Unit 3 - Genetics Flashcards
Outline a technique of gene transfer resulting in genetically modified organisms. [5]
The transfer of genes from one species to another is known as genetic modification.
Gene sequences can be generated from mRNA using reverse transcriptase, which is an enzyme that make DNA copies of RNA molecules called cDNA.
RE enzymes is used to cut out genes and some RE enzymes is used to cut open plasmid. RE enzymes cleave the sugar-phosphate backbone of gene to generate sticky ends. The gene of interest is inserted into a plasmid vector that has can been cut with the RE enzymes. The sticky ends of gene and vector plasmid is linked together by complementary base pairing (hydrogen bonding), then spliced together by DNA ligase to form recombinant plasmid and also seal nicks. Then the recombinant plasmid is introduced into host cells.
Explain the use of karyotyping in human genetics. [8]
Karyotypes are the no. and types of chromosomes in a eukaryotic cell.
Two procedures are used for obtaining cells containing fetal chromosomes, chorionic sampling and amniocentesis, from the fetus.
Then the cells are harvested and chemically induced to undertake cell division till it reaches metaphase.
Then burst the cells and spread chromosomes to take an image of the chromosomes, and arrange in a homologous pairs of decreasing length.
The karyotypes are used to identify sex of the organism, and to diagnose any chromosomal abnormalities.
Distinguish between autosomes and heterosomes in humans. [4]
Heterosomes determine sex and autosomes doesn’t determine sex.
Heterosomes:
- Females possess two copies of larger X chromosome.
- Males possess one copy of larger X chromosome and one copy of shorter Y chromosome.
- X chromosome carries many genes than Y chromosome.
Autosomes:
- Males and females have same type of autosomes.
- There are 22 pairs of autosomes.
Explain the cause of sickle-cell anemia and how this disease affects the humans. [8]
Sickle-cell anemia is caused by single base substitution mutation.
- It is due to a mutation of the gene that codes for the alpha-globin polypeptide in hemoglobin, Hb^A.
- The mutation converts the sixth codon of the gene from GAG to GTG on the non-transcribed strand, where CTC to CAC on the template strand. By this conversion a new allele is formed, called Hb^S.
- When the Hb^S allele is transcribed, the mRNA sequence’s sixth codon changes from GAG to GUG.
- When the mRNA is transcribed, the sixth amino acid in the polypeptide changes from glutamic acid to valine.
- The amino acid change alter the structure of hemoglobin, causing it to form insoluble fibrous strands. The insoluble hemoglobin cannot carry oxygen as effectively, and the formation of insoluble fibrous hemoglobin strands changes the shape of RBC to sickle shape.
- The sickle cells may form clots within the capillaries, blocking blood supply to vital organs.
Homozygous state (Hb^S,Hb^S) causes severe anemia.
Heterozygous state (Hb^A,Hb^S) causes less anemia also provides protection against malaria parasites.
Explain the processes involved in meiosis. [8]
Meiosis I:
1. Prophase I:
- Starts with a diploid cell.
- Its chromatin contains two uncoiled sets of chromosomes, one from each parent.
- After the DNA in the chromatin replicates, the chromatin condenses into two coiled sets of identical chromosomes.
- In a process called synapsis, each chromosome pairs up and binds to its corresponding homologous chromosomes forming a tetrad (four sister chromatids).
- In a process called crossing over, chromatids from each homologous chromosomes exchange segments of allele at chiasmata.
- Also called recombination, where crossing over randomly happens on every chromosomes, resulting in different gene combinations.
- Crossing over results in genetic variety in offspring.
- Then the nuclear membrane disappears.
- The centrioles move to opposite ends of the cell.
- Spindle fibers fan out from the centrioles.
- Metaphase I:
- The homologous chromosomes line up at the equator and attach to spindle fibers from opposite poles. - Anaphase I:
- Spindle fibers separate the homologous chromosomes in each tetrad and pull them to opposite poles of the cell. - Telophase I:
- One chromosome from each homologous pair at separate poles. However, each chromosomes are unidentical.
