3- GENETICS
Genes
● → basic unit of heredity, they provide instruc ons to make proteins.
● In humans, there are 20 to 30,000 genes.
● In the same pair, the 2 chromosomes are homologous (same genes).
● In body cells (soma c), the last chromosome pair can be XX (female) or XY (male).
● Locus → the physical place where genes are found.
● The VERSION of the gene is the allele (e.g. color of eyes).
Muta ons
● → random change of the gene c code during DNA replica on or transcrip on:
1) Subs tu on
2) Inser on
3) Dele on
4) Inversion
● Can be bene cial or not.
CYSTIC FIBROSIS
● Condi on in which people can’t get rid of mucus in the lungs → the CFTR channel is mutated so
that Chloride ions can’t pass, the external water poten al isn’t lowered and water can’t pass, so
mucus builds up on the cell’s outer surface.
● Mutant recessive allele.
● Triple dele on → three amino acids are not made so an en re protein is missing, its shape is
di erent and the CFTR channel can’t func on properly in the membrane.
● Most people a ected don’t live beyond their 20s, so they can’t reproduce.
SICKLE CELL ANEMIA
● Condi on in which red blood cells are mutated and have a ‘sickle’ shape, so can carry a reduced
amount of oxygen and potassium.
● Base subs tu on muta on → valine is produced instead of glutamic acid.
● Strong rela onship between sickle cell anemia and malaria infec on → the Plasmodium parasite
needs potassium to survive in an organism, so it can’t survive in people a ected by sickle cell
anemia.
● People with sickle cell anemia are much more resistant to malaria infec on.
STARGARDT’S DISEASE → lack of vitamin A that can lead to turning blind, some people get eye stem cell
transplant.
DNA sequencing
● Human Genome Project → mapping of all human genes.
● Frederick Sanger discovered the experiment (DNA replica on simula on).
1. 4 test tubes labelled A, T, G, C (4 bases) → in each test tube there are various copies of the
unknown DNA (single) strand, uorescent primer, four DNA nucleo des, DNA polymerase.
2. In each test tube is inserted 1% of altered nucleo des (dideoxynucleo des) that can’t form
phosphodiester bonds, so if these are picked for replica on it stops.
ff tititi ti tititi fitiff ti ti ti
fl ti ti ti titi tititi ti ti tititi ffti
, 3. DNA polymerase builds a complementary strand picking
nucleo des at random. If the altered ones are picked,
replica on stops. This will lead to di erent length molecules
(all ending in A* in A tube, T* in T, etc.)
4. ELECTROPHORESIS → the contents of the 4 test tubes are
run against each other on electrophoresis gel, and they’ll be
visible thanks to the uorescent primer. The ow of
electrons travels from nega ve to posi ve! The one that
goes furthest is the lightest and therefore the shortest
molecule (only 1 nucleo de). This will be the rst of the
unknown sequence. From here the sequence will be
deducted.
Prokaryo c chromosomes
● Naked and circular chromosomes.
● Not contained in a nucleus (because there is no nucleus).
● Some bacteria also have plasmids → small loops of DNA
that are not connected to the main bacterial chromosome.
● Plasmids are extra copies of the gene c material of the organism, and they replicate
independently of the main chromosome DNA.
Eukaryo c chromosomes
● Organized in pairs, one from
each parent.
● There are 23 pairs in total, 22
pair of autosomes and 1 pair
of sex chromosomes.
● Sex chromosomes → XX for
females and XY for males.
● Chromosomes in the same
pair are homologous → they
have the same genes, but not
necessarily the same alleles.
● This only applies to soma c
cells (body cells), because
gametes don’t come in pairs.
● They are linear and wrapped around histones (proteins), to allow supercoiling and gene
expression to occur.
● 8 histones make up a nucleosome.
● O en, they are shown in karyograms → physical representa on of the karyotype (how
chromosomes physically look).
ft ti titi fl titi ti fftiti flfi ti
Genes
● → basic unit of heredity, they provide instruc ons to make proteins.
