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IB Biology SL > Genetics > Flashcards

Genetics Flashcards

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1
Q

What is the definition of a gene?

A

A heritable factor that consists of a specific length of DNA and influences a specific characteristic

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2
Q

What is the definition of an allele?

A

One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the same gene. They are formed by mutations in the nucleotide code.

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3
Q

What is the definition of a locus?

A

The position of a gene on a particular chromosome

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4
Q

What is a gene mutation?

A

A permanent change in the base sequence of DNA

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5
Q

What is the genome?

A

The whole of the genetic information of an organism.

This includes all genes as well as non-coding DNA sequences.

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6
Q

What are the causes of sickle cell anaemia? (3)

A

Sickle cell anaemia results from a change to the 6th codon for the beta chain of haemoglobin

  1. DNA: The DNA sequence changes from GAG to GTG on the non-transcribed strand (CTC to CAC on the template strand)
  2. mRNA: The mRNA sequence changes from GAG to GUG at the 6th codon position
  3. Polypeptide: The sixth amino acid for the beta chain of haemoglobin is changed from glutamic acid to valine (Glu to Val)
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7
Q

What are the consequences of sickle cell anaemia? (5)

A
  1. The amino acid change (Glu → Val) alters the structure of haemoglobin, causing it to form insoluble fibrous strands
  2. The insoluble haemoglobin cannot carry oxygen as effectively, causing the individual to feel constantly tired
  3. The formation of fibrous haemoglobin strands changes the shape of the red blood cell to a sickle shape
  4. The sickle cells may form clots within the capillaries, blocking blood supply to vital organs and causing myriad health issues
  5. The sickle cells are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia)
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8
Q

What was the human genome project?

A

The Human Genome Project was an international research effort to determine the sequence of the human genome and identify the genes that it contains. It was estimated that humans have between 21 000 – 23 000 genes
• The Human Genome Project showed that most of the genome does not code for proteins (originally labelled “junk DNA”)
• Some of these regions consist of areas that can affect gene expression or are highly repetitive sequences called satellite DNA

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9
Q

What are homologous chromosomes?

A

A pair of chromosomes (one from each parent) that are the same length and contain the same genes in the same location

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10
Q

How is DNA organized in eukaryotes?

A

The genetic material of eukaryotic cells consist of multiple linear molecules of DNA that are associated with histone proteins. This results in a greatly compacted structure, allowing for more efficient storage

(DNA is complexed with eight histone proteins to form a complex called a nucleosome, they are linked by an
an additional histone protein to form a string of chromatosomes which coil to form a solenoid structure.
These fibres then form loops, which are compressed and folded around a protein scaffold to form chromatin)

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11
Q

Where is DNA located in prokaryotes? (2)

A
  1. Prokaryotes do not possess a nucleus. Instead genetic material is found free in a region of the cytoplasm called the nucleoid.
  2. It consists of he genetic material of a prokaryote consists of a single loop chromosome. The DNA of prokaryotic cells are naked, meaning it is not associated with proteins (for additional packing)
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12
Q

What are plasmids? (4)

A
  1. Plasmids are small separate (usually circular) DNA molecules that are sometimes present in prokaryotic cells.
  2. They are not responsible for normal life processes and are often associated with antibiotic resistance
  3. They can also be transferred from one bacterial cell to another through bacterial conjugation via sex pili
  4. A plasmids can self-replicate and autonomously synthesise proteins, they are ideal vectors for gene manipulation in labs
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13
Q

What is a karyogram?

A

A diagram or photograph of the chromosomes present in a nucleus arranged in homologous pairs of descending length.

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14
Q

What are autosomes?

A

Sex is determined by sex chromosomes but autosomes are chromosomes that do not determine sex.

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15
Q

What is a karyotype?

A

A property of a cell/ the number and appearance of different chromosomes present in a cell

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16
Q

Why is karyotyping used prenatally? (2)

A
  1. To determine the gender of the unborn child (via identification of the sex chromosomes)
  2. To test for chromosomal abnormalities (e.g. aneuploidies or translocations)
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17
Q

What is Down Syndrome?

A
  1. Down syndrome is a condition whereby the individual has three copies of chromosome 21 (i.e. trisomy 21)
  2. It is caused by a non-disjunction event in one of the parental gametes
  3. The extra genetic material causes mental and physical delays in the way the child develops
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18
Q

What is the importance of genome size?

