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Week 3 > Genetics > Flashcards

Genetics Flashcards

1
Q

Stages of meiosis

A
  • Interphase
  • Meiosis 1
  • Meiosis 2

Meiosis 1 and 2 stages:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
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2
Q

Prophase 1

A

Crossover between homologous chromosomes

2 pairs of homologous chromosomes (with 2 sister chromatids)

2n

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3
Q

Chiasma

A

The region where crossover occurs so genetic recombination can occur

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4
Q

Tetrads

A

Homologous chromosomes are organized in this manner

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5
Q

Meiosis 1 is also called

A

Reduction division

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6
Q

Meiosis interphase

A

Duplication of chromosome to form 2 sister chromatids

2n

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7
Q

Metaphase 1

A

Tetrads align along the midline

2n

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8
Q

Anaphase 1

A

Random segregation of the homologous chromosomes to opposite poles

2n

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9
Q

Telophase + cytokinesis 1

A

separation into 2 cells
1 copy of each chromosome (with sister chromatid)

n

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10
Q

Anaphase 2

A

Separation of sister chromatids

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11
Q

Telophase and cytokinesis 2

A

4 haploid gametes that are genetically distinct

n

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12
Q

Genetic diversity of the gametes in Meiosis happens at…

A
  1. Prophase 1 (crossover)

2. Anaphase 1 (random segregation)

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13
Q

46, XY –>

A

23 X
23 X
23 Y
23 Y

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14
Q

Male gametogenesis

A

Spermatogenesis

results in 4 genetically distinct spermatozoa

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15
Q

Female gametogenesis

A

Oogenesis

results in one ovum and 3 polar bodies

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16
Q

Fertilization

A

Haploid spermatozoa (23 chromosomes; n) join with haploid ovum (23 chr; n) to make diploid organism (23 pairs; 46 chr; 2n)

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17
Q

Mitosis stages

A
  • Interphase
  • Mitosis
    (PMAT)
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18
Q

Interphase

A 
Gap 1 (G1)
S phase
Gap 2 (G2)
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19
Q

What’s special about G2?

A

It enlarges the cytosol

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20
Q

Mitosis defintion

A

Cell division in somatic cells to form 2 new daughter cells that are identical genetically as the parent

Parent is diploid and daughter is diploid

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21
Q

S phase

A

DNA replication

Each of the 46 chromosomes is duplicated and has a sister chromatid linked at the centromere

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22
Q

G1

A

Cellular contents (not chromosomes) are duplicated

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23
Q

G2

A

Cell double checks the duplicated chromosomes for error and makes any repairs needed

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24
Q

Whats special about PMAT in mitosis?

A

There is a phase called prometaphase

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25
Q

Prophase (mitosis)

A
  • Breakdown of nuclear membrane
  • Spindle fibers appear
  • Chromosomes condense
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26
Q

Prometaphase

A

Spindle fibers attach to the chromosomes

- Chromosomes condense

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27
Q

Metaphase (mitosis)

A

Chromosomes align

maximally condensed

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28
Q

Anaphase (mitosis)

A
  • Centromeres divide

- Sister chromatids move to opposite poles

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29
Q

Telophase (mitosis)

A
  • Nuclear membrane reforms
  • Chromosomes decondense
  • Spindle fibers dissapear
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30
Q

Cytokinesis (mitosis)

A
  • Cytoplasm divides

- Parent cell becomes 2 daughter cells with identical genetic information

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31
Q

Whats the point of mitosis?

A
  • responsible for growth and development
  • important for cell replacement and healing
  • genetically identical daughter cells are formed which re-enter the cell cycle
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32
Q

Cancer in regards to mitosis?

