Transcript Year 11 Genetics topic

Science 1.9
Demonstrate understanding of
genetic variation.
SLO’s.
• The roles of, and the relationship between, chromosomes,
genes, alleles and DNA.
• How DNA carries instructions and how they are passed on
through generations.
• The importance of variations within populations for survival
and how this variation occurs.
• The purpose of mitosis and meiosis, where they occur and the
effect on chromosome number (note: the names of stages are
not required).
• The difference between phenotypes and genotypes.
• Simple monohybrid inheritance patterns showing complete
dominance, sex determination, possible genotypes, and
phenotype ratios.
Chromosome.
The chromosome, is the DNA strand, which
has coiled up.
DNA (Deoxyribonucleic acid)
The DNA strand, consists of ribose sugars,
phosphate atoms and base pairs (nucleotides).
Gene
The gene, is a section of the DNA strand, which
codes for a trait.
Allele
ATTCCGGATTAAGGCCAAA
ATTCCCGATTAAGGCCAAA
The mutant allele has one base that is
different, this causes the allele to code for a
different trait.
Putting it all together.
A chromosome is a tangle of
DNA, when the DNA is
unwound, bands can be
seen, these are genes.
Each gene codes for a protein,
which codes for a trait.
The variations of a gene, are
called the alleles.
DNA  proteins.
• DNA is a code, when it is read by molecules
within the cell, it is translated into a protein.
• DNA is made up of base pairs of nucleotides.
• A- Adenine
• T- Thymine
• C- Cytosine
• G- Guanine
• A bonds with T, while C bonds with G.
A=T
C≡G
DNA replication.
• Before a cell can divide, the DNA must make
an exact copy of itself.
• This is so each cell can have a full set of DNA.
• This occurs in mitosis and the first stage of
meiosis.
• How does it happen?
Helicase
enzyme
Parent strand
New strand
After the DNA strand is cut in half, new
nucleotides come in from the cytoplasm and
match up, making 2 strands.
‘old’
‘new’
Semi-conservative replication
Triplets.
• Each base pair is read as a set of 3.
• Each set of 3 codes for an amino acid.
• When many amino acids join together, they
make a protein.
• When the DNA is coding for a protein it is
changed to RNA and T becomes U.
Video link
http://www1.teachertube.com//googleSearch.
php?cx=012339422634307447803%3Ah-vlwwg9yy&cof=FORID%3A11&ie=UTF8&q=DNA+translation&sa=Search
Example.
CAA-TTG-GCA-ACT
Becomes the RNA
GUU-AAC-CGU-UGA
Becomes the protein
gly-asn-arg-stop
CTA-GAA-ACA-ACT
Becomes the RNA
GAU-CUU-UGU-UGA
Becomes the protein
asp-leu-cys-stop
So what does this mean for us?
• We each have a unique DNA code, which we
have inherited form our parents, we must
then make different variations of these
proteins...what does this mean for us?
• We all look different!
• Complete the transcription worksheet.
Human chromosomes.
Karyotype.
Human chromosomes.
• Each of your body cells has 23 pairs of
chromosomes, you inherited from your
parents.
• 22 ‘normal’ chromosomes, which code for
your height, hair colour, skin tone etc.
• 1 set of ‘sex’ chromosomes, which code for
your gender.
• XX  female, XY  male.
Male or female?
• In every pregnancy
there is 50% chance the
zygote will be male ♂ or
female ♀.
• Half of the man’s sperm
carry an X chromosome
and the other half a Y
chromosome.
X
• Complete Pgs 74&5.
Y
Male; sperm
Female; egg
X
X
XX ♀
XX ♀
XY ♂
XY ♂
Why do we look different to each other?
• Variation is the difference between you and
the person sitting next to you.
• We are all humans, so the variation tends to
be traits such as height, eye colour skin tone.
• There are 2 types of variation; continuous and
discontinuous.
Continuous variation.
• The trait fits on a range.
• E.g. height, hand span.
• With a large sample, most traits will form a
bell curve.
• Complete the exercise
on Pg 70.
Handspan of Year 11
4.5
4
3.5
Number of people
3
2.5
Series1
2
1.5
1
0.5
0
19-20
20-21
21-22
Hand span (cm )
22-23
23-24
Discontinuous variation.
• Also know as either/or variation.
• You either have the trait, or you don’t.
