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FunMed Genetics > The human genome and chromosomes > Flashcards

The human genome and chromosomes Flashcards

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1
Q

why is the human genome useful

A
  • Useful for understanding the structure of genomes
  • Understanding the biology of genomes
  • Understanding the biology of disease
  • Advancing the science of medicine
  • Improving the effectiveness of healthcare
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2
Q

describe the structure of the nuclear genome

A
  • 3.2x109 base pairs
  • 20,000 protein coding genes
  • 46 chromosomes
  • Inherited from both parents
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3
Q

how many chromosomes does each somatic cell have

A

Each somatic cell has 46 chromosomes which are mostly clearly seen at the metaphase stage of the cell cycle

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4
Q

how can you identify chromosomes in the karyotype

A

using G bands

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5
Q

what are G bands

A
  • staining technique used in karyotype, used to identify abnormalities in the chromosome
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6
Q

what is the short arm called (above the centromere) in the chromosome

A

p

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7
Q

what is the long arm called (below the centromere) in the chromosome

A

q

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8
Q

what does the centromere do and describe the structure

A
  • Keeps sister chromatids together
  • Attaches sister chromatids to microtubules
  • Repetitive DNA
  • Breaks during DNA replication
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9
Q

What does the G light band do and describe the structure

A
  • Gene rich – has lots of genes compared to the dark ones which have a few genes
  • GC-rich – lots of G and C nucleotides
  • Early replicating
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10
Q

What does the G dark band do and describe the structure

A
  • Gene poor
  • AT rich – lots of A and T nucleotides
  • Late replicating
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11
Q

what is an autosome

A

any chromosome that is not a sex chromosome and occurs in pairs

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12
Q

what are the sex chromosomes

A

XX female

XY male

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13
Q

what does diploid mean and how many chromosomes are in diploid cells

A

describes cells and nuclei or organisms in which each chromosome except the Y chromosome is represented twice

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14
Q

what does haploid mean and how many chromosomes are in haploid cells

A

Haploid are organisms that have a single set of unpaired chromosomes

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15
Q

what does aneuploidy mean

A

this is an abnormal number of chromosomes

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16
Q

Name the genes that you need to know

A
  • COL5A2 (2) - collagen
  • COL5A1 (9) – collagen
  • HBA1 (16) - alpha globin for haemoglobin
  • HBA2 (16) - alpha globin for haemoglobin
  • BTK (x) - crucial role in B cell development
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17
Q

What are coding sequences

A

encode proteins, constitute about 1.6% of human genome

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18
Q

what are non-coding sequences

A

encode other molecules (such as tRNA and rRNA) and regulates coding DNA function. Encode intergenic regions and introns: include control elements (such as enhancers and promoters) and repetitive sequences (telomeres)

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19
Q

what are axons

A

regions of gene that encode protein sequences

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20
Q

what are introns

A

non coding regions between the exons in genes

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21
Q

what are control elements

A

sequences such as promoters and enhancers that regulate transcription

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22
Q

what are pseudogene

A

– non-functional copy of a gene, arises from gene duplication followed by deleterious mutation in one copy

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23
Q

what are repetitive sequences

Study These Flashcards
A

– tandem repeats of closely related DNA sequences, constitute about 40% of human genome

24
Q

describe the process of making RNA (transcription)

