Download Mrs Single`s Genetics Powerpoint

AS 90948
Demonstrate
understanding of genetic
variation
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Make sure that you look at the explanatory
notes in your workbook and the specific
learning outcomes as this will allow you to
focus on what you need to be learning.
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DNA – its inheritance, continuity of life.
DNA and variation
Variation and evolution
DNA determining characteristics
DNA, genes, alleles and chromosomes
Genotypes and phenotypes
Homologous chromosomes and inheritance of
two copies of a gene
Alleles as versions of genes
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Role of mutations in forming new alleles
Meiosis and the production of gametes
Sexual reproduction and the production of
variation.
Monohybrid crosses showing complete
dominance, sex determination and genotypes
and phenotypes ratios
Inheritable and non-inheritable characteristics
Differing rates of survival depending on
phenotype
Variation in populations and survival
Advantages and disadvantages of sexual
reproduction
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Gene
Allele
Mutation
Genotype
Phenotype
Gamete
Zygote
Dominant
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Recessive
Homologous
Heterologous
Pure breeding
Punnett square
Pedigree chart
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DNA is Deoxyribonucleic acid
If is found in the nucleus of living cells
It is the chemical substance that codes for the
inheritable characteristics of living things, like
eye colour.
DNA is a double helix; like a twisted ladder so
that it takes up less room; it is very long.
The DNA molecule is made up of nucleotides
joined together by chemical bonds.
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Deoxyribonucleic acid.
Actually two molecules held together by
hydrogen bonds between base pairs.
A double helix.
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There are three parts to a nucleotide:
A ribose sugar unit
A phosphate group
A base unit, there are 4 types.
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The backbone of the
DNA molecule is
made out of the
sugars and phosphate
groups.
The rungs are made
out of the bases paired
up by hydrogen
bonds.
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There are four bases that make up the rungs:
A – adenine
T – thymine
A-T pair
C – cytosine
G – guanine
C-G pair
The bases always bond this way
Write the complementary sequence for this
strand:
AAC GCT ATA CGA TTA GCG TCG
THE BASE
PAIRS
Notice how
there are two
hydrogen
bonds between
A and T and
three between
G and C.
This is why A
can’t bond
with C etc.
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Link to
videos
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A molecule of DNA is very long. Human DNA
is about 5 billion bases long. It is the order of
the bases that codes for the characteristics of an
organism.
The DNA is organised into triplets. A triplet is
a series of three bases, such as ATC. Each
triplet codes for a amino acid. An amino acid is
a building block of proteins. So, The order of
triplets on a piece of DNA will specify the
order of amino acids, and therefore the protein
being made.
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DNA is passed from one generation to the next
and provides all the information for the cells in
a living organism to develop and carry out
their functions.
The genetic code for organisms is given by the
sequence of bases (specifically triplets) on the
DNA strand.
The characteristics of organisms is determined
by the genetic code.
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Traits or characteristics are determined by
Genes.
A gene is a length of DNA made up of
thousands of base pairs that codes for one
characteristic.
Unique code  unique gene  unique
characteristic.
One gene = one characteristic
A gene codes for the production of a protein.
The protein contributes to the characteristic, eg,
it may be an insulin protein to help glucose get
into cell, or a pigment that colours your hair.
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Thread-like structures bearing genes that are
found in the nuclei of cells.
Visible with a microscope during prophase of
cell division when the chromosomes are
seperating.
Humans have 46 chromosomes, 23 pairs.
Chromosomes are made of DNA
(Deoxyribonucleic acid).
Chromatin is how the DNA is found in the cell
when it is not dividing.
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22 autosomal (non sex chromosomes) pairs,
one of each pair is from each parent.
Chromosomes are numbered, 1 – 23.
One pair of sex chromosomes: male has X from
mum and Y from dad, girl has an X from both
parents.
If the cells that make sperm and egg do not
divide properly then an organism may have
missing chromosomes or extra chromosomes or
broken chromosomes.
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New cells are made all the time for growth and
repair of tissues and every new cell needs the
same DNA as the original.
DNA needs to be copied before a cell can
divide into two – DNA replication
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The double helix unwinds and the two strands of
DNA separate
The two original strands of DNA act as templates
to make new matching strands.
New nucleotides from within the nucleus, line up
according to their base pairing with the original
strand, A with T and G with C.
The nucleotides are joined by enzymes according
to the base pairing rules.
Each new piece of DNA (or chromosome) is made
of an old and a new piece of DNA (semiconservative).
