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Inheritance notes (BIOLOGY NOTES)
the booklet contains specifically notes under the same topic inheritance. It covers all aspects of the topic and it is written in simple language for better understanding of students.
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13 Inheritance# 126 Inheritance - key definitions
Inheritance is the transmission of
genetic information from one generation to
the next, leading to continuity of the species
and variation within it.
Key definitions
Chromosome A thread of DNA, made up of genes.
Allele An alternative form of a gene. Pairs of alleles occupy the
same relative positions on chromosome pairs.
Gene A section of DNA, which codes for the formation of a
protein controlling a specific characteristic of the organism.
Haploid A nucleus containing a single set of unpaired chromosomes,
nucleus e.g. in sperm and ova (eggs). In humans, the haploid
number is 23.
Diploid A nucleus containing pairs of chromosomes, e.g. in somatic
nucleus (body) cells, In humans the diploid number is 46.
Genotype The genetic make-up of an organism, e.g. Tt, where T and t
are alleles of a gene.
Phenotype The characteristics visible in an organism, controlled by the
genotype, e.g. a tall plant or a dwarf plant.
Homozygous Having a pair of identical alleles controlling the same
characteristics, e.g. TT, where T=tall. The organism will be
pure-breeding for that characteristics.
Heterozygous Having a pair of dissimilar alleles for a characteristic, e.g.
Tt.
Dominant A gene, e.g. T, that always shows in the phenotype of an
organism whether the organism is heterozygous (Tt) or
homozygous (TT).
Recessive A gene, e.g. t, that only has an effect on the phenotype
when the organism is homozygous (tt)
Video: The Human Genome Project, 3D Animation
https://www.youtube.com/watch?v=VJycRYBNtwY
, #127 Chromosomes, DNA, genes and alleles
In the nucleus of every cell there are a number of long threads
called chromosomes.
Chromosomes
Most of the time, the chromosomes are too thin to be seen except with an
electron microscope. But when a cell is dividing, they get shorter and fatter
so they can be seen with a light microscope.
Human chromosomes and
nucleus. Chromosomes are a
packaged form of DNA. The DNA
normally exists in a non-condensed
form in the cell nucleus (upper
right). It condenses into chromosomes
(centre and lower left) during cell
replication.
Human cells contain 46 chromosomes, which are in pairs. Sex cells (sperm
and ova) contain only 23 chromosomes. The 23 chromosomes comprise one
from each pair.
,Inheritance of sex in humans
Of the 23 pairs of chromosomes present is each human cell, one pair is the
sex chromosomes. These determine the sex of the individual. Male have XY,
female have XX. So the presence of a Y chromosome results in male
features developing.
DNA
Each chromosome contains
one very long molecule of
DNA. The DNA molecule
carries a code that instructs
the cell about which kind
of proteins it should
make. Each chromosome
carries instructions for
making many different
proteins.
Gene
Each chromosome is made up of a large number of genes coding for the
formation of different proteins which give us our characteristics. The gene
responsible for a particular characteristic is always on the same relative
position on the chromosome.
A part of a DNA molecule coding for one protein is called a gene.
, Alleles
When the chromosomes are in pairs, there may be a different form (allele)
of the gene on each chromosome.
Video: What is a Chromosome?
https://www.youtube.com/watch?v=xUrlreMaUrs
Video: What is DNA?
https://www.youtube.com/watch?v=zwibgNGe4aY
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