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Medicine Sem 1 > Genetics week 3,4,5 > Flashcards

Genetics week 3,4,5 Flashcards

1
Q

Where does genetic variations arise from?

A

From mutations, which are changes to the DNA sequence

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2
Q

Where do mutations occur in?

A

Germaline cells( that produce gametes) which can affect gametes
Somatic cells( Can lead to cancer)

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3
Q

What is an allele

A

Variations of a gene that difers in DNA sequence

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3
Q

What is the locus

A

specific location of a gene on a chromosome

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4
Q

What are mutations

A

changes in the DNA sequence

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5
Q

NAME the type of single-gene mutations

A
  • Base pair substitutions
  • Silent substitutions
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6
Q

NAME the 2 types of base pair substiutions that alter amino acids

A

Missense Mutations
Nonsense Mutations

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7
Q

Describe the 2 single gene mutations

A
  • Base pair mutations:When a base pair is replaced with another
    Silent mutations: No change in amino acid sequence due to genetic code redundancy
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8
Q

Describe the 2 basic types of muations

A

-Missense mutations: Alters one amino acid, potentially affecting protein function
-Nonsense Mutations: Creates a stop codon, leading to early termination of translation or mRNA decay

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9
Q

What is insertions and deletions

A

adding or removing base pairs

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10
Q

What is the frameshift mutation

A

It alters reading frame if the number of bases is not a multiple of 3 changing downstream amino acids

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11
Q

What is gene duplication

A

It is duplicating entire genes

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12
Q

What is Mobile Element insertions and name the diseases it has been linked to

A

Certain DNA sequences can copy themselves into new locations, causing frameshift mutations.
This has been linked to diseases like neurofibromatosis and muscular dystrophy

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13
Q

What is Tandem Repeat Extensions

A

Repeated DNA sequences may expand causing genetic diseases. Theses expand repeats can be passed to offspring, contributing to conditions like huntingtons disease.

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14
Q

Name the 3 consequences of mutations

A
  1. Gain of function mutations
    2.Loss of function mutations
  2. Dominant negative mutations
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15
Q

Explain the gain of funtion mutation and the consequences

A
  • Leads to an increased or innapropriate protein activity, resulting in a novel protein product( which can lead to huntingtons disease) and it results in overecpression (which can lead to Charcot-Marie-Tooth disease)
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16
Q

Explain the loss of funtcion mutation and the consequences

A
  • Results in a reduced or eliminated protein activity, often associated with recessive disorders where 50% of protein functions remain sufficent.
    And it can lead to hapiloinsufficency, which occurs when 50% functions is insufficent causing domina disorders like familial hypercholesterolemia
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17
Q

Explain the Dominant Negative mutations and the consequences

A

Results in an abnormal protein that interferes with the normal protein in heterozygotes. This is common in multimeric proteins such as Type 1 Collagen( which leads to distorted protein structure)

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18
Q

What does gain of function mutatins result in

A
  • Novel protein prodcut which can lead to huntingtins disease
  • Overexpression which can leas to Charcot- Marie-Tooth disease
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19
Q

What does loss of muation result in?

A
  • Hapilosuffiency, which occurs when 50% function is insufficent causing dominant disorders like familial hyppercholesterolemia
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20
Q

Name the three types of hemoglobin disorders

A
  • Structural abnormalities
  • Thalassemias
  • Hereditary Persistence of fetal hemoglboin(HPFH)
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21
Q

Explain structural abnormalities as a hemoglobin disorder

A
  • Mutations that alter the hemoglobin molecule
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22
Q

Explain Thalassemias as a hemoglobin disorder

A
  • It reduces the quantity of structurally normal a and b globin chains keading to imbalanced hemoglobin synthesis
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23
Q

Explain HPFH as a type of hemoglobin disorder

A
  • It causes the continued production of fetal hemoglobin after birth which can compensate for reduced adult hemoglobin without causing diseases.
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24
Q

Describe the structure of hemoglobin

A
  • Tetramer with 2 alpha and beta polypeptide chains
  • The beta chains are encoded on chromosome 11 and the alpha chains are encoded on chromosome 16
  • Equal production of alpha and beta chains is tightly regulated for normal oxygen transportation by hemoglobin
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25
Q

What is sickle cell caused by?