There are enzymes that check that replication is
correct to avoid mutations occurring.
www.hhmi.org/biointeractive/dna
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A supply of raw materials – free nucleotides
Energy from cellular respiration
Enzymes to catalyse the process
Information in existing DNA
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Mitosis is the making of normal body cells and
occurs in every living thing and every part of
an organism, eg, check cells.
Cell division for growth and repair
Two identical daughter cells are produced
from one cell with identical DNA to the parent
cell.
After mitosis all cells will have same number of
chromosomes as the parent cell and each other.
http://www.sciencekids.co.nz/videos/biolog
y/mitosis.html
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Chromosomes shorten and thicken
and become visible and they
replicate
Centromeres of chromosomes line up
along equator.
Spindle fibres attach to the
chromatids at their centromeres and
pull the chromosomes towards the
poles.
Two identical groups of daughter
chromosomes at each end of cell.
the cell membrane grows inwards
and cytoplasm divides to make two
identical daughter cells
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Once the DNA is replicated the chromatids will
separate during cell division.
Ensures that the daughter cell produced has
exactly the same genetic material.
If it didn’t then things can go wrong, eg,
cancer.
A tour of DNA
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A gene is a sequence of DNA bases located at a
specific place on a particular chromosome, called its
locus
All the genes an organism has is called its GENOME.
They direct how an organism is made and
maintained.
Each gene codes for the building of one protein.
Genes for a particular characteristic are found in the
same position on homologous chromosomes (a pair).
Alleles are different versions of a gene: eg, eyecolour –
you may have the blue allele, brown allele or maybe
both!
Different alleles have slightly different sequences of
bases, resulting in slightly different proteins being
made.
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Proteins are really important because
everything in a cell is either a protein, or made
by enzymes which are proteins.
Proteins are made out of amino acids joined
together.
There are only 20 types of amino acids. The
order of amino acids changes the protein.
Some important proteins are: collagen, keratin,
haemoglobin, insulin, melanin, oestrogen,
testosterone.
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Meiosis is cell division to produce sex cells –
sperm and eggs.
The daughter cells are genetically different
from each other.
The daughter cells have only half the number
of chromosomes as the parent cell
There are two divisions, whereas mitosis has
one.
Occurs in mature organisms – in mammals it
occurs in the ovaries and testes
Occurs in the stamens and ovules in plants
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Chromosomes shorten and become visible
They come together in homologous pairs and
crossing over occurs
Segregation - A spindle forms and homologous
chromosomes (each consisting of two chromatids)
are pulled apart to opposite poles.
Each cell splits into two daughter cells.
Each daughter cell has the haploid number of
chromosomes, but each chromosome is made of
two chromatids.
A new spindle forms and chromosomes are
arranged on the equator
Chromatids separate to the cell ends
Each daughter cell splits into two to finally form
four daughter cells, each with half the number of
chromosomes.
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Half the genetic material in an offspring comes
from the sperm and half from the egg.
The joining of a sperm and egg is random
producing variation
Crossing over during meiosis produces
variation as the original chromosomes now
have different alleles as portions of the
homologous chromosomes have swapped.
The offspring will have characteristics unique
to itself depending on the combinations of
alleles for each of its features.
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Sex is determined by two sex chromosomes
carried by the sperm and the egg and is
determined at fertilisation.
Y male, X female
Males – XY females have XX
The X and Y chromosomes act as homologous
chromosomes during cell division and
segregate like normal during the first division
of meiosis.
Each gamete (sperm or egg) gets only one sex
chromosome.
Half a man’s sperm have X and half have Y
All egg contain X chromosomes.
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Characteristics – features a living thing has, eg,
black fur. = traits.
Can be inherited – eg, gained from parents by
transmission of genes.
Can be acquired – eg, permed hair.
Characteristics Genetic variation within a
species enables the species to survive changes
in habitat better. There will always be a few
organisms that can survive, eg, antibiotic
resistance in bacteria.
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Variation, the small differences that exist
between individuals, can be described as being
either CONTINUOUS OR DISCONTINUOUS.
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Individuals fall into a number of distinct
classes or categories, and is based on features
that cannot be measured across a complete
range.
You either have the characteristic or you
don't.
Blood groups are a good example: you are
either one blood group or another - you can't
be in between.
controlled by alleles of a single gene or a small
number of genes. The environment has little
effect on this type of variation.
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Evolution is a change of representation of
specific versions of genes in a population
which leads to changes in the characteristics of
organisms.
There is a complete range of measurements
from one extreme to the other.
 Height is an example of continuous variation
 Other examples of continuous variation
include:
• Weight; Hand span; Shoe size; Milk yield in
cows.
 Combined effect of many genes (known as
polygenic inheritance).
 Often significantly affected by environmental
influences.
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