• E.g. Widows peak
• Complete the exercise
on Pg 69.
So what causes variation?
• Why do we all look different?
• Discuss in pairs why we each look different,
yet have the same number of eyes, ears and
noses.
• Why is variation important to species?
Cell division 1; mitosis.
• Cell division for growth and repair, is called
mitosis (my-toes grow).
• Identical copies of the daughter cell are
created through a series of steps, each cell has
2 copies of each chromosome.
• You can remember ‘IPMATC’ to help you learn
the stages.
• Pg 72.
Mitosis.
1. DNA unwinds.
2. DNA copies.
3. Copies move to
equator.
4. Copies divide.
5. Cell pulls apart.
6. Cell divides.
7. Two new cells.
Cell division 2; meiosis.
• Cell division for sexual reproduction, is called
meiosis.
• One ‘germ’ cell becomes 4 daughter cells,
each with half the chromosome number of a
full body cell.
• E.g. egg and sperm have only 1 copy of each
chromosome.
• Pg 73 & meiosis square dance.
Meiosis
1. DNA unwinds.
2. DNA crosses over &
copies.
3. Copies move to
equator.
4. Copies divide.
5. Cell pulls apart.
6. Cell divides.
7. Two new cells.
8. DNA moves
randomly to each
side of the cell.
9. Cells divide again.
10. Four new cells.
Early Prophase.
Late prophase.
Metaphase.
Anaphase.
Telophase.
Cytokinesis.
Why only 1 set?
Egg + Sperm = zygote.
Egg cell 23
chromosomes
• One set from
the egg +
one set from
the sperm =
full set for
the zygote.
Zygote 46 chromosomes (2n)
Full set
2 important processes.
• Crossing over; pieces of DNA are swapped
between chromatids.
2 important processes.
• Random assortment; which chromatid goes to
which cell is random.
Summary notes.
• Meiosis halves the number of chromosomes,
so when the egg and sperm join at
fertilization, the zygote has a full set.
• Each gamete has a unique combination of
DNA.
• The zygote then grows by mitosis, into an
embryo.
• If the sperm or egg has a mutation or wrong
number of chromosomes, the whole embryo
is affected.
So why use meiosis and sexual
reproduction?
• Why go to all the hassle of meiosis?
• Why go and find a mate to reproduce with?
• More on that later.
Gene-ious words!
Genotype
• The gene’s the organism
have inherited from its
parents.
• Organisms have two copies
of each gene.
• E.g. Hair colour
BB, Bb, bb.
Phenotype
• The appearance of the
gene’s inherited.
• The phenotype is how the
organism looks or how it
functions.
• E.g. Hair colour
Brown, blonde, ginga.
Ingene-ious words.
Allele
• The variations of a gene.
• If it wasn’t for allele’s we
would all have the same eye
colour.
• B- brown eyes
• b- blue eyes
• Both gene’s code for eye
colour but there are 2
allele’s.
Mutations.
• The only source of new
allele’s.
• Mutations can occur in may
ways, they alter the DNA so
a new allele is created.
• W- long wings
• w- short wings
• w*- curled wings
So that’s why I’ve got Mum’s eye colour,
but Dad’s hair!
• As you have one chromosome from each
parent, your homologous pairs have 2 copies
of each gene.
• The gene’s may be the same allele, or two
different allele’s.
• Pg 75.
Some alleles are DOMINANT!
• And some are recessive.
• You can have 3 possible allele combinations;
AA, Aa, aa.
• AA= homozygous dominant (dominant seen).
• Aa= heterozygous (dominant seen).
• aa = homozygous recessive (recessive seen).
Keyword alert!
1.
2.
3.
4.
5.
6.
Homozygous; 2 of the same alleles.
Heterozygous; 2 different alleles.
Dominant; 1 copy needed to show.
Recessive; 2 copies needed to show.
Genotype; gene code (bb).
Phenotype; what shows (blue eyes).
Simple examples.
•
•
•
•
•
B = brown eyes.
b = blue eyes.
BB = brown eyes.
Bb = brown eyes.
bb = blue eyes.
Working out inheritance.
Female
A
a
Male
a
• We use Punnet squares
to figure out
inheritance.
• First look at the parents
genotypes.
• Female- Aa
• Male- aa
a
Working out inheritance 2.
• Fill in the offspring's
genotypes.