Study These Flashcards
A
  1. Part of gene read from transcription start site – this is the point at which DNA starts to e read
  2. Transcirpted to pre-mrna include code from exons and introns
  3. Splicing gets to mRNA
  4. Then this goes through translation to make the protein
  5. In the upstream region there are the control elements these are the enhancer and promoter and they work together through chromatin looping.
    - If there is a mutation in the enhancer region it can prevent the chromatin looping and silence a gene
25
what do the intergenic region contain
contain control elements such as enhancers and promoters
26
what do splicing signals do
they remove the introns from the mRNA
27
what do non coding RNAs do
they regulate messenger RNA
28
define disomy
this is two copies of a chromosome
29
define polyploidy
gain of one or more haploid chromosome sets
30
define monosomy
one copy of a chromosome
31
define trisomy
three copies of a chromosome
32
define tetrasomy
four copies of a chromosome
33
define deletion
part of a chromosome containing genes and regulatory sequences is lost
34
define duplication
this is when a piece of chromosome may be duplicated, over expression of genes can be harmful because too many of certain proteins or gene regulating nucleic acids may disrupt metabolism
35
define inversion
a section of a chromosome may break off turn through 180 degrees and then join again - although all genes are still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed
36
describe the sex chromosome diseases
turner syndrome | klinefelter syndrome
37
describe all chromosome diseases
- Triploidy
38
describe the key features of Down syndrome
- trisomy 21 - 1 in 700 births - 60% aborted - 20% stillborn - Distinct facial appearance - Marked muscle hypotonia as a baby (floppy) - Learning difficulty - Congenital heart malformations - Have a single palmar crease
39
describe what can cause Down syndrome
- 95% have three separate copies of chromosome 21 - 4% have extra copy of chromosome 21 because of robertsonain translocation - 1% have mosaicism with normal and trisomy 21 cell lineages milder features because of the presence of the normal cells, this occurs post zygotically
40
what is down syndrome due to
- Trisomies associated with an increase in maternal age - Eggs held and crossing over stage in meipsis from approx. 6 months gestation - Wear and tear with increasing maternal age
41
describe Edwards syndrome
- 1 in 3000 births - Multiple malformations - Clenched hands with overlapping fingers - Die within first few weeks - If survives sever mental retardation
42
describe patau syndrome
- 1 in 5000 births - Multiple malformations - Affects midline structures particularly incomplete lobation of brain, cleft lip, congenital heart disease - Die within first few weeks - If survives then severe mental retardation
43
describe klnefelter syndrome
- 47 XXY - 1 in 1000 - Infertility - Poorly developed 2ndy sexual charatstics - Tall
44
describe Turner syndrome
- 45 X - 1 in 5000 - 99% lost in pregnancy - Short sature - Primary amenorrhoea - Congenital heart disease
45
How can you diagnose conditions prenatally
- amniocentesis - chronic villus sampling - non invasive techniques - for Down syndrome
46
describe amniocentesis
- Genetic testing of cells from the amniotic fluid - Ultrasound guidance – transabdominal sampling - 15-18 weeks
47
describe chronic villus sampling
- Genetic testing of tissue from the placenta - Ultrasound guidance – trans-abdominal or trans-cervical sampling - 12-14 weeks
48
describe non-invasive techniques
- For down syndrome: - Ultra sound imaging of nuchal translucency - 11-14 weeks
49
describe the X chromosome
- Contains 1100 genes - One of the two x chromosomes is randomly inactivated, therefore adult female is a mosaic of clones containing one or other x chromosome in an active state - Ensures that each somatic cell has only one functional x like in male somatic cells - Pseudoautosomal regions do not undergo activations as they contain genes which are present on the Y chromosomes and are involved in development
50
describe the Y chromosome
- Variable in size - Few genes - Many repeat sequence - Encodes the sex determining region of the y chromosome – SRY gene - SRY encondes a protein that is a member of the HMG group of transcription factors - SRY is responsible for male sex determination - Other genes on the Y chromosome are also important for male determination
51
Describe X inactivation
1. Xist is a long non-coding RNA which is encoded in the X inactivation centre on the X chromosome 2. Xist joins to the X chromosome from which it is expressed, 3. This leads to chromatin changes and spatial reorganisation of the chromosome leading to transcriptional inactivation and formation of the BARR BODY 4. males have no Barr bodies and females have 1 Barr body - X inactivation is reversed only in the germ cells - Barr Bodies indicate the number of inactive chromosomes
52
what does a telomere do
- Protective DNA and protein cap - Repetitive DNA – same sequence over and over again (TTAGG) and protein - Prevents DNA damage and chromosome fusion
53
describe translocation
joining one part of a chromosome to a second chromosome, in a balanced translocation part of the second chromosome joins to the first chromosome so there is no net gain or loss of material
54
describe robertsonain translocation
two chromosomes joining at their centromeres
55
Name the autosome causing diseases
- Down syndrome - Edwards syndrome - Patau syndrome

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