what is chrosomes what he heelped speically girls
Answers
Explanation:
The Y chromosome contains a "male-determining gene," the SRY gene, that causes testes to form in the embryo and results in development of external and internal male genitalia. If there is a mutation in the SRY gene, the embryo will develop female genitalia despite having XY chromosomes
Chromosomes are thread-like structures present in the nucleus, which carries genetic information from one generation to another. They play a vital role in cell division, heredity, variation, mutation, repair and regeneration.
In Eukaryotic cells, genetic material is present in the nucleus in chromosomes, which is made up of highly organized DNA molecules with histone proteins supporting its structure.
Chromosome means ‘coloured body’, that refers to its staining ability by certain dyes.
- Karl Nägeli in 1842 ,, first observe the rod-like structure present in the Nucleus of the plant...
- w. waldeyer in 1888 coined the term chromosomes..
- Walter sutton and Theodor boveri in 1902 suggested that chromosomes are the physical carrier of genes in eukaryotic cells..
The number of chromosomes in any species is constant for all the cells. The number of chromosomes in gametes (e.g. sperms, egg) is half of the somatic cell and known as a haploid set of chromosomes, which is the result of meiosis during sexual reproduction. Chromosome number is preserved in the mitotic division of somatic cells, which is required for an organism to grow, repair and regenerate.
Chromosome number varies in different species. A nematode species contains only 2 chromosomes in a cell, whereas a protozoan species contains as much as 1600 chromosomes in the cell. Most of the plant and animal species contain 8 to 50 number of chromosomes in its somatic cell. The number of chromosomes does not reflect the complexity of a species. A human cell contains total 23 pair of chromosomes (2n, total 23×2=46), of which 22 are autosomes and 1 sex chromosome.
Karyotyping is a technique to study the structure of chromosomes present in a species. Chromosomes are isolated, stained and photographed. This technique is useful in finding out any chromosomal abnormalities.
Karyotype of a human cell
Karyotype of a human cell (male)
Each cell has a pair of each kind of chromosome known as a homologous chromosome. Chromosomes are made up of chromatin, which contains a single molecule of DNA and associated proteins. Each chromosome contains hundreds and thousands of genes that can precisely code for several proteins in the cell. Structure of a chromosome can be best seen during cell division.
Main parts of chromosomes are:
Chromatid:
Each chromosome has two symmetrical structures called chromatids or sister chromatids which is visible in mitotic metaphase.
Each chromatid contains a single DNA molecule
At the anaphase of mitotic cell division, sister chromatids separate and migrate to opposite poles
Centromere and kinetochore: Sister chromatids are joined by the centromere.
Spindle fibres during cell division are attached at the centromere
The number and position of the centromere differs in different chromosomes..
The centromere is called primary constriction
Centromere divides the chromosome into two parts, the shorter arm is known as ‘p’ arm and the longer arm is known as ‘q’ arm.
The centromere contains a disc-shaped kinetochore, which has specific DNA sequence with special proteins bound to them..
The kinetochore provides the centre for polymerisation of tubulin proteins and assembly of microtubules
Secondary constriction and nucleolar organisers: Other than centromere, chromosomes possess secondary constrictions.
Secondary constrictions can be identified from centromere at anaphase because there is bending only at the centromere (primary constriction)
Secondary constrictions, which contain genes to form nucleoli are known as the nucleolar organiser
Telomere:
Terminal part of a chromosome is known as a telomere.
Telomeres are polar, which prevents the fusion of chromosomal segments
Satellite:
It is an elongated segment that is sometimes present on a chromosome at the secondary constriction.
The chromosomes with satellite are known as sat-chromosome
Chromatin:
Chromosome is made up of chromatin. Chromatin is made up of DNA, RNA and proteins. At interphase, chromosomes are visible as thin chromatin fibres present in the nucleoplasm. During cell division, the chromatin fibres condense and chromosomes are visible with distinct features.
The darkly stained, condensed region of chromatin is known as heterochromatin. It contains tightly packed DNA, which is genetically inactive
The light stained, diffused region of chromatin is known as euchromatin. It contains genetically active and loosely packed DNA
At prophase, the chromosomal material is visible as thin filaments known as chromonemata..
At interphase, bead-like structures are visible, which are an accumulation of chromatin material called chromomere. Chromatin with chromomere looks like a necklace with beads.....