Zusammenfassung der Ressource
B1
- Genes, Chromosomes and
DNA
- Most cells in body have a nucleus -
contains genetic material
- Genetic material arranged
into chromosmes
- Human body has 23
pairs of
chromosomes
- Chromosomes is a
long molecule of DNA
coiled up
- A gene is a short length
of chromosome
- Genes control the
development of different
characteristics
- Genes have different variations,
which form different characteristics
- Genes encode certain proteins
- Structural proteins make up things
like skin, hair, blood
- Functional proteins
make up enzymes etc.
- Genotype describes all the genes it has
- Phenotype is the
characteristic of
the gene
- Genetic factors affect things
like dimples, eye colour or
natural hair colour
- Environmental factors are physical
changes like scars or the dyeing of
hair
- Genes and Variation
- Chromosomes come in pairs (because
we have 2 parents)
- Each sex cell contains 23
individual chromosomes
- Upon fertilisation, the 23
chromosomes from each sex
cell combine to make 23
pairs.
- The two chromosomes in the pair contain the
exact same genes in the exact same places, they
may contain varying alleles
- Half a child's chromosomes
come from each parent
- Children get some alleles from each parent
- Children look similar to both but
identical to neither of their parents
- Homozygous: two alleles the
same for the particular gene
- Heterozygous: two alleles
different for the particular gene
- Dominant allele: only the characteristic of the
dominant allele is shown, as long as it is
present no matter what the genotype is
- Recessive allele: the characteristic is only
shown if the genotype is homozygous
recessive
- Sex Chromosomes
- 23rd chromosome pair labelled XY
- Men have XY
- Y causes
male
characteristics
- Women have XX
- Lack of Y causes female
characteristics
- Genetic
Disorders
- Cystic Fibrosis
- Symptoms
- Thick sticky
mucus in air
passages
- Breathing difficulty
- Chest infections
- Difficulty digesting food
- Caused by recessive allele
- Carried by 1 in 25 people
- For a child to have CF,
parents must be carriers
or sufferers
- 1 in 4 chance if both
parents are carriers
- Huntington's
- Symptoms
- Tremors
- Clumsiness
- Memory Loss
- Mood changes
- Poor Concentration
- Caused by a dominant allele
- Late onset
- 50% chance of child inheriting
if parent is a carrier
- Genetic Testing
- Embryos produced via IVF are tested using
pre-implantation gnetic diagnosis. Only used if parent
has history of genetic disorders.
- Healthy embryos implanted
- Faulty embryos discarded
- Tests aren't 100% accurate
- Misinterpreted
- Contaminated
- Not 100% safe. e.g. risk
of miscarriage when
testing fetuses
- Insurance refused for wrong alleles
- Clones
- Clones are genetically
identical organisms
- Differences arise due to
to environmental factors
- Natural Clones
- Asexual reproduction results in
identical offspring to the parent
and all siblings
- Bacteria (dividing into
two)
- Some plants reproduce asexually also.
Strawberry plants send out runners to plant
new clones at their tips
- Some animals reproduce asexually.
Female greenfly don't need to mate, they
can just lay eggs.
- Identical twins are also clones
- A single egg fertilised by sperm splits into two.
- The two embryos are genetically identical, two
genetically identical babies are born.
- Scientific Clones
- Nucleus of an egg is removed
- Nucleus from a donor cell is
removed (non -sex-cell)
- Cell is stimulated so it starts dividing
- Embryo produced is genetically identical to donor cell
- Stem Cells
- Can become
other types of cell
- Most normal cells are already
specialised
- Stem cells can specialise into other types
of cells, depending on the instructions
given
- Embryonic Stem cells
- Unspecialised cells found in early embryos
- Removed, embryo is then destroyed
- They can specialise into ANY type of cell
- Adult Stem Cells
- Unspecialised cells found in
adult animals
- Involved in maintaining and
repairing old and damaged
tissues
- Safely removed e.g. from bone
marrow - no embryos have to be
destroyed
- Can be used to replace blood cells to cure sickle cell anaemia
- Embryonic stem cells could be used to replace faulty cells in sick people. e.g. new organs