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From Flashcardlet > Genetics Test II > Flashcards

Genetics Test II Flashcards

1
Q

Bacteria Mobile Genetic Elements:

Transposons

A
  • Pieces of DNA that act as ‘jumping genes’ that change location on chromosome or plasmid chromosomal localisation
  • Can carry resistance or virulence genes
  • Encode transposase that catalyses the transposition event.
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2
Q

Bacteria Mobile Genetic Elements:

Insertion Sequences (IS elements)

A
  • Transposable elements that encode only the transposase
  • Multiple copies of the same IS within the genome provide targets for homologous recombination, rearrangements and replicon fusions.
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3
Q

Bacteria Mobile Genetic Elements:

Conjugative Transposons

A
  • Normally integrated into the chromosome

- Excise then transferred to recipient cells by conjugation.

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4
Q

Prokaryote Genome

A
  • Haploid
  • Contain a single circular chromosome
  • Often contain small circular DNA molecules “plasmid”
  • Only circular DNA molecules in prokaryotes replicate
  • Eukaryotes are often diploid and have linear chromosomes usually more than one
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5
Q

Operon

A

Organisation of microbial genome. Genes are arranged in operons

-Functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promotor.

e. g lac operon
- consist of lacZ, Y and A.
- regulated by the availability of glucose/lactose.

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6
Q

Core genome

A

Portion of the bacterial genome common to all stains in a defined set of species and required for basis cellular functions

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7
Q

Flexible Genome

A

Genes variably present between individual strains.

  • genes of the flexible genome play a role in adaptation
  • the plasticity of the flexible genome contributes to bacterial genome evolution
  • gene diversity increased mostly by horizontal gene transfer.
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8
Q

Horizontal Gene transfer

A

Transformation- bacterial cell can take up DNA from the environment or from plasmids

Transduction-phages of bacterial viruses that carry extra genes, they invade bacterial hosts and those genes are incorporated into bacterial genome

Conjugation-transfer of genetic material by cell to cell contact.

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9
Q

Bacterial Chromosome organisation

A
  • Compaction comes through the formation of loop structures held in place by proteins=further compacts DNA 10-fold
  • Negative supercoiling occurs under the control of enzyme; DNA gyrase and topisomerase I= compacts genome into a further 400 small loops
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10
Q

E.coli genome replication

A
  • replication starts are a single origin (oriC)
  • OriC is where enzyme assemble to form the machinery that will generate the replication fork.
  • In e.coli oriC consist of three A-T rich 13 mer repeats and four 9-mer repeats
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11
Q

Helicase

A

Helicase moves along one strand using ATP hydrolysis as an energy source to displace the other strand and unwind the DNA

  • Single strand binding proteins stabilise the strands
  • DNA polymerase III is involved in DNA replication and loaded at oriC to duplicate the chromosome. 5’-3’
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12
Q

Elongation of Genome Replication

A
  • DNA polymerase III can only add a nucleotide to the 3- end of a pre existing chain.
  • Replication proceeds bi-directionally from OriC.

Leading strand- DNA polymerase III adds nucleotides continuously to synthesis the new strand towards the replication fork

Lagging strand- DNA polymerase III adds nucleotides discontinually to synthesise the new strand away from the replication fork
-synthesised by a series of Okazaki fragments

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13
Q

Vertical gene transfer

A
  • occurs from one generation to the next

- used by organisms using sexual reproduction

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14
Q

Lateral (or horizontal) gene transfer

A
  • gene introduced from unrelated individuals or from different species
  • not from parent to offspring
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15
Q

Mechanisms of Transfer

A

Transformation-donor DNA added to bacterial growth medium and is taken up form the medium by the recipient and transfer DNA

Conjugation-donor carries a special plasmid type that allows it to directly contact the recipient and transfer DNA

Transduction-Donor DNA packaged within a bacteriophage and transferred to the recipient when it infects it.

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16
Q

Natural transformation

A
  • occurs in a few species of bacteria

- spontaneously take up DNA fragments from their surroundings

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17
Q

Artificial transformation

A
  • occurs in the majority of bacterial species

- take up DNA after lab procedures make their cell walls/membranes permeable to DNA

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18
Q

HFr bacteria

A

Cells whose chromosome carry and integrated plasmid.

-produce a high frequency (HFr) of recombinants for chromosomal genes in experiments.

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19
Q

Lytic Cycle

A

A phage injects its DNA into a bacterial cell:

  • takes over the cells’s protein synthesis and DNA replication machinary
  • forcing it to express the phage genes
  • produce phage proteins and replicate its DNA

Newly produced phage proteins and DNA assemble into phage particles
-infected cell burst releasing new viral particles ready to infect other cells

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20
Q

Temperate phages

A
  • Have lysogenic cycle as well as lytic
  • DNA integrates into host genome and multiplies
  • little or harm to host
  • integrated phase called prophage
  • possible to induce viral genome to excise(formation of new viruses)
  • bacterial adjacent genes sometimes cut out and incorporated as part of the genome (specialised transduction)
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21
Q

Antibiotic resistance

A

Bacteria change and become resistant to the antibiotics used to treat the infection they cause.

