additional copy of the 21st chromosome (Trisomy of 21). It has 47 chromosomes in each cell.

Klinefelter’s syndrome: It is a disorder with an extra X chromosome. So, it has 44+XXY chromosomes. A man becomes sterile or infertile.

Turner’s Syndrome: The syndrome due to lack of sex chromosome (XO) is called Turner’s syndrome. It has 45 chromosomes in each cell.

Answer the following questions:

a) what is a cell?
Ans: Cell is the structural and functional unit of life.

b) What are the genes?
Ans: Genes are the fragment of DNA which transfers the hereditary character of parents to offspring.

c)What is a somatic cell? Where are they found?
Ans: Any cells forming the body of an organism is called Somatic cell.
They are found in internal organs, muscles, and skin, etc.

d) What are homogenous chromosomes?
Ans: Two chromosomes of a pair which are similar in shape, size appearance and function are called homogenous chromosomes.

e) What is the cause of Down’s syndrome?
Ans: The causes of Down’s syndrome is an additional copy of the 21st chromosome (Trisomy of 21).

f) What is the symptom of Down’s syndrome?
Ans: Following are the symptom of Down’s syndrome:
i) Baby with dwarf will a small and round head.
ii) Their palm is thick with a crease, etc.

g) How does Klinefelter’s syndrome arise?
Ans: Klinefelter’s syndrome arises due to increases in sex chromosome.

h) How does Turner’s syndrome arise?
Ans: Turner’s syndrome arises due to deficiency of X-chromosome.

i) What are the symptoms of Turner’s syndrome?
Ans: Following are the symptom of Turner’s syndrome:
i) The women have poorly developed ovaries and secondary sexual characteristics, etc.


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