Genetics Flashcards
Colour blindness is caused by a recessive allele. A woman and her partner have normal vision. Their first child has colour blindness. What is the probability of their second child having colour blindness if it is a son? A. 100% B. 25% C. 50% D. 0%
C.
One type of gene mutation involves a base substitution. What are the consequences of the base substitutions in the two new sequences of DNA?
A. Both are mutations that would result in different polypeptides.
B. Sequence 2 would result in a changed polypeptide but sequence 1 would not.
C. All three DNA sequences would translate into the same polypeptide.
D. Only the original DNA and sequence 2 would translate into the same polypeptide.
D.
The sequence of the first six amino acids of the normal beta haemoglobin chain are listed.
Valine - Histidine - Leucine - Threonine - Proline - Glutamic Acid
What sequence of amino acids could there be in the first six amino acids of the sickle-cell beta haemoglobin chain? A. B. C. D.
D.
A mouse breeder performs a test cross using a brown mouse to determine the unknown genotype of a black mouse. There are four offspring produced by the cross. What conclusions can be drawn?
A. 1/4 brown offspring if heterozygous parent
B. 3/4 black offspring if heterozygous parent
C. All black offspring = MUST be homozygous parent
D. Any brown offspring = Parent MUST be heterozygous
D.
What evidence from the pedigree chart confirms that ACHOO syndrome is not X-linked dominant?
A. 4 females in pedigree affected and X-linked do not affect females.
B. Affected male in generation II
C. Affected female in generation II
D. If X-linked dominant, affected mom in gen II couldn’t produce unaffected son
B
Which of the following would be possible only if the ACHOO syndrome is inherited as autosomal recessive?
A. 2 unaffected parents have child with condition
B. At least 1 parent has to be affected to produce children that have condition
C. Affected and unaffected parent have affected child.
D. 2 unaffected parents have no affected children.
A.
A test cross resulted in these recombinants: tB Tb -- -- tb tb Which of the following was the parental cross? A. TB//tb x tb//tb B. TB//tB x tb//Tb C. Tb//tB x tb//tb D. TB//tb x TB//tb
A.
What is the difference between the alleles of a gene? A. Their position on the chromosome B. Their amino acid sequence C. Their pentose sugars D. Their base sequence
D.
Describe the use of DNA profiling in forensic investigations.
Restriction endonuclease used to cut satellite DNA into fragments. PCR then used to amplify DNA segments and separated by size by gel electrophoresis. Pattern of bands compared to bands of suspects.
Using a named example, discuss the effects of genetically modifying an organism.
Genetic modification is the transfer of genes between organisms such as when modifying corn crops using Bt toxin gene.
Benefits:
- makes corn resistant to pests like corn-borers
- less pesticide used, saves money
- more yield
- less land needed for crops, could be used for wildlife instead as crops more efficient
Cons:
- non-target insects like monarch butterflies might be killed
- gene might spread to other plants by cross pollination
- possibility of allergic reactions when crop eaten
- only favoured countries have tech to do so.
Outline the effects of a base substitution mutation in the case of sickle-cell anaemia.
DNA changes from GAG to GTG, which is a single base missense substitution. This means that the mRNA changes from GAG to GUG, which when translated produces valine rather than glutamic acid and this changes the shape of haemoglobin and hence RBCs. Reduces efficiency of RBCs and can also block capillaries making blood clots more likely. Causes severe anaemia.
Factor IX is a blood clotting protein which some haemophiliacs lack. In the future haemophilia could be treated using clotting factors synthesised by gm bacteria. Outline the basic technique used for gene transfer.
mRNA coding for factor IX extracted from human cell and copied to cDNA using reverse transcriptase. Gene transferred using plasmids. Restriction endonuclease are used to open plasmid and to cut DNA. This produces sticky ends on gene and plasmid, which is easily sealed using ligament. Recombinant plasmid taken up by bacteria and then cultured to produce factor IX
Explain how males inherit haemophilia and how females can become carriers for the condition.
Haemophilia due to X-linked recessive allele. Y chromosomes as a result don’t have the allele, so males only inherit from mothers, meaning trait cannot be masked by another (dominant) allele from father. As females inherit one X chromosome from each parent, the disease can be inherited from both mother and father. Carriers can only be female as only they can be heterozygous for the recessive allele.
Explain how meiosis results in an effectively infinite genetic variety of gametes.
1 homologous chromosome comes from mother and one from father; and these pair up in prophase I (synapsis) to form bivalents. Crossing-over is the exchange of genes between non-sister chromatids and this also occurs in prophase I. Junctions where genes cross-over are chiasmata. Crossing-over occurs at random positions and may occur more than once on same bivalent. This means chromosomes aren’t identical. In metaphase I, chromosomes line up in middle of cell and are separated in anaphase I depending on how they are orientated, which is random. The assortment of one chromosome is independent of others. Leads to 2^23 possible combinations
Explain the use of karyotyping in human genetics.
Karyotyping is the number and type of chromosomes in a cell; cells collected from chorionic villus or by amniocentesis; chromosomes then arranged in pairs according to size.
Karyotypes have many uses:
- identifying gender of embryo as males will have differently sized sex chromosomes, whilst females have equally sized.
- used for pre-natal diagnosis of chromosome abnormalities/non-disjunction; helping to identify trisomies like trisomy 21 (down); which may lead to decisions to abort foetuses.
