Heredity: Variations and Mutation Flashcards

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1
Q

Variations

A
  • diff in traits btwn individuals of same species
  • indiv traits dependent on interactions btwn genes and environment
  • genetic variation is heritable, but variations due to environment is not (e.g fair skin allele)
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2
Q

Genetic variation

A
  • crossing over (prophase I)
  • independent assortment (metaphase I and II)
  • random fertilisation (fusion of gametes)
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3
Q

Discontinuous variation

A
  • controlled by 1 or few genes
  • deals with a few clear-cut phenotypes
  • no additive effect (no in between) e.g. blood type
  • not affected by environmental conditions
  • permanent
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4
Q

Continuous variation

A
  • controlled by additive effect of many genes
  • e.g. many genes controlling height, skin colour
  • deals with range of phenotypes
  • affected by environmental conditions
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5
Q

Mutation

A
  • a result of error during replication (interphase) of gene/chromosome
  • may be inherited by next generation if mutation occur in germline cells (sex cells)
  • dominant mutations easily detected, recessive mutations usually hidden
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6
Q

Somatic mutation

A
  • occur in normal body cells/somatic cells

- cannot be inherited

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7
Q

Types of mutation

A
  • Chromosome mutation

- Gene mutation

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8
Q

Chromosome mutation

A
  • change in number/structure of chromosomes
  • causes Down’s Syndrome
  • extra chromosome, caused by 21st pair
  • non-disjunction during anaphase
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9
Q

Gene mutation

A
  • change in structure of DNA/sequence of nucleotide bases changed
  • change in base –> change amino acid –> change structure and function of protein
  • substitution, insertion or deletion of nucleotides
  • produces variation btwn indiv as results in new alleles of genes
  • albinism and sickle-cell anaemia
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10
Q

Substitution (Gene mutation)

A
  • replace/swap/change bases
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11
Q

Insertion/deletion (Gene mutation)

A
  • adding or removing base
  • affects reading of triplet code
  • more dangerous as it results in frameshift
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12
Q

Down’s syndrome (Chromosome mutation)

A
  • normal humans: 46 chromosomes in body cells
  • Down syndrome: 47 chromosomes, extra copy of chromosome 21 (trisomy 21)
  • chromosome in mutation in maternal body cell, when split into 2 gametes, 1 has 2 copies of chromosome 21, the other has none
  • fuses with male gamete with 1 chromosome 21
  • total: 3 chromosome 21 (trisomy 21)
  • draw out diagram
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13
Q

Albinism (Gene mutation)

A
  • caused by mutation in recessive allele
  • absence of pigment melanin
  • results in reddish-white skin, white hair, pink hair
  • get sunburnt easily, sensitive to sunlight
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14
Q

Sickle-cell anaemia (Gene mutation)

A
  • caused by mutation in gene controlling haemoglobin production
  • mutated gene (HbS) is co-dominant to normal gene (HbA)
  • both alleles produce their own protein, both expressed
  • sickle-shaped red blood cells have low oxygen carrying capacity, tend to clump tgt (blocks blood capillaries)
  • fatal, usually die young
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15
Q

Sickle-cell anaemia and malaria

A
  • heterozygous (carriers) for sickle-cell allele are more resistant
  • heterozygous individuals are common in areas where malaria is prevalent e.g. West Africa
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16
Q

Mutation and selection

A
  • mutations can be beneficial or harmful
  • indiv with harmful mutations will be eliminated
  • indiv with beneficial mutations may leave more offspring than normal indiv
  • nature ‘selects’ organisms with more favourable characteristics to survive and reproduce
17
Q

Mutagenic agents

A
  • greatly increase rate of mutations
  • radiation: UV light, X-ray, alpha&beta radiation, gamma rays
  • chemicals: mustard gas, formaldehyde
  • absence of mutagens–> rate of spontaneous mutation is extremely low