A

Result of uncontrolled mitotic divisions

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33
Q

Mendel’s 3 laws and ratios

A
  1. Law of dominance (3:1)
  2. Law of segregation
  3. Law of independent assortment

Dihybrid cross (9:3:3:1)

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34
Q

Wild type

A

Most frequently observed allele in a population

- Usually used to identify the control allele that is found in the starting strain

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35
Q

Dominant autosomal traits are shown in what frequency to M and F

A

50%

Equally in both sexes

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36
Q

Incomplete penetrance

A

The individual has the allele but they don’t show the trait

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37
Q

Variable expressivity

A

The range of the severity of the trait shown

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38
Q

Autosomal dominant traits

A
  • Only one allele for the trait to manifest

- Vertical inheritance

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39
Q

Autosomal dominant disorders

A

Food Actually Hurts My Stomach Lining (FAHMSL)

  1. Familal hypercholesterolemia
  2. Achondroplasia
  3. Huntingtons disease
  4. Marfan syndrome
  5. Sonic Hedgehog syndrome
  6. Lynch syndrome
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40
Q

Familial hypercholestrolemia

A

Due to LDLR deficiency

LDLR needed to clear LDL cholesterol from blood into the liver

The deficiency means too much cholesterol stays in the blood

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41
Q

Familial hypercholestrolemia genetic principle

A

Haploinsufficiency

One copy of the LDLR is nonfunctional

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42
Q

Haploinsufficiency

A

Both alleles are required to avoid disease but only one allele is functional

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43
Q

Achondroplasia

A

FGFR3 signals too early and is persistently active

FGFR3 encodes a receptor that responds to the hormone FGF (fibroblast growth factor)

The response is ossification and stop growing

Achondroplasia is premature ossification so dwarfism

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44
Q

Achondroplasia genetic principle

A

Gain of function

FGFR3 gene is not regulated and persistently on

45
Q

Gain of function

A

Protein does more than it should or acts in an unregulated manner

46
Q

Achondroplasia extra facts

A
  • Observable at birth

- Fully penetrant disorder

47
Q

Allelic heterogeneity

A

Different mutations on that same gene can lead to same or other disorders

Ex. FGFR3 gene mutation can lead to other disorders not just achondroplasia
Ex. Marfan syndrome

48
Q

Locus heterogeneity

A

Mutations at different genes can cause similar presentation

Ex. Other genes can cause dwarfism

49
Q

Huntington disease

A

CAG codes for glutamine

When there is an expansion of CAG codon it makes the Gln string too long causing neuronal death

50
Q

Huntington disease genetic principle

A

Attainment of a novel function (a type of gain of function)

This new function is not understood

51
Q

Huntington disease extra facts

A
  • fully penetrant
  • adult onset
  • if you have the CAG expansion you will get the disorder if you live long enough
52
Q

What is huntington disease due to?

A

Unstable repeat regions

This area is sometimes unstable but:

  • The longer the more unstable
  • Anticipation
53
Q

Anticipation

A

Disease gets worse in coming generations

Ex. huntingtons disease the disease might be more severe or have and earlier onset in later generations

54
Q

Marfan syndrome

A

Caused by mutation in fibrillin gene –> produces diff protein

*Both alleles are expressed but only need one allele with mutation for this disease

Leads to connective tissue problems like:

  • Chest wall deformity
  • Tall stature
  • Risk of heart defect
  • Eye lens subluxation
55
Q

Marfan syndrome genetic principles

A
  1. Haploinsufficiency
    Loss of expression from one of the fibrillin alleles
  2. Double negative
    Both alleles expressed but DN leads to the disorder (autosomal dominant)
  3. Allelic heterogeneity
    Different types of mutation in the same gene (fibrillin) can cause MS
56
Q

Sonic hedgehog mutation

A

SHH signalling is required for many things including the midline of the body and brain formation

Loss of one functional copy of SHH can cause holoprosencephaly (inability for brain to separate)

57
Q

SHH extra facts

A
  • Incomplete penetrance for some people who have on SHH mutation
  • Variable expressivity
58
Q

SHH genetic principles

A
  • Haploinsufficiency
  • Incomplete penetrance
  • Variable expressivity
59
Q

Lynch syndrome

A

Hereditary non-poyposis colon cancer
Caused by a mutation in one allele of a gene that that are part of the DNA mismatch repair system

called “care takers”

Genetic principle: 2 hit hypothesis

60
Q

2 hit hypothesis in Lynch syndrome

A

Heterozygosity is lost after second mutation occurs

Loss of both copies leads to accumulation of mutations in the cell

61
Q

Why are dominant disease alleles typically not inherited in the homozygous state?