A
  • It is caused by a single missense mutation, that substitutes valine for glutamic acid at position 6 of the glboin chain, leading to abnormal hemoglboin strutcure.
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26
Q

Explain the mechanism of sickle cell disease

A
  • Under low oxygen, hemoglobin aggregates, causing erythrocytes to take on a sickle cell shape
  • Sickled cells are rigid amd they get stuck in capillaries and adhere to vascular walls
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27
Q

What are the two types of Thalassemia

A

A- thalassemia
b - thalassemia

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28
Q

Explain what results in Thalassemia

A
  • It results from mutations that reduce the amount of a and b globin chains , leading to excess chains of the other type
29
Q

Explain alpha Thalassemia and what it is caused by

A
  • caused by deletions of a globin genes
  • Loss of 1 or 2 genes have minimal effect but the loss of 3 genes cause HbH disease with anemia
  • Loss of 4 a genes leads to hydrops fetalis , which is fatal before or shortly after birth
30
Q

Explain beta Thalassemia and what it is caused by

A

It results from single base mutations rather than gene deletions
- individuals w 1 mutated beta globin genes have beta thalassemia minor( mild or no symptoms)
- indivdulas w 2 mutated beta globin genes may develop b thalassemia major

31
Q

What are symptoms of thalassemia

A
  • anemia
  • growth reduction
  • increased infection risk
    bone deformities
32
Q

What is genotype?

A
  • An individuals genetic makeup at a specific locus
33
Q

What is phenotype

A

Observable or clinical traits

34
Q

Explain the envirnomental influences on genotype-phenotype

A

They can affect how the phenotype is expressed

35
Q

What is the basic pedigree structure used for?

A
  • Show family relationship and who is affected or not affected by a genetic disease
36
Q

Explain the degrees of relationships

A

1st- Parents, offspring,siblings
2nd- Grandparents, grandchildren,uncles,aunties, nieces and nephews#
3rd- cousins, great grand children

37
Q

What are the characteristics and transmission pattern of Autosomal Dominant Inheritance?

A
  • The affected offspring usually results from 1 hetergozygous parent and one unaffected parent
    Transmission pattern:
  • Both males and females are likely to inherit
  • There is no generation skipping
  • Father to son transmission is possinle
38
Q

What is the reccurence risk?

A

This is the probability that parents with a genetic disease will produce affected offspring

39
Q

What is the autosomal dominant recurrence risk?

A

When one parent is affected and the other is unaffected so each child has a 50% recurrence risk

40
Q

What is the inheritance pattern for autosmoal recessive diseases

A

-From 2 heterozygous carriers
- Punnet square shows how 25% of offpring will be affected, 25% unaffected and 50% will be carriers

41
Q

What is the Transmission characteristics of autosmal recessive inheritance?

A
  • Both males and females have equal chance of inheritance
  • The diseases is typically seen in syblings than cross multiple generations
42
Q

What is quasidominant inheritance+ the reccurence risk?

A
  • When a carrier of a reccesive allele mates with an affected homozygote
    The reccurence risk is 50%
43
Q

What is De Novo mutation?

A

A mutation that can cause a genetic disease in a child with no family history

44
Q

What is Germaline Mosaicism

A

When a mutation affects a parents germaline cells but not somatic cells, allowing them to pass the mutations to multiple offsprings without being affected themselves

45
Q

What is Age-dependent penetrance + example

A

When there is a delay in the onset of a gentic disease causing the symptoms to appear late in life rather than at birth.
e.g Huntingtons

46
Q

What is Variable expression + example

A

refers to the differing severity of the genetic diseases phenotype
-neurofribromatosis

47
Q

What is pleitropy

A

When a single gene has multiple effects on different body systems

48
Q

What is Anticipation?

