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Variation and Inheritance (Evolution (The theory of evolution was first…
Variation and Inheritance
Selective Breeding and Cloning
Selective Breeding
Selecting animals with desired traits to breed is called
selective breeding
.
e.g. A cow that produces more milk of a good quality when crossed with a bull that is larger in size (more meat and leather) would produce a calf which has most of the desired traits as above.
Desired qualities for farmers that could be reached using selective breeding include:
-Better appearance (domestic animals such as dogs)
-Better quality of meat, milk etc. (sheep, cows)
-Better resistance to disease
-Any other desired trait that is relevant to a particular animal
Cloning
Two methods of cloning (in plants) are:
-Tissue cutting
-Tissue culture
Two methods (in animals) are: -Embryo transplants
-Adult cell cloning
A
clone
is an organism that is
genetically identical
to its parent.
Steps to cloning
Step 4: Next, the nucleus from the said cell is taken.
Step 5: The egg cell from a different sheep is taken.
Step 3: A skin cell is taken from the sheep.
Step 6: The nucleus from the skin cell is then inserted into the egg cell.
Step 2: The sheep goes to a laboratory.
Step 7: This newly formed egg cell is then placed back in the womb of the sheep it was taken from.
Step 1: Farmer picks an animal (e.g. a sheep).
Step 8: In the surrogate sheep the lamb grows naturally.
Evolution
The theory of evolution was first discovered by naturalist, Charles Darwin. The theory was that organisms shared a
common ancestor
and gradually changed over time, making
variations
and different species.
In 1831, Darwin travelled to the Galapagos Islands in South America and found a number of different finches with different beaks which were dependent on where the finches lived.
Darwin could see the similarities between fossils and living organisms. An example of this is the peppered moth. Before the Industrial Revolution in Britain, most peppered moths were pale and camouflaged against the pale birch trees and the black moths stood out and were eaten by the birds. During the Industrial Revolution, the trees turned black with soot meaning the black moths camouflaged against the trees whereas the white moths did not.
At the time of Darwin discovering this theory, many people feared God and believed in Genesis and so were against his theory, saying it was blasphemous. Darwin was ex-communicated from the Church.
When people say "survival of the fittest", they are referring to
natural selection
. This means you either adapt or die. Some individuals, Darwin thought, were better suited to a particular environment and therefore had a better chance at survival.
In a nutshell, the theory contained 4 parts: -Each species shows
variation
-There is
competition
within species for food, living space, water, mating partners etc.
-The
better adapted
members of a species are
more likely
to survive (natural selection)
and
-These survivors pass on their
better genes
to their offspring who will also show the
beneficial variation
DNA, Genes and Chromosomes
DNA
Sections of DNA which code for characteristic are called genes. Out of 46 chromosomes, 22 pairs are identical but the 23rd pair do not always match. These are the sex chromosomes that determine whether you're male or female.
The female chromosomes are identical (XX) but the male chromosomes are not identical (XY).
Inside each of your normal body cells there is a
nucleus
. This contains 23 pairs of chromosomes made up of the chemical
DNA (
Deoxyribonucleic acid).
DNA is a long molecule that is shaped liked a
double helix
. The DNA molecule contains four different molecules called
bases
. There are four different bases are arranged in a sequence.
A section of DNA is a
gene
. The sequence of bases is the code that determines what gene you have. Different genes control the development of different characteristics by issuing instructions to the cell.
The long DNA molecule is twisted up to form a
chromosome
, which are found in the nucleus.
Bases are identified by their
initials
. They form pairs when matched up one another. Base pairs hold the two strands of the helix together. It is the sequence of these bases and of the DNA molecule that forms the
genetic code
.
Chromosomes
Each chromosomes may have
different version
of a gene.
Different versions of a gene, that code for different versions of a characteristic, are called
alleles
.
Chromosomes
come in pairs (one you inherited from the mother and one from the father) that contain the
same
type of genes that code for the same type of genes that code for the same characteristics.
Genes
The instructions for each characteristic are called
genes
.
Variation is the differences we see between species and also within species and can be caused by genes, environment or both.
These instructions are found in the
nucleus
.
An example of genetic variation is eye colour. An example of environmental variation is whether you have a scar. An example of a variation affected by both is height.
A half comes from the egg and half from the sperm.
A characteristic that can take any value is any value is a
continuous variation (line graph)
.
The instructions that make up a plant or animal comes from their
parents
.
A characteristic that can only have certain values (category) is a
discontinuous variation (bar chart)
.
Alleles
If the alleles in a matching pair are the
same
(homozygous), then working out the colour of the petals is easy.l
If the alleles in a matching pair are
different
(heterozygous), then it becomes more difficult.
Some alleles are
dominant
to other forms of a gene and will always be expressed.
Breeding Plants
Step 3: Remove the anthers to ensure that Flower B is not fertilised by its own pollen.
Step 4: Rub the pollen over the stigma of Flower B.
Step 2: Flower A produces pollen and Flower B receives the pollen in its stigma.
Step 5: Put a polystyrene bag over the flower to protect the stigma of Plant B so it isn't pollinated by other pollen.
Step 1: Choose two plants with desirable characteristics.
Step 6: Hopefully fertilisation happens and a unique plant will be made.