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Human Biology ATAR > Genetics > Flashcards

Genetics Flashcards

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1
Q

DNA

A
  • Deoxyribose nucleic acid - Found in the nucleus - All DNA has a similar structure
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2
Q

Major components of DNA

A
  • Sugars - Phosphates - Bases - These make up the ‘back bone’ of the DNA structure
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3
Q

4 types of bases (an their pairs)

A
  • Adenine always pairs with thymine - Guanine always pairs with cytosine
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4
Q

What is a nucleotide?

A
  • Sub-unit of the DNA molecule - Consists of one sugar, one phosphate and one base molecule
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5
Q

What is a chromosome?

A

DNA wrapped into a double helix structure around proteins called histones

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6
Q

What is a gene?

A
  • Each section of DNA that controls a trait - Humans have around 25,000 genes in their chromosomes - Genes for a particular trait are controlled at a particular point in the chromosome
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7
Q

Somatic cells

A

46 chromosomes (23 pairs)

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8
Q

Gametes

A

23 single chromosomes

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9
Q

Homologous pair

A

a pair of chromosomes containing the pair of genes for a particular trait

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10
Q

What are alleles?

A
  • The alternative forms of a gene that are available - The pairs of alleles that each person inherits from their parents control and determine the characteristics of the individual - Many genes have two alleles (dominant and recessive)
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11
Q

What is a genotype?

A
  • The genetic makeup of an individual - It is inherited - E.g. BB/bb/Bb
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12
Q

What is a phenotype

A
  • The observed expression of the alleles for the characteristics - Determined by the genotype and the environment
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13
Q

What is monogenic inheritance?

A
  • Exists when an individual receives just one pair of alleles for a trait - E.g. blood groupings - The traits are discrete (either there or not there) - Only two alleles for the trait - Only two phenotype
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14
Q

What is polygenic inheritance

A
  • Many pairs of genes control the trait - Continuous variation of the trait - Alleles will have an additive effect - E.g. skin colour height and weight - Continuous traits = many phenotypes
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15
Q

Skin colour

A
  • Is a polygenic trait - Many genes contribute - Continuous variation - Depends on the amount of melanin in the skin
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16
Q

What do melanocytes produce?

A

Melanocytes produce structures called melanosomes that contain melanin and are found in the bottom of the epidermis of the skin

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17
Q

How is melanin produced?

A

It is made from an amino acid called tyrosine

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18
Q

Amounts of melanocytes and melanosomes in different people

A

Most people have similar amounts of melanocytes and varying amounts of melanosomes

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19
Q

Darker skinned people

A
  • Can convert more tyrosine into melanin because they have more tyrosinase - More melanosomes containing more melanin - There are also more evenly distributed throughout the skin - This prevents burning
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20
Q

Pale skin

A
  • Less tyrosinase and therefore can’t convert as much tyrosine into melanin - Melanin is not evenly distributed and form clumps - Burns when exposed to UV light
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21
Q

Tyrosinase (enzyme)

A
  • Brings about the production of melanin - Stimulated by UV rays - People with the enzyme will become darker skinned in the sun - Those with less tyrosinase will tan less well - Therefore, the environment affects the phenotype - Darker skin will prevent sun burn
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22
Q

What is a mutation?

A
  • A permanent change to a gene or chromosome leading to a new characteristic in an organism - Due to changes in the base sequences in a section of DNA which alters the types of proteins that will be synthesised by the body - Can be advantageous or disadvantageous
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23
Q

What is a mutant?

A

An organism with a characteristic resulting from a mutation

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24
Q

What are mutagens?