- Spindle fibers disappears
- Nuclear membrane reforms around the chromosomes.
- Finally cytokinesis occurs, where the cell divides into two haploid cells.
- Each haploid cell contains one set of chromosomes.
Meiosis II:
1. Prophase II:
- No DNA replication occurs.
- The nuclear membrane disappears.
- The spindle fibers fan out from the centrioles.
- Metaphase II:
- The each chromosomes line up at the equator.
- The spindle fibers attach to the chromosomes. - Anaphase II:
- The sister chromatids of each chromosome separate and move to opposite poles.
- Once the sister chromatids are separated, they are called chromosomes. - Telophase II:
- The spindle fibers disappear.
- The nuclear membrane reforms.
- Cytokinesis occurs in both the cells, forming four haploid cells.
- Each containing only one set of chromosomes.
Explain how meiosis promotes variation. [8]
In crossing over from prophase I, the non-sister chromatids from each homologous chromosomes exchange segments of alleles.
When homologous chromosome line up in metaphase I, their orientation is random.
Then the tetrads are separated in anaphase I and moved to opposite poles.
Crossing over therefore leads to independent assortment of chromosomes.
Humans can produce 2^23 combinations by random orientation.
Describe the use of DNA profiling in forensic investigations. [6]
A DNA sample is collected and then amplified using PCR.
Satellite DNA are cut with specific restriction enzymes to generate fragments, which their length will differ between individuals due to the variable length of their short tandem repeats. The fragments are separated using gel electrophoresis.
In forensic investigations, suspect’s patterns of bands on DNA should complete match with the DNA sample taken from criminal.
Giving one specific example, discuss genetic modification in organisms including the potential benefits and harmful effects. [8]
GMO are organisms where its characteristics are altered by addition/removal of a gene.
Universal genetic code allows specific gene to be transferred between species. Gene transfer involves splicing genes into a vector, after placed in host, the host cells are cloned.
Example of genetic modification - Bt-corn
Potential benefits:
- Increased yield
- Less need of pesticides
Harmful effects:
- Possibility of cross pollination
- New traits could cause allergic reactions
- Reduces genetic variation
Using a named example of a GM crop, discuss the specific ethical issues of its use. [6]
Bt corn is a genetically modified maze that incorporates an insecticide producing gene from the bacterium, Bacillus thuringiensis. The insecticide is lethal to corn borers, which would otherwise reduce the crop yield.
Benefits:
- Increased crop yield
- Less need of pesticides
Harmful effects:
- Ingestion of toxin by non-target species.
- Removal of traits cause adverse health reactions.
Discuss the ethical issues of therapeutic cloning in humans. [8]
Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical use.
Somatic cells are removed from adult donor and cultured, then an unfertilized egg is removed to produce an enucleated egg cell. The enucleated egg cell is fused with the somatic cell to form a diploid egg cell.
An electric current is then delivered to stimulate the egg to divide and develop into an embryo. The embryo is then implanted into uterus and it will develop into a genetic clone.
Pros:
- Stem cells from embryos have greater flexibility.
- Pluripotent stem cells can give rise to all cells.
- No need for immunosuppressive drugs.
Cons:
- Manipulation of human embryos are not ethically acceptable.
- Process of extracting embryonic stem cells may involve killing the embryo.
Outline outcomes of the human genome project. [4]
- Mapping: number, location, size and sequence of genes.
- Screening: production of specific gene probes to detect the carriers of genetic diseases.
- Medicine: discovery of new proteins have lead to improved treatments.
- Ancestry: comparisons with other genomes have provided insight into the evolution.
State one similarity and difference between the structure of genes and short tandem repeats. [2]
Similarity: Both made of DNA
Difference: Genes have longer base sequences that code for proteins, without repeats.
Outline the role of short tandem repeats in DNA profiling. [2]
Short tandem repeats allow individuals to be distinguished, and have unique pattern of bands in each individual.
Distinguish between sex-linked genes and genes with linked loci. [1]
Sex-linked genes are on the sex chromosome. whereas genes with linked loci are on the same autosome.
