Transcript Variation and Selection

Variation and Selection
variation
Objectives:
*State the differences between continuous and
discontinuous variation
**Identify and explain the examples of variation
*** Differentiate between inherited and environmental
variations
Home work: due in on 25/10
Describe how you would investigate the effect of an environmental variation on
the growth of plants of genetically identical nature. Give full practical details
that ensure that you have designed a valid investigation.
Starter
• In what ways are these people different?
• Which characteristics are due to genetics and
which are environmental?
We are similar to chimps and monkeys in
many ways but we are significantly different
from them. This is why we do not belong to
the same species.
In Biology variation means :
• Differences between species – used in constructing keys
• Differences within a species
We will concentrate only on the second point here as we have
looked at the first in classification unit.
There are ……. types of variation within a species
They are :
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Discontinuous variation
Discontinuous variations are entirely genetically controlled
They cannot be altered by external conditions.
You are either male or female, there are no intermediates
Your ABO blood group is either A, B, AB or O
Genetic defects such as colour blindness, albinism,
achondroplastic dwarfism, sickle cell anaemia are all
genetically controlled and expressed in a discontinuous way
You either have these conditions or you do not. There are no
intermediate states. Data about such variations can only be plotted as -----Other examples of discontinuous variations are:
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percentage
in population
of Britain
Discontinuous variation in blood group. The figures cannot
be made to fit a smooth curve because there are no intermediates
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Continuous variation
Continuous variation describes the situation in which there are
a great many intermediates between the extremes and there are no clear
divisions between the intermediates .
For example, there is a range of heights in this class. If you divide the class into groups.
People do not belong to one or other of a small number of distinct categories.
If you are divided into groups (e.g. !65cm -170cm etc) you can plot a frequency
histogram.
Mean height will be in the middle of the range corresponding to the group with largest
number of you
Variations such as these are under genetic control but there are
several pairs of genes involved.
The genome AA BB CC DD might give tall feature while the
genome aa bb cc dd might be responsible for shortness.*
Genomes AaBbCcDd or AABbCCdd or aaBBccDd and all the
other possible combinations would give intermediate heights
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There are as
many categories
of hair colour as
there are children
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Continuous variation also occurs when the characteristics
are controlled by the genes and the environment
Your height will depend on the genes you inherit and
on
the amount of food you eat during your growing
period, or exercise you do, or the age that you go
through your growth spurts.
Other examples can be length of your index finger.
In plants it can be length of leaves.
The next slide shows the range of heights of army recruits
Continuous variation
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thousands
of men
height in inches
There seem to be distinct categories of height but this is because
measurements are made to the nearest inch
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If measurements could be made to the nearest millimetre
there would be a smooth transition in the heights
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This is how continuous variation would appear in a graph
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Inheritance vs Environment
Identical twins .
Just how identical are they?
Identical twins separated at
birth.
Just how different are they?
Mexican hat plants asexually reproduce to make lots of tiny plantlets around
the leaves. You can detach them grow them as individual plants . Any variation
you see wil be …………………
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Inherited variations result from the activity of genes
They are genetically controlled
Genetically controlled variations cannot be altered
For example, hair colour, skin colour*, blood group,
finger prints and sex cannot be changed naturally
Mutations
Objectives:
*Define the term mutation and describe Down’s
syndrome as an example of mutation
**Describe the possible effects of radiation and
certain chemicals on the rate of mutations
***Describe sickle cell anaemia as an example
of mutation
Starter: Make two lines
http://biology-animations.blogspot.com/2011/07/genetic-mutation-animation.html
Mutation
• Mutations cause new forms of genes.
• They alter the sequence of the DNA.
• Most mutations are spontaneous or natural and only
present in body cells (eg) skin cells, nerve cells, red blood
cells.
• However some mutations are present in the reproductive
cells, sperm and egg cells.
•
•
These mutations can be inherited and so passed on to the person’s offspring.
Some mutations occur completely spontaneously, but some are caused by:
– U-V light
– Exposure to x-rays
– Exposure to radiation
– Exposes to certain chemicals(BENZPYRENE in cigarette smoke)
Result in body cells-cancer,
in sex cells variations in offspring
Mutations
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A mutation is a spontaneous change in a gene or
Chromosome that may cause a change in phenotype. Some
can be harmful, some beneficial and some have no effect
Gene mutations may arise when a gene fails to make an exact
copy of itself during replication prior to meiosis or mitosis. Eg. Eye
colour in fruit fly.
Mutant
Albino a mutation for
gene controlling melanin
production
Chromosome mutations can result from:
Damage to, or loss of a chromosome
Incomplete separation of chromosomes at meiosis leading to
extra chromosomes in one gamete
Part of a chromosome becoming attached to another chromosome
(translocation)
Doubling the whole set of chromosomes
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Chromosome mutations in humans usually result in spontaneous
abortion of the foetus But a proportion survive e.g.
Downs syndrome. The affected person has one extra chromosome
in their genome (i.e. 47 instead of 46 chromosomes)
This happens during meiosis when an egg cell is formed .In egg the
21st chromosome doesn’t separate properly causing an egg with 24
chromosomes.
This results in characteristic facial features, varying degrees of
mental impairment and, usually, a very cheerful disposition
Klinefelters syndrome. The affected male has an extra
X chromosome (XXY)
The person appears to be a normal male but he is infertile
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Gene mutations
Gene mutations often arise as a result of damage to or faulty
replication of DNA
If a nucleotide is not copied accurately, the triplet which contains
the fault will not code for the correct amino acid
A protein with an incorrect amino acid will not function properly
If the protein is an enzyme, this means that the enzyme will not work
The cell chemistry will be disrupted if an essential enzyme fails
to function normally
This means that most gene mutations have a damaging effect
on the cells and the whole organism.
