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Mendel was correct, but…. There are important exceptions to most of his principles involving dominant and recessive alleles. Such as…some alleles are neither dominant nor recessive.
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Mendel was correct, but… There are important exceptions to most of his principles involving dominant and recessive alleles.
Sometimes one trait is not completely dominant over another. These traits do not blend together, but each allele has its own degree of influence. This is known as incomplete dominance.
Incomplete Dominance Which allele is dominant in this case?
Incomplete dominance The phenomenon in which the effects of both alleles are apparent in the phenotype.
R=redW=whiteRW=Pink • R R W W RW RW RW RW Both genes express themselves equally so you get a pink color in the petals.
However, by crossing two pink flowers together there is a different outcome. • There is a possibility of obtaining one white, two pink, or one red flower. W R W R WW WR WR RR
Neither! The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes
Codominance • The phenomenon in which the effects of both alleles are apparent in the phenotype.
Codominance A similar situation to incomplete dominance, however instead of the appearance of blending of colors, both colors are expressed.
Identify which traits show codominance or incomplete dominance a) Birds can be blue, white, or white with blue-tipped feathers. b) Flowers can be white, pink, or red. c) A Hoo can have curly hair, spiked hair, or a mix of both curly and spiked. d) A Sneech can be tall, medium, or short. e) A Bleexo can be spotted, black, or white.
In fact, in most organisms, genetics is more complicated because the majority of genes have more than 2 alleles.
Multiple alleles • This does not mean that an individual can have more than 2 alleles. It only means that more than 2 possible alleles exist in a population.
For example human genes for blood type.A single gene with 4 known alleles that display a pattern of dominance that can produce 4 different blood types.
Polygenic Traits • Traits that are controlled by 2 or more genes. EX: Eye color—many genes are used in producing eye color. Different combinations of alleles for these genes produce very different eye colors.
AND…to make things even more interesting , many important traits are controlled by more than one gene.
Selective Breeding The process of selecting a few organisms with desired traits to serve as parents of the next generation.
Selective Breeding • For example, people have bred horses that are particularly fast or strong. And farmers have bred crops that produce large fruit or that grow in specific climates. Over the past 12,000 years, dogs have been selectively bred to produce more than 150 breeds.
