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MCD - Genetics > Chromosomes, abnormalities and birth defects > Flashcards

Chromosomes, abnormalities and birth defects Flashcards

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1
Q

Explain the classification of congenital defects: MALFORMATION

A

-Primary structural defect (cleft lip)
-Single organ showing multifactorial inheritance
(genetic and environmental)

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2
Q

Explain the classification of congenital defects: DISRUPTION

A
  • Secondary abnormal structure of an organ or tissue (amniotic band causing digital amputation)
  • Caused by ischaemia, infection and trauma (NOT genetic, only predispose)
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3
Q

Explain the classification of congenital defects: DEFORMATION

A
  • Abnormal mechanical force causing distortion (club foot)

- Occurs in late pregnancy, good prognosis as underlying structure is normal

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4
Q

Explain the classification of congenital defects: SYNDROME

A
  • Consistent pattern of abnormalities with a specific underlying cause (Down Syndrome)
  • Includes chromosomal abnormalities
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5
Q

Explain the classification of congenital defects: DYSPLASIA

A

-Abnormal organisation of cells into tissues (thanatophoric dysplasia - short flat bones, small thorax, large head)
-Single gene defect
-↑ recurrence risk for siblings and offspring

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6
Q

Explain the classification of congenital defects: SEQUENCE

A
  • Abnormalities initiated by a primary factor (↓ amniotic fluid = Potter sequence)
  • Caused by oligohydramnios (↓ fluid due to failure to produce urine0
  • Genes can be the initial factor
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7
Q

Explain the classification of congenital defects: ASSOCIATION

A
  • Non-random occurrence of abnormalities NOT explained by syndrome
  • Typically unknown cause
  • VACTERL association - Vertebral, Anal, Cardiac, Tracheo-Oesophagal, Renal, Limb
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8
Q

What are the different types of chromosomes?

A 
Metacentric = centromere in the middle
Submetacentric = centre towards one side
Acrocentric = No short arms, only satellites
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9
Q

What is a karyotype?

A
  • Described in terms of both number and structure
  • Visualised by staining with giemsa
  • 22 pairs of autosomal and 1 pair of sex chromosomes
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10
Q

What does chromosomes binding/standard human banding pattern show?

A

Start from centromere (11)

  1. Chromosome number
  2. P or Q arm
  3. Band number
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11
Q

What is aneuploidy?

A 
Numerical chromosomal abnormality 
-loss or gain of chromosomes 
Monosomy = loss of 1 (almost always lethal)
Trisomy = gain of 1 (can be tolerated)
Tetrasomy = gain of 2 (can be tolerated)
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12
Q

What are the types of structural chromosomal abnormalities?

A
  • Translocations
  • Rings
  • Insertions
  • Inversions
  • Deletions
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13
Q

What is mosaicism (chromosomal abnormalities)?

A

Different cell lineages do not contain identical chromosomes (more than 1 lineages in tissue)

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14
Q

Outline partial aneuploidy (chromosome translocations)?

A 
NORMAL = no translocation
BALANCED = direct switch of DNA (no loss of genes)
UNBALANCED = Part of chromosome is lost (non-viable embryo)
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15
Q

What happens when someone with balanced translocations undergo meiosis?

A

chromosomes form quadrivalent instead of bivalent

can cause disease

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16
Q

What is a derivative?

A

A chromosome that looks like it has had a translocation

17
Q

Trisomy 21 - Down Syndrome (Clinical features)

A

1 in 700 birthe
Strong association between incidence and maternal age (above 35)
-Newborn period = severe hypotonia, excess nuchal skin
-Craniofacial = macroglossia, small ears, epicanthic folds, upward sloping palpebral fissures, brushfield spot
-Limbs = single palmer crease, wide gap between 1st and 2nd toes
Cardiac = Atrial and ventricular septal defects
Other = short statue, duodenal atresia

18
Q

Trisomy 21 - Down Syndrome (Cause)

A

95% = non-disjunction during meiosis I (75%) and meiosis II (25%)
4% = Translocations
-Robertsonian translocation
-Mosaicism

19
Q

What is Robertsonian translocation?

A

breakage of the.

acrocentric 21st chromosomes and fusion of the long arms

20
Q

Trisomy 13 - Patau Syndrome

A

-Heart defects
-Holoprosencephaly (cleft lip/palate, hype
telorism = increased distance between two organs)
-Mental retardation

21
Q

Trisomy 18 - Edwards Syndrome

A
  • Heart defects
  • Kidney malformation
  • Digestive Tract defects
  • Mental retardation
22
Q

Monosomy X - Turner Syndrome

A
  • Sex chromosome aneuploidy
  • 1 in 3000 live female births
  • Generalised oedema and neck swelling ( can be detected in 2nd trimester)
  • Low posterior hairline, short 4th metacarpals, webbed neck, aorta defect in 15% of cases
  • (ADULTS) short statue, ovarian failure/infertility
  • TREATMENT = oestrogen replacement for secondary sexual characteristics and prevention of osteoporosis
23
Q

Polysomy X - Kleinfelter’s Syndrome (47,XXY)

A
  • 1 in 1000 live male births
  • Clumsiness, verbal learning disability
  • Taller than average, long lower limbs
  • 30% moderately sever gynaecomastia
  • Infertility
  • ↑ risk of leg ulcers, osteoporosis and breast carcinoma
  • X from either mother or father
24
Q

How can someone with XX be male?

A

Due to translocation of the sex determining region on the Y (SRY) onto the X chromosome

25
Q

Define dosage compensation

A

-Process by which organisms equalise expression of genes between members of different biological sexes
Mechanisms:
-Random inactivation of single X chromosome in females
-Increased (2) expression of X genes in males
-Decreased (0.5) expression of both X genes in hermaphrodites

26
Q

What is a genomic disorder/copy number variant?

A
  • Caused by a loss or gain of DNA/chromosome
  • Most are harmless, natural process
  • Harmless = small size. no important gene, inherited
  • Harmful = gig, important gene, not inherited
27
Q

What is an example of a deletion syndrome (genomic disorder)?

A

Di George Syndrome

  • Cardiac abnormalities (tetralogy of Fallot) = a heart defect that features 4 problems
  • hole between lower chambers, obstruction from the heart to the lungs, aorta lies over the hole in the lower chambers, muscle of the lower right chamber is overly thickened
  • Hypoplastic thymus (underdeveloped)
  • Hypocalcaemia (electrolyte imbalance)
28
Q

Charcot Marie Tooth disease type 1 A

A
  • Muscle weakness
  • Hypotonia (floppy baby)
  • Missing reflexes
  • Foot deformities (high arches/flat feet)
  • Lack of sensation in hands and arms
29
Q

What is the PMP22 gene?

A

Peripheral Myelin Protein 22 gene = codes for an integral membrane protein in the myelin of the peripheral nervous system

30
Q

Outline the classification of congenial defects

A 
SINGLE:
-Malformation
-Disruption
-Deformation
-Dysplasia
MULTIPLE:
-Sequence
-Syndrome
-Association

MCD - Genetics (6 decks)

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