B1 - You and your genes Flashcards
State the two types of cell
Eukaryotic (animals and plants)
&
prokaryotic
What is the difference between a
eukaryotic and prokaryotic cell?
A eukaryotic cell contains a nucleus and
membrane-bound organelles. A
prokaryotic cell does not.
How can the structure of eukaryotic cells
be observed?
Using a light microscope
How is genetic information stored in a
eukaryotic cell?
Within the nucleus, arranged in
chromosomes
How is genetic information stored in a
prokaryotic cell?
Found free within the cytoplasm as:
● Single large loop of circular DNA
● Plasmids
What are plasmids?
● Small, circular loops of DNA found free in the
cytoplasm and separate from the main DNA
● Carry genes that provide genetic advantages
e.g. antibiotic resistance
Define genome
The entire genetic material of an
organism
What is a chromosome?
A long, coiled molecule of DNA that
carries genetic information in the form of
genes
What is DNA?
A double-stranded polymer of
nucleotides, wound to form a double
helix
Define gene
A section of DNA that codes for a
specific sequence of amino acids which
undergo polymerisation to form a protein
What are alleles?
Different versions of the same gene
Define genotype
An organism’s genetic composition,
describes all alleles
Define phenotype
An organism’s observable characteristics
due to interactions of the genotype and
environment (which can modify the
phenotype)
What are the monomers of DNA?
Nucleotides
What are DNA nucleotides made up of?
● Common sugar
● Phosphate group
● One of four bases: A, T, C or G
Describe how nucleotides interact to
form a molecule of DNA
● Sugar and phosphate molecules join to form a
sugar-phosphate backbone in each DNA strand
● Base connected to each sugar
● Complementary base pairing: A pairs with T, C pairs with G
Explain how a gene codes for a protein
● A sequence of three bases in a gene forms a triplet
● Each triplet codes for an amino acid
● The order of amino acids determines the structure
and function of protein formed
Describe the differences between mRNA
and DNA
mRNA is single stranded whereas
DNA is double stranded
● mRNA uses U whereas DNA uses T
What is protein synthesis?
The formation of a protein from a gene
Outline protein synthesis
In the nucleus, DNA is used as a template to form mRNA
- mRNA exits the nucleus, moving into the cytoplasm where
it attaches to a ribosome - The ribosome joins amino acids in a specific order,
dictated by mRNA to form a protein.
Why does mRNA rather than DNA join to
a ribosome in the cytoplasm
DNA is too large to leave the nucleus so
cannot reach the ribosome
What is a mutation?
A random change to the base sequence
of DNA which results in genetic variants
State the three types of gene mutation
● Insertion
● Deletion
● Substitution
Describe the effect of a gene mutation in
coding DNA
● If a mutation changes the sequence of amino acids,
protein structure and function may change
● If a mutation does not change the sequence of amino
acids, there is no effect on protein structure or
function
What is non-coding DNA?
DNA which does not code for a protein
but instead controls gene expression
Describe the effect of a gene mutation in
non-coding DNA
Gene expression may be altered,
affecting protein production and the
resulting phenotype
What are gametes?
Reproductive cells (e.g. egg and sperm
cells) that contain a single copy of each
chromosome
Describe sexual reproduction in terms of
chromosome number
● Two gametes with a single copy of each
chromosome fuse
● Resulting embryo has two chromosomes for
each gene and two copies of each allele
Define homozygous
Having two identical alleles of a gene
e.g. FF or ff
Define heterozygous
Having two different alleles of a gene
e.g. Ff
What is a dominant allele?
Describes an allele that is always expressed
Represented with a capital letter e.g. F
What is a recessive allele?
An allele that is only expressed in the
absence of a dominant allele
Represented with a small letter e.g. f
What is the problem with single gene
crosses?
Most characteristics are controlled by
multiple alleles rather than just one
What are sex chromosomes?
A pair of chromosomes that determines sex:
● Males have an X and a Y chromosome
● Females have two X chromosomes
Why does the inheritance of a Y
chromosome mean that an embryo
develops into a male?
Testes development in an embryo is
stimulated by a gene present on the Y
chromosome
Other than using a punnett square, how
else can single gene inheritance be
represented?
Using a family tree
Outline how the work of Mendel helped
scientists to develop their understanding
of genetics
● Mendel studied the inheritance of different phenotypes of pea plants
● He established a correlation between parent and offspring phenotypes
● He noted that inheritance was determined by ‘units’ passed on to
descendants
● Using gene crosses, he devised the terms ‘dominant’ and ‘recessive’
What is genome sequencing?
Finding out the order of nucleotides in
the DNA of an organism, enabling the
function and interaction of genes to be
assessed
Why is genome sequencing important?
● Allows the comparison of genomes of healthy
individuals with patients who have a disease
● Potential disease-causing alleles are identified
● Individuals can then undergo genetic testing for these
alleles
Outline how genetic testing can be used
to improve healthcare (3)
● Enables awareness of potential risks and the introduction
of lifestyle changes to reduce these associated risks
● Enables early treatment plans to begin
● Prediction of a patient’s reaction to certain drugs -
‘personalised medicine’
Outline the drawbacks of using genetic
testing in healthcare
● Discrimination by employers, insurance firms
etc. if a person is likely to develop a disease
● Person may develop anxiety, depression etc.
Outline how genetic testing can be used
in family planning
● Parental carrier testing - parents tested for the presence of recessive disease-causing alleles
● Prenatal testing - egg fertilised In vitro, embryo tested for
genetic disorders
● Fetus tested for genetic disorders via amniocentesis or
chorionic villus sampling (CVS)
Outline the drawbacks of using genetic
testing in family planning
● False-positive/false-negatives
● Ethical considerations - involves the destruction of
embryos and potential terminations
● Amniocentesis and CVS carry a slight risk of miscarriage
● Could lead to ‘designer babies’
What is genetic engineering?
● The changing of the genome of an organism by the
insertion of a desired gene from another organism
● Enables the formation of an organism with beneficial
characteristics
Describe the process of genetic
engineering
- Desired gene isolated using enzymes
- Gene replicated
- Gene placed into vector (e.g. plasmid, virus)
- Vector mixed with and ‘taken up’ by target cells
- Modified cells identified, selected and cultured
Describe the benefits of genetic
engineering
● Increased crop yields for growing population e.g.
herbicide-resistance, disease-resistance
● Useful in medicine e.g. insulin-producing bacteria, antithrombin in goat milk
● GM crops produce scarce resources e.g. GM golden rice
produces beta-carotene (source of vitamin A in the body)
Describe the risks of genetic engineering
● Long-term effects of consumption of GM crops unknown
● Negative environmental impacts e.g. reduction in
biodiversity, impact on food chain, contamination of
non-GM crops forming ‘superweeds’
● Late-onset health problems in GM animals