A
  1. Very rare so its rarer to have 2 people with the same dominant disorder to mate and have offspring
  2. Dominant disease alleles are more severe when homozygous
62
Q

Lynch syndrome genetic principle

A

Loss of heterozygosity

63
Q

Autosomal recessive trait

A
  • Individual must inherit a non functional allele from each parent
  • Functional allele is haplosufficient
  • horizontal inheritance
  • mainly enzyme deficiencies
64
Q

Autosomal recessive disorders

A

TAPSC

  • Tay Sachs disease
  • Phenylketonuria
  • Cystic fibrosis
  • Alpha 1 antitrypsin deficiency
  • Sickle cell disease
65
Q

Tay Sachs disease

A

Deficiency of HEXA (hexosaminidase A activity) enzyme

Loss of both HEXA alleles

Decline of CNS starts at 6 months due to accumulation of a specific ganglioside in the lysosomes

66
Q

Tay Sachs disease genetic principle

A

Founder effect in Ashkenazi Jewish populations

67
Q

Founder effect

A

Lack of genetic diversity due to population rising from small number of ancestors

68
Q

Phenylketonuria (PKU)

A

Deficiency of phenyalanine hydroxylase enzyme

Inability to degrade Phenylalanine which builds up and goes to the brain (too much) so other amino acids dont get into the brain

Diagnosed at birth

69
Q

PKU treatment

A
  • Special diet

- Formula

70
Q

PKU genetic principle

A

Genetic disease (inborn error of metabolism)

71
Q

Cystic fibrosis

A

Deficiency of ion channel by CFTR gene mutation

Causes mucus to accumulate in the luminal space:

  • Pancreatic insufficiency
  • Frequent pulmonary infections
  • High salt water content in sweat
  • Males may have congenital absence of vans deferens

Usually the channel allows Cl –> Na –> water

72
Q

CF genetic principle

A

Ion channel

73
Q

Explain 2/3 carrier risk

A

If disorder is fully penetrant and both parents are carriers then we can deduce a 2/3 carrier risk in a healthy child

74
Q

Alpha 1 antitrypsin deficiency (AATD)

A

Deficiency of a protease inhibitor (elastase)

75
Q

Neutrophils

A

Work to fight infections in the lungs and secrete elastase (protease enzyme) to degrade elastin so they can migrate and get to the invading bacteria

76
Q

AAT

A

Liver cells secrete AAT to travel to the lungs to protect from elastase

Gene that encodes called SERPINA1

77
Q

Alpha 1 antitrypsin name

A

Trypsin is the founding member of the serine protease enzyme (bc serine in the active site)

AAT inhibts trypsin

78
Q

2 alleles of AAT

A
  1. M allele (functional)

2. Z allele (leads to AATD when homozygous)

79
Q

Z allele

A
  • Doesn’t bind well to elastase (loss of function)
  • Degraded more quickly (loss of function)
  • Polymerizes in liver when synthesized (attainment of novel function)
80
Q

AATD genetic principles

A
  1. Loss of function

2. Attainment of novel function

81
Q

Disease features of AATD caused by homozygosity of the Z allele

A
  1. COPD
    - Adult onset
    - Increased by smoking
    - loss of function of protease inhibitor
  2. Liver disease
    - often paediatric (10%)
    - polymerization in the rough ER causes liver damage
    - polymerization can be thought of as attainment of novel function
82
Q

Sickle cell disease (SCD)

A

Single base pair change in DNA causes structural variation in hemoglobin (transport oxygen)

Glutamate 6 to valine change causes the Hb to polymerize and change the shape of the red blood cells

83
Q

Glu6Val

A

Normally Glu is at position 6 which is the outer surface and soluble

switched to Val makes it hydrophobic and causes Hb proteins to polymerize

84
Q

Sickle cell disorder and malaria

A

Heterozygous advantage for malaria due to selection pressure

Pseudodominance

85
Q

Pseudodominance definition

A

SCD is autosomal recessive but the allele can be found in high frequency because of selective pressure from malaria

