Chemistry, asked by vikash19524, 1 month ago

Read the following and answer any four questions from 17 (i) to 17 (v)

17. A blue color flower denoted by BB is cross breed with that of white color flower plant

denoted by bb.

1)State the color of flower you would except in the F1 generation plants-

a) Blue

b) White

c) Mixture between the two

d) None​

Answers

Answered by harshikach522
0

Answer:

Polygenic Inheritance: Human skin color is a good example of polygenic (multiple gene) inheritance. Assume that three "dominant" capital letter genes (A, B and C) control dark pigmentation because more melanin is produced. The "recessive"alleles of these three genes (a, b & c) control light pigmentation because lower amounts of melanin are produced. The words dominant and recessive are placed in quotation marks because these pairs of alleles are not truly dominant and recessive as in some of the garden pea traits that Gregor Mendel studied. A genotype with all "dominant" capital genes (AABBCC) has the maximum amount of melanin and very dark skin. A genotype with all "recessive" small case genes (aabbcc) has the lowest amount of melanin and very light skin. Each "dominant" capital gene produces one unit of color, so that a wide range of intermediate skin colors are produced, depending on the number of "dominant" capital genes in the genotype. For example, a genotype with three "dominant" capital genes and three small case "recessive" genes (AaBbCc) has a medium amount of melanin and an intermediate skin color. This latter genotype would be characteristic of a mulatto.

In the following cross between two mulatto genotypes (AaBbCc x AaBbCc), each parent produces eight different types of gametes and these gametes combine with each other in 64 different ways resulting in a total of seven skin colors. The skin colors can be represented by the number of capital letters, ranging from zero (no capital letters) to six (all capital letters). The approximate shades of skin color corresponding to each genotype are shown in Table 1. Note: Skin color may involve at least four pairs of alleles with nine (or more) shades of skin color.

The cross in Table 1 can also be shown with the bionomial expansion (a + b)6 where the letter a = number of capital letters and the letter b = number of small case letters. Each term in the expression represents the number of offspring with a specific skin color phenotype based on the number of capital letters in the genotype. For example, 20 offspring have three capital letters in their genotype and have a skin color that is intermediate between very dark with all caps (AABBCC) and very light with no caps (aabbcc).

(a + b)6

= a6

+ 6 a5b

+ 15 a4b2

+ 20 a3b3

+ 15 a2b4

+ 6 ab5

+ b6

6 Caps

5 Caps

4 Caps

3 Caps

2 Caps

1 Cap

0 Caps

Multiple gene (polygenic) inheritance explains many plant and animal traits where there is a wide variation between extreme phenotypes, with most individuals having intermediate phenotypes. Some examples of polygenic inheritance are: human skin and eye color; height, weight and inteligence in people; and kernel color of wheat. In fact, kernel color in wheat is nicely shown in Table 2. Table 2 is essential the same as Table 1, except the extremes in color are dark red and white, rather than black and white. In polygenic inheritance the "dominant" capital genes are additive, each capital gene adding one unit of color to the genotype. With more capital genes, the phenotype (appearance) gets darker. The garden peas studied by Gregor Mendel involved pairs of alleles with only three possible genotypes and two phenotypes per trait. For example, the gene for round pea (R) is dominant over the gene for wrinkled pea (r) and only three genotypes are possible: RR, Rr and rr. These three genotypes produce only two phenotypes: Round (RR and Rr) and wrinkled (rr). There are no intermediate traits between round and wrinkled. If all human characteristics were controlled by simple pairs of dominant and recessive alleles like the one Mendel studied, we would have tall and short people with no intermediates. Polygenic inheritance is yet another exception to Mendel's genetic ratios.

Hope it helps you ✌️

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