Transcript File - Miss Jenkins

Achievement Standard Number
90163
B1.3 Aspects of Biology
Transfer of
genetic
information
Genetics objectives
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roles of, and relationships between, chromosomes, genes,
alleles and DNA
structure and replication of DNA and its role in the transfer of
genetic information. The structure is limited to double helix,
molecular groups (sugar, base, phosphate), base pairing
cell division through mitosis and meiosis. Biological ideas
relating to mitosis and meiosis are limited to purpose, where
they occur, sequence of events (the names of stages are not
required), reasons for maintenance or change of chromosome
number, significance of the number of cells produced
solution of genetic problems limited to sex determination, simple
monohybrid inheritance patterns for alleles showing complete
dominance
applications of genetics, eg selective breeding, breeding
techniques, genetic modification, cloning.
Genetics wordlist
• Variation – differences in characteristics in a
species eg. different skin colours, eye colour,
height etc
• Gamete – a sex cell (egg or sperm)
• Zygote - a cell that is formed when a sperm and
an ovum combine their chromosomes at
conception.
• Fertilisation – the joining of gametes (eg. an
egg and a sperm) as part of sexual
reproduction.
• Chromosome – made of a long strand of coiled up
DNA. Found in the nucleus of a cell. Humans have
46 chromosomes in body cells and 23
chromosomes in gametes.
• Karyotype – when the chromosomes in a cell are
arranged in homologous pairs to show the no. of
chromosomes, the sex of the individual and any
abnormalities.
• Gene – made of DNA and it contains instructions, it
is found on a section of a chromosome. A
chromosome may contain thousands of genes.
Humans have more than 30,000 different genes in
total.
• Allele – a form of a gene.
eg. R = can tongue roll, r = can’t tongue roll
• Dominant - an allele that masks the
presence of a recessive allele in the
phenotype and always is expressed when
present in a genotype. We use capital
letters to represent dominant alleles. Eg
BB, Bb.
• Recessive - an allele that is masked in the
phenotype by the presence of a dominant
allele. Recessive alleles are only
expressed in the phenotype when the
genotype is homozygous recessive (bb).
•
•
•
•
•
Homozygous – 2 of the same alleles eg bb
or BB
Heterozygous – 2 different alleles. eg Bb
Pure breeding - offspring that are the result
of mating between genetically similar kinds
of parents. Pure bred animals have
homozygous alleles eg BB or bb.
Genotype - the genetic makeup of an
individual eg BB, Bb or bb
Phenotype - the observable or detectable
characteristics of an individual organism eg
blue eyes.
• Trait / Characterisitic – the phenotype of an
organisms, a notable feature of an organism. We all
have different combinations of traits.
• Phenotype ratio – a ratio that shows the proportion of
particular phenotypes that have resulted in a cross.
Eg 3 red : 1 white flower
• Punnett square - a simple method of showing all of
the potential combinations of offspring genotypes that
can occur and their probability given the parent
genotypes.
• Pedigree chart – a branching tree diagram that
shows traits being passed through a family.
• Semi-conservative – one half of the original DNA
strand is kept (conserved) in a new strand after DNA
replication. The new strand contains half old and half
new DNA.
DNA
DNA is a double stranded molecule found in the
nucleus of the cells of living things.
It is made up of about 3 billion pairs of 4
different bases, we use letters to represent
the 4 bases found in all living things
A = adenine
T = thymine
C = cytosine
G = guanine
DNA
Nucleotides
phosphate
Sugar (deoxyribose)
Base
(A, T, C or G)
DNA Base pairing rule - A and T pair together
- C and G pair together
DNA Replication
Chromosomes are found in
the nucleus, they are made
of DNA. DNA never leaves
the nucleus.
Humans have 23 pairs of
chromosomes (a total of
46) in every cell in our
bodies (except our eggs or
sperm – they have a half
set of only 23
chromosomes.
Different living things have
different numbers of chromosomes
Human Karyotype (male)
Genes
Genes are the basic units of heredity in living
cells.
They consist of a length of DNA that contains
instructions ("codes") for making a specific
protein.
Through these proteins, our genes influence
almost everything about us, including how tall we
will be, how we process foods, and how we
respond to infections and medicines.