Sickle cell anaemia(inherited)
Inherited diseases are caused by faulty alleles,
most of which are recessive
People with SCA are homozygous(HsHs) for this allele. However
heterozygous people (HsHN) are carriers of the disease and have no
problems but they are resistant to malaria as parasites can’t enter their
RBC which is a mutation favoured by nature . The alleles are codominant
(incomplete dominance) so heterozygous RBCs are a mixture of both.
1. What is the probability of children getting SCA if both parents are
heterozygous?
1 in 4 or 25%
Natural Selection
Objectives:
*Describe how the best adapted individuals
survive to pass on their genes to their offspring
**State that competition leads to differential
survival
Starter:
What is natural selection?
Use the first objective to answer
The process by which organisms well adapted to their environments have a
greater chance to breed and pass on their genes to the next generation than
those that are less well adapted.
h/w due in on 31/10
The factors for natural selection:
Variation
Over – population
Competition leading to differential survival
Adaptation
Evolution
Variation
Caused by gene mutation
. Some are advantageous
to the individuals that
expresses them e.g.
camouflage
Caused by sexual reproduction. During
meiosis the alleles of different genes are
reshuffled to give new combination in
the gametes. During fertilisation alleles
from two different individuals are
combined in the same nucleus
Over-population: How does it help in natural selection?
In spite of plants and animals producing millions of gametes many of which get fertilised
the population remains stable. This is because most of the eggs e.g. in sockeye salmon
are eaten by predators, or young ones die from disease or starvation . Similarly many
poppy seeds may be eaten by birds or not dispersed in the right place or no water or
nutrition. Although enough is produced so that the population is stable
Competition: How does competition help in natural selection?
Organisms surviving the early stages of life compete for resources like plants for water,
light, space and nutrients animals for food, water, territories and mates. The struggle for
existence. This leads to survival of some who are successful competitors.( differential
survival ) This is because they have features that help them gain the resources they need.
Competition is most within the same species as they need the same resources. Individuals
of different species also compete but it is not as fierce e.g. one feeds at night other feeds
during the day.
Adaptation : How does it help natural selection?
The organisms that survive are the best adapted to their particular environment because
of their inherited features and they grow rapidly, breed successfully to pass on their genes
to their offsprings.
Evolution : How does it help natural selection?
If the environment does not change the naturally selected population does not
change much. Extremely variant ones do not survive e.g. very long or short
winged female sparrows are killed by stormy weather before they can breed. If
environment changes some survive changed conditions because of the right
features and compete and breed successfully. Natural selection brings about
changes in species over time leading to evolution. The idea first proposed by …..?
Non resistant
Antibiotic Resistance :
Resistant because
of mutation
Normal bacterial
Population
Antibiotic taken
for infection
Antibiotic
continued
Resistant bacteria grow due to mutation which
enables them to produce an enzyme that break down
the antibiotics and reproduce but non resistant ones
stop growing or reproducing or killed
All non resistant bacteria killed Selection
has taken place for resistant ones
Artificial Selection and Genetic
Engineering
Objectives:
*Describe the role of artificial selection with
examples in producing varieties of animals and
plants with increased economic importance
**Define the term genetic engineering
***Describe how bacteria can be genetically
engineered to produce human insulin
Starter: What characteristics would be
selectively breed for in farm animals?
Mark your homework
Copy and fill in blanks with words provided.
naturally when DNA is incorrectly copied during replication.
Mutations can occur _________
nucleus of one cell. As the cells _________
divide
Gene mutation may start in a single ________
to produce more cells, the number of cells carrying the new form increase.
uncontrollable
Mutations that occur in body cells can cause __________
cell division, resulting in
cancer. Most mutations are ___________.
However, they also play a part in how
harmful
species ________.
evolve
Changing by acquiring new forms of old genes is how living
things have evolved by ________
natural ________.
selection
All correct A*, 1 wrong A, 2 wrongs B, 3 wrongs C , 4 wrongs D, 5 wrongs E, 6
wrongs F, 7 or more wrongs U
evolve
nucleus
naturally
divide
natural
uncontrollable
harmful
selection
H/w due in on 1/11
Answer either
Core question:
Describe the procedure a farmer would take to
improve the milk yield of a herd of cows.
or
Extension question:
List the stages that show how the insulin gene
was removed from a human cell and grown in a
bacterial cell.
Selective breeding or Artificial Selection
• Process:
– Select wanted characteristics e.g. fast growth, high
yield , disease resistance, docile nature, short stem(so
less straw)
– Select individuals with characteristics
– Cross breed
– Select suitable offspring
– Cross breed over many generations
• Advantages:
– Improved agricultural yields
• Disadvantages:
– Reduce gene pool leading; to reduction in variation
accumulation of harmful recessive characteristics due
to inbreeding. e.g. lameness in dog due to
underdeveloped hip joints
Why do these mice glow in the
dark?
It’s because they’ve had a
jellyfish gene inserted into
their DNA.
The gene codes for a
fluorescent protein.
With the jellyfish gene in
their cells, the mice make
the protein and glow too.
This is an example of recombinant DNA technology, more
commonly called genetic engineering
So Genetic engineering is
a process by which a
section of DNA(gene)
from one organism is
inserted into the DNA of
another organism. This
allows transfer of genes
between unrelated
species who can’t breed
with each other hence
can’t be achieved by
artificial selection
Genetic engineering of bacteria
Genetic engineering of plants