A

Genome size can vary greatly between organisms and is not a valid indicator of genetic complexity. It simply refers to the total length of DNA in an organism

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19
Q

What is meiosis?

A

Meiosis is a reduction division of one diploid nucleus to form four haploid nuclei. Meiosis produces gametes.

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20
Q

What is autoradiography?

A
  1. Autoradiography was created by John Cairns to measure the length of DNA molecules.
  2. Cairns used autoradiography to visualize the chromosomes whilst uncoiled, allowing for more accurate indications of length.
  3. By using tritiated uracil (3H-U), regions of active transcription can be identified within the uncoiled chromosome
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21
Q

Outline the stages of Meiosis I

A

P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

22
Q

Outline the stages of Meiosis II

A

P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells

23
Q

What is crossing over? (3)

A
  1. Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase I
  2. The exchange of genetic material occurs between non-sister chromatids at points called chiasmata
  3. As a consequence of this recombination all four chromatids will be genetically different
24
Q

What is random orientation? (2)

A
  1. When homologous chromosomes line up in metaphase I their orientation towards the poles is random
  2. The orientation means that different combinations of maternal/paternal chromosome can be inherited when the bivalents separate in anaphase I
25
Q

What is non-disjunction? (3)

A
  1. A non-disjunction is an error in meiosis, where the chromosome pairs fail to split during cell division
  2. It occurs in anaphase I where homologous pairs fail to split, or in anaphase II where the sister chromatids fail to split
  3. As a result there will be too many or too few chromosomes in the final gamete cell (gamete would have 22 or 24 chromosomes - Down Syndrome)
26
Q

What makes sexual reproduction produce variation? (3)

A
  1. Crossing over (in prophase I)
  2. Random assortment of chromosomes (in metaphase I)
  3. Random fusion of gametes from different parents
27
Q

What are the main differences between Metaphase I and II?

A

Meiosis I
Replication prior to
Crossing over during prophase I
Homologous pairs line up randomly in metaphase I
Homologous pairs are separated into chromosomes in anaphase I

Meiosis II
No replication
No crossing over during prophase II
Chromosomes line up randomly in metaphase II
Chromosomes are separated into chromatids during anaphase II

28
Q

Define genotypes

A

The alleles of an organism/symbolic representation

29
Q

Define phenotype

A

The characteristic or trait of an organism (Brown eyes or blue eyes, etc)

30
Q

What is the difference between a dominant and recessive allele?

A

Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.
Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state.

31
Q

What is are codominant alleles?

A

Pairs of alleles that both affect the phenotype when present in a heterozygote.

32
Q

What did Mendel discover? (3)

A

Through performing experiments on a variety of different pea plants, Mendel established:

  1. Law of Segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene
  2. Law of Independent Assortment: The segregation of alleles for one gene occurs independently to that of any other gene*
  3. Principle of Dominance: Recessive alleles will be masked by dominant alleles†
33
Q

ABO Blood Group

A 
Phenotype    Genotype 
A                    IAIA or IAi
B                    IBIB or IBi
AB                  IAIB
O                    ii
34
Q

What is sex linkage?

A
  1. Sex linkage refers to when a gene controlling a characteristic is located on a sex chromosome (X or Y)
  2. Since the Y chromosome is shorter than the X chromosome, sex-linked conditions are usually X-linked as very few genes exist on the shorter
  3. • X-linked recessive diseases such as colour blindness and hemophilia are more common in males because they only carry one X chromosome, therefore if they inherit the X chromosome with the disease, they will also have the disease
  4. This also means that males can only pass these alleles onto their daughters as their sons only receive the Y chromosome
35
Q

What can cause mutations? (3)

A

Mutations can be spontaneous (caused by copying errors during DNA replication), or induced by exposure to external elements. Factors that can include mutations include:
o Radiation: UV Radiation from the sun, gamma radiation from radioisotopes, X-rays from medical equipment
o Chemical: Reactive oxygen species, alkylating agents (found in cigarettes)
o Biological Agents: Bacteria, viruses

36
Q

What is a polymerase chain reaction? (3)

A

Polymerase chain reaction is used to copy and amplify minute quantities of DNA. It can be useful when only a small amount of DNA is available but a large amount is required to undergo testing. PCR occurs in a thermal cycler and involves a repeat procedure of 3 steps:

  1. Denaturation – DNA sample is heated to separate it into two single strands (~95ºC for 1 min)
  2. Annealing – DNA primers attach to the 3’ ends of the target sequence (~55ºC for 1 min)
  3. Elongation – A heat-tolerant DNA polymerase (Taq) binds to the primer and copies the strand (~72ºC for 2 min)
37
Q

What is gel electrophoresis? (5)

A

Separate fragments of DNA are moved through an electric field in order to create a DNA profile.