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22
Q

What is evolution?

A

Evolution is the molecular process that operates on genetic information. Mutations, recombination, gene conversion provide the genome with the means to involve. Also natural selection, drift and gene flow.

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23
Q

Four levels of gene duplication

A
  • exons duplicate or shuffle
  • entire genes duplicate to create multigene families
  • multigene families duplicate to produce gene super families.
  • entire genome duplicates to double the number of copies of every gene and gene families.
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24
Q

Charles Darwin’s Theory of Evolution

A
  • variation exist among individuals of a population
  • variants forms of traits can be inherited
  • some variant traits confer an increased chance of survival
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25
Q

Theory of natural selection

A

Differences between species were thought to consist mainly of mutations that had been fixed by positive selection that increase the fitness of a species.

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26
Q

Theory of molecular evolution

A

Majority of evolutionary changes at the molecular level are not caused by selection acting on advantageous mutants but by random fixation of selectively neutral or very nearly neutral mutants through the cumulative effect of sampling drift under continued input of new mutations.

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27
Q

Out of Africa

A
  • Homo sapiens evolved from Homo erectus from Africa

- descendents migrated from Africa and replaced hominids.

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28
Q

Multi-regional hypotheis

A

-Modern humans occurred in different parts of the world

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29
Q

Homo neanderthalensis

A
  • closest evolutionary relatives of present day humans before disappearing 30 000 years ago
  • co existed with Homo sapies
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30
Q

Non coding RNA

A

ncRNA is a RNA molecule that functions without being translated into protein.

  • tRNA
  • rRNA
  • miRNA
  • siRNA
  • lncRNA
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31
Q

ncRNA in Translation

A
  • rRNAs catalyse the translation of nucleotides sequences to protein
  • tRNA form ‘adaptor molecules’ between mRNA and protein
  • snoRNAs are involved in the maturation of rRNA
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32
Q

ncRNA regulation gene expression

A
  • small specialised RNAs that prevent the expression of specific genes
  • occurs through complementary base pairing
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33
Q

miRNAs

A
  • mediate RNA interference
  • specialised RNA preventing expression of specific genes through complementary base pairing
  • miRNAs are processed from longer primary transcripts

Responsible for the post-transcriptional regulation of many mRNA via:

  • translational repression
  • enhancement of mrRNA turnover
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34
Q

siRNA

A
  • The siRNA pathway is responsible for detecting exogenous dsRNA. Destroys transcripts derived from invading RNA
  • Pathway may protect cells from invading viral dsRNAs by destroying those RNAs
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35
Q

lncRNA

A

Functions:

  • signaling
  • serve as molecular decoys
  • guiding ribonulceoprotein complexes to specific chromatin sites
  • participating as scaffolds in the formation of complexes.

lncRNA promotors are bound and regulated by transcriptional factors.

36
Q

How does the developing embryo establish the proper number of body segments?

A

-early in development, the products of segmentation genes subdivide the body into an array of identical body segments

37
Q

How does each body segment know what kind of structures it should form?

A

-Later in development, the products of the homeotic genes assign a unique identity to each segment

38
Q

Two different genes sets control embryonic development in Drosophila:

A

Maternal genes-mRNA that is layed down in the egg

Zygotic genes-gap genes, pair rule genes and segmentation polarity genes.

39
Q

Early Drosophila Development

A

Synical blastoderm-formed by 13 rapid mitotic divisions without any cell division

Cellular blastoderm-formed by cellularisation that begins during interphase of 14th division

40
Q

Genes responsible for segment formation

A

Maternal genes
-expressed by mother and the mRNAs deposited in egg, not translated until after fertilisation

Gap genes

  • expression begins at syncytial blastoderm stage and controlled by maternal gene products
  • divides initially into 4 segments

Pair rule genes
-seven zone of expression are controlled by gap gene products

Segment polarity genes-expression in 14 segments is controlled by pair rule gene products.

