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PHAY0003 > Genetics > Flashcards

Genetics Flashcards

1
Q

What is the genetic code?

A

The instructions of a gene that codes how to make a protein

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2
Q

What is the genome?

A

The entire genetic material present in a cell of an organism, over 3 billion base pairs

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3
Q

How is the human genome organised?

A

22 paired chromosomes (autosomal) and a pair of sex chromosomes which are all large linear DNA molecules found in the nucleus

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4
Q

What is genetic inheritance?

A

The transfer of traits from parents to offspring, passing on the genetic material through reproduction

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5
Q

Who first studied genetic inheritance?

A

Mendel

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6
Q

Describe briefly the work of Mendel

A

He grew thousands of pea plants in his garden. He studied 7 traits including seed shape and colour. He crossed plants through cross-pollination and studied the inheritance of genes

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7
Q

What is the dominant trait?

A

The trait that is expressed by the alleles regardless if both or one allele is present

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8
Q

What is the difference between homozygous and heterozygous genotypes?

A

Homozygous: 2 identical alleles
Heterozygous: 2 different alleles

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9
Q

What is the recessive trait?

A

The trait expressed when the dominant allele is absent.

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10
Q

What is the law of segregation?

A

When an organism makes gametes, each gamete receives one allele for each trait per parent at random

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11
Q

What is the difference between gene and allele?

A

A gene is a section of DNA responsible for a certain trait e.g eye colour, hair colour, height. An allele is a form of the gene e.g blue eyes, green eyes, brown hair, blonde hair

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12
Q

What is the law of independent assortment?

A

Genes for different traits are inherited independently of one another

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13
Q

What is the genotype?

A

The set of alleles present for a gene

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14
Q

What is the phenotype?

A

The observable traits for

a gene depending on the alleles present

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15
Q

What are the 6 flaws behind Mendel’s model?

A

Genes tend to have more than 2 alleles.
Incomplete dominance: 2 alleles can produce a phenotype which is a mix of both rather than one dominating.
Codominance: 2 alleles may both be present rather than one dominating.
Lethal alleles: Some genes can prevent survival when homozygous or heterozygous.
Pleiotropy: Some genes affect more than one characteristic.
Sex linkage: genes carried on the X or Y chromosome have different inheritance patterns

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16
Q

What are homologous chromosomes?

A

When the pair of chromosomes from the father and mother are identical

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17
Q

How many human pairs of chromosomes are homologous and how many are non-homologous?

A

22 pairs are homologous, the sex chromosome pair is non-homologous

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18
Q

What is the definition for gene?

A

A segment f DNA that codes for the synthesis of one particular protein

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19
Q

What is epigenetics?

A

The study of changes in an organism not caused by an alteration of the genetic code - it is caused by a modification of gene expression as they age. E.g organisms with the same genetics can have different observable traits

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20
Q

Give an example of an epigenetic mechanism

A

DNA methylation, 3-year-old twins showed very similar distribution of DNA methylation where as 50-year-old twins showed changed to their distribution of DNA methylation

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21
Q

What is a mutation?

A

A change in nucleotide sequence of the genome of an organism

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22
Q

Give 3 ways mutations can occur

A

Errors during DNA replication
Damage to DNA or the repair pathways
Insertion or deletion of segments of DNA due to mobile genetic elements

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23
Q

What is evolution and natural selection caused by?

A

Mutations/ genetic variation

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24
Q

What are the 3 point mutations of DNA?

A

Substitution, insertion, deletion

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25
Q

Describe substitution mutation

A

One base incorrectly added during replication and so changes the complementary strand, it can change the amino acid sequence

26
Q

Describe insertion mutation

A

One or more extra nucleotides are inserted into replicating DNA resulting in a frameshift in the amino acid sequence

27
Q

Describe deletion mutation

A

One or more nucleotides are “skipped” during replication resulting in a frameshift in the amino acid sequence

28
Q

Describe the 3 results to point mutations

A

Silent: no change
Nonsense: A stop codon is made
Missense: the amino acid coded is changed

29
Q

What is the difference between conservative and non-conservative missense point mutations?

A

Conservative: Different amino acid but of the same kind e.g still basic
Non-conservative: different amino acid with different type e.g changed from basic to polar

30
Q

Describe the 4 chromosomal mutations

A

Inversion: one region of chromosome is flipped and reinserted
Deletion: A region (gene) of chromosome is lost
Duplication: A region of chromosome is repeated increasing the dose of that gene
Translocation: A region form a chromosome is attached to another chromosome

31
Q

Describe the 2 copy number variations

A

Gene amplification: The number of copies of a gene is increased and are positioned one after another
Expanding trinucleotide repeat: A triplet in a gene is repeated one after another

32
Q

Give an intrinsic (natural) risk factors for mutations occuring

A

Random errors in DNA replication

33
Q

Give 3 non-intrinsic (unnatural) risk factors for mutations that are endogenous

A

Biological aging
Hormones
Inflammation

34
Q

Give 3 non-intrinsic (unnatural) risk factors for mutations that are exogenous

A

Radiation
Chemical carcinogens
Tumour causing viruses

35
Q

What is polymorphism

A

More than one possibility of something, variability between individuals

36
Q

What are SNPs?

