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Medicine > Chromosomes > Flashcards

Chromosomes Flashcards

1
Q

Which letter stands for long and short arm?

A 
P = short
Q = long
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2
Q

What do acrocentric and metacentric mean?

A

Acrocentric = centromere near the end of a chromosome

Submetacentric = in the middle of acro and meta

Metacentric = centromere in the centre of a chromosome

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3
Q

What is significant about chromosome numbers?

A

1 to 22 is largest to smallest

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4
Q

What is Giemsa?

A

A DNA-binding dye giving characteristic light/dark banding (G-banding) on chromosomes

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5
Q

What does a light band represent vs dark band in G-staining?

A

Active transcription occurring at light bands (DNA looser, euchromatin)
Inactive areas stain dark

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6
Q

What is FISH?

A

Diagnostic tool for when you KNOW what you’re looking for
Fluorescent In Situ Hybridisation
Fluorescently labelled ssDNA probe anneals to complementary target sequence in metaphase spread

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7
Q

What is array CGH, and what is it used for?

A

CGH = comparative genome hybridisation

To detect regions of gene amplification/loss, especially in cancer (unusual chromosome pattern) and dysmorphic individuals (usually due to chromosomal abnormality)

Test DNA labelled green
Normal DNA labelled red

Amplification = green
Loss = red
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8
Q

Why is an array CGH used over FISH and other tools?

A

Very high resolution

Can detect dosage abnormalities that are not visible cytogenetically

Abnormalities not always relevant - check by looking at parents

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9
Q

How is array CGH carried out?

A

Control DNA (green) and Patient DNA (Red) applied to microarray, containing lots of wells with probes for different genes in it

DNA gain = red
DNA loss = green
DNA same = yellow

Fluorescent signals measured by microarray scanner - computer then makes a plot and can compare to a genome online

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10
Q

How is sex determined? Evidence for this…

A

Female is default

If Y chromosome is present, then male develops

Y chromosome has sex-determining region called SRY

Evidence:

  • XX males had SRY gene present
  • XY females have SRY deletion
  • XX mice with SRY inserted became males
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11
Q

What is SRY?

A

Transcription regulator that determines maleness

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12
Q

What does SRY do?

A

Stimulates transcription of genes leading to development of testis from Wolffian ducts (Testosterone release)

Sertoli cells in testis release Mullerian Inhibitory Factor which inhibits female gentalia production (which develops from Mullerian ducts)

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13
Q

What is the Lyon hypothesis relating to X chromosomes?

A

That early in embryonic life, paternal or maternal X is randomly inactivated - propagates through mitosis

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14
Q

Is X-inactivation always random, complete and permanent?

A

No

Random mostly, though structurally abnormal X usually inactivated preferentially

Complete mostly, though some genes escape inactivation

Permanent mostly, though reversed in germ cell development

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15
Q

What is a Barr Body?

A

Darkly stained mass found close to nuclear membrane representing inactivated X chromosome

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16
Q

What about 2?

A

1

17
Q

Turner syndrome

  • features
  • karyotype
A

Features:

  • wide neck
  • short stature
  • wide carrying angle (hands point outwards when hanging by sides)
  • shield chest
  • primary amenorrhoea (no menstrual cycle)
  • infertility
  • cardiac abnormalities (coarctation of aorta)

Karyotype
-45X

18
Q

Kleinfelter Syndrome:

  • features
  • karyotype
A

Features

  • tall stature
  • mildly impaired IQ
  • breast development
  • testicular atrophy
  • feminised physique
  • not much male pubic hair

Karyotype
-47XXY

19
Q

Triple X:

  • features (think supermodel lol)
  • karyotype
A

Features:

  • tall
  • feminine
  • slight intellectual impairment

Karyotype:
-47XXX

20
Q

XYY features and karyotype

A

Features
-associated with criminal tendencies

Karyotype
-47XYY

21
Q

Down syndrome

  • Features
  • Karyotype
A

Features

  • almond shaped eyes
  • single palmar crease
  • widened sandal gap (great toe gap)
  • tongue sticking out due to —> poor muscle tone
  • sometimes intellectual diasbility
  • cardiac problems (septal defects)
  • thyroid problems
  • develop Alzheimer’s
  • Liquid tumours (lymphomas/leukaemias)

Karyotype
-Trisomy 21

22
Q

What is it called when an extra chromosome ends up in a gamete?

A

Non-dysfunction event

23
Q

Patau syndrome

  • features
  • karyotype
A

Features

  • clefting
  • finger and toe abnormalities
  • don’t usually survive first year
  • severe intellectual disability
  • heart defects
  • scalp defects

Karyotype
-trisomy 13

24
Q

Edward’s Syndrome

  • features
  • karyotype
A

Features

  • severely clenched fingers
  • protuberant back of head
  • ‘rocker-bottom’ feet
  • severe intellectual disability
  • cardiac abnormalities

Karyotype
-trisomy 18

25
Q

Risk of trisomy increases with…

A

Maternal age

26
Q

What is a chromosome translocation?

A

Transfer of genetic material from one chromosome to another

27
Q

What is a reciprocal translocation?

A

One break in two different chromosomes

The breaks are exchanged between the two

28
Q

What is a balanced vs unbalanced reciprocal translocation?

A

One of the two chromosome copies of each chromosome involved (say 3 and 21) will have a reciprocal translocation

If a gamete contains the two copies that are not-translocated, then NORMAL
If a gamete contains one non-translocated and one translocated copy, then UNBALANCED (two possible combinations for this)
If a gamete contains both translocated copies, then BALANCED

29
Q

What is a Robertsonian translocation? Two types…?

A

Homologous acrocentrics

  • two of the same chromosome (e.g.14) that are acrocentric (centromere near edge of chromosome)
  • q arms join together

Non-homologous acrocentrics
-q arms still join together, but chromosomes of a different number (e.g. 14 and 21)

30
Q

Other than non-disjunction, how else can trisomy 21 occur?

A

Unbalanced Robertsonian translocation

Non-homologous acrocentric translocation of q arm of 21 and 14, such that there is one 21 and two 14s, one with a 21 stuck on it

In an unbalanced gamete that causes trisomy 21, it will receive one normal chromosome 21 and one chromosome 14 with the 21 stuck on it

If this fuses with a normal gamete, there will be two chromosome 21s and 14s respectively, but one of the 14s will have a 21 stuck on it

31
Q

What is a chromosome inversion? Pericentric vs paracentric

A

Break a chromosome, rotates 180, then reinserts

Pericentric involves both arms, paracentric only one arm

32
Q

What is chromosome duplication?

A

When part of one chromosome is added to another (not exchanged)

Medicine (62 decks)

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