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Biochem Exam 2 > Chromosomes (rearrangements) > Flashcards

Chromosomes (rearrangements) Flashcards

1
Q

what are the two basic types of human chromosomes?

A

autosome
sex

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2
Q

autosome chromosomes

A

identical in both males and females; numbered by size (22 out of 23)

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3
Q

sex chromosomes

A

23rd pair that differs between males and females (females: XX; males: XY)

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4
Q

how many chromosomes do each human cell have?

A

23 pairs of chromosomes –> 46 total chromosomes

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5
Q

karyotyping/karyotype

A

karyotyping: the process of sorting human chromosomes pairs by size and morphology
karyotype: human chromosomes lined up in pairs

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6
Q

Chromosome painting

A

using probes (aka fluorescent DNA molecules) to bind to specific sequences on Chr → when viewed under a fluorescence microscope, they “paint” the Chr in different colors (can detect chromosomal rearrangements)

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7
Q

somatic cells

A

body cells (ie. muscle, skin, blood)
Contains a complete set of chromosomes (26 in humans)
are diploid cells

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8
Q

diploid cells

A

In each diploid cell, humans have 23 homologous pairs (aka homologs) → total 46 chromosomes
In diploid cells, one set of chromosomes is inherited from the mother and the second is inherited from the father
Total number of chromosomes in diploid cells → described as 2n

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9
Q

what are homologs (homologous pairs of chromosomes) and how can they differ among each other?

A

Think of homologs as a matching set: they are NOT exactly identical
Approximately same length, centromere position, and staining pattern
The maternal and paternal chromosomes in a homologous pair have the same genes at the same locus BUT possibility DIFFERENT ALLELES
One homolog from mother, one homolog from father
During meiosis, homologs pair together

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10
Q

the maternal and paternal chromosomes in a homologous pair have the same ___ at the same ___ BUT possibility DIFFERENT ___

A

genes, locus, alleles

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11
Q

what are the two types of human cells?

A

somatic (body) cells: diploid
sex cells: haploid

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12
Q

sex cells

A

cells in the germ line (produces gametes, or egg and sperm cells)
Female gametes: ova or egg cells
Male gametes: sperm
Are haploid cells

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13
Q

haploid cells

A

In each haploid cell, human sex cells have TOTAL of 23 chromosomes (since they aren’t paired)
Total number of chromosomes in diploid cells → described as n

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14
Q

what are the components of chromosome structure?

A

Centromere: divides the chromosomes into the “p” arm (small) and “q” arm (long)
Telomeres: at both ends of each chromosome
Chromatid: one of the two identical copies/halves of a chromosome

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15
Q

where are chromosomes found in the cell?

A

nucleus

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16
Q

how is each band within a region numbered? (directionality)

A

Each band within a region is numbered centromere TO telomere

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17
Q

“p” arm vs “q” arm

A

“p” arm (small) and “q” arm (long)

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18
Q

band nomenclature: ie. q21.1

A

“q-two-one-point-one” = q arm, region 2, band 1, subband 1 (NOT q-twenty-one-point-one)

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19
Q

what are the effects of chromosomal rearrangements?

A

Change chromosomal structure
Can alter the function of one or more genes and can change the pattern of gene transmission

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20
Q

how do transposable elements cause chromosomal rearrangements?

A

transposable elements (aka jumping genes): DNA sequences that can change their position within the genome, potentially altering the function and regulation of genes

Transposable elements can insert into genes → alter their function and can cause chromosomal rearrangements

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21
Q

what are the four types of chromosomal rearrangements?

