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Y1 PRINCIPLES > Genetics > Flashcards

Genetics Flashcards

1
Q

Each human has how many pairs of chromosomes?

A

23 pairs in total 22 autosomal pairs, 1 sex-linked pair

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2
Q

Direction DNA chain is read?

A

5 Carbon — 3 Hydroxyl (strands in antiparallel fashion)

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3
Q

Bases in DNA vs RNA

A

A-T, C-G

A-U, C-G

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4
Q

Role of histone proteins

A

+ proteins that bind to negative sugar-phosphate backbone of DNA —– NUCLEOSOMES

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5
Q

G0 phase of the cell cycle

A

Most cells are resting, carrying out their normal function

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6
Q

G1 phase of the cell cycle

A

1st growth phase as chromosomes become ready to be replicated

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7
Q

S phase of the cell cycle

A

DNA replication occurs

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8
Q

G2 phase of the cell cycle

A

2nd growth phase involving proteins etc.

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9
Q

M phase of the cell cycle

A

Mitosis - mechanical separation of cell into two daughter cells Two daughter cells are identical, diploid cells
PMAT: prophase, metaphase, anaphase, telophase

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10
Q

Stage cytokinesis occurs in the cell cycle

A

Separation of cytoplasm into daughter cells - TELOPHASE

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11
Q

Variation occurs during meiosis by two main methods, which are?

A

Crossing over Independent segregation of homologous chromosomes

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12
Q

In meiosis, one diploid cell becomes..

A

Four haploid daughter cells

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13
Q

Sequence of bases that initiates the transcription of certain genes

A

Promoter

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14
Q

Sequence of bases that signal the beginning and end of transcription

A

Start and stop codons

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15
Q

Chemical that unwinds DNA

A

RNA polymerase

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16
Q

Sense strand is the binding strand to DNA - True/False

A

False - exact copy of sense strand (antisense is the binding strand)

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17
Q

Difference between introns vs exons

A

INTRONS: non coding sequences of mRNA not in final protein (spliced out)
EXONS: coding sequence of mRNA not in final protein (1-2% codes)

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18
Q

Examples of sequence variations between/within genes?

A

Single nucleotide polymorphisms (SNPs) Deletions/duplications

Changes in promotor or exon sequence
Copy number variations (CNVs) - extra or missing stretches of DNA

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19
Q

A polymorphism is…

A

A change in the genome that does not cause disease in its own right, but can predispose to a common disease

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20
Q

Chromosome 22 looks like a…

A

Teddy bear

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21
Q

The term used to describe a picture acting as description of persons chromosomal make up

A

Karyotype

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22
Q

A chromosome consists of…

A

Telomeres at each end Short arm (p) Centromere Long arm (q)

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23
Q

A chromosome is metacentric/acrocentric/telocentric if…

A

Both arms are roughly the same length
The p (short) arm is so short it is hard to observe
The centromere is located at the terminal end of the chromosome

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24
Q

An aneuploidy is…

A

An abnormal number of chromosomes Monosomy - missing chromosome from one pair Trisomy - extra chromosome in a pair

25
Q

Reciprocal translocations are when…

A

Segments from two different chromosomes have been exchanged

26
Q

Robertsonian translocations are when…

A

A chromosome attaches to another chromosome at the centromere Only occurs with 13, 14, 15, 21, 22 - two acrocentric chromosomes stuck end-end creating a normal phenotype

27
Q

Monosomy of the sex chromosomes causes…

A

Turners syndrome 45XO

28
Q

Trisomy of chromosome 21 causes…

A

Downs syndrome

29
Q

What is FISH?

A

DNA probes specifically bind to areas of individual chromosomes and apply a fluorescein stain to make the chromosome visible Useful for detecting aneuploidies

30
Q

What is Array CGH?

A

Genomewide search to detect polymorphisms using dye and a scanner to show abnormalities between the sample and a reference (QUANTITIES)

31
Q

What is G banding?

