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Medical Genetics > Lab 5 - Chromosomes and Their Aberrations > Flashcards

Lab 5 - Chromosomes and Their Aberrations Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

How many chromosomes does all cells in the human organism contain?

A

23 pairs, total of 46 chromosomes. One from the mother and one from the father.

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2
Q

How many chromosomes does each egg cell and each sperm cell contains?

A

A haploid set of 23 chromosomes (1n)

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3
Q

How many chromosomes does a fertilized egg contain?

A

A diploid set of 46 chromosomes (2n)

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4
Q

Autosome

A

An autosome is a chromosome that is not an allosome (a sex chromosome).

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5
Q

How many pairs of autosomes is there in male and female?

A

22 pairs

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6
Q

Sex chromosomes

A

Males: XY
Females: XX

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7
Q

Centromere and its divisions

A

The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids (a dyad). It contains a repetitive-satellite DNA sequences and divides the chromosomes into a short arm p (petite) and long arm q.

Can be divided to:
Metacentric
Submetacentric
Acrocentric chromosomes

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8
Q

Metacentric chromosome

A

Centromere is positioned in the middle

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9
Q

Submetacentric chromosome

A

Centromere is positioned between the middle and the end of the chromosome

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10
Q

Acrocentric chromosomes

A

Centromere is positioned at the end, separating a normal long arm from a short arm that contains only multiple (hundreds) copies of rRNA genes (chromosomal satellites)

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11
Q

Sequence homology

A

Strictly, refers to the situation where nucleic acid or protein sequences are similar because they have a common evolutionary origin

Enables binding and recombination at meiosis, which is not only essential for the generation of haploid set of chromosomes, but also an important factor in the diversification of the species

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12
Q

Histones

A

Highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes

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13
Q

Core histones and Linker histone

A

Core histones: H2A, H2B, H3, H4

Linker histone: H1

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14
Q

Nucleosome

A

Basic packing unit in a chromosome that consist of 8 core histones and 146 base pairs of DNA

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15
Q

How many core histones is the DNA double strand wound around?

A

8 core histones, two of each core histones

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16
Q

How many full twists does the DNA complete?

A

1.75 full twists, which correspond to 146 base pairs

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17
Q

Chromatin

A

The combination of DNA and (histone and nonhistone) proteins that makes up a chromosome

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18
Q

Euchromatin

A

Relatively loosed packed chromatin that represents transcriptionally active DNA or may be recognized as light bands during chromosome analysis (G-banding)

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19
Q

Heterochromatin

A

Highly condensed chromatin that represents transcriptionally inactive (often repetitive) DNA or may be recognized as dark bands during chromosome analysis (G-banding)

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20
Q

Telomeres

A

A region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes

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21
Q

Telomeres repeats

A

TTAGGG

22
Q

Euploidy

A

A normal diploid chromosome complement (2N) of 46 chromosomes (46,XX or 46,XY)

23
Q

Aneuploidy

A

Changes in the total number of chromosomes

They arise from faulty segregation of the chromosomes in meiosis or mitosis

The risk is largely dependent of maternal age

Not inherited

24
Q

Somatic mosaic

A

Somatic mosaicism occurs when the somatic cells of the body are of more than one genotype. In the more common mosaics, different genotypes arise from a single fertilized egg cell, due to mitotic errors at first or later cleavages

25
Q

Polyploidy

A

Is the state of a cell or organism having more than two paired (homologous) sets of chromosomes.

Multiples of haploid chromosome complement of greater than 2n

26
Q

Triploidy cause

A

Fertilization of an oocyte by two spermatozoa.

27
Q

Digynic triploidy

A

Maternal origin. Fertilization of a diploid ovum by a haploid sperm

Growth retardation, large head, the placenta is small and fibrotic

28
Q

Diandric triploidy

A

From the father. Fertilization of a haploid ovum by two sperm. Results in a partial mole with large cystic placenta, normal size fetus with microcephaly

29
Q

Tetraploidy

A

A quadruple chromosome complement.

92,XXXX or 92,XXYY

30
Q

Monosomies

A

One copy of chromosome. Result in a very early spontaneous miscarriage

Example: Monosomy X (Turner syndrome)

31
Q

Most common cause of chromosome structual abnormalities?

A

Deletions

Other causes are ionizing radiation, viral infections, various chemicals

32
Q

Balanced structural chromosome abnormality

A

No loss or gain in the chromosomes despite recombination, the entire genetic material is normal

33
Q

Unbalanced structural chromosome abnormality

A

Gain or loss of chromosome segments and are clinically relevant. Structurally denoted according to the origin of their centromere, called derivative chromosomes

34
Q

Deletion

A

When a chromosome breaks at two sites and the segment between them get lost

35
Q

Contiguous gene syndrome

A

The presence of several distinct (dominant-inherited) monogenic disorders, caused by deletion affecting several neighboring genes

36
Q

Duplication

A

A chromosome segment appears in two (often sequentially inserted) copies on a single homolog. Most often by a nonhomologous recombination in the first meiotic division

37
Q

Inversion

A

When a chromosome segment between two breaks is rotated 180 degrees before reinsertion. The gene copy and number remains the same

38
Q

Pericentric inversions

A

Include the centromere. One breakpoint is on the short arm and one on the long arm

39
Q

Paracentric inversions

A

Do not include the centromere

40
Q

Isochromosome

A

Unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other. The chromosome consists of two copies of either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a simultaneous duplication and deletion of genetic material.

41
Q

Ring chromosome

A

When a chromosome breaks at both ends and the ends join together.

Ex: Turner syndrome

42
Q

Marker chromosome

A

Small fragment of a chromosome, found by FISH testing or array analysis. They develop as either isochromosomes or inverted duplications.

Ex: Pallister-Killian syndrome (isochromosomes 12p), Cat-eye syndrome (inverse duplication, 22q11)

43
Q

Translocation

A

Exchange of chromosome segments between nonhomologous chromosome

44
Q

Reciprocal translocation

A

Transfer of chromosomal material from one chromosome to another, and vice versa. The total number of chromosomes remains unchanged.

45
Q

Robertsonian translocation

A

Fusion of two acrocentric chromosomes in the centromeres, with the loss of the respective short arms and the reduction of total number of chromosomes to 45

Robertsonian translocations generally occur in the five acrocentric chromosome pairs, namely 13, 14, 15, 21 and 22.

46
Q

Mosaic

A

The occurrence of two or more genetically different cell lines within a tissue or within an organism

47
Q

Germline mosacism

A

Mutations that occur de novo in a family may have arisen relatively early in germ cell development, resulting in a significant number of gametes that carry the mutation

48
Q

Mosaicism can cause

A

Mosaic down syndrome (mosaic trisomy 21)

Neurofibromatosis type 1

49
Q

Karyotype

A

Number and appearance of the chromosomes in an individuals cell

50
Q

Components of a karyotype

A

Total number of chromosomes and the specific sex chromosomes, followed by any specific numerical abnormality and/or structural abnormality that is present

51
Q

Karyotype of a male with down syndrome

A

47,XY,21

Medical Genetics (10 decks)

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