  1. Enzymes cut DNA into different sized fragments
  2. The DNA sample is placed at one end of the porous gel
  3. This side of the gel with the DNA sample is exposed to a negative electrical current
  4. The DNA fragments move through the gel and stop at different points, creating a band
  5. The bands are dyed so we can see them

Affected by charge and size

38
Q

What is DNA profiling? (8)

A

DNA profiling is a technique where individuals can be identified and compared via their DNA profiles

  1. Restriction enzymes are used to break DNA into small fragments
  2. Fragments are subjected to electrophoresis
  3. Portions of DNA placed on gel
  4. Electric field/Voltage applied
  5. Negatively charged portions of DNA migrate to positive electrode
  6. DNA portions separated by size/small portions of DNA travel further through the gel
  7. DNA sequences stained
  8. Observed under UV light
39
Q

What are some of the application of DNA profiling? (5)

A

o Establishing paternity
o Comparing DNA at a crime scene with potential suspects
o Released prisoners that are wrongly convicted
o Identifying people who died last century
o Establishing relationships in populations to determine migrating patterns of evolutionary relationships

40
Q

What is gene transfer?

A

Gene transfer: Taking a gene from one organism and placing it into another organism

41
Q

What is the process for gene transfer? (4)

A
  1. Isolation of gene and vector (by PCR and centrifugation)
  2. Digestion of gene and vector (by restriction endonuclease, creating sticky/blunt ends)
  3. Ligation of gene and vector (by DNA ligase)
  4. Selection and expression of transgenic construct
42
Q

What are clones?

A

Clones are groups of genetically identical organisms, derived from a single original parent cell.

43
Q

What are GMOs?

A

An organism with a gene that has been artificially inserted into its genome (done by gene modification) e.g. golden rice (beta carotene-> Vitamin A), cold tolerant tomatoes (artic fish)

44
Q

Environmental Benefits and Risks of GMOs? (2x2)

A

Benefits
1. Pest-resistant crops can be made. Therefore less spraying of pesticides
2. Longer shelf-life therefore less spoilage
Risks:
1. Non-target organisms can be affected
2. GMOs reduces biodiversity

45
Q

Health Benefits and Risks of GMOs?

A

Benefits
1. Nutritional value of food improved by increasing nutrient content
2. Crops could be produced that lack toxins or alleges
Risks
1. Proteins from transferred genes could be toxic or cause allergic reactions
2. Antibiotic resistance genes used as markers during gene transfer could spread to bacteria

46
Q

Somatic Cell Transfer (5)

A

Reproductive cloning was first done in 1996 when Dolly the sheep was cloned

  1. A somatic cell from the original sheep was collected and the nucleus (and therefore the DNA was removed)
  2. A donor egg from another sheep was collected and all of the DNA was removed from the egg
  3. The DNA from the donor sheep was placed inn the empty egg
  4. The embryo was placed in the uterus of a surrogate sheep
  5. The embryo developed and Dolly the shape was born who was an exact copy
47
Q

What is therapeutic cloning?

A

Making one type of cell to replace damaged cells in the body using undifferentiated cells

48
Q

What is binary fission? (2)

A
  1. The parent organism divides equally in two, so as to produce two genetically identical daughter organisms
  2. This method of cloning occurs in Planaria (flatworms) but is also common to bacteria and protists (e.g. euglena, amoeba)
49
Q

What is budding?

A
  1. Cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent
  2. This method of cloning occurs in Hydra but is also common to many species of yeast
50
Q

Fragmentation

A
  1. New organisms grow from a separated fragment of the parent organism
  2. This method of cloning is common to starfish and certain species of annelid worms
51
Q

Parthenogenesis

A
  1. Embryos are formed from unfertilised ova (via the production of a diploid egg cells by the female)
  2. This method of cloning occurs in certain species of insect, fish, amphibians and reptiles

IB Biology SL (7 decks)

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