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genetics 2 Flashcards

frequences and second deck

1
Q

what is meant by fitness

A

Fitness” means the relative ability of organisms to survive (long enough) to pass on their genes.​

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2
Q

how does alleles affect fitness

A

not at all in most cases (neutral allele)​

 - sometimes decrease (deleterious allele)​

 - rarely increase (advantageous allele)​
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3
Q

mutation of recessive genes affects carriers yes or no

A

no because the dominant allele masks off the effect of the recessive allele

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4
Q

factors that influence whether a mutation of the recessive gene will affect the carrier

A

selective pressure for example sickle cell which is advantageous for malaria resistance.

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5
Q

de novo mutation

A

mutation in a first generation

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6
Q

what is the hardy weinberg equation

A

an equation to calculate how allele frequencies are transmitted from one generation to another.

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7
Q

findings of hardy weinberg equilibrium

A

1.the allele frequencies will remain constant generation to generation .
2.the relative proportion of genotype frequencies will remain constant generation to generation.

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8
Q

assumptions of HWE

A

Mutation can be ignored​

- Migration is negligible (No gene flow)​

- Mating is random​

- No selective pressure​

- Population size is large​

- Allele frequencies are equal in the sexes​
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9
Q

mutation effect on population genetics

A

mutations will increase the proportion of new alleles

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10
Q

migration effect on population genetics

A

there is introduction of new alleles as a result of migration or intermarriage which leads to a new gene frequency in hybrid population.

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11
Q

gene flow

A

transfer of genes by migration and mutation

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12
Q

non random mating effect on population genetics

A

non random mating will increase the mutant alleles thereby increasing the proportion of affected homozygotes.

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13
Q

examples of non random mating

A

1.Assortative mating​
- Choosing of partners due to shared characteristics​ example Deafness & sign language​

​2.Consanguinity​
- Marriage between close blood relatives.​
-Cultural pressures for inter-marriage within clans / religions etc.​

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14
Q

negative natural selection effect on population

A

there is reduced reproductive fitness
there is decreased prevalence of traits
there is gradual reduction of the mutant allele

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15
Q

positive effect of natural selection

A

increased in the reproductive fitness
increased prevalence of adaptive traits
heterozygote advantage

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16
Q

what is meant by heterozygous advantage

A

defect of a molecule in the body leading to advantageous effects on other aspects of the body.

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17
Q

how does small population size affect HWE

A

small population exhibits genetic drift which causes founder effect.

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18
Q

what is genetic drift

A

Random fluctuation of one allele transmitted to high proportion of offspring by chance.​

​

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19
Q

what is founder effect

A

The reduction in genetic variation that results when a small subset of a large population is used to establish a new colony.​

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20
Q

founder effect and bottle neck effect

A

the original population through genetic drift is reduced , there is therefore reduced genetic diversity , through what is known as the founder effect a new generation and colony is started by a few members of the original population .

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21
Q

cultural and geographic founder mutations

A

examples include ;Dominant​

Hereditary breast cancer gene mutations BRCA1/2​

Ashkenazi jewish​

Polish​

Lithuanian​

Scandinavian population isolates​

Orkney BRCA1 mutation​

Recessive​

Ashkenazi- Tay-Sachs etc. ​

North-west European Celtic cystic fibrosis mutation​

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22
Q

applications of HWE

A

Useful for calculating risk in genetic counselling​

​

Useful for planning population based carrier screening programmes​

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23
Q

does cancer arise form genetic mutation yes /no

A

yes

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24
Q

somatic mutation

A

occurs in the autosomal chromosomes and is non inheritable

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25
Q

germline mutations

A

occurs in the sex chromosomes and can be inherited that is passed down to an offspring

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26
Q

tumors have the ability to divide and produce cells that are identical with them what is the name for this characteristic

A

they are said to have clonal expansion

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27
Q

examples of mutated molecules that are associated with cancer

A

oncogenes
tumor suppressor genes for example RB and p53
DNA damage response genes.

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28
Q

what are oncogenes

A

these are genes that have undergone mutation and could stimulate rapid cell proliferation and cause cancer.

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29
Q

oncogenes in cancer

A

one mutation is sufficient for the development of cancer because of the accelerated cell division .

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30
Q

tumor suppressor genes in cancer

A

they are the checkpoint inhibitors at the cell cycle.
they also promote apoptosis
cancer only arises when both of the tumor suppressor genes from both parents fail.

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31
Q

tumor suppressor genes in cancer tree

A

normal genes that prevent cancer to a 1st generation who undergoes mutation is susceptible to cancer but doesn`t have cancer to 2nd generation of the person who has a mutation and has a loss of the cancer gene.

32
Q

DNA damage response gene and cancer

A

cancer arises when both of the gens fail which speeds up the accumulation of mutations in other critical genes

33
Q

example of cancer that is associated with the failure of the MMR genes

A

colorectal cancer

34
Q

failure of the mismatch repair gene results in

A

microsatellite instability is caused when there is a difference in a small region of the DNA form the original DNA this could be addition of base pairs

35
Q

micro-satellite instability and cancer

A

cells with abnormal MMR tend to have accumulated errors which might lead to cancer .
MMR gene is meant to repair and correct errors that spontaneously occur during DNA replication for example short insertions and deletions.

36
Q

what are microsatellites

A

they are repeated sequences of the DNA that can be made of 1 to 6 base pairs.

37
Q

what is microsatellite instability

A

this refers to the changes in the sequences of the mirco-satellite sequences and it is the phenotypic evidence that the MMR is not working properly

38
Q

phenotypic evidence that the MMR is not working properly

A

microsatellite instability

39
Q

what is a benign tumor

A

lacks ability to metastasis but may be having an effect on the health ie if in the brain it is causing the brain to be squeezed hence there is pain.