• Work out the genotype a
ratio or percentage.
• 50% Aa
a
• 50% aa
• 1:1
A
a
Aa
aa
Aa
aa
Working out inheritance 3.
• Work out the
phenotype ratio or
percentage.
• 50% auburn
• 50% brown
• 1:1
A
a
a
Aa
aa
a
Aa
aa
Tounge rollers.
• 3 rollers, 1 non roller.
• What are the parents genotype?
Red flowers (R).
• 1000 red flowers + 0 white flowers.
• 1000 white flowers + 0 red flowers.
• 750 red flowers, 250 white flowers.
Examples.
• Work through the examples of monohybrid
crosses Pg 44 & 45.
• Extra for experts; move onto the dihybrid
crosses sheet also.
Pedigree charts.
Pedigree charts.
• Pedigree charts show inheritance of traits,
particularly in human diseases.
• E.g. haemophilia in the British royal family,
• Key;
• Normal ♂
♀
• Carrier
• Sufferer
So…
• Is haemophilia dominant or recessive?
• How did you know?
• Complete the worksheet.
1. Using the pedigree, state why the gene for mid-digital hair is a dominant
characteristic.
Mid-digital hair is a dominant characteristic as more family members show the
trait (9) than do not (4). This indicates that the gene is expressed more often
and also the offspring C1,2,3 all show the trait.
2. Which individual(s) from A1 and A2 is/are heterozygous?
Both parents are heterozygous (Hh) as they have produced 2 off spring with
mid-digital hair (B1,6) and two without mid-digital hair (B2, 4).
• 3. What is the probability that individual B1 is
heterozygous; show your reasoning.
• There is a 50% chance that B1 is heterozygous. As
shown in the Punnet square below; when two
heterozygous individuals conceive a child, they have a
50% chance of being heterozygous, a 25% chance of
being homozygous dominant and a 25% chance of
being homozygous recessive
H
h
H
HH
Hh
h
Hh
hh
• 4. Individuals C1, C2 & C3 are all heterozygous. Using H to
represent mid-digital hair and h to represent no hair, give
the genotype of their mother; show your reasoning.
• Their mother was HH, homozygous dominant. As shown in
the Punnet square below; when a homozygous recessive
individual and a homozygous dominant individual conceive
a child, there is a 100% chance they will be heterozygous
for that trait, (unless a mutation occurs).
H
H
h
Hh
Hh
h
Hh
Hh
The Royal Family of Spain.
Gaze upon the family tree,
If the level of inbreeding is clear to thee,
Then, I feel, it is time to flee.
Ancestry
Charles was born in Madrid, the only surviving
son of his predecessor, King Philip IV of Spain
and his second Queen (and niece), Mariana of
Austria, another Habsburg. His birth was greeted
with joy by the Spanish, who feared the
disputed succession which could have ensued if
Philip IV had left no male heir.
• 17th century European noble culture commonly
matched cousin to first cousin and uncle to niece,
to preserve a prosperous family's properties.
Charles's own immediate pedigree was
exceptionally populated with nieces giving birth
to children of their uncles: Charles's mother was
a niece of Charles's father, being a daughter of
Maria Anna of Spain (1606–46) and Emperor
Ferdinand III. Thus, Empress Maria Anna was
simultaneously his aunt and grandmother and
Margarita of Austria was both his grandmother
and great-grandmother. This inbreeding had
given many in the family hereditary weaknesses.
That Habsburg generation was more prone to
still-births than were peasants in Spanish villages.
There was also insanity in Charles's family; his
great-great-great(-great-great, depending along
which lineage one counts) grandmother, Joanna
of Castile ("Joanna the Mad"), mother of the
Spanish King Charles I (who was also Holy
Roman Emperor Charles V) became insane early
in life. Joanna was two of Charles' 16 greatgreat-great-grandmothers, six of his 32 greatgreat-great-great-grandmothers, and six of his
64 great-great-great-great-great-grandmothers.
• Dating to approximately the year 1550, outbreeding in
Charles II's lineage had ceased. From then on, all his
ancestors were in one way or another descendants of
Joanna the Mad and Philip I of Castile, and among
these just the royal houses of Spain, Austria and
Bavaria. Charles II's genome was actually more
homozygous than that of an average child whose
parents are siblings. He was born physically and
mentally disabled, and disfigured. Possibly through
affliction with mandibular prognathism, he was unable
to chew. His tongue was so large that his speech could
barely be understood, and he frequently drooled. It has
been suggested that he suffered from the endocrine
disease acromegaly, or his inbred lineage may have led
to a combination of rare genetic disorders such as
combined pituitary hormone deficiency and distal renal
tubular acidosis.