1/8 chance for carrier

86
Q

Pseudodominance reasons we may see it

A
  1. High frequency of the recessive allele
  2. Consanguinity
  3. Luck
87
Q

Codominace

A
  • Both alleles are expressed
  • Both are equally detected

Ex. sometimes sickle cell trait

88
Q

Karyotype

A
  • Staining metaphase stage chromosomes

- Metaphase stage chromosomes are condensed

89
Q

X chromosome inactivation

A
  • one of the X chromosomes are inactivated
  • occurs during fetal development
  • usually random
90
Q

How is the X chromosome inactivated?

A
  • Expresses RNA from gene called XIST
  • XIST RNA coats the chromosome that expressed it
  • other proteins help
  • then the genes on that x chromosome are silenced
91
Q

Why are males hemizygous

A

Due to XY

92
Q

Why are males hemizygous for the genes on the X chromosome

A

Due to XY

93
Q

X linked disorders

A
  • Glucose 6 phosphate dehydrogenase deficiency
  • Red-green color blindness
  • Hemophilia A and B
  • Lesch-Nyhan syndrome
  • Duchenne muscular dystrophy
94
Q

Glucose 6 phosphate dehydrogenase deficiency

(G6PD deficiency) caused by:

A

exposure to:

  1. Sulfa drugs
  2. Primaquine
  3. Fava beans
  4. Other
95
Q

Glucose 6 phosphate dehydrogenase deficiency

G6PD deficiency

A

Anemia due to oxidative damage in red blood cells

People with this are sensitive to oxidizing agents

96
Q

G6PD

A
  1. is an enzyme that puts glucose in the pentose phosphate shunt (NADH and ribose sugar) and is needed for NADPH production
  2. NADPH needed to maintain glutathione in a reduced active form
  3. Glutathione is needed to protect RBC from oxidative damage
97
Q

Why is complete loss of G6PD activity lethal?

A

All proteins packaged into the RBC must function for the lifetime of the cell

But decrease in protein stability or reduction will impact the red blood cell

98
Q

G6PD Deficiency genetic principle

A

Some mutations can be driven to high frequency in the population due to environmental pressures

99
Q

Red- green color blindness

A

More common in males because it is X linked

Caused by inappropriate crossing over because of unequal intragenic recombination during meiosis that may lead to loss of gene

100
Q

R + G color blindness genetic principle

A

Deletion/duplication mutation can occur due to repetitive regions

1 red gene and 1,2,3 green gene

101
Q

Hemophilia A and B

A

Bleeding disorder
Lack of blood clotting
Mainly in males

Females may show symptoms

if they are carriers but less then men

If a carrier female is affected it could be bc of non random x inactivation

102
Q

What pathogenic variants in the gene cause hemophilia A

A

Factor 8 (F8) and Factor 9 (F9)

103
Q

Lesch-Nyhan syndrome

A

Caused by mutation of gene encoding hypoxanthine guanosine phophoribosyl transferase (HGPRT) enzyme

Inability to salvage purines (A and G) increased reliance on de novo synthesis –> causes excessive disposal of uric acid

104
Q

What is the symptoms of Lesch-Nyhan syndrome?

A
  • Intellectual disability
  • Seizure
  • Self destructive behaviour
105
Q

2 routes for purine bases

A
  1. Synthesized de novo

2. Salvaged

106
Q

Duchenne muscular dystrophy (DMD)

A
  • Encodes the dystrophin protein
  • required for muscle fiber integrity
  • links actin cytoskeleton of the muscle fiber to the plasma membrane –> links to extracellular matrix
107
Q

Lesch-Nyhan syndrome genetic principle

A

X linked disorder caused by deficiency of an enzyme

108
Q

DMD genetic principle

A

Boys have genetic fitness to 0 = they cant reproduce

109
Q

What is the 2/3 rule?

A

When your sibling is affected by an autosomal recessive then theres a 2/3 chance you are a carrier?

Week 3 (3 decks)

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