Genetics 10 Flashcards
Define genetics
The study of genes and inheritance
Define a chromosome
A structure in the nucleus of a cell that contains DNA
Define DNA
A molecule that carries genetic information for the development and functioning of an organism
Define a triplet codon
A group of 3 bases on mRNA that code for an amino acid
Define a polypeptide
A string of amino acids that connects with other polypeptides to form a protein
Define a genotype
The pair of genes that controls a specific characteristic in an organism (e.g. RR, rr, Rr)
Define a phenotype
The observable characteristic that results from one genotype (e.g. tall, short)
Define an allele
An alternative form of a specified gene (e.g. R for round, r for wrinkled)
Define the term homozygous
refers to a gene pair where both alleles are the same (e.g. RR)
Define the term heterozygous
refers to a gene pair where the alleles are different (E.g. Rr)
Define a mutation
The changing of a gene that results in a variant form that is permanent
Define a mutagen
Any environmental agent that causes a mutation. Can be chemical, physical or biological.
Define the term homologous
Chromosomes that carry the same genes that code for the same thing
Define the term diploid
The presence of two copies of each chromosome in an organism’s cells, with each parent contributing a chromosome to each pair.
Define the term haploid
The presence of only one of each chromosome in an organism’s cells
Describe the steps of X-Ray Crystallography
- x-rays are beamed at a sample of a chemical
- x-rays are diffracted by atoms in the chemical substance
- diffracted rays strike a screen behind the sample and are detected
- pattern of diffraction is used to work out the position of the atoms in the chemical substance
Describe the process of transcription
- The DNA for one gene unwinds
- Helicase “unzips” DNA
- RNA polymerase attaches free-floating nucleotides to the complimentary bases on the sense strand
- The mRNA strand detaches and leaves nucleus and enters the ribosome
Describe the process of translation
- The mRNA enters the ribosome
- The ribosome reads the sequence of bases on mRNA in triplet codons
- Free-floating transfer RNA attach to the triplet codons by complementary base pairing of their anticodon site
- Each tRNA brings its amino acid and places it in line
- The amino acids are connected in a chain & the tRNA detaches
- The amino acid chain forms a polypeptide
Describe the structure of a nucleotide
A phosphate attached to a pentagonal sugar molecule attached to a base
Which bases have a double hydrogen bond and which have a triple hydrogen bond?
A-T is a double bond, C-G is a triple bond
Give examples of a chemical mutagen
- tar
- asbestos
- benzene
How do chemicals cause mutations?
They are usually structurally similar to DNA. Prolonged exposure may lead to their incorporation in DNA by mistake during DNA replication, disrupting the normal DNA sequence.
How do physical mutagens cause mutations?
High energy electromagnetic radiation can penetrate cells & be absorbed by chemical bonds in DNA. The energy absorbed can break covalent bonds in DNA.
Give examples of physical mutagens
- UV light
- X-rays
- gamma rays
How do biological mutagens cause mutations?
They infiltrate cells and insert their own DNA into the host DNA
Give examples of biological mutagens
- viruses
- bacteria
- fungi
What are the types of mutations
- Point mutations - occurs with a single base pair
- Chromosomal mutations - occurs with a section of genes on a chromosome
What are the types of point mutations?
- point substitution to another nucleotide (e.g. ACT → AGT)
- point insertion with frameshift (e.g. ACT → GACT)
- point deletion with frameshift (e.g. ACT → AT)
What are the types of chromosomal mutations?
- chromosomal deletion - section breaks off and disappears (ABCDEF → ABCD)
- chromosomal duplication - section is copied and added (ABCDEF → ABCDCDEF)
- chromosome inversion - section is detached, rotated 180° and attached (e.g. ABCDEF → ABDCEF)
- chromosome translocation - section detaches from one chromosome and attaches to a different chromosome
What are the effects of point substitution?
- silent mutation - triplet codon codes for the same amino acid → no change
- nonsense mutation - triplet codon changed to a stop codon; cuts polypeptide short → major change to phenotype
- missense mutation - triplet codon codes for a different amino acid; resultant polypeptide is less functional → minor change to phenotype
What are the effects of a point insertion/deletion?
Frameshift - likely to cause a major change to amino acid sequence in the polypeptide → major change in phenotype
What are the effects of a chromosomal mutation?
- likely to lead to amino acid sequence change in polypeptide → major phenotype change
- many genes are affected → many phenotypes changed
What is the difference between a somatic and germline mutation?
