Basic Mendelism - BIOL003 PDF

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Basic Mendelism - L1- Prof. Steve Jones Tuesday, 14 January 2020 20:46

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2/3 die from their genes

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Die now from dementia + cancer rather than bacterial illnesses

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Cheaper

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23,000 genes that make proteins in the human genome

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Lots of data now available 100,000 genomes sequenced by NHS

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1994 = 50 genes marked, they caused single loci diseases 2018 = 4,000 genes marked Any two human genomes vary at 3 million sites

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Corn yield increased by 8x since 1940s

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Darwin - " descent with modification" Thought genetics was blending ≠ Fleeming Jenkin "red and yellow paint = purple, can never get red back"

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On right is the most recent tree of life.

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Galton = Darwin's cousin Left money to UCL for genetics Was a eugenicist

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William inherits sticky out ears and a crown, only one is genetic Be aware not everything inherited is due to genetics

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Pellagra dries skin, can lead to blindness Families up to four generations with pellagra Considered genetic, it's not Down to vitamin A deficiency, clears up with increase in vitamin A

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Darwin - offspring inherit genetically what parents acquire in life Mendel counted, didn't measure Thought of gene as particle not fluid

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Studied discrete characters in peas - round, wrinkled; yellow or green Instead of e.g. milk yield (measurement) which was done before Can self-fertilise, anther + pollen = male, ovary = female

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Had access to pure lines kept by breeders Pure lines = many generations had same characteristics

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P1 -> the first parental generation F1 -> the first filial generation; filial = denoting the offspring of a cross. All yellow, NOT mix of greeny-yellow, NOT blending inheritance

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Self-fertilisation of F1 1st finding = always got both phenotypes Green phenotype reappeared, couldn't happen if genes fluid, couldn't "unmix" 2nd finding = clear ratio of 3:1 yellow to green

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He suggested adult peas have two particles for each character; pollen and egg have only one - meet at fertilisation

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F2s selfed Green F2s = all offspring green 1/3 Yellow F2s = only yellow offspring 2/3 Yellow F2s = green and yellow So 3:1 previous ratio in 2nd gen was actually 1:2:1 ratio

Mendel's 1st law - the law of segregation: two members of gene pair segregate into separate gametes; half carrying one member of the pair and the other half the other member 

Applied his knowledge to other characteristics = there was general application

Gamete -> a mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote. Zygote -> a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum. Locus -> the position of a gene or mutation on a chromosome. Allele -> each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. Dominant -> a dominant trait is one that is phenotypically expressed in heterozygotes. Recessive -> a gene that can be masked by a dominant gene. Homozygote -> A nucleus, cell or organism where the alleles for a particular gene on each chromosome are identical. Heterozygote -> A nucleus, cell or organism possessing two different alleles for a particular gene.

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Study pedigrees Consanguineous -> relating to or denoting people descended from the same ancestor China pedigrees back 100s yrs

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Dominant easier to study than recessive

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Everyone affected has 1 affected parents Never skips generation 1/2 children of affected are affected

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Dominant pedigree = know everyone's genotype

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Habsburg lip - jutting lower jaw; lisping From pedigree, looks like a dominant condition

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Huntington's disease = dominant, comes late in life Mother or father shows signs at ≈ 40, 1/2 chance of you inheriting

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Her mother showed signs of the disease She went to Lake Maracaibo, Venezuela; high freq of hunt there She studied 18000 people, worked out massive pedigree 4000 blood samples Found gene locus Developed a test for disease, didn't take it herself, but didn't suffer

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Recessive: affected child born to normal parents Cell membrane disease 1/250,000 births have cystic fib

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Most common single gene abnormality in Europe = cystic fib 1/25 have single copy of disease

Condition skips generations Affected people may have unaffected parents 1/4 children are affected in a family with affected children You can't work out the genotype of everyone, only know they're a carrier if they have affected children

Only know probabilities of who are potential carriers

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Know where on chromosome 7 the gene is found Now find genotype by look at damaged allele in the DNA Now know everyone carries 2-3 lethal singular copies of genes

This is one of the first treatments which is actually treating the disease, not just defeating the symptoms - but it's only for one variant of the gene so can help hardly anyone. Maybe more treatments will be found in the future.

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