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Genetics > Chromosomes > Flashcards

Chromosomes Flashcards

1
Q

Chromosomes which are not sex chromosomes

A

Autosomes

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2
Q

Sex chromosomes males have

A

XY

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3
Q

Sex chromosomes females have

A

XX

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4
Q

Constriction within a chromosome which divides it into two arms

A

Centromere

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5
Q

Label given to the short arm of a chromosome

A

P arm

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6
Q

Label given to the long arm of a chromosome

A

Q arm

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7
Q

Type of chromosome which has its centromere in the centre

A

Metacentric

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8
Q

Type of chromosome which has its centromere close to the centre but one arm is slightly longer than the other

A

Submetacentric

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9
Q

Type of chromosome where the centromere is significantly to one side

A

Acrocentric

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10
Q

Type of chromosome where the centromere is almost completely to one side with one arm being extremely short

A

Telocentric

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11
Q

Cells which contain different chromosomal numbers to the normal diploid cells

A

Aneuploid cells

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12
Q

Occurrence where all cells contain three copies of each chromosome instead of two copies - so 69 total chromosomes

A

Triploidy

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13
Q

Cause of triploidy

A

Non-disjunction during meiosis - one gamete has two copies of every chromosome and another gamete has no chromosomes; if the gamete with two copies of each chromosome pairs with a normal gamete the resulting foetus will be triploid

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14
Q

Outcome of triploidy in human foetuses

A

Spontaneous abortion

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15
Q

Non-disjunction for only one chromosome during meiosis resulting in the foetus having three copies of a single chromosome

A

Trisomy

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16
Q

Non-disjunction for only one chromosome during meiosis resulting in the foetus having only one copy of a chromosome

A

Monosomy

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17
Q

Trisomies of autosomes which are compatible with life

A

13
18
21

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18
Q

Cause of mosaic trisomy or monosomy

A

Non-disjunction occurs during mitosis just after the two gametes fuse; resulting in two distinct cell lines, one with the normal chromosomal makeup and another with a trisomy or monosomy

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19
Q

Syndrome caused by trisomy 21

A

Down’s syndrome

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20
Q

Syndrome caused by trisomy 18

A

Edward’s syndrome

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21
Q

Syndrome caused by trisomy 13

A

Patau syndrome

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22
Q

Syndrome caused by monosomy X

A

Turner’s syndrome

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23
Q

Syndrome caused by trisomy XXY

A

Klinefelter’s syndrome

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24
Q

Findings before birth in Down’s syndrome

A

Reduced maternal levels of alpha fetoprotein
Increased beta HCG
Increased nuchal thickness
Increased levels of inhibin A

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25
Q

Percentage of cases of Down’s syndrome caused by meiotic non-disjunction

A

95%

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26
Q

Three chromosomal causes of Down’s syndrome

A

Meiotic non-disjunction
Mosaicism
Robertsonian translocation

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27
Q

Percentage of cases of Down’s syndrome caused by Robertsonian translocation

28
Q

Percentage of cases of Down’s syndrome caused by mosaicism

29
Q

Steps occurring in Robertsonian translocation leading to Down’s syndrome

A

When acrocentric chromosomes (including 21) break at their centromeres the long arm of chromosome 21 joins with the long arm of another acrocentric chromosome (e.g. chromosome 14)
The two short arms left over are usually lost - often unimportant due to limited genetic material
During meiosis the combined chromosome and the normal copy of chromosome 21 go into one gamete, while the normal chromosome 14 goes into another gamete
The gamete with two copies of chromosome 21 is fertilised by another gamete with one copy of chromosome 21
The resulting foetus has three copies of chromosome 21

30
Q

Rate of Down’s syndrome to mothers age 20

31
Q

Rate of Down’s syndrome in mothers aged 30

32
Q

Rate of Down’s syndrome in mothers aged 40

33
Q

Rate of Down’s syndrome in mothers aged 45

34
Q

Percentage of cases of trisomy 21 Down’s syndrome caused by maternal meiotic error

