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BMS05 > Human Chromosomes & Abnormalities > Flashcards

Human Chromosomes & Abnormalities Flashcards

1
Q

What is the chromosome number in a human somatic cell?

A

46

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2
Q

How are the chromosomes ordered? What is the exception?

A

Ordered by size/length

21 is actually smaller than 22

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3
Q

What are homologous chromosomes?

A

Chromosomes with the same genes in the same order

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4
Q

What are the G bands when looking at a karyotype?

A

Regions of chromosomes which take up Giemsa stain

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5
Q

What are telomeres?

A

Tandem repeats of short, G-rich sequences

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6
Q

What the the p and q arms?

A

Centromere divides chromosome into two parts

Shorter segment is p arm

Longer segment is q arm

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7
Q

Describe rDNA.

A

DNA encoding rRNA on 5 chromosome pairs only

Does not take up Giemsa stain

Found on P arm

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8
Q

In what type of DNA is the rDNA found?

A

Non-centromeric heterochromatin

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9
Q

What does 9q34.1 represent?

A

Chromosome 9, q arm

Region 3, band 4, sub band 1

ABL1 oncogene associated with chronic myeloid leukaemia

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10
Q

What gene is found at Xp21?

A

Duchenne muscular dystrophy gene

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11
Q

What gene is found from 7q22.3 - 7q23.1?

A

Cystic fibrosis gene

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12
Q

What is FISH?

A

Fluorescence in situ hybridisation

Specific cloned DNA sequences tagged with fluorescent chemicals are hybridised to chromosome’s DNA sequence

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13
Q

What can chromosome painting be used for?

A

Detect structural abnormalities in chromosomes

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14
Q

What determines the sex of an organism?

A

Presence/absence of Y chromosome

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15
Q

How does the Y chromosome cause an organism to be male?

A

SRY gene encodes testes determining factor which initiates testes formation

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16
Q

What is testosterone?

A

Androgenic steroid hormone

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17
Q

What do Leydig cells of testis do?

A

Secrete testosterone in the presence of LH which activates male-specific gene expression

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18
Q

Why are adult females called genetic mosaics?

A

One randomly-chosen X chromosome is inactivated in each cell of the blastocyst

Persists through cell division

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19
Q

How does the inactivated X chromosome appear histologically?

A

As a ‘Barr body’

Dark circle at the periphery of the nucleus

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20
Q

In what percentage of spontaneous abortions have chromosomal abnormalities?

A

50%

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21
Q

What is polyploidy?

A

Multiple full sets of chromosomes

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22
Q

What is triploidy?

A

Three full sets of chromosomes (3n)

23
Q

Is triploidy survivable?

A

No, all die within 3 months

24
Q

What is tetraploidy?

A

Four full sets of chromosomes (4n)

25
Q

Is tetraploidy survivable?

A

No, very rare live births and short-lived

26
Q

What is aneuploidy?

A

Abnormal number of chromosomes

27
Q

Why does aneuploidy occur?

A

Non-disjunction during meiosis anaphase

28
Q

Why do chromosomal abnormalities result in developmental issues?

A

Abnormal gene dosage

29
Q

What is nullisomy?

A

Loss of one homologous pair

30
Q

What is monosomy?

A

Loss of a single chromosome

31
Q

Give an example of monosomy.

A

Turner syndrome

32
Q

What is trisomy?

A

One extra chromosome

33
Q

Give two examples of sex aneuploidy.

A

Turner syndrome

Klinefelter syndrome

34
Q

What is the genotype which results in Turner syndrome?

A

XO

35
Q

Describe Klinefelter syndrome.

A

Males with extra X chromosome

Common cause of male infertility

Tall stature, learning difficulties, underdeveloped testes

May have breast development

36
Q

Describe Turner syndrome.

A

Females with one X chromosome

> 90% of cases spontaneously aborted

Do not develop secondary sexual characteristics

Mainly infertile

37
Q

Which three trisomies can survive birth?

A

Down syndrome 21

Edwards syndrome 18

Patau syndrome 13

38
Q

Describe Down syndrome.

A

Trisomy of chromosome 21

Many developmental abnormalities, low IQ

Premature ageing

As maternal age increases, incidence increases

39
Q

Why do those with Down syndrome live longer than other trisomies?

A

Chromosome 21 is the shortest so less abnormal gene dosage

40
Q

Why are numerical sex chromosome abnormalities not always fatal?

A

Lyonisation

Few genes on Y chromosome

41
Q

Why are there abnormalities in sex aneuploidies if lyonisation occurs?

A

Pseudoautosomal region on X chromosome is not included in lyonisation

Gives abnormal gene dosage

42
Q

What causes chromosome structural abnormalities?

A

Breaks in chromosomes

43
Q

What can induce breaks in chromosomes? (5)

A

Radiation

Viruses

Chemicals

Transposable elements

Errors in crossing over

44
Q

Give an example of a deletion abnormality.

A

Cri-du-chat syndrome

45
Q

What is Cri-du-chat syndrome?

A

5p- (part of p arm deleted on chromosome 5)

Mental retardation

Physical abnormalities result in larynx defects

46
Q

What are the two types of inversions?

A

Pericentric

Paracentric

47
Q

What is a pericentric inversion?

A

Inversion of part of chromosome containing centromere

48
Q

What is a paracentric inversion?

A

Inversion on one chromosome arm

49
Q

When do inversions cause problems?

A

Duplication and deletion can occur during meiosis

Children will have severe chromosomal abnormalities

50
Q

Describe looping in meiosis.

A

Regions of chromosomes must line up with homologous region in pair

Inversions cause looping of chromosome and chromosomes join together instead of swapping material

Spindle pulls and breaks chromosomes - deletion of acentric fragments

51
Q

What is a translocation?

A

Change in position of chromosome segments

52
Q

What are the two types of interchromosomal translocations?

A

Reciprocal

Non-reciprocal

53
Q

What is the difference between inter- and intra- chromosomal translocations?

A

Inter = between different homologous chromosomes

Intra = within a chromosome

54
Q

Why are interchromosomal translocations bad (meiosis)?

A

Heterozygote with interchromosomal translocation

Segregation leads to genetically imbalanced gametes

Children have severe abnormalities

BMS05 (3 decks)

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