A
  • Agents that are known to increase the rate at which mutations occur - E.g. UV light, X-rays, radiation, chemicals such as sulphur dioxide or antibiotics
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25
Q

Somatic mutations

A
  • Occur in a body cell - The reproductive cells are not affected and once the organism dies, the mutation will be lost
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26
Q

Germ-line mutations

A
  • Mutation occurring in the gametes - The individual is not usually affected - The individual will produce gametes with changed DNA
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27
Q

Main types of mutations

A
  • Gene mutations - Chromosomal mutations
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28
Q

Gene mutations

A
  • Change in a single gene - They occur during the replication of the DNA molecule before cell division - If the DNA copies incorrectly, the changed DNA will continue to be copied in all future divisions - May code for a new amino acid and a completely different protein
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29
Q

What is a point mutation?

A

a change in one base

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30
Q

Albinism

A
  • The result of a missing protein - The protein responsible for the pigment (melanin) of hair, skin and eyes is missing - Patients have whitish blond hair, extremely pale skin and pinkish eyes
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31
Q

Duchene muscular dystrophy

A
  • The deletion of a base - Missing the protein dystrophin - May arise through a mutation in the mother, which can then be inherited by her sons - Results in the wasting of the leg muscles and later, the arms, shoulders and chest - Usually becomes apparent around the age of 3 to 5 years, when muscle weakness becomes evident - Eventually death occurs due to failure of the respiratory muscles - Boys with the Duchene form of muscular dystrophy are unlikely to live for more than 20 to 25 years
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32
Q

Cystic fibrosis

A
  • The mutation occurs in a huge gene on chromosome 7 - Changes to the DNA of the CFTR gene results in different amino acids in the CFTR protein - The CFTR protein regulates the development of the chloride channels in the cell membrane - Without it the person cannot transport chloride ions and regulate the movement of water into and out of the cells - The person suffers from salty tasting skin, persistent coughing, wheezing and digestive problems - Thick, sticky mucous blocks the airway, as well as the pancreatic and bile ducts
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33
Q

Lethal recessive alleles

A

Cause the death of the embryo or foetus (miscarriage or spontaneous abortion) or the early death of the child

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34
Q

Tay-sachs disease (TSD)

A
  • Disorder of lipid metabolism that is inherited in an autosomal recessive pattern - Lethal recessive condition - The missing enzyme results in the accumulation of a fatty substance in the nervous system - A baby with two recessive alleles develops normally for the first two months, then deterioration causing mental and physical disabilities begins - Death usually occurs in early childhood
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35
Q

Chromosomal mutations

A

Occur when there is a change in the whole or part of the chromosome. Many genes can be affected

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36
Q

Types of chromosomal mutations

A
  1. Deletion – part of the chromosome is lost 2. Duplication – a section of the chromosome occurs twice 3. Inversion – breaks occur in a chromosome and the broken piece joins back in, but the wrong way around 4. Translocation – part of a chromosome breaks off and is re-joined to the wrong chromosome 5. Non-disjunction – during meiosis, a chromosome pair does not separate, so one daughter cell has one extra chromosome (trisomy) and one has one less (monosomy)
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37
Q

Examples of non-disjunction (monosomy)

A
  • Cri-du-chat - Turners
38
Q

Cri-du-chat

A
  • Due to a missing portion of chromosome 5 - Infants often have problems with the larynx and nervous system
39
Q

Turners syndrome

A
  • Due to a missing sex chromosome - These individuals are born female, but are short in stature, lack secondary sex characteristics and are infertile
40
Q

Examples of non-disjunction (trisomy)

A
  • Down-syndrome - Patau syndrome - Klinefelter syndrome
41
Q

Down syndrome

A
  • Occurs when an individual has an extra chromosome 21
42
Q

Patau syndrome

A
  • Occurs when an individual has an extra chromosome 13 - Individuals often have a small head, mental retardation, an extra finger on each hand, a cleft palate and malformation of the eyes and ears
43
Q

Klinefelter syndrome

A
  • Occurs when individuals have an extra X or Y chromosome
44
Q

What is biotechnology?

A

Uses cellular processes to make products that are of use to humans. It includes genetic testing, gene manipulation, cell replacement therapies and tissue engineering

45
Q

How has the age of our population changed?