35
Q

Physical features of Edward’s syndrome

A

Rocker bottom feet
Low set ears
Micrognathia
Clenched hands

36
Q

Physical features of Patau syndrome

A

Polydactyly
Cleft lip and palate
Microcephaly
Microphthalmia

37
Q

Percentage of cases of trisomy 13 caused by maternal meiotic non-disjunction

38
Q

Percentage of cases of trisomy 18 caused by maternal meiotic non-disjunction

39
Q

Percentage of cases of Turner’s syndrome caused by paternal non-disjunction

40
Q

Percentage of cases of Turner’s syndrome caused by maternal meiotic non-disjunction

41
Q

Physical features of Turner’s syndrome

A 
Short stature
Broad chest and widely spaced nipples
Webbed neck
Low hairline
Arms that turn out at the elbow
Scoliosis
42
Q

Comorbidities associated with Turner’s syndrome

A

Hypothyroidism and other autoimmune conditions
Diabetes
Osteoporosis (due to lack of oestrogen)
Learning disabilities or behavioural problems (IQ usually normal)
Congenital heart disease in 50%
Structural abnormalities of the kidneys and ureters
Middle ear issues and hearing loss

43
Q

Percentage of patients with Turner’s syndrome who are able to have children without fertility treatment

44
Q

Incidence of Turner’s syndrome

A

1 in 2000 live born female babies

45
Q

General IQ and developmental features of patients with Turner’s syndrome

A

Average or near average intelligence
Weaker non-verbal skills including arithmetic
Weaker visuospatial processing
Weaker social skills

46
Q

Percentage of cases of Klinefelter syndrome caused by maternal non-disjunction

47
Q

Percentage of cases of Klinefelter syndrome caused by paternal non-disjunction

48
Q

Comorbidities associated with Klinefelter syndrome

A

Infertility in almost all patients
Increased risk of breast cancer compared to other males
Increased risk of autoimmune disorders

49
Q

Cognitive, developmental and psychiatric features of Klinefelter syndrome

A

Autism in 10%
Increased anxiety and depression
Some deficits often present in reading, language learning, and executive functions

50
Q

Facial features of Down’s syndrome

A 
Flat head
Protruding tongue due to small mouth
Slanted eyes and epicanthic folds
Brushfield spots in iris
Flat nasal bridge
Small chin
51
Q

Non facial physical features of Down’s syndrome

A

Single palmar crease
Separation of first and second toes
Hypotonia
Short stature

52
Q

Medical comorbidities common in patients with Down’s syndrome

A

Mild to moderate intellectual disability
Epilepsy
Visual problems - refraction errors, strabismus, cataracts
Hearing problems - chronic ear infections, poor eustachian tube function
Congenital heart disease - most commonly AVSD
ALL, AML
Hypothyroidism
Diabetes
Infertility
GI problems - Hirschsprung’s disease, duodenal atresia, constipation

53
Q

Form of Down’s syndrome which has a high recurrence rate

A

Robertsonian translocation Down’s syndrome

54
Q

Alleles which are found on the same chromosome

55
Q

Alleles that are close together and likely to be inherited together in the case of synapsis

A

Linked alleles

56
Q

Alleles that are close together and likely to be inherited together in the case of synapsis

A

Linked alleles

57
Q

Unit genetic distances are expressed in

A

centiMorgans (cM)

58
Q

Score used to estimate the likelihood that two loci are linked

59
Q

LOD score taken to mean two loci are linked

60
Q

LOD score taken to mean two loci are not linked

61
Q

An organism who has more than one genetically distinct population of cells arising from a single zygote

62
Q

An organism who has more than one genetically distinct population of cells arising from more than one zygote

63
Q

Percentage recombination frequency equal to 1 centiMorgan

64
Q

Number of base pairs of DNA equivalent to 1 centiMorgan

65
Q

Type of chromosome where the centromere makes up the whole chromosome

A

Holocentric

Genetics (9 decks)

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