Inheritance Flashcards
why should you double the DNA
ensures that the two new (daughter) cells produced will both receive full copies of the parental DNA
semi conservative replication
new DNA molecule has conserved half of the original DNA and then used this to create a new strand
The DNA is copied
In each new DNA molecule produced, one of the polynucleotide DNA strands (half of the new DNA molecule) is from the original DNA molecule being copied
The other polynucleotide DNA strand (the other half of the new DNA molecule) has to be newly created by the cell
importance of retaining one original DNA strand
ensures there is genetic continuity between generations of cells
This is important because cells in our body are replaced regularly and therefore we need the new cells to be able to do the same role as the old ones
what happens after the enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands
Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing
The new nucleotides are then joined together by the enzyme DNA polymerase
The original strand and the new strand join together through hydrogen bonding between base pairs to form the new DNA molecule
how does the enzyme DNA polymerase synthesis new DNA strand
catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands, creating the sugar-phosphate backbone of the new DNA strands
the two extra phosphates and uses the energy released to create the phosphodiester bonds
how does the enzyme DNA polymerase synthesis new DNA strand
catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands, creating the sugar-phosphate backbone of the new DNA strands
what forms between complementary base pairs of template and the new DNA strands
Hydrogen bonds
what direction is the new strand made and from what direction is DNA unzipped
DNA polymerase can only build the new strand in one direction (5’ to 3’ direction)
As DNA is ‘unzipped’ from the 3’ towards the 5’ end, DNA polymerase will attach to the 3’ end of the original strand and move towards the replication fork
what is the leading strand
This template strand that the DNA polymerase attaches to
when is the lagging strand
The other template strand created during DNA replication
what does it mean if the DNA polymerase moves away from replication fork on lagging strand
DNA polymerase enzyme can only synthesise the lagging DNA strand in short segments (called Okazaki fragments)
what is needed to join lagging strands together
DNA ligase is needed to join these lagging strand segments together to form a continuous complementary DNA strand
what does DNA ligase do
catalysing the formation of phosphodiester bonds between the segments to create a continuous sugar-phosphate backbone
what is a gene mutation
change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
why do mutations not alter polypeptide
the genetic code is degenerate
what is insertion of nucleotides
A mutation that occurs when a nucleotide is randomly inserted into the DNA sequence
does insertion mutations have a knock on effect
An insertion mutation also has a knock-on effect on other base triplets by changing the triplets further on in the DNA sequence
This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function
deletion of nucleotide
A mutation that occurs when a nucleotide is randomly deleted from the DNA sequence
changes the triplet in which the deletion has occurred, and also changes every group of three bases further on in the DNA sequence
substitution of nucleotides
a base in the DNA sequence is randomly swapped for a different base
what is a silent/missense/nonsense mutation
silent: mutation doesn’t alter the amino acid sequence
missense: alters a single amino acid
nonsense: creates a premature stop codon
duplication mutation
production of one or more copies of a gene or a region of a chromosome
the second copy can undergo mutations which enable it to develop new functions
inversion mutation
crossing-over in meiosis
The DNA of a single gene is cut in two places
The cut portion is inverted 180° then rejoined to the same place within the gene
The result is a large section of the gene that is ‘backwards’ and therefore multiple amino acids are affected
what is a chromosome
long DNA molecule which contains genes that code for several different proteins
what is a homologous pair of chromosomes
a pair of chromosomes that match in size and shape, and that contain the same genes at the same loci
genotype
alleles of a gene possessed by that individual
uses of genetic screening
Identifying individuals who are carrying an allele at a gene locus for a particular disorder
testing a foetus before birth; this is prenatal testing
The screening of embryos prior to implantation during fertility treatment
what is IVF
fertilisation is carried out in the lab; embryos produced in this way can be implanted into the uterus where they develop into a foetus
benefits of PGD
The sample of DNA to be analysed can be obtained by taking cell samples from embryos produced during IVF
Reduces the chances of having a baby with a genetic disorder
It avoids abortion as it is carried out before implantation of the embryo
how is the DNA in prenatal testing obtained
chorionic villus sampling
amniocentesis
explain chorionic villus sampling
This involves removing and testing a small sample of cells from the placenta using a fine needle
The cells contain foetal DNA which can be analysed for genetic disorders, allowing parents to make informed decisions about the pregnancy and foetus
It is carried out at around 11-14 weeks of pregnancy
The process has a 1-2 % risk of miscarriage
explain amniocentesis
involves removing and testing a small sample of cells from amniotic fluid using a fine needle
The amniotic fluid is the fluid that surrounds the foetus within the uterus
The fluid contains foetal cells which contain DNA to be analysed
It is carried out at around 15-20 weeks of pregnancy
The procedure has a 1% risk of miscarriage
why does a person with cystic fibrosis have such symptoms
mucus {thicker / stickier} than normal
(pancreatic) enzymes cannot enter intestine because pancreatic duct blocked with mucus
(high energy diet required because) digestion is less efficient
pancreatic enzymes trapped behind mucus damage pancreatic cells such as those that produce insulin
cysts form in pancreas
sperm cannot leave the testes because sperm duct blocked with mucus
* sperm duct absent therefore sperm cannot pass through
gene mutation
(causing a) non-functioning CFTR protein channel chloride ions cannot move out of epithelial cells
accumulation of sodium and chloride ions in the cells {causing water to move out of mucus by osmosis
why does cystic fibrosis affect rate of oxygen uptake
{ thick / sticky / viscous } mucus (1)
* (accumulation of mucus) which cannot be moved by cilia (1)
* restricting air flow through { bronchioles / bronchi } (1)
* {increases diffusion distance / reduces surface area for gas exchange } in the alveoli (1)
why should children be given dietary supplements and digestive enzymes
cystic fibrosis causes the production of {thicker / stickier} mucus (1)
which blocks the pancreatic duct
prevents} enzymes digesting {carbohydrates / lipids / proteins} (in intestines) (1)
(resulting in) reduced {absorption of products of digestion into the {blood(1)
* linkage of reduced vitamins to slower growth rate (1)
* {dietary supplements / digestive enzymes}
would increase growth rate (1)
why not have chronic villus testing
test result may be inaccurate (1)
(increased) risk of miscarriage (due to the procedure) (1)
false positive may lead to termination of healthy fetus (1)
{ prenatal testing / abortion} against values or beliefs of the parents (1)
What is a inherited recessive conditions
faulty allele expressed in homozygous recessive condition
why offspring have palomino coat colour
(palomino / offspring) is heterozygous (1)
*
*
therefore { incomplete dominance / co-dominance } occurs (1)
because both alleles are expressed (1)
one ethical issue with use of prenatal genetic screening
either
* it may result in a choice of an abortion (1)
* it is unethical to cause the death of a foetus (1)
(risk of) {incorrect result / false positive / false negative }
* healthy foetus could be aborted / parents not prepared for child with {genetic disease / achondroplasia} (1)
why do offspring have palomino coat colour
because it is heterozygous so incomplete dominance occurs so both alleles expressed
what is incomplete dominance
Both alleles influence the phenotype in a heterozygous individual