- Somatic: occurs in a cell that is not a gamete
* cannot be passed to offspring
* can be passed on in local cell divisiion
* affects one part of the organism - Germline: occurs in cells that will become gametes
* will be passed to offspring
* mutation will be in all cells of the offspring
* can potentially affect the whole offspring
What were the dependent, independant and controlled variables in Mendel’s work?
Independant - genotype of the plant
Dependant - resultant phenotype of the plant
Controlled - amount of water & sun, type of soil, type of plant, cross-breeding
Which protein does DNA coil around?
Histone
Why was maths important to Mendel’s work?
it helped explain his observations and ensured that he repeated the experiments enough times to make sure his results weren’t due to chance
What were Mendel’s Laws of Inheritance?
- Law of segregation - every phenotype is controlled by two hereditary factors, These separate and get passed on to the offspring. Each offspring inherits one hereditary factor for each characteristic from each parent
- Law of dominance - when there are two hereditary factors in a pair, one will be expressed while the other is masked
- Law of independent assortment - hereditary factors for different characteristics separate and are passed on independently of one another
What are the stages of Meiosis?
- Late Interphase
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- Cytokinesis I
- Interphase II
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
- Cytokinesis II
Describe Late interphase
- Chromosomes duplicate but remain connected at the centromere
- Centrosome duplicates
Describe prophase I
- Homologous duplicated chromosomes pair up and form a “bridge” or synapse
- Crossing over: sections of genes are swapped between non-sister chromatids via the synapse
- spindle fibres reach from centrosomes to centromeres
- nuclear membrane breaks down
- centrosomes move to opposite ends of cell
Describe metaphase
- chromosomes line up in homologous pairs along the middle of the cell
Describe anaphase
- homologous chromosomes separate and are pulled to opposite ends of the cell
Describe telophase
- chromosomes arrive at opposite poles of the cell
- spindle fibres break down
- nuclear membrane forms at each pole around each cluster of chromosomes
Describe cytokinesis
new membrane forms to produce new cells
Describe interphase II
- chromosomes are NOT duplicated
- centrosome is duplicated
Describe prophase II
- nuclear membrane breaks down
- centrosomes move to opposite ends of cell
- spindle fibres reach from centrosomes to centromeres
Who discovered the shape of DNA?
Watson, Crick, Franklin and Wilkins using X-ray crystallography
What are the similarities and differences between a parent and daughter cell in meiosis?
Similarities: both contain chromosomes, both have a nucleus
Differences: parent cells are diploid & daughter cells are haploid, parent cells contain maternal and paternal chromosomes & daughter cells may only contain chromosomes from one parent, each daughter cell has half the number of chromosomes as the parent cell
Outline the steps of DNA replication
- double helix unwinds
- DNA unzipped down the middle by helicase
- free-floating nucleotides attached by DNA polymerase, pairing with complementary base
- Errors (mismatched bases) are identified & repaired by DNA Polymerase I
Why is it important that DNA replication is done without error?
- full instructions for cells need to be passed on to offspring
- instruction must not be corrupted otherwise the action is done wrong/cannot be carried out
How does Mendel’s law of segregation apply to meiosis?
- Every characteristic (phenotype) is controlled by two hereditary factors → chromosomes exist in homologous pairs
- these separate and are passed to offspring → one chromosome of each homologous pair is distributed to each gamete
- each offspring inherits one hereditary factor for each characteristic from each parent → at fertilisation, chromosomes re-form homologous pairs
How does Mendel’s law of independent assortment apply to meiosis?
Hereditary factors for different characteristics separate and are passed on independently of one another → chromosomes line up randomly in Metaphase I so that genes can be passed on independently of one another, however genes on the same chromosome are passed on together
What is biotechnology?
the use of biological processes (or products of these processes) as tools to create new products that fulfil human needs
What is genetic engineering?
any technology that has to do with the selection, copying, or modification of a single gene
What are the pros and cons of BT cotton?
Pros:
* pest-resistant
* reduced pesticide use
* improved farmer’s livelihoods
* lower production cost
* increased yield
Cons:
* kills non-pests
* expensive seeds
* pests can become resistant
* increased use of water & fertilisers
* farmers depend on seed companies
What are the pros and cons of the Hep B vaccine?
Pros:
* low production cost
* can be given to people with impaired immune systems
* better for transportation & storage
Cons:
* may require boosters
* low ability to invoke an immune response
What are the pros and cons of golden rice?
Pros:
* provides more nutrition
* provides vitamins
* reduces stomach problems
* reduced pesticides
Cons:
* expensive
* can’t be a replacement for all nutrients
What are the pros and cons of Cystic Fibrosis Gene Therapy?
Pros:
* life-saving
* low health risk
* doesn’t affect other genes
Cons:
* limited control
* may cause cancer
* expensive
