Genetics

Question 1

Strands of dna are replicated how?

Answer 1

5–>3 direction and pair up int anti parallel directoin

Question 2

4 bases:

Answer 2

thymine-adenine

guinine-cytosine

Question 3

sugar phosphate back bone

Answer 3

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Question 4

DNA strand associates with proteins (including Histones) and is wound into a structure called a chromosome

Answer 4

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Question 5

DNA can be damaged during replication, repair mechanisms exist, when these are defected, disease occurs

Answer 5

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Question 6

cell cycle:

Answer 6

G1–>S–>G2–>M–>G1

Question 7

what occurs at the s phase

Answer 7

DNA synthesis

Question 8

function of DNA helicase

Answer 8

unzips DNA

Question 9

function of DNA polymerase

Answer 9

copies 5-3 strand and 3-5 strand in okazaki fragments

Question 10

funtion of DNA ligase

Answer 10

joins okazaki fragments

Question 11

mitosis

Answer 11

One diploid parent cell becomes 2 identical diploid daughter cells

Question 12

meiosis

Answer 12

One diploid parent cell becomes 4 haploid daughter cells
Crossing over occurs
Gamete formation

Question 13

RNA

Answer 13

single stranded
ribose sugar
uracil replaces thymine

Question 14

Transcription/Translation

Answer 14

DNA transcribed to pre mRNA
Pre mRNA spliced (removal of introns [non-coding sections of DNA] to mRNA
mRNA translated to protein
3 bases encode 1 amino acid or a stop codon
Protein is modified and moved around the cell

Question 15

variation between cells

Answer 15

changes in promoter sequence

changes in exon sequence

Question 16

cell cycle more detail

Answer 16

GO cell cycle: most cells are resting, carrying out their normal function
G1 cell cycle: 1st growth phase as chromosomes become ready to be replicated
S phase: DNA replication
G2 cell cycle: 2nd growth phase involving proteins
M phase: mitosis, mechanical separation of cell into two daughter cells. Identical, diploid cells

Question 17

23 pairs of chromosomes

Answer 17

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Question 18

SNPs (Single Nucleotide Polymorphisms)

Answer 18

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Question 19

where do mutations occur in the cell cycle

Answer 19

between G2 and M or between G1 and S

Question 20

how does variation occur in meioisis

Answer 20

• Crossing over

- Independent segregation of homologous chromosomes

Question 21

what is polymorphism

Answer 21

a change in the genome that does not cause disease in its own right but can predispose to a common disease

Question 22

what is a mutation

Answer 22

gene change that causes a genetic disorder

Question 23

Neuploidy

Answer 23

an abnormal number of chromosomes

Question 24

what are histones

Answer 24

proteins wrappped around DNA

Question 25

PCR

Answer 25

- Can select one small piece of human genome from a patient and amplify it - Pieces can be sequenced to find mutations

Question 26

Microarray CGH

Answer 26

- 1st line chromosome test - Detects any missing or duplicated piece of chromosome - Find polymorphisms

Question 27

FISH

Answer 27

fluorescent probe is attached to a gene, can recognise changes to sequence

Question 28

what is expression

Answer 28

is the process by which info from a gene is used in the synthesis of a functional gene product

Question 29

what is penetrance

Answer 29

the extent to which a particular gene is expressed in the phentype

Question 30

Mendelian diseases are rare and likely to have a huge effect on individual. Common mutations are likely to have little effect on individual and may require other things for disease to actually be triggered. Mendelian Disorders (umbrella term for below) = a disease that is caused by a change in a single gene

Answer 30

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Question 31

Autosomal dominant

Answer 31

- disease seen in all generations - 50% risk of affected child if parent affected - males and females are equally affected

Question 32

Autosomal recessive

Answer 32

- 2 faulty copies required to cause disease - oftern only one generation affected - 1 in 4 risk of contraction disease if parents are carriers - increased likelihood in incestious families

Question 33

X linked- recessive

Answer 33

- y chromosome is irrelevent - eg Haemophilia - If mother carrier, 50% chance daughter carrier, 50% chance male affected - no male to male transmission - X-linked inheritance almost always affects males because mutation on X chromosome and males do not have allele on Y chromosome to counteract.

Question 34

X-inactivation

Answer 34

cell only requires one working copy of the x chromosome. in females, each cell has a random X chromosome inactivated

Question 35

Mitochondrial

Answer 35

- Mitochondrial DNA contains important genes for mitochondrial metabolic pathways and ribosomal RNAs - Inherited almost exclusively maternally

Question 36

Mitochondrial disease occurs when diseased mitochondria passed from mother to child Epigenetic variation functional modifications to the genome that do not involve a change in nucleotide sequence

Answer 36

``` symptoms: oMyopathy oDiabetes oDeafness oOptic atrophy oStroke like episodes oEncephalitis ```

Question 37

how do mutations cause disease?

Answer 37

- only have one working copy is not enough eg Haploinsufficiency - abnormal protein interferences with normal protein eg dominant negative - mutation activated gene eg gain of funtion mutation - loss of hereozygosity

Question 38

Mendelian disorders

Answer 38

- High penetrance | - Small environmental contribution

Question 39

Multifactorial disease

Answer 39

- Genetic change just another risk factor - Penetrance for any one mutation is low - Individual genetic factors can be treated the same way as other environmental risk factors. Mutation in genes combine with environmental factors to cause disease.

Question 40

Characteristics gained by cells on progression to cancer

Answer 40

- Proliferation - Evasion of immune response - Acquire a vascular supply - Avoid apoptosis - Metastasis

Question 41

mutations in cells can cause damage to control genes that allow cells to divide in uncontrolled fashion

Answer 41

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Question 42

tumour suppressors

Answer 42

stop cells dividing if switched on

Question 43

oncogenes

Answer 43

start cells dividing when switched on

Question 44

mosaicism

Answer 44

the presence of 2+ populations of cells with different genotypes in one individual. Somatic happens within body cells and not passed onto children. Gonadal affects sex cells and is passed onto children. (in all cancers there are normally at least 3 different groups of cells with different genotypes.)

Question 45

gonadal mosaicism

Answer 45

Causes recurrence risk for autosomal dominant conditions even if parent unaffected

Question 46

somatic mosaicism

Answer 46

All cells suffer mutations as they divide | Repair mechanisms exist

Question 47

BRCA 1/2

Answer 47

responsible for a small proportion of familial breast/ovarian cancer. Patients have 80% lifetime risk of developing cancer. The gene is associated with DNA repair.

Question 48

CF

Answer 48

common mutations are F508Del and G551D. Population carrier frequency of a CF mutation is either 1/24 or 1/25

Question 49

turners syndrome

Answer 49

monosomy of the sex chromosomes (missing chromosome from one pair)

Question 50

downs syndrome

Answer 50

trisomy of chromosome 21 (extra chromosome)

Question 51

Methylation inhibits DNA transcription

Answer 51

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Question 52

imprinting

Answer 52

Variation in gene expression depending on which parent you inherit the gene from e.g. in Angelman's syndrome, mother's UBE3A works fine but father's is methylated

Question 53

Heteroplasmy

Answer 53

different daughter cells contain different proportions of mutant mitochondria

Question 54

``` 47 XY +21 - Down syndrome, trisomy 21 47 XY +14 - Miscarriage, trisomy 14 47 XY +18 - Edward Syndrome, trisomy 18 45 X - Turner syndrome 47 XXY - Klinefelter syndrome ```

Answer 54

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