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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 • 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 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 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) 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 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 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 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 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 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 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 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 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 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