Although most of our cells have the
same genes, not all genes are active
in every cell. Heart cells synthesize
proteins required for that organ's
structure and function; liver cells
make liver proteins, and so on.
In other words, not all the genes
are "switched on" and expressed as
proteins within every cell. Within an
individual cell, the same genes may
be switched on at some times and
switched off at other times.
Problems with genes
We know a lot about the position of genes on
chromosomes by looking at the chromosomes of
people with genetic diseases.
Scientists can work out what the gene sequence
should be like from healthy people and can see
what has gone wrong in someone with a genetic
disease. New discoveries are being made often.
The following picture shows human chromosomes
5, 6, 7 and 8 and the positions of genes that we
know about so far.
Cell division
Mitosis
Meiosis
Purpose To create cells
To create gametes
identical to the original (eggs or sperm) that
cell and to keep the
contain HALF the
chromosome number
original chromosome
the same.
number
Growth and repair
Where
it
occurs
In all body cells for
growth and repair
In the ovaries in
females to make
eggs
In the testes of
males to make sperm
Cell division Mitosis
Mitosis occurs in every
cell in our body – without
mitosis we wouldn’t grow
or heal cuts and injuries.
Mitosis is a cell division
where the chromosome
number is kept the same
and two identical cells
are produced from one.
Cell division
- Meiosis
Meiosis occurs in the
ovaries of females to
make eggs and the
testes of males to
make sperm.
Two divisions occur,
making four cells that
have half the number
of chromosomes that
the original cell had.
Fertilisation
Egg
23 chromosomes
Zygote
46 chromosomes
Sperm
23
Alleles
• One of two or more forms of a gene at a given position on a
chromosome. They are caused by a difference in the sequence of DNA.
• A gene which controls eye colour in humans may have two alternative
forms – an allele that can produce blue eyes (b), and an allele that
produces brown eyes (B). In a plant that occurs in tall and short forms,
there may be an allele that tends to produce tall plants (T) and an
alternative allele that produces short plants (t).
• The individual genes that form a pair of alleles are located at exactly the
same point along a chromosome. There will always be two genes for a
characteristic in a cell.
Genotype
TT = homozygous dominant
Tt = heterozygous
tt = homozygous recessive
Phenotype
TT = tall plant
Tt = tall plant
tt = short plant
Alleles
T
t
a
a
b
B
C
U
r
y
Z
C
u
r
Y
Z
ZZ =
homozygous
dominant
Uu =
heterozygous
aa =
homozygous
recessive
Monohybrid cross
The study of single-gene inheritance is done
through
monohybrid crosses.
- Capital letters represent dominant alleles
- Lower case letters represent recessive alleles
e.g. coat colour in guinea pigs
Genotype
Phenotype
BB
Black
Homozygous = 2 of the
same alleles eg BB or bb
Bb
Black
Heterozygous = Bb
bb
white
A cross between 2 heterozygous black guinea
pigs ( Bb x Bb ) expressed as a ratio
Possible
fertilisations
B
b
B
b
Place parents alleles at the top
and side of the punnet square
Possible
fertilisations
B
b
B BB Bb
b Bb bb
3 black : 1 white
Sex determination
What are the chances of having a boy or a girl???
Everyone has a pair of chromosomes that determine our sex
XX = female XY = male
X X
X XX XX
Y XY XY
The punnett square on the left
shows us the probabilities that a
man and woman are faced with
each time they have a child.
XX = 50%
XY = 50%
If you have had two boys it does
not mean you will have a girl next,
each time a new zygote is formed
the chances or it being male or
female are 50 : 50.
Contemporary Applications of Genetics
• In the exam the
questions will be
resource based.
• The context will be
selected from
selective breeding,
cloning or genetic
modification.
Selective breeding
Selective breeding is when we
choose animals with good traits for
breeding.
Eg. Bulls are chosen to mate with
many cows to pass on his good
genes.
Selective breeding
• Also called artificial selection
The steps for selective breeding are:
• Select the stock or plants that have the best
characteristics.
• Breed them with each other.
• Select the best of the offspring and combine
them with the best that you already have.
• Continue this process over many generations
until you have the desired traits
Selective breeding - Dogs
Cloning
• Cloning is the creation of an organism that is an exact
genetic copy of another. This means that every single bit
of DNA is the same between the two!