● In humans, there are 20 to 30,000 genes.
● In the same pair, the 2 chromosomes are homologous (same genes).
● In body cells (soma c), the last chromosome pair can be XX (female) or XY (male).
● Locus → the physical place where genes are found.
● The VERSION of the gene is the allele (e.g. color of eyes).
Muta ons
● → random change of the gene c code during DNA replica on or transcrip on:
1) Subs tu on
2) Inser on
3) Dele on
4) Inversion
● Can be bene cial or not.
CYSTIC FIBROSIS
● Condi on in which people can’t get rid of mucus in the lungs → the CFTR channel is mutated so
that Chloride ions can’t pass, the external water poten al isn’t lowered and water can’t pass, so
mucus builds up on the cell’s outer surface.
● Mutant recessive allele.
● Triple dele on → three amino acids are not made so an en re protein is missing, its shape is
di erent and the CFTR channel can’t func on properly in the membrane.
● Most people a ected don’t live beyond their 20s, so they can’t reproduce.
SICKLE CELL ANEMIA
● Condi on in which red blood cells are mutated and have a ‘sickle’ shape, so can carry a reduced
amount of oxygen and potassium.
● Base subs tu on muta on → valine is produced instead of glutamic acid.
● Strong rela onship between sickle cell anemia and malaria infec on → the Plasmodium parasite
needs potassium to survive in an organism, so it can’t survive in people a ected by sickle cell
anemia.
● People with sickle cell anemia are much more resistant to malaria infec on.
STARGARDT’S DISEASE → lack of vitamin A that can lead to turning blind, some people get eye stem cell
transplant.
DNA sequencing
● Human Genome Project → mapping of all human genes.
● Frederick Sanger discovered the experiment (DNA replica on simula on).
1. 4 test tubes labelled A, T, G, C (4 bases) → in each test tube there are various copies of the
unknown DNA (single) strand, uorescent primer, four DNA nucleo des, DNA polymerase.
2. In each test tube is inserted 1% of altered nucleo des (dideoxynucleo des) that can’t form
phosphodiester bonds, so if these are picked for replica on it stops.
ff tititi ti tititi fitiff ti ti ti
fl ti ti ti titi tititi ti ti tititi ffti
, 3. DNA polymerase builds a complementary strand picking
nucleo des at random. If the altered ones are picked,
replica on stops. This will lead to di erent length molecules
(all ending in A* in A tube, T* in T, etc.)
4. ELECTROPHORESIS → the contents of the 4 test tubes are
run against each other on electrophoresis gel, and they’ll be
visible thanks to the uorescent primer. The ow of
electrons travels from nega ve to posi ve! The one that
goes furthest is the lightest and therefore the shortest
molecule (only 1 nucleo de). This will be the rst of the
unknown sequence. From here the sequence will be
deducted.
Prokaryo c chromosomes
● Naked and circular chromosomes.
● Not contained in a nucleus (because there is no nucleus).
● Some bacteria also have plasmids → small loops of DNA
that are not connected to the main bacterial chromosome.
● Plasmids are extra copies of the gene c material of the organism, and they replicate
independently of the main chromosome DNA.
Eukaryo c chromosomes
● Organized in pairs, one from
each parent.
● There are 23 pairs in total, 22
pair of autosomes and 1 pair
of sex chromosomes.
● Sex chromosomes → XX for
females and XY for males.
● Chromosomes in the same
pair are homologous → they
have the same genes, but not
necessarily the same alleles.
● This only applies to soma c
cells (body cells), because
gametes don’t come in pairs.
● They are linear and wrapped around histones (proteins), to allow supercoiling and gene
expression to occur.
● 8 histones make up a nucleosome.
● O en, they are shown in karyograms → physical representa on of the karyotype (how
chromosomes physically look).
ft ti titi fl titi ti fftiti flfi ti