A

Forces bands to appear on chromosomes using stains, helping to identify particular genetic diseases - unique pattern of bands for each chromosome

32
Q

Extra chromosome 18 causes…

A

Edwards syndrome

33
Q

Extra Y/X chromosome causes…

A

Klinefelters syndrome

34
Q

Methods of targeted testing for small genetic changes…(2)

A

PCR - original DNA strand is duplicated and then copies are made increasing the mutation which is detected when compared to the trace
NGS - DNA fragmented and rebuilt using the reference to show mutations

35
Q

Types of point mutations

A

MISSENSE single nucleotide change creates a codon that codes for a different AA
NONSENSE single nucleotide change codes for a premature stop codon
INSERTION
DELETION

36
Q

Types of genetic changes (3)

A

MUTATION
POLYMORPHISM
VARIANT OF UNKNOWN SIGNIFICANCE

37
Q

Autosomal dominant disease occurs when…

A

There is one faulty copy of the gene Seen in all generations 50% risk of affected child if parent affected

38
Q

Autosomal recessive disease occurs when…

A

There are 2 faulty copies of the gene Often only one generation affected 25% risk of affected child if parents are carriers Increased likelihood if parents are related

39
Q

X-linked disease occurs when…

A

The disease is carried on the X-chromosome

  • only 50% of male children of a female carrier affected
  • 50% of female children of a female carrier affected
  • All male children of a male carrier normal
  • All female children of a male carrier will be carriers
40
Q

What is a caveat?

A

Female carrier shows mild features of X-linked disease

41
Q

Process preventing a double dose of gene products

A

X INACTIVATION: one X chromosome of females randomly inactivated using XIST gene of XQ13 via METHYLATION

42
Q

Methylation inhibits which process?

A

DNA transcription - chemic modification that does not change base sequence but interacts with histones on DNA

43
Q

The term used to describe X inactivation ‘gone wrong’ is….

A

SKEWING: Inactivation of one X chromosome favoured over another - mutation in XIST gene - results in uneven number of cells with X chromosome inactivation

44
Q

Penetrance is defined as…

A

The likelihood of having the disease given you have the genetic mutation

45
Q

Mendelian inheritance encompasses which disorders?

A

Autosomal dominant
Autosomal recessive
X-linked
Mitochondrial

46
Q

Penetrance in…

a) Mendelian disorder
b) Multifactorial disease

A

a) High - controlled by mutation in single gene with a small environmental input
b) Low - genetic change attributed to environmental input

47
Q

Common disease - common variant hypothesis

A

Common disease causing variants will be found in all human populations which show a disease but not necessarily expressed in phenotype

48
Q

What is imprinting? What is it controlled by?

A

Variation in gene expression depending on which parent you inherit the gene from e.g. in Angelman’s syndrome, mother’s UBE3A works fine but father’s is methylated - controlled by methylation

49
Q

Mitochondrial disease occurs when…

A

Diseased mitochondria passed from mother to child

50
Q

Heteroplasmy is when

A

Different daughter cells contain different proportions of mutant mitochondria (similar to mosaicism)

51
Q

What is mosaicism?

A

Occurs when cells within the same person have a different genetic makeup (causes cancer)

52
Q

Epigenetic variation describes…

A

Functional modifications to the genome that do not involve a change in the nucleotide sequence

53
Q

Where are the 2 checkpoints in the cell cycle where DNA can acquire mutations?

A

Between G2 and M Between G1 and S

54
Q

What is the function of oncogenes?

A

Promote cell division

55
Q

What is the function of tumour suppressors?

A

Inhibit cell division

56
Q

Only one copy of the tumour suppressor gene is required to be mutated for cancer to occur. True/False?

A

False 2 copies required (2 Hit Hypothesis)

57
Q

Cancer is most often inherited as a high penetrance Mendelian disorder. True/False?

A

False More usually multifactorial

58
Q

Risk of breast cancer:

a) High
b) Medium
c) Low (population risk)

A

a) BRCA1 mutation
b) mother/sister breast cancer at 45
c) mother with breast cancer at 70

Y1 PRINCIPLES (10 decks)

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