• You might not believe it, but there are human clones
among us right now. They weren't made in a lab, though:
they're identical twins, created naturally. Below, we'll see
how natural identical twins relate to modern cloning
technologies.
• How is cloning done?
• You may have first heard of cloning when Dolly the
Sheep showed up on the scene in 1997. Cloning
technologies have been around for much longer than
Dolly, though. The first animal, a tadpole was cloned in
1952. Mice, pigs, cats, and rabbits have also been
cloned.
Celebrity Sheep Has Died at Age 6
Dolly, the first mammal to be cloned from adult
DNA, was put down by lethal injection Feb. 14,
2003. Prior to her death, Dolly had been suffering
from lung cancer and crippling arthritis. Although
most Finn Dorset sheep live to be 11 to 12 years
of age, postmortem examination of Dolly seemed
to indicate that, other than her cancer and
arthritis, she appeared to be quite normal. The
unnamed sheep from which Dolly was cloned
had died several years prior to her creation. Dolly
was a mother to six lambs, bred the old-fashioned
way.
Image credit: Roslin Institute Image Library, http://www.roslin.ac.uk/imagelibrary/
• Scientists are looking at therapeutic cloning that
can be used to generate tissues and organs for
transplants.
• To do this DNA would be extracted from the
person needing a transplant and inserted into an
egg. Once the egg (with the persons DNA) starts
to divide, the stem cells that can be transformed
into any type of tissue would be harvested.
These stem cells would be used to generate an
organ or tissue that is a genetic match to the
recipient. In theory the cloned organ could then
be transplanted without risk of tissue rejection.
Injection of nucleus into egg cell
during the cloning process
Blunt
end
pipette
Empty cell
Nucleus
put in
by
sharp
ended
pipette
Cloning – any
Advantages?
Genetic modification
• This involves moving sections of DNA
(genes) from one organism to another so
that it produces useful biological products.
• Bacteria is currently used to produce
human insulin for diabetes sufferers.
• It also produces human growth hormone
for children who aren’t growing properly.
Stages of genetic engineering
• The useful gene is “cut out” by enzymes.
• Particular enzymes will cut out particular parts
of DNA
• The DNA of a bacterium is then cut (by
enzymes) and the human gene is inserted.
• This splicing of a new gene is again controlled
by enzymes.
• The bacteria is then cultivated and soon there
are millions of bacteria producing human
insulin.
How it occurs
Genetic modification
Comparison
Selective Breeding
• Some people think that it is wrong to
manipulate nature.
• Is it right to produce cows that would die if we
didn’t milk them, because we have bred them to
produce too much milk.
• Is it right to breed pigs with so much meat on
them that they have trouble standing up.
• Is it wrong to breed tomatoes or potatoes that
are heavy cropping.
Cloning:
• Groups of scientists want to clone human
embryos to get replacement tissues and organs
for people who need them.
• Using organs from embryos cloned from
themselves, would save the lives of people who
would otherwise die because they have
rejected transplanted organs.
• A lot of people argue that to create a life for
spare parts and then kill it is wrong.
• This is the stage that a lot of countries allow
abortion at.
Genetic engineering:
 A big problem is the possibility of making designer
babies – people may want there child to be perfect
and not carry diseases, need to wear glasses, have
the perfect nose etc.
 Changing the genetic make-up of any organisms may
effect ecosystems in ways laboratory tests can’t
predict.
 Large seed companies can make money every year by
selling plants that won’t produce fertile seeds, or by
producing plants that are resistant to their weed
killers.
 G.E. can also be used to produce crops that grow in
places that they wouldn’t normally and this could save
lives
The future
• One day in the not-too-distant future, your health care
provider may talk to you about obtaining a single blood
sample for DNA analysis, the results of which will be
recorded in a computer chip on a wallet-sized plastic card.
This card will contain specific aspects of your genetic
makeup that can be identified as needed. The genetic
information contained there may be used in several ways:
• To predict your risk of developing certain diseases, allowing
their earlier diagnosis or possible prevention.
• To more accurately diagnose the cause of symptoms or
diseases you may experience.
• To help your health care provider more accurately select
the medicine most likely to be of benefit and least likely to
cause you harm.
• To help scientists more efficiently discover and develop
safer, more effective medicines aimed at the root causes of
diseases, not just their symptoms.