A

Deletion (deficiency): removes a segment of DNA
Duplication: results in an increase in copy number of a particular chromosomal region (occurs in ALL organisms)
Inversion: a segment of chromosome is reversed end to end (rotated 180 degrees)
Translocation: the exchange of genetic material between 2 NON-HOMOLOGOUS chromosomes

22
Q

interstitial vs terminal deletions

A

Interstitial: deletion located WITHIN a chromosome
Terminal: deletion that removes the END of a chromosome

23
Q

intragenic vs multigenic deletions

A

Intragenic: small deletions only affecting ONE gene
Multigenic: deletions that span MULTIPLE genes

24
Q

homozygous deletion (del/del)

A

Occurs when BOTH alleles of a gene are deleted from an individual’s chromosomes
If deleted region does NOT contain any genes essential for survival → an individual homozygous for a deletion will live
Large deletions spanning multiple genes → results in homozygous lethality (removing essential genes)

25
Q

Heterozygous deletion (Del/+)

A

Occurs when only ONE allele of a gene is deleted while the other allele remains intact
Some heterozygotes are viable and fertile, but other instances might be detrimental

26
Q

In general, humans cannot survive even as heterozygotes with deletions that remove more than around ___ of the genome

A

3%

27
Q

what is an example of a heterozygous deletion?

A

‘Cri du chat’ syndrome (aka ‘5p minus’ syndrome): a deletion of all or part of the short p-arm of chromosome 5 → often don’t live past childhood

28
Q

what is an example of a duplication?

A

red-green color blindness (aka daltonism)
the OPN1LW (red) and OPN1MW (yellow, green) genes are located
on the X chromosome –> affects more men than women

29
Q

chromosomal inversions

A

A rearrangement in which a segment of chromosome is reversed end to end (rotated 180 degrees)
Occurs when TWO breaks occur within ONE chromosome → the genetic material in between the breaks in inverted

Relatively rare events and unlikely that multiple patients with the same inversion are found
EXCEPTION: if the inversion breakpoint falls within or near a gene that has previously been associated with the disorder through other types of mutations

30
Q

what are the 2 types of inversion mutations?

A

pericentric
paracentric

31
Q

what is an example of inversion mutation?

A

hemophilia A: recurrent inversion mutations in the coagulation factor VIII gene on the X chromosome causes hemophilia A (also caused by mobile genetic element-induced mutations)

individuals with hemophilia A experience prolonged bleeding because their blood doesn’t clot properly –> can lead to excessive bleeding from even minor injuries, and, in more severe cases, spontaneous bleeding (internal bleeding without any clear injury).

32
Q

pericentric vs paracentric inversion mutations

A

Pericentric: break occurs between TWO arms of a chromosome and the inverted segment DOES include the CENTROMERE (remember: pEri → cEntromere)
Paracentric: a break to only ONE arm of chromosome and inverted segment does NOT include centromere

33
Q

reciprocal translocation

A

a two -way translocations: exchange chromosomal segments between 2 DIFFERENT (non-homologous) chromosomes → often balanced
Most typical type of translocation

34
Q

what are the three types of chromosomal translocations?

A

reciprocal
nonreciprocal
robertsonian
- occurs between non-homologous chromosomes

35
Q

balanced translocation

A

when the 2 breaks do NOT pass through a gene and there is NO GAIN or LOSS of material

36
Q

nonreciprocal translocation

A

one-way translocation: transfer a chromosomal segment from one chromosome to a NONHOMOLOGOUS chromosome → receiving chromosome becomes longer than normal/original size and the transferring chromosome becomes shorter

37
Q

robertsonian translocations

A

Usually occurs in acrocentric chromosomes (small p-arm: ie. 13, 14, 15, 21, 22)
Most common kind of chromosome rearrangement known in people: about 1 of 1000 newborns have this type of translocation
balanced form
unbalanced form

38
Q

what are the two forms of robertsonian translocation?

