| genotype | all the alleles of an organism |
| genotype | all the alleles of an organism |
| DNA replication | semi conservative process
new DNA contains an old strand and a new strand of DNA
ensures genetic information is passed down from generation to generation |
| who proposed the idea of semi conservative DNA replication? | Meselson and Stahl |
| DNA replication process | DNA helicase breaks the hydrogen bonds between DNA nucleotides and DNA unwinds making two separate strands
complementary base pairing occurs between the template strands and the free nucleotides
DNA polymerase forms phosphodiester bonds between adjacent nucleotides through condensation reactions |
| what is the role of DNA polymerase? | to form phosphodiester bonds through condensation reactions between DNA nucleotides during DNA replication |
| Outline Meselson and Stahl's experiment | They first grew bacteria in nitrogen-15 for several generations
they then grew the same bacteria in nitrogen-14 for one generation
the DNA from the bacteria got extracted
After centrifuging the DNA they found 1 bar with a mix of heavy and light DNA
after centrifuging the second time, 2 bars containing only light DNA and heavy-light DNA
this gave evidence that the conservative and dispersive models were not correct and only the semi-conservative model applied |
| what are gene mutations? | changes in a base sequence in DNA |
| what are the 5 types of gene mutations? | substitution
inversion
insertion
deletion
duplication |
| gene | a sequence of bases on a DNA molecule that codes for a sequence of amino acids |
| allele | one of different forms of the same gene |
| genotype | all the alleles of an organism |
| phenotype | an organisms physical characteristics resulting from the interaction of its genotype with the environment |
| recessive | traits only expressed when the genotype is homozygous |
| dominant | alleles that will always be expressed even if there is only one copy |
| incomplete dominance | a form of intermediate inheritance where one allele for a specific trait is not completely expressed over its paired allele resulting in a third phenotype where the expressed physical trait is a combination of the dominant and recessive phenotypes |
| homozygote | an individual with two identical alleles for a particular gene |
| hetrozygote | an individual with two different alleles of a particular gene |
| monohybrid inheritance | the inheritance of only one characteristic |
| how is gas exchange affected in someone with cystic fibrosis? | build up of mucus in lungs traps bacteria means increased risk of infection
mucus in airways decreases SA of alveoli so reduced SA for gas exchange |
| what is cystic fibrosis? | a genetic disorder caused by a mutation of a gene which codes for the CFTR protein |
| why is cystic fibrosis caused by gene mutation? | gene mutation causes change in base sequence
which changes the amino acid
polypeptide chain folds differently causing different tertiary structure
CFTR protein cannot carry out its function properly |
| what does the CFTR protein do? | channel protein that transports Cl⁻ ions out of cells and into mucus which causes water to move into the mucus by osmosis
in CF, the Cl⁻ ions and water does not move out of the cells and mucus becomes thick and sticky |
| how does CF affect the digestive system? | pancreatic duct is blocked by mucus so digestive enzymes don't reach the small intestine so food is not properly digested and vitamins and minerals are not absorbed
in the pancreas mucus can cause cysts which damages insulin producing cells leading to diabetes |
| how does CF affect the reproductive system? | cervical mucus prevents the sperm from reaching the egg
the sperm duct is blocked by mucus so sperm cant leave the testes |
| what is genetic screening? | a test which determines if the DNA of an individual contains alleles for genetic disorders |
| PGD | pre-implantation genetic diagnosis
IVF embryos tested for genetic disorders before being placed in woman's uterus |
| two types of prenatal testing | chorionic villus sampling (CVS)
amniocentesis |
| chorionic villus sampling | carried out 10-12 week into pregnancy
sample of embryonic tissue taken from the placenta to analyse the DNA
done by passing a plastic tube through the vagina or inserting a needle into the uterus through the abdomen
generally quicker than amniocentesis |
| amniocentesis | carried out 14-18 weeks into pregnancy
amniotic fluid sample full of foetal cell's DNA is analysed
needle is inserted through the abdomen into the uterus
results usually come in 2-3 weeks because cells need to be grown in a culture first |
| advantages of genetic screening | make more informed decisions
opportunity to seek medical help
lessens anxiety
disease can be moderated by change in lifestyle
parents are better prepared to take care of the child
avoids misdiagnosis if family members have the condition |
| disadvantages of genetic screening | risk of false positive so healthy baby could be aborted
designer baby-selection of traits
very expensive process
does not check all possible mutations that may affect the child
could increase anxiety |