40
Q

what is meant by dysplasia

A

this are abnormal cells that could form a benign or malignant tumor or not.

41
Q

malignant

A

they have na ability to metastasise and they are invasive .

42
Q

examples of cancer syndromes caused by defect in the mismatch repair gene

A

HNPCC and lynch syndrome and the genes involved are the MLH1 ,MSH2,MSH6,PMS2,PMS1

43
Q

example of cancer caused by a defect in the tumor suppressor gene process

A

breast and ovarian cancer -BRCA1 , BRCA2 GENES
FAP -APC GENE
retinoblastoma -RB GENE
li fraumeni syndrome -P53 gene

44
Q

example of cancers caused by inherited oncogene dysfunction

A

familial medullary thyroid cancer and multiple endocrine neoplasia -RETINOBLASTOMA GENE

45
Q

Examples of autosomal recessive syndromes

A

this is where the gene copies have inherited mutations.
Example MYH polyposis

46
Q

what is a de novo mutation

A

mutation that happens in the first generation person.( a new mutation that is not inherited )

47
Q

new mutation that occurs in the germ cell of a parent

A

de novo mutation

48
Q

examples of diseases where de novo mutations are common

A

Familial adenomatous polyposis ~30% of cases
Multiple endocrine neoplasia 2B ~50% of cases
Hereditary retinoblastoma ~50% of cases

49
Q

differences in non inheritable and heritable retinoblastoma

A

tumor in non-heritable is unilateral and heritable retinoblastoma bilateral.
there is no family history in non-inheritable cancer and there is heritable there is family history .

50
Q

what are the risk factors for breast cancers

A

ageing
family history
early menarche ( menstrual period , more exposure to oestrogen hormone )
late menopause
oestrogen use
dietary factors example alcohol
lack of exercise

51
Q

high risk genes contributing to familial breast cancer

A

BRCA1
BRCA2
TP53
PALB2
PTEN
STK11
CHEK2 homozygotes
ATM mutation c.7271T>G

52
Q

genes that have moderate risk of contracting breast cancer

A

CHEK2 heterozygous mutation
ATM (except c.7271T>G)
BRIP1

53
Q

high risk genes contributing to familial ovarian cancer

A

BRCA1
BRCA2
TP53
RAD51C
RAD51D
Mis-match repair genes

54
Q

moderate risk genes contributing to familial ovarian cancer

A

PALB2
BARD1

55
Q

lifetime risk of BRCA1 associated cancers

A

breast cancer (50-85%)
secondary breast cancer (40-60%)
ovarian cancer (15-45%)
possible increased risk of other cancers for example prostrate and colon

56
Q

lifetime risk of BRCA2 gene cancer

A

breast cancer (50 -80%)
ovarian cancer ( 10-20%)
male breast cancer (6%)
increased risk of prostrate , pancreatic cancer a nd laryngeal cancer.

57
Q

risk factors for colorectal cancer

A

Ageing
Personal history of CRC or adenomas
High-fat, low-fibre diet
Inflammatory bowel disease
Family history of CRC

58
Q

adenoma to carcinoma sequence

A

a normal epithelium through APC mutation there is hyperproliferative epithelium that is formed and there is k ras mutation which leads to formation of an adenoma p53 mutations leads to formation of a carcinoma .

59
Q

clinical features of HNPCC

A

early but variable at CRC diagnosis at 45 years old
tumor is at the site throughout the colon rather than the descending colon.
extracolonic cancers that are associated include ; endometrium , ovary , stomach , urinary tract , small bowel , bile ducts , sebaceous skin tumors.

60
Q
A
61
Q

FAP presentations

A

estimated pentrance for adenomas is 90%
the risk of extracolonic tumors that is in the upper GI, desmoid ,osteoma , thyroid , brain and other.CHRPE MAY BE PRESENT

62
Q

what is FAP

A

familial adematous polyposis which is the formation of polyps on the walls of colon.
they increase the risk of cancer by 100%

63
Q

What is Congenital hypertrophy of the retinal pigment epithelium ( CHRPE)

A

this is the increase in the size of the epithelium of the retina.

64
Q

what is attenuated FAP symptoms

A

Later onset (CRC ~age 50)
Few colonic adenomas
Not associated with CHRPE
Upper GI lesions
Associated with mutations at 5’ and 3’ ends of APC gene

65
Q

what are the symptoms of recessive MYH polyposis

A

similar to the clinical GI features of the attenuated FAP

66
Q

how does modifier genes influence the genetic risk

A

1.they explain why families with history of cancer have no identified mutation.
2.also explains the differences in cancer penetrance in families with same mutation.

67
Q

what is a modifier gene

A

this is a gene that is modified form the original gene that mutated therefore it is attenuated.

68
Q

management of cancer risk in adenomatous polyposis syndrome

A

Surveillance
Surgery
Chemoprevention

69
Q

advances

A

Exome sequencing

Genome sequencing

What to do with results . .

70
Q

advances in clinical practice have been influenced by

A

technology

71
Q

clinical assessment of the family members

A

history
pedigree
clinical examination
genetic test that is microarray and gene tests
synthesis

72
Q

negative selection

A

-Reduces reproductive fitness.
- decreases the prevalence of traits.
- leads to gradual reduction of mutant allele

73
Q

positive selection

A
  • Increases reproductive fitness.
  • Increases the prevalence of adaptive traits.
    -Heterozygote advantage
74
Q

example of heterozygous advantage

A

1.sickle cell anemia , thalassemia and glucose -6 -phosphate dehydrogenase deficiency all are providing resistance towards malaria.
2.cystic fibrosis offers resistance against cholera and typhoid .
3.congenital adrenal hyperplasia -influenza B
4.GM2 gangliosidosis resistance against TB

75
Q
A

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