A

The maximum age to which people can live does not seem to have changed a great deal, although the number of people reaching theses ages has increased enormously

46
Q

What is a genome?

A

The complete set of genetic information of an organism

47
Q

The human genome project

A
  • The compete sequence of the nucleotides that make up approximately 21,000 genes in our chromosomes - An international research effort - Mapped the location of all 46 chromosomes in the human nucleus - Completed in 2003, but analysis of the data is continuing - 4,000 genetic disorders have been identified on the chromosomes already - Identified the location of all these faulty genes
48
Q

Why is the human genome project important?

A
  • If you are able to identify where faulty genes are, they can be replaced with healthy ones (gene replacement therapy) - If you know where genes are located that cause diseases, then you can monitor the gene expression - If you know where genes that cause diseases are located, then you can screen for these diseases using genetic tests so that you are aware of the disease - The diseases could be prevented by changes in lifestyle or preventative drug treatment
49
Q

Hereditary diseases

A
  • Caused by defective genetic information being transmitted from one generation to another - Inherited in the same fashion as ‘healthy’ traits - Often caused by mutations to the normal DNA
50
Q

What is a mutation?

A

A disruption (change) to a healthy nucleotide sequence

51
Q

What is DNA sequencing?

A

The determination of the precise order of nucleotides in a sample of DNA

52
Q

Spastic paraplegia

A
  • Progressive limb weaknesses and stiffness resulting in paralysis - Symptoms begin from mid-20’s to mid-50’s - Researchers studies families in which the disease occurred - Sequences (alleles) in parts of chromosome 2 were different in affected family members (from those not affected) - No cure – treatment involves physical therapy to try to improve muscle strength and safeguard muscular movements - Knowing the location of the responsible gene allows people to be screened for the disorder and to seek effective treatment to prevent the disease or reduce its effects
53
Q

DNA sequencing can be used to determine alleles for:

A
  1. Sickle cell anaemia 2. Cystic fibrosis 3. Some cancers 4. Spastic paraplegia 5. Can also be used for maternity and paternity testing
54
Q

Gel electrophoresis

A
  • The DNA pieces are placed on a bed of semi-solid gel - An electrical current is passed through electrodes at either end - The DNA (negatively charged), moves through the gel towards the positive electrode - The smaller segments move faster than the larger ones, resulting in a pattern of bands
55
Q

Restriction enzymes

A
  • Cut long strands of DNA into shorter pieces of DNA - Cuts are made at particular sequences in the DNA called recognition sites
56
Q

Types of restriction fragments

A
  • Blunt ends - Sticky ends
57
Q

What is the banding pattern called?

A

DNA fingerprint or DNA profile

58
Q

Polymerase chain reaction

A

segments of DNA are artificially multiplied through a series of repeated cycles of duplication using an enzyme called DNA polymerase

59
Q

What is the role of a primer?

A
  • Initiates duplication - A segment of DNA, complementary to the target sequence of DNA, which initiates replication by the DNA polymerase
60
Q

What is a chain reaction?

A

Compounding amplification of the ordinary molecule

61
Q

Steps to PCR

A
  1. Denaturation: the DNA is heated to 96®C causing the DNA to split into two strands o At this temperature, the DNA polymerase was destroyed o More of the enzyme had to be added after the heating stage 2. Annealing: o DNA is cooled o Primers are required (begin the duplication at a certain point) o The primers join bases together to form a complementary strand 3. Extension: o The enzyme DNA polymerase is used to duplicate the targeted section of DNA o Both the original and complementary strands can be used to make more DNA
62
Q

DNA polymmerase

A
  • Occurs in living things - Duplicated DNA when cells divide - Lives at a temperature of 37.5®C - It is destroyed during the heating stage of PCR
63
Q

Taq polymerase

A
  • Used as a substitute for DNA polymerase - Does not breakdown when heated and can be used throughout the entire process
64
Q

DNA fingerprinting is used to…

A
  1. Determine biological relationships 2. Trace ancestry 3. Identify victims and criminals 4. Identify disaster victims 5. Predict disease
65
Q

