Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
26 Cards in this Set
- Front
- Back
|
when talking about inheritance what do we usually mean
best way to look at inheritance what does the family pedigree diagram show |
When we talk about inheritance we are usually referring to what is happening within a family.
Often the best way to look at inheritance is to look at a family pedigree as is shown here in this diagram. This figure shows the relationship between each of the members in a 4 generation family. |
|
|
diagonal lines throught symbols indicate
|
that that individual has deceased or died
|
|
|
females/males shown as
|
females drawn as circles
males indicated by square |
|
|
healthy individuals shown as
diseased individual shown as carriers shown as |
healthy individuals shows as empty shapes
diseased showed with shaded/coulured shapes carriers shown as stripy or dotted shape |
|
|
2 individuals joined at the same time line indicate what
|
indicates that they were born at the same time
|
|
|
what if those 2 are joined by a horizontal line
|
then this indicates that they are both twin sisters
|
|
|
how is genetic information passed on from generation to the next and what exactly is it
|
info passed on from generations is carried on chromosomes
these are structures made up of dioxyribose nucleic acid or dna for short and also protiens cells in humans contain 23 pairs of chromosomes chromosomes also determine sex |
|
|
male chromosomes
female chromosomes |
male xy
female xx |
|
|
how many copies of each chromosome in humans
how are they labelled |
2 copies of each chromosomes
labelled 1-22 |
|
|
where are these derived from
what do chromosomes carry |
one of each pair is derived from the mother and one of each pair is derived from the father
dna that chromosomes carry a coded message, the genetic code, which can be translated in the cells |
|
|
how is dna stored in a chromosome
outline the seperate stages |
at its smallest, the dna is exists as a double helical structure
the dna is then wound around protiens called histones, this results in the beads on a string form of chromatin further up, chromatin is packed into chromatin fibres known as nucleosomes nucleosomes are in turn attached to a chromosome scaffold made of protien these chromosomes scaffolds are condensed into large folds and this is what is visible during the metaphase stage of cell division |
|
|
structure of the double helix
|
made from 2 antiparralel polynucleotide chains held together by h2 bonds
h2 bonds between the aromatic bases which encode the mesage found in dna |
|
|
outline the different types of aromatic bases
|
there are 2 types of aromatic bases, found in dna, purines and pyrimidimes
purines are adenine and guanine which are double ringed structures pyrimidines are cytosine and thymine, and uracil which is only found in rna molecules and pyrimidines are both single ringed structures |
|
|
what are mutations
what can they lead to how many different types of mutations outline |
mutations are heritable permanent changes in the base sequences of dna
can lead to disease point mutations are single base changes and can be of 2 types, transition is where a purine is substituted for another transversion where area purine is subsitituted for a pyrimidine, also there are deletions/insertions- these include the loss or gain of bases, much more serious consequence, can lead to the production of a non functional gene |
|
|
what isnt altered with point mutations
|
with point mutations the amino acid coded for may be altered but the downstream sequence remains unaltered
|
|
|
what happens with a frameshift mutation
what is completely changed |
With a frameshift mutation we see that the loss of 2 bases changes the entire coding sequence Downstream of the mutation completely changes the amino acid content of the coded protein.
|
|
|
how do mutations arise
what happens during dna polymers how are errors removed |
mutation is a natural phenomenon, and drives the evolution process
dna replication is very accurate, error though is 1 in 10^10 bases. during replication, polymerase inserts new bases using standard watson crick base pairing (Good_comes After-Tryin) occasional errors are removed by by exonuclease function in the dna polymerase, by a 3' to 5' function dna replication proceeds in a 5' to 3' direction as we all know exonuclease removes the wrong base allowing the correct base to bind |
|
|
what are mutagens
outline the different types of mutagens |
agents that cause mutagens
can be physical agents such as Ionising radiation e.g. xrays, gamma rays which cause strand breaks or sugar or base destruction they can also be due to non ionising radiation, e..g U.v. light , can cause new chemical bonds to form e.g. pyrimidine dimers. these are the agents that can initiate skin cancer |
|
|
what else is there in addition to physial agents
examples outline |
there are also chemical agents that cause mutation
base analogs- these mimic the normal bases found in dna and cause altered base pairing if introduced Nitrous acids- de aminates cytosine to uracil, causing gc to at transitions ALkylating agents- methylmethane sulfates fro examples can donate alkyl groups can result in legions which result in error prone repair of dna |
|
|
what is an
allele dominant recessive genotype phenotype |
allele is a different form of the same gene, some are said to be dominant
dominant - e.g. ABO BLOOD GROUPS, gene for blood group A is dominant over the gene for blood group O recessive, - an allele who's character is only expressed in the absence of the dominant allele genotpye- the genetic components phenotype- the visible appearance |
|
|
what is diploid
advantages of the diploid state |
organisms with 2 copies of each chromosome are called diploid
if lethal recessive allele is present, it will only be expressed if both parents posess the gene, otherwise only 50% will be carries |
|
|
what are single gene disorders
|
result from mutations in single genes, and can be autosomal recessive e.g. sickle cell disesase, or they can be dominant in the case of autosomalHuntingtons disease. or they can be linked to one of the 6 chromosomes,
or they can be sex linked, e.g. amelogensis imperfecta |
|
|
genes not located on the sex chromosomes
|
they are said to be autosomal
|
|
|
frequency of
cystic fibrosis sickle cell anaemia thallasemias |
cystic fibrosis -1 in 2000 euopeans
sickles cell - 1/50in africa where malaria is endemic thallasemias - 1/50 in asia and the mediterannean |
|
|
significance of frequency rates
|
just having one copy of the gene does not lead to disease as these are recessive disorders. However it is clear that the risk of two individuals, who carry a defective gene, mating and producing offspring, is much greater in these areas. As a result the incidence of individuals inheriting two defective alleles and therefore expressing the disease is greatly increased
|
|
|
summary
|
We can use family studies to help to characterise inherited disorders.
Many genes can exist in more than one form , or allele. Mutations can arise through natural processes or by environmental influences. Some of these alleles are dominant and will be expressed no matter what the other allele is. Finally recessive genes only manifest themselves if they are present in two copies per cell. |
