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| Question | Answer |
| Define Gene | A heritable factor that controls a specific characteristic |
| Define Allele | An alternative form of a gene |
| Define Genome | whole genetic information of an organism |
| Define gene mutation | change in base sequence of a section of DNA coding for a particular feature |
| State that eukaryote chromosomes are made of DNA and proteins | Eukaryote chromosomes are made of DNA and proteins |
| Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia. | DNA sequence for beta chain of haemoglobin changed from GAG to GAG changes mRNA codon GAG to GUG = change in amino acid (Glutamic acid to Valine) alters shape = becomes insoluble cannot effectively carry oxygen could cause blood clots reduce red blood cell count (sickle cells destroyed quicker) heterozygous individuals have increased resistance to malaria (adv.) |
| State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei. | Meiosis is a reduction division of a diploid nucleus to form haploid nuclei. |
| Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down syndrome (trisomy 21). | If gamete has an extra chromosome (two copies) and fuses with normal gamete (1copy) = zygote with 3 copies: trisomy |
| State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure | In karyotyping, chromosomes are arranged in pairs according to their size and structure |
| State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities. | Karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities. |
| State that some genes have more than two alleles (multiple alleles). | Some genes have more than two alleles (multiple alleles). |
| State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans | Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans |
| Define sex linkage. | refers to when a gene controlling a characteristic is found on a sex chromosome |
| Describe the inheritance of colour blindness and hemophilia as examples of sex linkage | Colour blindness and haemophilia are both examples of X-linked recessive conditions The gene loci for these conditions are found on the non-homologous region of the X chromosome (they are not present of the Y chromosome) As males only have one allele for this gene they cannot be a carrier for the condition This means they have a higher frequency of being recessive and expressing the trait Males will always inherit an X-linked recessive condition from their mother Females will only inherit an X-linked recessive condition if they receive a recessive allele from both parents |
| State that a human female can be homozygous or heterozygous with respect to sex-linked genes. | A human female can be homozygous or heterozygous with respect to sex-linked genes. |
| Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA | 1. Denaturation: DNA sample is heated to separate it into two strands 2. Annealing: DNA primers attach to opposite ends of the target sequence 3. Elongation: A heat-tolerant DNA polymerase (Taq) copies the strands |
| State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size. | In gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size. |
| State that gel electrophoresis of DNA is used in DNA profiling. | gel electrophoresis of DNA is used in DNA profiling. |
| State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal. | When genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal. |
| Define clone. | a group of genetically identical organisms or a group of cells derived from a single parent cell |
| State two examples of the current uses of genetically modified crops or animals. | Engineering animals to enhance production Sheep produce more wool when engineered with the gene for the enzyme responsible for the production of cysteine - the main amino acid in the keratin protein of wool 1. Engineering crops to extend shelf life of fresh produce Tomatoes (Flavr Savr) have been engineered to have an extended keeping quality by switching off the gene for ripening and thus delaying the natural process of softening of fruit |
| Ethical issues for therapeutic cloning in humans | May be used to cure serious diseases or disabilities with cell therapy (replacing bad cells with good ones) Cells are taken at a stage when the embryo has no nervous system and can arguably feel no pain Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions) |
| Ethnic issues against therapeutic cloning in humans | Involves the creation and destruction of human embryos May develop into cancerous cells and cause tumours Very expensive and might not be accessible for all |
| Potential benefits effects of one example of genetic modification | Results in increased productivity of food production requires less land for comparable yield Less use of chemical pesticides, reducing the economic cost of farming reduces need for deforestation |
| Possible harmful effects of one example of genetic modification | May result in competition with native plant species Possibility of cross pollination Reduces genetic variation / biodiversity |
| Define genotype | the allele combination of an organism |
| Define phenotype | The characteristic |
| Define dominant allele | The allele expressed in heterozygous state |
| Define recessive allele | The allele not expressed in heterozygous state |
| Define co-dominant allele | pair of alleles both effect the phenotype in heterozygous state |
| Define Homozygous | identical alleles |
| Define heterozygous | different alleles |
| Define carrier | heterozygous individual carrying recessive disease condition |
| Define test cross | crossing known genotype with unknown homozygous genotype |
| Outline three outcomes of the sequencing of the complete human genome. | Mapping: We now know the number, location and basic sequence of human genes Screening: This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic disease conditions Medicine: With the discovery of new proteins and their functions, we can develop improved treatments (pharmacogenetics and rational drug design) Ancestry: It will give us improved insight into the origins, evolution and historical migratory patterns of humans |
| Explain that female carriers are heterozygous for X-linked recessive alleles | An individual with a recessive allele for a disease condition that is masked by a normal dominant allele is said to be a carrier Carriers are heterozygous and can potentially pass the trait on to the next generation, but do not suffer from the defective condition themselves Females can be carriers for X-linked recessive conditions as have two X chromosomes - males (XY) cannot be carriers As a male only inherits an X chromosome from his mother, his chances of inheriting the disease condition from a carrier mother is greater |
| Analyse DNA profiles to draw conclusions about paternity or forensic investigations | Paternity Testing: Children inherit half of their alleles from each parent and thus should possess a combination of their parents alleles Forensic Investigation: Suspect DNA should be a complete match with the sample taken from a crime scene if a conviction is to occur |
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