7/30/2023 0 Comments Example of principle of dominanceDespite the presence of several alleles of the same gene in a population, an individual can have only two alleles.Ĭharacteristics, (i) There are more than two alleles of the same gene, e.g., 15 alleles for eye colour in Drosophila, 3 alleles for blood groups in humans, 4 alleles for coat colour in Rabbit, (ii) All the multiple alleles occur on the same gene locus of the same chromosome or its homologue. The coat colour of rabbits (Agouti, Chinchilla, Himalayan and Albino types) is also regulated by multiple alleles. Some of these alleles are wine (w w), coral (w c0), blood (w bl), cherry (w c), apricot (w a), eosine (w e), buff (w b), tinged (w f), honey (w h), ecru (w ec), pearl (w P), and ivory (w i). Thus the wild type of allele for red eye colour (w + or W) in Drosophila melanogaster mutated to form allele for white eye (w).įurther mutations in both have produced as much as 15 alleles which are recessive to wild type and dominant over white eye (w) but have incomplete intermediate dominance over one another. They show meristic type of germinal variations, e.g., eye colour in Drosophila, self incompatibility in some plants. Multiple alleles are produced due to repeated mutation of the same gene but in different directions. ![]() It is the presence of more than two alleles of a gene. The allele for sickle cell haemoglobin Hb S is codominant with allele for normal haemoglobin Hb A. The effect is actually produced due to fine mixing of red and white hair (hence mosaic). It is considered to be due to incomplete dominance of red colour allele over white colour allele. On cross-breeding, the individuals of the F 1, generation are found to have roan colour (Fig. (iii) There are two types of pure short horned cattle, red and white. F 2 generation produces three types of fowls- 1 black: 2 blue: 1 white. Incidentally the blue coloured fowls are favoured as delicacy. 5.9) due to occurrence of fine alternate black and white stripes on the feathers. If the two forms are crossed, F 1, individuals appear blue coloured (Fig. (ii) Andalusian fowls have two pure forms, black and white. ![]() The pink colour apparently appears either due to mixing of red and white colours (incomplete dominance) or expression of a single gene for pigmented flower which produces only pink colour (quantitative inheritance). If the latter are selfed, the plants of F 2 generation are of three types- red, pink and white flowered in the ratio of 1 2 1. ![]() When the two types of plants are crossed, the hybrids or plants of F 1 generation have pink flowers (Figs. Gulbansi) and Antirrhinum majus (Snapdragon or Dog flower), there are two types of flower colour in pure state, red and white. ![]() In Mirabilis jalapa (Four O’ Clock, vern. (i) Carl Correns reported incomplete dominance in case of flowers of Four O’ Clock. F 2 phenotypic ratio is 1: 2: 1, similar to genotypic ratio. It is however, considered by some workers to be an example of quantitative inheritance where only a single gene pair is involved. Incomplete or mosaic inheritance is not an example of pre-mendelian concept of blending inheritance because the parental types reappear in the F 2 generation. The expression of the character in a hybrid or F, individual is intermediate or a fine mixture of the expression of the two factors (as found in homozygous state).
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