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Asexual reproduction
Advantages: Lack of need to find a mate
Rapid reproductive cycle
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Meiosis: forms 4 genetically different haploid (half number of chromosomes) daughter cells / gametes
Only happens in reproductive organs: ovaries/testes
Produces: sperm/ egg & pollen / ovule
2 divisions
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Genome: entire DNA of organism
Gene: section of DNA on a chromosome that codes for a specific protein – inherited factor
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Order of bases in section of DNA decides order of amino acids in the protein – determines shape/function of
protein (enzyme): phenotype – characteristics
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Genetic variants in non-coding DNA of gene can affect phenotype
Non-coding DNA: RNA binding site – may not bind as efficiently – affects how much mRNA transcribed: alters quantity of
protein produced: can alter phenotype
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Mendel – results published in 1866
Noted how characteristics in plants were passed on through generations
First person to succeed in predicting how traits transfer

Studied 1 trait at a time to control variables & analyse data mathematically
His work not recognised until later: microscopes not discovered – no knowledge of cells / chromosomes / DNA / genes
Conclusions: Characteristics in plants determined by ‘hereditary units’ (genes)
Hereditary units passed onto offspring unchanged from both parents – 1 from each
Hereditary units can be dominant / recessive
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Chromosome: long/coiled up molecules of DNA – found in nucleus (of eukaryotic cells)
Allele: different form of genes
Dominant: ‘capital’ – overrule recessive allele – determines characteristic
Recessive: ‘lower case’ – to be displayed: both alleles must be recessive
Homozygous: 2 alleles for particular gene are the same
Heterozygous: 2 alleles for particular gene are different
Genotype: 2 letters – combination of alleles – 2 alleles present on pair of chromosomes
Phenotype: characteristics – homo/heterozygous + characteristic
Gamete: 1 letter – reproductive cell: passes generations – haploid (half number of chromosomes than normal cell)
Zygote:
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sex of offspring determined at fertilisation
Every human body cell: 23 matched pairs of chromosomes
23rd pair labelled XX or XY – two chromosomes determining sex
Male XY: Y causes male characteristics
Female XX: XX combinations causes female characteristics
All eggs have X
Sperm can have X or Y
use genetic diagrams: equal chance
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Inheritance of blood groups: O - A - B – AB – alleles: O / A / B
Codominance: one allele isn’t dominant over the other – A & B
O: recessive
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Most phenotypic features result from multiple genes rather than single gene inheritance
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Human Genome Project
Big idea: find every single human gene
Now they’ve all been found – scientists trying to find out what they do
Helped identify 1800 genes related to disease – high potential benefits for medicine
potential applications within medicine
Understanding genome can indicate persons risk of developing diseases
Sickle cell anaemia: changed shape of haemoglobin – but malaria can’t hold to it (positive mutation)
Can help identify which medicines are best to treat illnesses – alleles can effect how medicines work on body
Gene therapy – cystic fibrosis
Prediction/Prevention of disease: different genes & lifestyle factors cause many common diseases (cancers / heart disease)
If doctors knew what genes made people likely to get disease, they could:
tailor advice to avoid it
regularly check us to ensure early treatment if susceptible disease is developed
Testing/Treatment for inherited disorders – caused by presence of 1+ faulty alleles in person’s genome
Doctors can identify genes/alleles suspected to cause inherited disease faster – can test people for it – possible to develop
better treatment/cure
New / better medicines
HGP highlighted common genetic variations – some affect how individuals react to certain diseases/treatments
Scientists can: design drugs tailored to people with particular genetic variation
determine how well existing drug will work for individual
Allow us to design more effective treatments with fewer side-effects
identify how some patients will respond to particular drug
identify appropriate dosage for patient
Drawbacks
Increased stress: told about potential of disease from young age
Gene-ism: people with genetic problems under pressure not to have children
Discrimination by employers/insurers: life insurance less likely for people with genetic likelihood of serious disease
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Most genetic mutations have no effect on phenotype
some mutations have small effect on phenotype
rarely, a single mutation will significantly affect phenotype



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