Recombinant DNA (rDNA)

A
  • Introduction of foreign DNA into a cell - Genes (alleles) from one organism are added to the chromosomes of another organism - There is an enormous potential to replace faulty genes with healthy ones
66
Q

Transgenic organisms

A
  • Any organism whose genome has been altered by the transfer of a gene or genes from another organism - The introduced genes become part of the transgenic organism’s DNA and are then passed on the subsequent generations
67
Q

Florescent genes

A
  • Jelly fish contain a florescent gene to make then glow in the dark - The florescent gene is removed from the jelly fish - Viruses are used to insert the gene into a single-celled mouse embryo
68
Q

Introducing genes into a cell

A
  • Use of vectors: carry the gene from one place to another o Bacteriophages o Plasmids (found in bacteria) - Use of restriction enzymes
69
Q

Restriction enzymes

A
  • Able to cut up pieces of DNA at specific base sequences - Cuts the DNA from the donor genome to expose the gene of interest - Cuts the DNA of the vector so that the gene of interest can be inserted
70
Q

Recognition sites

A

the sequence of bases where a particular enzyme always cuts

71
Q

What is a vector?

A

a bacteriophage or virus used to transfer genetic material from one cell to another

72
Q

Bacteriophages

A
  • Also called phages - Viruses that infect bacterial cells - The viruses’ DNA is cut and the gene of interest is inserted into the viruses’ DNA - Viruses are then used as vectors to introduce genes to a cell’s DNA
73
Q

Plasmids

A
  • Circular stands of DNA found within bacteria - Capable of self-replication - Can be cut by a restriction enzyme - Desired genes can then be inserted into the plasmid - The plasmid is placed back into the bacteria - The plasmid reproduces, amplifying the amount of DNA available
74
Q

DNA ligase

A
  • An enzyme that is capable of joining or recombining pieces of DNA - Originally found in a bacterium called Escherichia coli (E. coli) - Ligation is the process where pieces of DNAQ are joined together
75
Q

Steps in the rDNA process

A
  1. Isolate the desired gene 2. Insert the gene into the vector and clone it (viruses or plasmids in bacteria) 3. Large quantities of the vector are introduced to the selected host cell
76
Q

Insulin production

A
  • Identify and isolate the gene for insulin production from human pancreas cells using restriction enzymes - Remove plasmid from bacterium. Use a restriction enzyme to cut the plasmid. The plasmid is used as a vector for this process - Combine spliced plasmid and the insulin gene. Sticky ends combine. Ligase is used to permanently join the insulin gene to the plasmid - The transgenic plasmid is placed back into the bacterium. The plasmid undergoes self-replication - The transgenic bacterium undergoes mitosis, producing more transgenic bacteria capable of transcribing and translating the insulin gene - This produces large quantities of insulin. The insulin is drained off, bottled and then injected into diabetics
77
Q

Factor VII production

A
  • Identify and isolate the gene for factor VIII production from a human liver cell using restriction enzymes - Remove plasmid from bacterium. Use a restriction enzyme to cut the plasmid. The plasmid is used as a vector for this process - Combine spliced plasmid and the factor VIII gene. Sticky ends combine. Ligase is used to permanently join the factor VIII gene to the plasmid - The transgenic plasmid is placed into a mammalian cell. The plasmid undergoes self-replication - The mammalian cell undergoes mitosis, producing more plasmids capable of transcribing and translating the insulin gene - This produces large quantities of factor VIII. The factor VIII is drained off, bottled and then injected into haemophiliacs
78
Q

Vaccine production

A
  • Identify and isolate the gene for the (attenuated) antigen form a pathogen using restriction enzymes - Remove plasmid from bacterium. Use a restriction enzyme to cut the plasmid. The plasmid is used as a vector for this process - Combine spliced plasmid and the antigen gene. Sticky ends combine. Ligase is used to permanently join the antigen gene to the plasmid - The transgenic plasmid is placed into a yeast cell. The plasmid undergoes self-replication - The transgenic bacterium undergoes mitosis, producing more plasmids capable of transcribing and translating the antigen gene - This produces large quantities of the antigen. The antigen is drained off, bottled and then used to vaccinate people
79
Q

