Inheritance Flashcards

Content • The Passage of Information from Parent to Offspring • The Nature of Genes and Alleles, and their Role in Determining the Phenotype • Monohybrid Crosses • Variation • Natural and Artificial Selection

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1
Q

explain the terms dominant, recessive, codominant, phenotype and genotype

A
  • dominant allele: expresses itself & gives the same phenotypes in both the homozygous & heterozygous conditions
  • recessive allele: does not express itself in the heterozygous condition, express only in homozygous condition
  • co-dominance: results when the 2 alleles controlling a trait both express themselves in the organism
  • phenotype: refers to expressed trait in an organism, for eg, the outwards appearance of an organism
  • genotype: is the genetic make-up (airs of alleles) of an organism, that is, the combination of genes in an organism
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2
Q

explain why observed ratios often differ from expected ratios

A
  • small sample size
  • ratio figures are based on chance & probabilities
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3
Q

key headings for genetic diagrams

A
  1. phenotypes of parents
  2. genotypes of parents
  3. gametes
  4. offspring genotypes
  5. offspring phenotypes
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4
Q

explain co-dominance with examples

A
  • co-dominance occurs when 2 alleles controlling a specific trait are both expressed in an organism
  • in blood grouping, the allele for blood type A is co-dminant to the allele for blood type B
  • if a homozygous individual for blood type A has an offsrpng with a homozygous individual with blood type B, the offspring will have both the A and B alleles resulting in AB blood type
  • so the offspring will have both antigens A & B and no antiboodies for blood type A or B
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5
Q

explain mutiple alleles

A

~ is a term used for a gene that exist in more than 2 alleles
eg, occurence of blood group
- IA & IB are dominant over IO

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6
Q

define mutation & describe the examples

A

mutation: sudden, random change in the structure of gene or in chromosme number, eg:
Sickle-cell anaemia:
- where the gene mutation results in the change in the structure of the gene (a change in sequence of bases or nucelotides in DNA)
- mutated gene produces haemoglobin S(HbS), a change in 3D shape of haemoglobin
- HbS molecules clump tgt, making cell sickle-shaped
- when oxygen conc in blood decreases, RBCs become sickle-shaped which interfers with the oxygen-carrying capacity of the RBCs and makes them fragile

down’s syndrome:
- normally, zygotes with extra chromosomes would fail to develop
- offspring of 2 normal parents might get an extra copy of chromosome 21, they have 47 chromosomes
- the older the mother, the higher the chances that copies of chromosome 21 will not separate during gamete formation

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7
Q

factors increasing rate of mutation

A

mutagenic agents/mutagens
- ultraviolet light, and alpha, beta & gamma radiations
- chemicals present in certain concentrations such as tar & formaldehyde(in cigarette smoke), lysergic acid diethylamide(LSD)

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8
Q

describe the difference between continuous and discontinuous variation and give examples of each

A
  1. DV: deals with a few clear-cut phenotypes, CV: deals with a range of phenotypes
  2. DV: controlled by 1 or a few genes, CV: controlled by many genes
  3. DV: genes do not show additive effect, CV: genes show additive effect
  4. DV: relative unaffected by environmental condition, CV: greatly affected by environmental conditions
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9
Q

variation & competition

A
  • In natural selecttion, nature select those varieties that are more competitive, more resistant to diseases & better adapted to changes in env, to survive & reproduce their kind
  • the other varities that are susceptible to diseases or environmental changes may die
  • mutation provides new genes or alleles (variations) for natural selection to operate on
  • hence, variation and competition lead to differential survival of, and reproduction by, those organisms best fitted to the environment
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10
Q

examples of environmental factors that act as forces of natural selection

A
  • food shortage
  • diseases
  • predation
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11
Q

explain the role of natural selection as a possible mechanism for evolution

A
  • more beneficial quaitites may accumulate in a species over the years
  • the new breed of organisms may be better adapted to their new env
  • hence, evolution happened
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12
Q

examples of artificial selection - selective breeding

A
  • breeding of soya bean plants: breeders want seeds that have high oil content - analyse seeds & select plants that produce seeds with high oil content
  • cows that produce plenty of milk & good meat are selected & used as female parents for the next generation - breeders mate cows with desirable traits with a bull that has known required traits so that they are more likely to obtain the desirable gene combi
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13
Q

artificial vs natural selection

A

NS: selection occurs when natural environmental conditions change
while
AS: humans select the varieties of organism that suit their needs

NS: varieties produced by mutations
while
AS: varieties are produced by selective breeding

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