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302 Scientific basis of medicine > Genetics 3) Chromosomes 1 > Flashcards

Genetics 3) Chromosomes 1 Flashcards

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1
Q

What is the function of chromosomes?

A

Allow cellular DNA to be stably maintained and function as vessels of genetic inheritance

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2
Q

How is 2.17m of DNA contained in 40um nucleus?

A

Structures such as nucleosomes and chromatin fibre

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3
Q

Describe the structure of chromosomes

A

Short arm and long arm
Telomeres to protect ends of chromosomes
Centromeres to hold sister chromatids together

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4
Q

What is the function of telomeres?

A

Protects ends of chromosomes so they aren’t recognised as DNA breaks do won’t be susceptible to DNA repair

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5
Q

What does metacentric mean?

A

Centromere is in middle of chromosome

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6
Q

What does sub-metacentric mean?

A

Centromere is closer to one telomere

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7
Q

What does acrocentric mean?

A

Centromere is very near telomere so short arm is very short

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8
Q

What is mitosis?

A

Type of cell division in which each parent cell gives rise to 2 daughter cells each having the same number of chromosomes as the parent

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9
Q

What are the 2 divisions in meiosis?

A

Meiosis I - reductional division

Meiosis II - equational division

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10
Q

Describe the human karyotype

A

Normal human somatic cell has 46 chromosomes

44 autosomes and 2 sex chromosomes

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11
Q

How is a person’s karyotype determined?

A

Using 20 metaphase cells stained with giemsa satin which reveals a unique banding that helps identify each chromosome

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12
Q

Describe the cytogenetic notation

A

Total number of chromosomes, sex chromosomes, irregularity

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13
Q

What are the types of chromosomal abnormalities

A

Aneuploidy

Structural

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14
Q

How can aneuploid gametes be generated?

A

Meiotic nondisjunction
During maternal meiosis I
During meiosis II if chromatids fail to separate leading to disomic gametes and nullisomic gametes

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15
Q

What happens if mitotic nondisjunction occurs early in the development of an initial trisomy conceptus?

A

1 copy of trisomy chromosome is lost

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16
Q

What is trisomy 21?

A

Down’s syndrome

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17
Q

What is the prevalence of trisomy 21?

A

1 in 700-1000 live births

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18
Q

What is the maternal age effect of trisomy 21?

A

1 in 35 at 43 years old

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19
Q

What are the clinical features of trisomy 21?

A 
Learning defects
Dysmorphic features
Heart defects
Early onset Alzheimers 
Intestinal blockage 
Short and broad hands
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20
Q

What is the karyotype for trisomy 21?

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A

95% have primary (full) trisomy 47,XX,+21 or 47,XY,+21
1-2% have mosaicism 46,XX / 47,XX,+21
4% have translocation 46,XX,der(14;21)(q10;q10),+21

21
Q

What is the incidence of trisomy 18?

22
Q

What is the maternal age effect of trisomy 18?

Study These Flashcards
A

1 in 500 at 43 years old

23
Q

What are the clinical features of trisomy 18?

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A

Severe mental disability
Dysmorphic features - micrognathia, prominent occupant
Rocker-bottom feet, clenched fists with overlapping fingers
Congenital heart defects

24
Q

What is the karyotype of trisomy 18?

Study These Flashcards
A

Primary trisomy: 47,XX,+18 or 47,XY,+18

5% have mosaic form

25
What is the incidence of trisomy 13 (Patau's syndrome)
1 in 5000 live births
26
What is the maternal age effect of trisomy 13?
1 in 1100
27
What is the maternal age effect?
Main risk factor for trisomy | Mitotic nondisjunction and recombination
28
What is the incidence of Kleinfelter syndrome?
1 in 500 to 1 in 1000 newborn males
29
What are the clinical features of Kleinfelter's syndrome?
``` Tall stature, long limbs Gynaecomastic Small testes or cryptorchidism Infertility, azoospermia Delayed or incomplete puberty ```
30
What is the karyotype for Kleinfelter's syndrome?
47,XXY Mosaic: 47,XXY/46,XY 48,XXXY or 49,XXXXY
31
What is the incidence of Turner syndrome?
1 in every 2000 live female births
32
What are the clinical features of Turner's syndrome?
Short stature Infertility Poor breast development Constriction of aorta
33
What is the karyotype for Turner's syndrome?
45,X monosomy | Mosaicism: 45X/46XX, 45,X/46XiXq, 45X/46XY
34
What is the incidence of XYY syndrome?
1 in 1000 newborn males
35
What are the clinical features of XYY syndrome?
``` Often asymptomatic Learning disability, speech delay Low muscle tone Taller than expected Normal sexual development and fertility but can sometimes develop testicular failure ```
36
What is the karyotype of XYY syndrome?
47,XYY | 47,XYY/46,XY
37
What is the incidence of triple X syndrome?
1 in 1000 newborn females
38
What are the clinical features of triple X syndrome?
Largely asymptomatic Seizures or kidney abnormalities in 10% Taller Risk of learning disabilities, delayed development of speech or language skills Doesn't cause unusual physical features or infertility
39
What is the karyotype of triple X syndrome?
47,XXX | 47,XXX / 46,XX
40
What is the mechanism of X-inactivation?
Randomly occurs in all cells 2 weeks post fertilisation Begins at X-inactivation centre X-inactive specific transcript (List) RNA is expressed on inactive X Xist transcripts coat X chromosome leading to inactivation
41
What is chromosome translocation rearrangement?
Chromosome segment is transferred to a non-homologous chromosome or to a new site on same chromosome
42
What is a reciprocal translocation?
2 way exchange of material between any 2 homologous chromosomes Incidence of 1 in 500 newborn Balanced carriers are phenotypically normal but carry reproductive risks Chromosome segregation in carrier of autosomal translocation leads to 5 possible pairs of daughter gametocytes
43
What is a Robertsonian translocation?
Fusion of 2 acrocentric chromosomes Incidence of 1 in 1000 newborns Phenotype is normal in balanced carriers but has reproductive risk
44
What is the karyotype of translocation Down's?
Carrier: 45,XX,-14,-21,+t(14q21q) Affected: 46,XX,-14,+t(14q21q)
45
What is an isochromosome?
Centromere fission | 2 identical arms - 1 duplicated and other is deleted
46
Give an example of a deletion syndrome
Cri du chat
47
What is Cri du chat syndrome?
Named for its high pitched cry Incidence of 1 in 20,000-50,000 newborns Most are de novo, 10% are inherited Deletion on chromosome 5p
48
What are the clinical features of cri du chat syndrome?
Slow growth Microcephaly Moderate-severe mental disability
49
Give example of duplication and deletion of chromosome 17
Deletion - Smith magenis syndrome | Duplication - Potocki Lupski syndrome

302 Scientific basis of medicine (28 decks)

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