Lecture 12

Question 1

With Y linked traits what happens when the father has it?

Answer 1

-all male offspring will have it as the get the Y from dad

Question 2

What characterises recessive inheritance?

Answer 2

Unaffected parents have affected child - skipping a generation

dominant never skips a generation!

Question 3

How do you distinguish autosomal and X-linked recessive?

Answer 3

female affected= if X linked, her father has to have it!

Question 4

Give examples of diseases that are autosomal recessive.

Answer 4

Albinism

PKU

Alkaptonuria

Thalassaemia

Cystic Fibrosis

Tay Sachs

Question 5

Give four exaples of X linked recessive traits:

Answer 5

Colour blindness

Haemophilia

Duchenne Muscular Dystrophy

Androgen insensitivity

Question 6

What ar ethe characteristics of X linked recessive inheritance?

Answer 6

Unaffected parents have an affected child

More males affected than females

No father to son transmission

Affected female has an affected father
An affected female will have all affected sons

Question 7

What ar ethe characteristics of dominant inheritance?

Answer 7

-affected child has to have at least one affected parent, it never skips a generation

Question 8

What is the inheritance? And why?

Answer 8

left: can’t be x-linked because there is a transmission from father to son so autosomal dominant
right: more likely to be X linked dominant as all the daughters have it of the affected father

Question 9

Give example of autosomal dominant trait.

Answer 9

-widow’s peak

Question 10

What does a double line, crossed individual, diamond,

Answer 10

double line= when offspring mated to parents

crossed off individual= dies before the pedigree taken

diamond= if unsure if male or female

Question 11

What inheritance? Why?

Answer 11

rare trait- can’t say here that parents heterozygous, affected daughters recessive
-must be father carrying the allele but it’s sex limited to females
identification- if only females affected
can describe it as sex limited or reduced penetrance,not penetrant in males

Question 12

What happens in a X-linked dominant inheritance?

Answer 12

-affected father has all affected daughters!

Question 13

How can you denature or melt DNA? (separate the strands)

Answer 13

DNA can be made single stranded by- heating to +80C

• adding a strong alkali ( eg., NaOH)
• at 80 degrees the strands dissociate (the H+ bonds break)
• alkali pH 9-10
• the immediate response of the DNA is to snap shut asi it’s unstable when single stranded, as in replication where have to keep it open with proteins otherwise it will “look” for a complementary sequence and hybridise

Question 14

What is hybridisation of DNA? What is it used for?

Answer 14

Once single stranded (ss) DNA will hybridise (join) with other complementary ss DNA or RNA

• use to highlight sequences in the single stranded DNA
• make oligoprobe (oligo=artifically made) this can be either another sequence of DNA(complementary to the sequence of interest) or RNA

-DNA probe:only need to know the sequence and send the order to a lab- get it back

-you tag the oligoprobe with a fluorescent tag so you can see when it hybridises or tag it with radioactive material
RNA- works the same way just U instead of T but will still hybridise

Question 15

What is a restriction enzyme?

Answer 15

-endonuclease (endo= within)

cut the DNA within unlike exonuclease that cuts at the end

• originally from bacteria,they have these enzymes that cut the viral DNA as soon as it’s injected =this is process of RESTRICTION
• to protect their DNA bacteria methylate the regions of DNA that would be recognised by the viral DNA

Question 16

How do you amplify DNA?

Answer 16

PCR

Question 17

What is a type II restrictiona enzyme?

Answer 17

Type II restriction enzymes cut DNA within a specific sequence of bases called a recognition sequence
Hydrolizes the phosphodiester bonds

• Type II recognise specific DNA sequence, there is a Type I of these enzymes but they aren’t as specific in which sequences they recognise= these sequences are called the recognition sequences
• when binds to the recognition sequence= hydrolises the phosphodiester bonds(strong)

Question 18

What are blunt and sticky ends?

Answer 18

if you want to ligate have to do an extra step whereas with sticky easier to attach to new ones because have unattached bases

-if they cut vertically at the same point= blunt ends

if some unequal, overhanging= sticky ends

Question 19

What is the recognition sequence described as?

Answer 19

paleodromic= reading the top is the same as reading the bottom from the other end, spelled the same way forwards and backwards

Question 20

How are restriction enzymes named?

Answer 20

normally take name from the bacterium from which they’ve been isolated= first letter of the genus, two letters of the species
-highly specific recognition sequences, there cut

Question 21

What so you get when cutting linear DNA?

Answer 21

-mpre pieces of linear DNA

Question 22

What do you get when cutting a circular DNA?

Answer 22

if DNA circular, cutting makes it linear
with linear- 3 sequences that are the restriction enzyme’s recognition = 4 pieces of DNA
circular- if 3 sequences then get 3 pieces of DNA (must first separate the circle)

Question 23

What is gel electrophoresis for?

Answer 23

-to figure out which pieces of DNA do we have

DNA of different sizes can be sorted by gel electrophoresis
 The medium (gel) can be designed to separate fragments of different sizes

the DNA fragments will move different distance depending on their size

Question 24

What two media are used as gel in gel electrophoresis?

Answer 24

1. agarose 0.5 - 2% separates 200 -50 000bp (smaller sizes when higher concentration)
2. polyacrylamide – used for fragments <500bp can separate single bp differences, can separate single bp differences

-the bigger bits don’t move as far as the smaller bits, also the denser the better (agrose) as better separation(when denser must run for longer)

• always run a standard to compare to, in this DNA fragments of known size then can work out the size of the unknowns, graph the movement of the fragments
• add compounds that make it easier to see the DNA (fluorescent etc)