41
Q

Morphogen

A
  • Substance that defines different cell fates in a conc. dependent manner
  • Two maternal effect gene product [bicoid (bcd) and nanos (nos)]

bcd is highest at anterior and lowest at the posterior

nos is lowest at anterior and highest at posterior

42
Q

Localisation of Bicoid mRNA and Protein

A
  • bcd mRNA localised to the anterior pole of the oocyte
  • bcd protein diffuses from the anterior pole of the embryo to produce an anterior to posterior gradient
  • bcd protein acts as transposon factor and translation repressor
43
Q

Distribution of mRNA of the 4 maternal effect genes within oocytes

A

Bicoid-mRNA localises to anterior pole

Nanos-mRNA localises to the posterior pole

Hunchback and caudal- mRNAs are uniformly distributed along the axis of the embryo

44
Q

Distribution of the protein product

A
  • bicoid protein represses translation of caudal mRNA. Causes posterior to anterior gradient of caudal protein
  • nanos protein represses translation of hunchback mRNA. Causes anterior to posterior gradient of hunchback protein
45
Q

Zones of Gap gene expression

A

Gap genes are the first zygotic genes to be expressed.

  • Binding sites in promoter regions of gap genes have different affinities for bcd, cad and hb proteins
  • some gap genes encode transcription factors that control expression of other gap genes

Gap gene control division of the body axis into rough generalised regions.

46
Q

Homeotic genes

A

Each segment establishes its own unique identity through the activation of homeotic genes.

Transcription of homeotic genes is controlled by gap, pair rule and segmentation genes

Homeotic mutations cause particular segments to develop as if they were located somewhere else

Cluster of genes found on chromosome 3.

47
Q

Totipotent

A
  • fertilised egg
  • grow into any other cell type
  • example: new organism
48
Q

Pluriopotent

A
  • embryonic stem cell
  • grow into any cell except totipotent cells
  • example: neurons, skin, muscle, kidney
49
Q

Multipotent

A
  • adult stem cell (example from blood)
  • grow into cells of closely related cell family
  • example: red blood cells, platelets, white blood cells
50
Q

Types of adult stem cells:

Hematopoietic stem cells

A
  • give rise to all the types of blood cells

- red blood cells, B lymphocytes, T lymphocytes, natural killer cells, monocytes, macrophage`\

51
Q

Types of adult stem cells:

Mesenchymal stem cells

A

-bone cells, cartilage cells, fat cells and other connective tissue such as tendons

52
Q

Types of adult stem cells:

Neural Stem cells

A

-In the brain give rise to its three major cells types: nerve cells, non neuronal cells (astrocytes, oligodendrocytes)

53
Q

Types of adult stem cells:

Skin stem cells

A

-Occur in the basal layer of the epidermis and at the base of hair folicles

54
Q

Genes

A
  • basic unit of biological information
  • specific segment of DNA in a discrete region of a chromosome that serves as a unit of function by encoding a particular RNA or protein
55
Q

Meiosis

A
  • Chromosomes duplicate (during interphase) and homologous chromosomes exchange information (chromosomal cross over) before a first division called meiosis I
  • The daughter cell divides again in meiosis II, splitting up sister chromatids to form haploid gametes

During interphase, the chromosome doubles.
Meiosis I and II the nucleus doubles.

56
Q

Non disjunction

A
  • Mistake in chromosome segregation during meiosis I or II
  • can result in abnormal chromosome number
  • eg. down syndrome
57
Q

Hybrid sterility

A
  • many hybrids between species are sterile because chromosomes cannot pair properly
  • e.g. mule
58
Q

Independent assortment

A

Of nonhomologs creates different combinations of alleles

59
Q

Crossin over

A

Between homologs creates different combinations of alleles within each chromosome.

60
Q

Mitosis stages

A
  1. Prophase
  2. Prometaphase
  3. Metaphase
  4. Anaphase
  5. Telophase
61
Q

Monohybrid cross

A
  • True breeding plants with two forms of a single trait are crossed
  • Progeny showed only one form of the trait
62
Q

Test cross

A

Are a way to establish genotype. Mating an individual showing the dominant phenotype with a recessive phenotype.

63
Q

The law of independent assortment

A

Each pair of alleles segregates independently of each other pair of alleles during gamete formation.

64
Q

Law of segregation

A

Each allele segregates into separate gametes, established by metaphase 1

65
Q

Autosomal dominance

A
  • Dominant trait almost always appears in each generation
  • Affected individual have an affected parent
  • Appears equally in both sexes
66
Q

Polydactyly

A

extra fingers and or toes

67
Q

Huntington disease

A
  • progressive neurodegenerative disorder
  • affects both sexes
  • onset in usually mid life
  • caused by a CAG repeat expansion in exon 1 of huntingtin gene (HTT) on chromosome 4p16.3
  • The more repeats you have, the earlier the onset.
68
Q

Anchondroplasia

A

Most frequent form of dwarfism

  • mutation in FGFR3 gene
  • Two copies of the mutant gene=death
  • Heterozygous= anchondroplasia
  • FGFR3 is mainly expressed in cartilage. It inhibits bone growth
69
Q

PTC tasting

A
  • Humans vary in their ability to detect the bitter substance PTC.
  • Protects us from ingesting toxic substances which typically taste bitter.
70
Q

How does the HaeIII enzyme discriminate between the C-G polymorphism in the TAS2R38 gene?