A

Single Nucleotide Polymorphism, when one nucleotide is different

37
Q

What is STRPs?

A

Short Tandem Repeat Polymorphism, when a triplet is repeated making the gene different

38
Q

What is a genetic disorder?

A

A health condition caused by abnormalities in the genome

39
Q

How do genetic disorders occur?

A

Mutations in either a single gene, multiple genes or by a chromosomal abnormality

40
Q

When are mutations inherited (3)

A

Before embryonic development
If both parents are carriers of a faulty gene making it observable
Through being inherited by a parent with the disorder

41
Q

When is a genetic disorder also a hereditary disease?

A

When it is inherited form one or both parents

42
Q

What does it mean when a disease is multifactorial?

A

Combinations of genes are affected, epigenetics plays a big role

43
Q

What is an autosomal dominant disorder?

A

When a single mutated allele is dominant resulting in the disorder even though the other is normal. e.g Huntingdon’s disease

44
Q

What is autosomal recessive disorders?

A

When the mutated allele is recessive and so is inherited so only affects the person if both parents are carriers. E.g Cystic fibrosis

45
Q

Why are males more affected by X-linked recessive mutations than females

A

Males only have one X chromosome, therefore if this is mutated, the make will have the disorder eve if it is recessive. However, females have 2 X chromosomes and so if the mutated allele is recessive, the normal dominant one will mean the female is just a carrier of the disorder unless both chromosomes are mutated. E.g Red-green colour blindness

46
Q

What is the NHS Genomic Medicine Service?

A

A service that allows the whole genome to be sequences to help improve healthcare. It aims to sequence 500,000 genomes by 2023/24 including for all children with cancer or seriously ill with a genetic disorder

47
Q

What is DNA sequencing?

A

The process of determining the sequence of nucleotides in a section of DNA and was first developed by Frederick Sanger

48
Q

What is required for Sanger Sequencing? (5)

A

DNA template
Oligonucleotide primer (starter) that has 32P at the 5’ end
DNA sequencing polymerase
4 deoxynucleoside triphosphates (dNTPs)
4 dideoxy nucleoside triphosphates (lack 2’ and 3’-OH groups) (dDNTPs)

49
Q

Why do dideoxy nucleoside triphosphates act as chain terminators?

A

They are missing the OH so the chain cannot continue

50
Q

Describe Sanger Sequencing

A

The 5 required parts are added to 4 test tubes - one for each ddNTP base. The DNA begins to form using the primer, dNTPS and polymerase. However, since there is also a ddNTP in the test tube, these sometimes substitute in for dNTPS, causing the chain to terminate. Different length chains form but they will always end with the terminator nucleoside that was added to that test tube e.g Tube 1 will end in ddTAP, Tube 2 will end with ddTGP ect. The fragments then undergo gel electrophoresis which separates them based on size and the sequence can be worked out

51
Q

Describe NGS (next generation sequencing)

A

An overall term used to describe modern sequencing technologies. It is much cheaper and faster than Sanger Sequencing. Includes various methods such as Illumina (Solexa). It is able to produce thousands of sequences concurrently

52
Q

Describe Illumina (Solexa) sequencing

A

Each nucleotide to be added is fluorescently labelled and has a terminator. The slide containing a portions of DNA is flooded with these nucleotides and polymerase. The nucleotides will pair up with the DNA strands. An image is taken each time a new base is added which will be signalled by fluorescence. The terminators are removed after each addition so that the chain can continue

53
Q

Why is Illumina Sequencing much faster than Sanger Sequencing?

A

More than one strand of DNA is on the slide so multiple portions can be sequenced each time.

54
Q

Describe Ion Torrent Sequencing

A

A portion of DNA is added to a slide. A single species of dNTP, buffers and polymerase floods the slide. When the dNTP is added to the chain, an H+ ion is released causing the pH to decrease which allows us to determine if and how many of that base was added. The process is repeated and the different nucleotides are cycled through

55
Q

Describe Nanopore Sequencing

A

A MiniON device is used. An enzyme unwinds DNA and feeds one strand through a protein pore. Each base is shaped differently and results in different disruptions to the electrical current in the device allowing the sequence to be read.

56
Q

What is the Human Genome Project?

A

An international scientific research project where the entire human genome was sequenced. It used Sanger Sequencing and was completed in 20003.

57
Q

What is the ENCODE project?

A

It looks at what were the functional elements of the human genome (which parts code for proteins). It discovered that only 2% of the genome codes for proteins

58
Q

What is the 1000 Genome Project?

A

The largest public catalogue of human variation and genotype data. Its aim is to find the most genetic variants with frequencies of at least 1%.

59
Q

What is the 100,000 Genomes Project?

A

It sequenced 100,000 genomes from NHS patients with cancer or rare diseases. It is working towards 5 million

60
Q

Give 2 medical applications of NGS

A

It helps to understand healthy and disease stated

It helps to identify genetic diseases

61
Q

Give 3 industry applications of NGS

A

Prognostics (diagnosing before it happens)
Diagnostics
Discover of new targets for drug design

PHAY0003 (22 decks)

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