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Genotype & Phenotype

Genotype & Phenotype. Chapter 9. Inherited Characteristics. Information controlling inherited characteristics is passed on during sexual reproduction E.g. leaf shape coat colour in dogs wing type in flies tongue rolling in humans. True Breeding.

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Genotype & Phenotype

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  1. Genotype & Phenotype Chapter 9

  2. Inherited Characteristics • Information controlling inherited characteristics is passed on during sexual reproduction • E.g. • leaf shape • coat colour in dogs • wing type in flies • tongue rolling in humans

  3. True Breeding • When a characteristic is passed on identically through several generations • E.g. flower colour • Offspring are identical to their parents for that characteristic • Also known as pure breeding

  4. Single factor (monohybrid) cross • Investigates the inheritance of one characteristic only • 2 true breeding species are bred (crossed) together • They only ever differ in one characteristic • PHENOTYPE: The physical appearance of a characteristic

  5. Monohybrid cross (ctd.) • When two true breeding species are crossed, the offspring produced all appear the same • These are the first generation (F1) • When these F1 are interbred, the offspring often produce a 3:1 ratio • e.g. 3 red flower : 1white flower • These are the second generation (F2)

  6. Monohybrid cross (ctd.) • The characteristic that comes through in the F1 generation is dominant • E.g. purple flowers • The characteristic that’s masked is recessive • E.g white flowers • All monohybrid crosses produce a 3 : 1 ratio

  7. Genes & Genotype • Genes control each inherited characteristic • The complete set of genes is known as the GENOTYPE • At least 2 forms of each gene exist within a species • Different forms of a gene are known as alleles • every cell has two alleles, one from each parent e.g PP • Every gamete has only one allele e.g P

  8. Homozygous & Heterozygous • When an organism possesses two identical alleles of a gene e.g. PP or pp, • - it is said to be homozygous (true breeding) • If the alleles differ, the genotype is said to be heterozygous • E.g Pp • Organisms can have the same phenotype but a different genotype

  9. Observed vs. predicted figures • Monohybrid crosses should always produce a 3:1 ratio in the F2 generation • However in real life this rarely happens • This is because fertilisation is a random process • There is always an element of chance

  10. Human Inheritance • Humans are unsuitable for genetic study • - too few offspring, too many genes • However a family tree can trace inheritance • E.g - red hair colour is recessive • - children can have red hair even if their parents don’t • Element of chance always applies

  11. Co-Dominance • Some alleles are co-dominant • That means no allele is fully dominant or recessive • E.g. blood group • A & B are co-dominant to each other • A & B are completely dominant over O • So, AB genotype = AB phenotype • But, AO, or BO, genotype = A or B phenotype

  12. Polygenic Inheritance • Many characteristics are controlled by several different genes • Therefore there are a range of phenotypes possible • E.g. height – varies without distinct groups • E.g. Skin colour – wide range of colours • These are controlled by polygenic inheritance

  13. Phenotype and environment • Some characteristics are solely dependent on genotype • E.g. blood group • But, phenotype can be influenced by environmental factors • Genotype + Environment --- phenotype • This can be shown by studying clones or twins - genetically identical • Any differences must be due to environmental factors • If these species breed, offspring will not inherit the physical changes

  14. Natural Selection • Every species can potentially produce far more offspring than environment can support • Members of a species all show slight differences in phenotype • E.g Peppered Moth • Organisms with favourable phenotypes will be better adapted to their environment • Their favourable characteristics will be passed on to the next generation • Those with unsuitable characteristics will die out and will not get to reproduce • Also known as SURVIVAL OF THE FITTEST

  15. Evolution • The present biodiversity on the earth is due to natural selection over millions of years. • This is known as EVOLUTION • In time more and more complex lifeforms will continue to develop • Provided that human activity doesn’t wipe out too many habitats

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