A
  • HaeIII cuts at the sequence 5’-GGCC-3’
  • A G not at the position 145 of the non taster allele changes the sequence so that it is no longer recognised by the restriction enzyme
71
Q

Cystic firbrosis

A

Its an autosomal recessive condition.

  • a genetic disorder that affects the respiratory and digestive system
  • CF is a life shortening exocrine disorder. Thick excessive sticky mucous builds up in the lungs, pancreas and digestive organs
  • Chromosome 7q31.2
72
Q

CFTR

A

The CFTR gene encodes:

  • amino acid membrane bound glycoprotein
  • a member of the ABC transporter superfamily
  • chloride channel that is regulated by phosphorylation and gated by ATP binding and hydrolysis at its nucleotide binding domains.

CFTR protein regulates ionic balance by allowing the transport of chloride ions across the epithelial cell

Abnormal CFTR protein-allows cell to retain water, thick dehydrated mucous builds up outside the cells. Clogging and blockage. Respiratory and digestive problems

73
Q

CF mutant alleles

A

Most common CF mutant allele is the △F508 mutation.

  • most common mutation is a 3-bp deletion in exon 10 of CFTR gene
  • deletion of phenylalanine at codon position 508 (△F508 )
  • results in a complete lack of Cl- channel production or in channels that cannot migrate to the cell membrane
74
Q

Summary of the 6 classes of Mutation

A

Class I- leads to defective protein products
Class II- defective protein processing
Class III- defect in the channel regulation
Class IV-defective in conductance through the channel
Class V- abnormal splicing
Class VI- defection regulation of other ion channels

75
Q

Albinism

A

Deficiency in melanin production
-decrease or absent pigmentation
Phenotype: white hair and skin, blue eyes

76
Q

Oculocutaneous Albinism (OCA)

A

Autosomal recessive disorder in which melanin is reduced or absent.

OCA1A-complete lack of tyrosinase activity due to production of an inactive enzyme or no enzyme

OCA1B- reduced activity of tyrosinase

OCA1 is caused by mutant TYR gene. Chromosome 11q14.3

77
Q

What happens if there is a mutation in the TRY gene?

A
  • Mutation cause reduced or no tyrosinase enzyme activity

- OCA1 results from deficient catalytic activity of tyrosinase during the melanin biosynthetic pathway.

78
Q

Tay Sachs Disease (TSD)

A
  • Excessive accumulation of gangliosids (lipid molecules) in ganglion cells of retina because enzyme in missing.
  • rare lysosomal storage disease affecting the central nervous system
  • lysosome are cellular organelles that contain enzymes to break down waste material and cellular debris.
  • excessive accumulation of fats (gangliosides) in the brain and nerve cells.
79
Q

Sex linked genes

A

Genes located on these chromosomes (X and Y).

80
Q

Sex influenced traits

A

Traits that can show up in both sexes but are expressed differently in each sex due to hormonal differences

  • allele is dominant in one sex and recessive in the other
  • eg. pattern baldness related to testosterone, feather plumage in chickens
81
Q

Sex linked traits

A
  • Traits carried on the X-chromosome
  • Recessive six linked traits are more common than dominant
  • Males are more susceptible to sex linked conditions that females
  • Traits that affect a structure or function occurring in one sex
82
Q

Sex limited traits

A

-are traits that are visible only within one sex

83
Q

Nonobstructive spermatogenic failure

A
  • Y linked trait
  • a condition that leads to infertility problems in males.
  • absent or severely reduced sperm
  • Yq11.21
84
Q

X-linked dominant traits:

Congenital generalised hypertrichosis

A
  • extra hair follicles

- dense and more abundant upper body

85
Q

X-linked dominant traits:

Incontinentia pigmenti

A
  • swirls of skin pigment arise when melanin penetrates the deeper skin layer
  • born with streaky, blistering areas
  • highly variable abnormalities of the skin, hair, nails, teeth, eyes and central nervous system in affected females
  • blistering areas turn into rough bumps that eventually leaves behind darkened skin
  • males usually die before 2nd trimester
  • Cause by NEMO gene, a deletion in part of the NEMO gene
  • 10 exons on chromosome Xq28
86
Q

X linked recessive disorder:

Ichthyosis

A
  • deficiency of an enzyme that removes cholesterol from skin.
  • upper skin layer cannot peal off (brown and scaly)
  • results from steriod sulphatase (STS) enzyme deficiency
  • caused by mutation or deletion of the STC gene
  • Chromosome Xp22.3
87
Q

X linked recessive disorder:

Hemophilia A

A
  • most common bleeding disorder
  • caused by deficient or defective coagulation factor (factor VIII). Key factor in the clotting cascade
  • Cause by mutation in coagulation factor VIII (F8) on chromosome Xq28

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