A

Balanced form: normal phenotype
Reciprocal exchange between 2 acrocentric chromosomes → results in…
1 large metacentric chromosome (fusion of the long q arms) and 1 very small chromosome (fusion of the short p arms) –> this chromosome carries so few genes that it does NOT cause genetic imbalance (only loses from 46 → 45 total chromosomes)

Unbalanced form: produces chromosome imbalance
Causes multiple malformations and mental retardation

39
Q

give two examples of robertsonian translocations

A
  1. trisomy 13 (patau syndrome): extra copy of Chr 13 (usually lethal within 1yr if infant survives to even be born)
  2. trisomy 21 (down syndrome): extra copy of Chr 21 (t(14;21))
40
Q

A man with robertsonian translocation on Chr 21-14 marries healthy woman.
Probability to have a down syndrome child:
Probability to have a healthy child (no carrier):
Probability to have a child with the Roberstonian carrier (but live, normal):
Probability to have a down syndrome child out of the alive children:
Probability to have an alive child:
Probability to have a carrier child out of the live child:

A

Probability to have a down syndrome child: 1/6
Probability to have a healthy child (no carrier): 1/6
Probability to have a child with the Roberstonian carrier (but live, normal): 1/6
Probability to have a down syndrome child out of the alive children: 1/3
Probability to have an alive child: 1/2
Probability to have a carrier child out of the live child: 1/3

41
Q

what are 2 chromosomal translocations found in cancer?

A
  1. Chronic myeloid leukemia (CML):
  2. Alveolar rhabdomyosarcoma (ARMS)
42
Q

Chronic myeloid leukemia (CML)

A

Chr 9 (region q34) and Chr 22 (region q11) → t(9;22)(q34;q11)
- the ABL1 gene normally on Chr 9; BCR gene normally on Chr 22
–> results in an oncogenic BCR-ABL1 gene fusion, which creates a philadelphia chromosome (PH or Ph’) which is talking about the changed Chr 22

43
Q

Alveolar rhabdomyosarcoma (ARMS)

A

Translocations → causes the fusion (chimeric) gene: t(2;13)(q35;q14) → PAX3-FOXO1
ARMS having the fusion gene → worst clinical outcome

44
Q

Chromosomal translocation nomenclature: t(9;22)(q34.1;q11.2)

A

First set of parentheses = the chromosomes involved
9 = first chromosome involved;
22 = second chromosome involved

Second set of parentheses = the chromosome bands involved + indicates the breakpoints on the arms
q34.1 = q-arm region 3 band 4 sub-band 1
q11.1 = 1-arm region 1 band 1 sub-band 2

45
Q

What are acrocentric chromosomes and some examples?

A

chromosomes with a short p-arm
Chr 13, 14, 15, 21, 22

46
Q

What is the most common kind of chromosome rearrangement known in people?

A

robertsonian translocations (1 in 1000 newborns)

47
Q

What is the most typical type of translocation?

A

reciprocal translocations

48
Q

what are the chromosomes involved in trisomy 13 (patau syndrome)?

A

Chr 13 and Chr 14 (extra copy of Chr 13)

49
Q

what are the chromosomes involved in trisomy 21 (down syndrome)?

A

Chr 14 and Chr 21 (extra copy of Chr 21)

50
Q

What does a carrier of trisomy 13 and trisomy 21 look like?

A

carrier of trisomy 13 and trisomy 14 is the balanced form of Robertsonian translocation

trisomy 13: 1 Chr13, 1 Chr 14, 1 metacentric Chr of 13&14
trisomy 21: 1 Chr14, 1 Chr 21, 1 metacentric Chr of 21&14
–> the total number of each type of chromosome is still 2 of each which is why they have normal phenotype

51
Q

What does an affected individual with trisomy 13 or trisomy 21 look like?

A

trisomy 13: 1 Chr 13, 1 Chr 13, 1 combined Chr of 13&14, 1 Chr 14
–> net: 3 Chr 13, 2 Chr 14

trisomy 21: 1 Chr 21, 1 Chr 21, 1 Chr 14, 1 combined Chr of 14&21
–> net: 3 Chr 21, 2 Chr 14

Biochem Exam 2 (6 decks)

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