Genetics
Chromosomes: a threadlike strand of DNA that appear in a cell
nucleus during cell division, (consisting of genes that are responsible for the
transmission of hereditary characteristics)
Sex chromosome - (genetics) a chromosome that determines
the sex of an individual; "mammals normally have two sex chromosomes"
Autosome: A
chromosome not involved in sex determination.
Euchromatin is a lightly packed form of chromatin (DNA, RNA and
protein) that is rich in gene concentration, and is often (but not always) under active transcription.
Heterochromatin is a tightly packed form of DNA
Barr body The
condensed, inactive, single X-chromosome , appearing as a densely staining
mass, that is found in the nuclei of somatic cells of female mammals. It is
named after its discoverer, Murray Barr.
The number of Barr bodies is thus one less
than the number of X-chromosomes.
The human abnormalities called
Kleinefelter's syndrome and Turner's syndrome both result from an unnatural
presence or absence of a Barr body.
Kleinefelter's syndrome(47XXY
genetically male but contain Barr body
and
Turner's syndrome (45X0 genetically female but
contain no Barr body .
Chromatin granule- the
readily stainable substance of a cell nucleus consisting of DNA and RNA and
various proteins; during mitotic division it condenses into chromosomes
Chromatid - one of two identical strands
into which a chromosome splits during mitosis
Gene: a part of DNA molecule of a chromosome which directs the synthesis of a
specific polypeptide chain.
Codon: a sequence of three adjacent nucleotides which codes for one amino acid
Haploid: the condition in which the cell contains one set of chromosomes (23).
This is the chromosome number in a normal gamete
Homologous chromosomes: chromosomes which pair during
meiosis & contain identical loci.
Locus: the site of a gene on a chromosome.
Alleles : Different
forms of the same gene are called alleles,
Every trait (character :ex: hair colour)
has two alleles one cone from mother and another come from father .
Alleles are commonly represented by letters: A(black hair ) , a (brown hair )
Homozygous : If an organism has
two copies of the same allele, for example AA (mother gene contain information
about black hair and father gene contain information about black hair) or aa,(
mother gene contain information about brown hair and father gene contain information
about brown hair) it is homozygous
for that trait.
Heterozygous:
If the organism has one copy of two
different alleles, for example Aa(
mother gene contain information about black hair and father gene contain
information about brown hair), it is heterozygous.
Dominant and Recessive: Alleles can be dominant or
recessive.
A dominant allele takes precedence over a recessive
allele.
Genotype: the genetic constitution of an individual
Phenotype: the appearance of an individual
which results from the interaction of the environment & the genotype.
Mendel’s law:
Gregor Mendel describes the
inheritance of traits passed from one generation to the next.
The mendel‘s law
has three parts:
1. The Law of Dominance
Mendel's law of dominance states that one gene (dominant gene) is dominant
or powerful can mask the expression of other gene (recessive gene).
Single dominant gene can express the character
Two dose of recessive genes can express the character
2. The Law of Segregation
Mendel's second law, the law of segregation, states that two alleles of a
gene segregated or separated during formation of gametes.
So one copy of parent gene
only
pass
to their offspring for a particular
trait .
Offspring gets second copy of gene
from another parent.
These
segregation or separation occur
during meiosis.
3. The Law of Independent Assortment
During gamete formation alleles of
genes located on different chromosomes are assorted or distributed
independently. The transmission of one character does not influence the
transmission of other character.
Kyryotype: the number, size and shape of the chromosomes of an
individual
Mutation: a change in genetic material, either of a single gene or in the number
or structure of the chromosomes
Non-disjunction: the failure of two members of a homologous pair chromosome
to separate during cell division so that both pass to the same daughter cell
DNA: deriboxynucleic
acid that carries
the genetic information
in cells and some
viruses, consisting of two long chains
of nucleotides twisted into a double helix.
Nucleotide: each of which consists of
1. a pentose sugar
2. a phosphate group.
3. Four nitrogenous bases: cytosine
[C], guanine [G], adenine [A] or thymine [T],
DNA
replication:
the process of copying the nucleotide sequence of the genome from one
generation to the next.
Transcription: the process whereby genetic information is
transmitted from the DNA in the chromosomes to messenger RNA.
Translation means the
synthesis of protein from RNA
RNA: the nucleic acid which is found mainly in the nucleolus and
ribosome
Composition of RNA : it is formed by single stand
nucleotide . Each nucleotide contain pentose suger , phosphate, four
nitrogenous bases : (A), cytosine
(C), guanine (G), or uracil (U). Adenine
There are three types of RNA: 1. mRNA 2. tRNA
3.rRNA
Messenger RNA (mRNA): it transfers genetic information
from the nucleus to the ribosomes in the cytoplasm and also acts as a template
for the synthesis of polypeptides.
Transfer RNA: transfers activated amino
acids from the cytoplasm to messenger RNA.
Ribosomal RNA : (rRNA) is responsible for the
translation of mRNA to protein.
itis the RNA
component of the ribosome which is essential for protein synthesis in all
living organisms. rRNA is the predominant RNA in most cells, composing around
80% of cellular RNA. Ribosomes are approximately 60% rRNA and 40% protein by
weight.
Genome: the entire gene carried by
a cell.