Human growth hormone production

A
  • Identify and isolate the gene for HCG production from a human pancreas cells using restriction enzymes - Remove plasmid from bacterium. Use a restriction enzyme to cut the plasmid. The plasmid is used as a vector for this process - Combine spliced plasmid and the HCG gene. Sticky ends combine. Ligase is used to permanently join the HCG gene to the plasmid - The transgenic plasmid is placed into a bacterium. The plasmid undergoes self-replication - The transgenic bacterium undergoes mitosis, producing more transgenic bacteria capable of transcribing and translating the HCG gene - This produces large quantities of HCG. The insulin is drained off, bottled and then injected people who are producing too little of their own hormone
80
Q

What is gene therapy?

A

Involves the transfer of genetic material, and the uptake of that material into the cell nuclei of the body - The transfer of a therapeutic or working copy of a gene into specific cells of an individual in order to repair a faulty gene - Only somatic cells are targeted

81
Q

Vectors

A
  • Used to introduce DNA to a host (body) cell - Generally, plasmids or viruses - Introduced either in vivo or vitro
82
Q

A viral vector must:

A
  1. Target the right cell 2. Integrate the gene into the host cell DNA 3. Activate the gene 4. Avoid harmful side-effects
83
Q

Disadvantages to viral vectors

A
  1. Can only carry a limited amount of genetic material 2. Can cause illness in patient 3. Can be destroyed by the immune system
84
Q

Gene therapy for cystic fibrosis

A
  • Cells are removed form a heathy patient that carries the CFTR gene - In a laboratory, a virus is altered using a restriction enzyme so that it cannot reproduce - The healthy CFTR gene is inserted into the virus - The altered virus is mixed with the lung cells of the patient that carries the faulty CFTR gene - The cells of the patient become genetically altered as it now contains the CFTR gene - The altered cells produce the desired hormone or protein, which is CFTR, preventing mucous from building up in the lungs
85
Q

Gene therapy for Huntington’s disease

A
  • Caused by a faulty gene on chromosome 4 - Brain cells are removed from a healthy patient that carries the correct Huntington’s disease - In a laboratory, a virus is altered using a restriction enzyme so that it cannot reproduce - The healthy Huntington’s gene is inserted into the virus - The altered virus is mixed with the brain cells of the patient that carries the faulty Huntington’s gene - The cells of the patient become genetically altered as it now contains the heathy Huntington’s gene - The altered cells are injected into the brain of the patient - The altered cells produce the Huntington’s protein
86
Q

Pros and cons to plasmids

A
  • Can transfer large amounts of DNA - Less efficient at getting into cells - Are sometimes wrapped in a cell membrane (liposomes) to make it easier to enter a cell
87
Q

Cell replacement therapy

A
  • Involves the transfer of cells with the relevant (healthy) function into the patient. - Uses stem cells - Healthy cells derived from stem cells are introduced into the body - These healthy, differentiated cells function in the place of the damaged cells
88
Q

Embryonic stem cells

A
  • Harvested from 4-6 day old blastocysts - From the inner cell mass - Can differentiate into any one of over 200 cell types found in the body - They are pluripotent
89
Q

Parkinson’s and Alzheimer’s

A
  • Are both neurodegenerative disorders in which cell replacement therapy can be used - In both diseases, dying neurons can be replaced with healthy neurons derived from stem cells
90
Q

Stem cells and tissue engineering

A
  • uses a scaffold on which stem cells are induced to grow on, to produce a three dimensional tissue - the cell-covered scaffold is then implanted into the patient at the site where new tissue is needed - used for tissues including bone, skin, cartilage and adipose tissue

Human Biology ATAR (13 decks)

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