genetics and inheritance Flashcards

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1
Q

State three causes of genetic variation.

A
  • Mutation
  • Crossing over
  • Independent segregation / assortment (of homologous chromosomes)
  • Random fusion of gametes / fertilisation / mating
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2
Q

What is meant by a genome?

A
  • (All) the DNA in a cell/organism;
  • ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
  • ‘the total number of DNA bases in a cell/organism’
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3
Q

What is a gene pool?

A
  • All the alleles in a population;
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4
Q

How do multiple alleles of a gene arise?

A
  • mutations;
  • which are different / at different positions in the gene;
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5
Q

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

A
  • Small sample size;
  • Fusion/fertilisation of gametes is random;
  • Linked Genes; Sex-linkage / crossing over;
  • Epistasis;
  • Lethal genotypes;
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6
Q

What is meant by a recessive allele?

A
  • Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;
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7
Q

What does Hardy Weinberg’s equation predict

A
  • The frequency/proportion of alleles (of a particular gene);
  • Will stay constant from one generation to the next/over generations / no genetic change over time;
  • Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration;
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8
Q

Define gene linkage

A
  • (Genes/loci) on same chromosome;
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9
Q

Define epistasis

A
  • The allele of one gene affects or masks the expression of another in the phenotype;
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10
Q

Describe why observed phenotypes don’t match expected values.

A
  • Fertilisation is random
    OR
  • Fusion of gametes is random;
  • Small/not-large population/sample;
  • Selection advantage/disadvantage/lethal alleles;
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11
Q

Define codominance

A
  • Both alleles expressed in the phenotype;
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12
Q

Rules for Dominant alleles

A
  • Affected offspring MUST have at least one affected parent.
  • Unaffected parents ONLY have unaffected offspring.
  • If both parents are affected and have an unaffected offspring, both parents must be Heterozygous
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13
Q

Rules for recessive alleles

A
  • Unaffected parents can have an affected offspring (if they are Heterozygous)
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14
Q

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.

A
  • (Recessive) allele is always expressed in males / males have one (recessive) allele;
  • Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;
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15
Q

Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage

A

Dominant : recessive

  1. 3:1
  2. 9:3:3:1
  3. 9:4:3 or 15:1 or 9:7
  4. 3:1 (no x over) (no other pattern other than four phenotypes with recombination of alleles)
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16
Q

What is meant by the term phenotype.

A
  • (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);
  • (Expression / appearance / characteristic due to) interaction with environment;
17
Q

Explain how a single base substitution causes a change in the structure of a polypeptide.

A
  • Change in (sequence of) amino acid(s)/primary structure;
  • Change in hydrogen/ionic/disulfide bonds;
  • Alters tertiary/30 structure;