A

Genetic diseases that have an earlier onsent in more recent generations

49
Q

What is imprinting?

A

Certain genes are expressed only if inherited from a specific parent

50
Q

Why are female stomatic cells inactivated?

A
  • To balance the levels of X-linked gene products between male and femals
51
Q

What happens once a x chromosome is inactivated?

A
  • It will remain inactive and It leads to a permenant mosaic pattern of X chromosome activty in females
52
Q

X inactivation

Why does the Lyon hypothesis state?

A
  • It states that X inactivation occurs early in female embryonic development
  • And the X chromosomes contributed by the father is inactivatedd in some cells
    and the cells that the X chromsome contributed by the mother is inactivated.
53
Q

Where is the XIST gene and role

A

-It is in the X inactivation center, which is crucial for X chromosomes inactivation.
- XIST,produces a long noncoding RNA (lncRNA) that is transcribed only on the inactive X chromosomes in females.

54
Q

Where is the IncRNA(long noncoding RNA) and its function

A

-Remains in the nucleus
-coating the inactive X chromosomes and recruiting proetins to inhibit transcription

55
Q

Where are sex linked genes located and where is the main focus?

A

-On the x or y chromosomes
- Main focus is on the x linked genes as y chromosomes contain few genes

56
Q

what is X-linked inheritance categorised as

A
  • X-linked Recessive or dominant
56
Q

Why is the classfication of X-linked inheritance ambigous?

A

-Due to variable expression of traits
- incomplete penetrance
- Effects of random x inactivation in females

57
Q

What is incomplete penetrance?

A

When not all carriers show symptoms

58
Q

Name the diseases caused by X-Linked reccesive genes

A
  • Hemophilia A
  • Duchenne Muscular dystophy
  • Red - green colour blindness
59
Q

What is the inheritance pattern of X-linked recessive inheritance

A
  • The females inherit 2 X chromosomes so they can be:
  • Homozygous normal,heterozygous (carrier) or homozygous for the diesease allele
  • The males inherit one x chromosomes and they are hemizygous, so they will express an x linked disease if they inherit a disease causing allele
60
Q

What are the inheritance characteristics of X linked recessive diseeases?

A
  • Generation skipping (when a female carrier passes the genese without expressing it)
  • No father to son transmisson ( as the father passes the Y chromosome)
  • Affected males pass the gene to all daughters(who are carriers)
61
Q

By using the common mating pattern in X linked resseive disorders give the percentages of the offspring being carriers and etc

A

50% daughters are carriers
50% sons are affected
50% of daughters and sons are normal

62
Q

Name 3 examples of X linked dominant diseases

A
  • Rett syndroome
    -Incontinentia Pigmentic Type
  • Hypophosphatemic rickets
63
Q

Explain the difference in the effect of the Xlinked dominant disorders in males vs females

A

-Males are hemizygous and they experience severe effects
- Females have milder symptoms due to then have one noermal x chromosome

64
Q

What is the inheritance pattern in Xlinked dominant inheritance.

A

Affected females: There is a 50% chance of passing the allele to offpsings
Affected males:the affected allele is passed to all daughters

65
Q

What are the inheritance characteristics of Xlinked Dominant inheritance

A
  • Both male and females can be affcted, but females are more likely
    -No father to son transmission
  • Affected fathers pass the trait to All daughter
    Generation skipping is rare/uncommon
66
Q

What are barr bodies

A

Dense chromatin masses in the femal nuclei

67
Q

What do Barr bodies show?

A
  • Reduced Transcriptional activity
  • Delayed DNA replication during the Sphase
68
Q

Explain the biochemical evidence supporting the lyon hypothesis

A

-They enzyeme G6PD being coded on the X chromosome in equal amounts in amels and females due to doasge compensation

Medicine Sem 1 (18 decks)

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