Transcript Slide 1
Starter – talk for one minute about the diagram
Thursday, April 30, 2020
Chapter 3: Genetics Title: Genes
Learning Objectives:
We are learning….
• What is a gene?
Keywords: • gene • chromosome • homologous • allele • sickle cell anemia • What is the relationship between genes and chromosomes?
• What is an allele?
• What is the relationship between genes, mutation and sickle cell anemia?
• What is the human genome project?
Starter: How are these words linked?
Chromosome, DNA, amino acid, meiosis, nucleus, mitosis
Introduction to genetics
Chimpanzees are set apart from all other organisms because their parents wee chimpanzees and their offspring will also be chimpanzees.
Every living organism inherits its own blueprint for life in the chromosomes and genes that are passed to it from its parents.
The study of genetics attempts to explain this process of heredity and it also plays a very significant role in the modern world, from plant and animal breeding to human health and disease.
What is DNA?
Chromosomes and their genes are made of a molecule called DNA.
DNA
stands for
d
eoxyribo
n
ucleic
a
cid.
Each chromosome is a very long molecule of
tightly coiled
DNA.
4 of 47
DNA molecules carry the code that controls what your cells are made of and what they do. Which part of a DNA molecule holds this information?
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• • •
Genes
Sections of DNA Code for the manufacture of proteins The position of a gene on a chromosome is its
locus
6 of 36
Different versions of genes
The chromosomes in a matching pair contain the
same type
of genes that code for the same characteristics.
gene for petal colour version for red petals gene for petal colour version for yellow petals
Each chromosome may have a
different version
of a gene. Different versions of a gene, that code for different versions of a characteristic, are called
alleles
.
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Pairs of alleles – homozygous
If the alleles in a matching pair are the
same
, they are called
homozygous alleles
.
allele for yellow petals allele for yellow petals allele for red petals allele for red petals 7 of 36
What colour are the flowers with these homozygous pairs of alleles?
(Click twice on each bud to reveal the flower; click again to close them.)
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Representing alleles
Letters
are used to represent different alleles.
A
dominant allele
is always a
capital letter. allele for red petals = R
A
recessive allele
is always the
corresponding small letter
.
allele for yellow petals = r 8 of 36
The allele pair for each characteristic is called the
genotype
.
What colour are flowers with the genotype
Rr
?
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Allele
• • • • • Each gene exists in 2 or more forms Each of these forms is an allele A homologous pair may have different alleles of the same gene If there are different alleles of a gene on homologous chromosomes, the organism is
heterozygous for that gene (e.g. B,b)
If the alleles are the same, the organism is
homozygous (B, B)
Multiple alleles and blood groups
In humans, the inheritance of the ABO blood groups is determined by a gene, I, which has three different alleles.
Any two of these can occur at a single locus at any one time.
Blood group
A B AB O
Possible genotypes
I
A
I
A
or I
A
I
O
I
B
I
B
or I
B
I
O
I
A
I
B
I
O
I
O
Multiple alleles and blood groups
Allele A causes the production of antigen A on red blood cells Allele B causes the production of antigen B on red blood cells Allele O causes no production of antigens on red blood cells (universal donor) Alleles A and B are codominant and allele O recessive to both. is
Blood group Possible genotypes
A B AB O I
A
I
A
or I
A
I
O
I
B
I
B
or I
B
I
O
I
A
I
B
I
O
I
O
Try a cross between individuals with blood group A and an individual with blood group B
Protein synthesis summary – how many mistakes can you spot?
A C C A A cytoplasm A C C G A G T
RNA
translation T G G T T Nucleus: T A G C ribosome T C A
tRNA
transcription Phe Leu Leu Ser
PROTEIN
Gly
Guess the mutation – match the mutation to the pictures
Mutation type
Addition Inversion Substitution
An example of how mutagens cause damage to the genes controlling the normal cell cycle is shown below.
After exposure to UV light, adjacent thymine bases in DNA become cross linked to form a ‘thymine dimer’ (lesions form between bases).
This disrupts the normal base pairing and throws the controlling gene’s instructions into chaos.
So what are mutations?
Any change in the structure or the amount of DNA of an organism is called a mutation .
Most mutations occur in somatic (body) cells and are not passed from one generation to the next.
Only those mutations which occur in the formation of gametes can be inherited.
These mutations produce sudden and distinct differences between individuals.
Michael Berryman is an American actor who has appeared in many horror films. He was born with a rare genetic condition which prevents him from developing hair, sweat glands or fingernails and claims to have had "twenty-six birth defects."
Changes in gene structure – point mutations
Changes in the structure of DNA which occur at a single locus on a chromosome are called gene mutations or point mutations .
Any change in the sequence of nucleotides will produce the wrong sequence of amino acids in the protein it makes.
This protein is often an enzyme.
Why might this be a problem?
Complete the card sort to find out how sickle cell anaemia is caused.
Problems with the code
A mutation in the code, or if part of the code is missing, can lead to a lack of an enzyme or a faulty enzyme being formed.
Sickle cell anaemia is a hereditary condition caused by a gene mutation.
The replacement of just one base in the DNA molecule results in the wrong amino acid being incorporated into two of the polypeptide chains which make up the haemoglobin molecule.
The abnormal haemoglobin causes red blood cells to become sickle-shaped, resulting in anaemia and possible death.
Over 12 500 people in the UK have sickle cell anaemia. The majority of them are of African or Caribbean descent.
Types of gene mutation – the causes Duplication
A portion of the nucleotide becomes repeated.
Addition (insertion)
An extra nucleotide sequence becomes inserted in the chain.
Deletion
A portion of the nucleotide chain is removed from the sequence.
Inversion
A nucleotide sequence becomes separated from the chain. It rejoins in its original position, only inverted (backwards). The nucleotide sequence of this portion is therefore reversed.
Substitution
One of the nucleotides is replaced by another which has a different organic base.
Draw a diagram for each followed by a simple explanation.
Types of gene mutations – the causes
The human genome project
Why is determining an organism’s genome sequence important?
Most types of cell in an organism contain a complete copy of its genome. The organisation is quite complicated, but the simplest fact about any genome is that it is a collection of DNA sequences – long strings of the chemical ‘letters’ A, T, G and C (adenine, thymine, guanine and cytosine) in a particular order.
Learn to read an organism’s genome sequence, and compare it with that of other organisms, and it can tell you lots of different things.
The human genome sequence contains a wealth of information about human biology, in both health and disease. Our DNA is a window on evolution and recent human history – including the migration of people around the world.
DNA sequencing – the Sanger technique
The human genome project
Why is determining an organism’s genome sequence important?
The genome sequences of other species have many other uses. The genomes of organisms used in farming, from rice and wheat to pigs and cattle, are being sequenced to help to breed improved strains. But the vast majority of the many thousands of genomes already completed are from bacteria. Some are species that cause diseases in people, as well as in agriculturally important animals or plants.
Others are important for maintaining health or have potential uses in the industrial production of biologically active chemicals and enzymes.
Genomic information is used to track harmful microbes such as those that cause infection in hospitals, as well as to aid the development of new drugs. New influenza strains have their genomes read quickly to understand how the virus spreads and to speed up vaccine production.
Knowledge of genome sequences also speeds up developments in biotechnology and is finding uses in tracking biodiversity and policing trade in protected species.
Main Activity:
Success Criteria:
What I’m looking for…..
Plenary: Your little sister is playing in the living room whilst your parents watch the news. She hears an item about genetically inherited illness. She knows you are studying genetics at school so she asks you, “What is a gene?” You have five minutes in pairs to write out an answer she will understand.
How successful were we this lesson?
Learning Objective