• Consequently, Charles II is known in Spanish history as
El Hechizado ("The Hexed") from the popular belief –
to which Charles himself subscribed – that his physical
and mental disabilities were caused by "sorcery." The
king went so far as to be exorcised.
• Not having learned to speak until the age of four nor to
walk until eight, Charles was treated as virtually an
infant until he was ten years old. Fearing the frail child
would be overtaxed, his caretakers did not force
Charles to attend school. The indolence of the young
Charles was indulged to such an extent that at times he
was not expected to be clean. When his half-brother
Don John of Austria, a natural son of Philip IV, obtained
power by exiling the queen mother from court, he
covered his nose and insisted that the king at least
brush his hair.
How do genotypes become
phenotypes?
• PROTEINS!!!
• Your DNA codes for proteins to be made in
your body, it is these proteins that create the
look of your phenotype.
DNA sequence; AAAATGCTTCTCCAA
Protein coded for; Keratin
Variation.
•
•
•
•
•
•
•
How does variation occur in a species?
Gene mutations.
Chromosome mutations.
Independent assortment.
Recombination.
Mate selection & sexual reproduction.
Environmental factors.
Clay model
Mutations.
A
T
C
T
A
G
A
T
C
A
A
G
Chromosome mutation.
• The chromosome is
changed in a large way, this
often changes the proteins
the chromosome codes for.
• This type of mutation is
almost always harmful.
ATGGCCTTAA
ATGGCCTTAA
T TCCG
T TCCG
Gene mutation.
• The DNA strand is changed,
so the protein made to
express the gene is
different.
• Some mutations are
harmful, others are helpful.
A
T
C
T
A
G
A
T
C
A
A
G
Mutations.
Whole chromosome insertion
• 1 or more whole extra
chromosome is present in
every cell.
• E.g. Down’s syndrome.
An extra chromosome 21.
Whole chromosome deletion.
• 1 or more whole
chromosome is absent from
every cell.
• E.g. Turner’s syndrome.
Missing one X chromosome.
Mutations.
• Mutations can occur in both gamete’s (sperm
and egg) and also in body cells (cancer).
• In order to be passed on to offspring, the
mutation must occur in a gamete (meiosis).
• A body cell mutation can not be passed on.
• Mutations are the only source of new genetic
material.
• Mutations can be; beneficial, silent or
harmful.
Mutations.
• Helpful; gives organism an advantage.
• Silent; no effect on organism.
• Harmful; kills, disables or makes the organism
sterile.
Variation- 2 important processes.
Random assortment
• The chromosomes are
randomly sorted into the
gamete’s in meiosis.
• This makes each gamete
unique in their gene
combination.
Crossing over
• Pieces of chromosome are
swapped during crossing
over, creating new
combinations of allele’s on
each chromosome.
Non genetic variation
Mate selection
• Many animals choose their
mate for the desirable
characteristics.
• Different combinations of
allele’s will be present on
the offspring depending on
the mate selected.
• Sexual reproduction creates
new combinations of
allele’s.
Environmental factors.
• Environmental factors may
influence the expression of
the genotype.
• E.g. Temperature, pH, wind
exposure, availability of
food, level of parental care.
Mate selection
Environmental factors.
Tomato with sunlight
Tomato without adequate light
To re-cap...
• As you can see many traits are inherited from
parents to offspring. These are called
inheritable traits.
• Some variations are not inherited, they are
controlled by the environment. These are
called non-inheritable traits.
Why is variation so important?
• Imagine swine flu rampaged through
Lawrence; who would survive? Who would
die? How would you know?
DEAD
DEAD
• Why are there some many people with red
hair in Waitahuna? What if the climate heated
up and the red head’s couldn’t survive? How
would this impact on the (Homer) population?
• Disease & environmental changes effect
populations.
SO DEAD
DEAD
DEAD
Darwin thinks you look like a
monkey...
Survival of the fittest.
• Evolution is the modern theory of how
organisms change and adapt over time.
