Topic 3: Genetics

Outline a possible cause of Down syndrome. (4)
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Outline a possible cause of Down syndrome. (4)
Down syndrome- condition where individuals has 3 copies of chromosome 21
-Caused by non-disjunction event in one of parental gametes
-occurs in anaphase I/II in meiosis
-occurs when pair of homologous fail to separate during meiosis
Linked genes(1)
genes that are located on the same chromosome
Sickle cell anemia affects the ability of red blood cells to transport oxygen. Explain the consequence of mutation causing sickle-cell anemia in relation to processes of transcription and translation(6)
-caused by single base substitution
-mRNA: its sequence changed from GAG to GUG
-During translation, have one amino acid subtituted for another cause glutamic acid replaced by valine
-sickle cell shape cause formation of clots within capillaries-> block blood supply to organs
Describe how human skin colour is determined genetically(5)
-example of polygenic inheritance
-combination of alleles determine phenotype allow for range of skin colour
-more than 2 genes contribute to a person's skin colour due to amount of melanin in skin
-the more recessive alleles, the lighter skin colour
Explain the causes of sickle-cell anemia(8)
-caused by gene mutation
-due to base subtitution
- DNA changed from CTC to CAC
-mRNA changed from GAG to GUG
-In polypeptide chain, glutamic acid replace by valine
-disable haemoglobin's ability to carry oxygen
Outline a technique used for gene transfer(5)
-using plasmid
-plasmid is a circular DNA molecule
-each restriction enzyme cuts at specific base sequence-> creates sticky ends
-DNA ligase used to splice
-recombinant DNA inserted into host cell
Explain, with a named example, how polygenic inheritance gives rise to continuous variation(2)
-skin colour control by at least several genes
-no alleles are dominant
Describe the inheritance of colour blindness in humans(3)
-Sex-linked condition
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Describe the process of blood clotting(4)
-clotting factor released by platelets
-cascade reactions
-prothrombin to thrombin
-thrombin converts fibrinogen to fibrin
Factor IX is a blood clotting protein which some hemophiliacs lack. In the future hemophilia could be treated using clotting factors synthesized by genetically modified bacteria. Outline the basic technique used for this gene transfer.(6)
- mRNA copies to DNA
-plasmid use
-restriction enzyme use to cut DNA
-sealed using ligase
-recombinant plasmid containing desired gene taken up by bacteria
Explain how males inherit hemophilia and how females become carriers for the condition(8)- hemophilia is a recessive trait - sex linked - gene is on X chromosome - Males inherit X chromosome from their mother - Males have only one copy so recessive trait is not masked - 50% of hemophilia - Carrier is heterozygous for the gene - females inherit X chromosome from father and one from mother - affected males have carrier daughters - hemophilia could inherit from either parentExplain the use of karyoptying in human genetics(8)- karyotype is a number and image of chromosomes in a cell - cells collected from chorionic villus - identify gender -Male is XY and female is XX - used identify non-disjunction and chromosome mutations - down syndrome due to extra chromosome 21 - may lead to decision to abort the fetus - prepare for consequences of abnormaility in offspringOutline the outcomes of the human genome project(4)- complete human DNA sequence - identification of all human genes - discover protein structures - find evidence for ancestorsDiscuss the role of gene and chromosomes in determining individual and shared character features of the member of a species(7)- genes have multiple alleles - alleles can be dominant or recessive - all members of a species have shared genes - all human have 46 chromosomes - some individuals have extra chromosome - X and Y determine the gender of individualExplain how meiosis results in an effectively infinite genetic variety in gametes (8)- 1 chromosome from mother and 1 from father - homologous chromosome pair in prophase I - crossing over formation in prophase I - recombination of linked genes - random orientation in metaphase I - independent assortment of chromosomes - 4 genetical different nuclei