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George Mendel's Laws (How he developed the Laws (Studied: (Colour of…
George Mendel's Laws
1] Law of segregation
Each inherited trait is defined by a gene pair
Alleles of parental genes separate during the formation of gametes
Gametes therefore only contain 1 gene allele of the pair
Offspring therefore only inherit one allele from each parent
2] Law of independent assortment
Genes for different traits are sorted separately from one another
Inheritance of one trait is not dependent on the inheritance of another
3]Law of dominance
An organism with alternative forms of a gene will express the form that is dominant
How he developed the Laws
Experimented using pea plants
Studied:
Colour of plant's flowers + location on plant
Shape & colour of pea pods & seeds
Length of plant stems
Transferred pollen (male sex cells) from stamen of one plant to the pistil of another
Fertilised first & second generations generations
How we know his work is relevant
Meiosis
Proves the law of segregation & assortment
Haploid cells, fuse together during fertilisation = diploid
Random assortment of genes
Recombination - ensures genes are independent from one another
Law of dominance
Observed in the phenotype, first generation and second
Fruit Flies
Thomas Hunt - studied genetic variation
Found a white-eyed variation in male fruit fly
Mated mutant white-eye male with red-eyed female
F1 = 100% red-eyed
F2 = 3:1 red:white-eyed - expected
White-eyed flies were only males - unexpected
Suggested it was carried on X chromosome - proved traits where genetic and the result of genes
Supported the law of segregation + dominance
As only females got the characteristic if both X chromosomes were had the recessive gene - males got the characteristic with just one affected chromosome as they don't have an alternative form of the X chromosome
Proved each genetic trait is defined by a gene pair
Limitations
Dominance does not always occur
Can be 2 dominants - form co-dominance E.g. Blood groups
Didn't factor in environmental influences on the phenotype