• Charles Darwin (1809-1882) wrote the book
on evolution “The theory of Evolution by
natural selection”.
• His theory has now been proven using
evidence from the fossil record.
Everyone out of the gene pool!
• The gene pool is all of the gene’s and allele’s in
one population.
• How an individual is effected by pest
infestations, disease, drought etc, is often
determined by their gene’s.
Gene pool exercise.
1. Initial gene pool.
2. Natural selection (favours dominant
individuals.)
3. Founder effect.
4. Immigration and emigration.
Initial gene pool.
• The gene pool of the un-disturbed population.
• It represents all of the allele’s in the
population.
Natural selection (favours dominant
individuals.)
Stabilising selection
Natural selection.
Natural selection (favours dominant
individuals.)
Directional
selection; selects
against one extreme
Natural selection (favours dominant
individuals.)
Disruptive selection;
selects against the
middle
Founder effect.
• A small number of individuals are isolated
from the main population.
• Only the alleles that are contained within the
founding population are present in the new
population.
• The new population may be completely
different to the original population.
Immigration and emigration.
• Individuals moving in to a population may
bring in new alleles (immigration).
• Individual moving out of a population may
eliminate alleles (emigration).
Displays.
• http://www.youtube.com/watch?v=HyvxlUpEj
gI&feature=related
• Why do the male birds put on a display?
• What is the advantage it gains them?
Plumage.
So why is variation so important?
• It ensures the survival of a species!
Applications of genetics.
• Animal breeding.
• Genetic engineering.
• Cloning.
Animal breeding.
• For thousands of years people have chosen
animals for their specific traits and bred them
with one another.
• In this way they controlled (to some extent)
what the offspring would look like, act like and
what type of product they would gain from
them.
• Animals which are homozygous for the
desired trait are called pure breeding.
Example.
• Purebred dogs; the generations of animals are
recorded and any animals which do not
display the traits are not allowed to breed.
Advantages and disadvantages to
selective breeding.
• Breeders can mostly
control the traits of the
offspring.
• Breeders can remove
offspring which do not
show the correct traits.
• Groups of animals can
have very limited gene
pools.
• Animals may display
more recessive traits.
• Animals can have less
diversity leaving them
more vulnerable to
disease.
Genetic engineering.
• Genetic engineering, also called genetic
modification, is the direct human
manipulation of an organism's genome using
modern DNA technology. It involves the
introduction of foreign DNA or synthetic genes
into the organism of interest. The introduction
of new DNA does not require the use of
classical genetic methods, however traditional
breeding methods are typically used for the
propagation of recombinant organisms.
Reading.
• We shall read the information sheet on GE
and try and re-frame it into English!
Cloning.
• Cloning is the process of creating new
organisms from one body cell of another
individual.
• The most famous example is Dolly the sheep.
Nuclear Transfer
(as used with Dolly)
Dolly was created by transplanting a nucleus
from a cell of one sheep into the enucleated
egg of another. The nucleus-egg
combination was stimulated with electricity
to fuse the two and to stimulate cell
division. The new cell divided and was
placed in the uterus of a ewe to develop.
Dolly was born months later.
118
Therapeutic cloning
(Stem Cell Technology)
• Therapeutic cloning is the process by which a person's DNA is
used to grow an embryonic clone. However, instead of
inserting this embryo into a surrogate mother, its cells are
used to grow stem cells. These stem cells can be used as a
human repair kit. They can grow replacement organs, such as
hearts, livers and skin. These organs would not suffer from
rejection. They can also be used to grow neurons to cure
those who suffer from Alzheimer's or other diseases.
120
Summary.
• Time to summarize the notes from this topic
and begin to study for your exam.
• Check the SLO’s and make sure you
understand everything we have covered.
• Check your key words list and vocab
understanding.
Genes determine many of the features of organisms, such
as the eye colour of humans.
A gene is a part of a DNA molecule.
Brown eyes are due to a dominant allele and blue are due
to a recessive allele.
• Discuss how information in DNA gives organisms (like
the humans above) their individual features, such as
eye colour. In your answer, you should:
• Explain the difference between a gene and an allele
• Draw a labelled diagram in the box on page 3 to show
the relationship between a gene and an allele and the
structure of a DNA molecule
• Explain how the base sequence on DNA determines a
particular feature (e.g. eye colour) and different forms
(variations) of that feature (e.g. brown or blue eyes).