2.Write about maternal effect?
Maternal effect :The development of some characters in many organism is government or markly
influence by the genotype of the female parents, this is known as maternal effect. All through such
characters are governed by nuclear genes they still show the following features
1) Reciprical difference in F1. 2)Reciprical difference in most cases disappear. 3)It comsiderably samller
variation in F2 as compare to that on F3
In some extream cases, there may be no phenotype segregation in F2 , but it does Become evident
only in the F3. Many important characteristics of both plants and animals show maternal effects of which
some example are describe below
An extreame example of maternal effect is known in the snail limnara.. In this snail, the direction of
coiling of its shape cell is control by a single nuclear gene D/d, the dominant allele - D produces right
handed coiling, while its recessive allel d produces left handed coiling. The direction of cell colling in an
individuals is governed by the genotype of its female parent. and not by its own genotype. As a result, pre
cross between female with left handed coil (dd) and makes having right handed (DD) produced. F₁
progeny (Dd) with left handed coil, since the genotype of the female parent was dd. In F₂ segregation of
Dd produces three genotypes (Dd. dd, DD) in ratio 1:2:1 but all the F₂ snail
exhibit right handed coiling since there female parent had the genotype Dd, which directs right handed
colling in the progony. The F3 progery from the F₂ Individuals with the genotypes DD and Dd will show
right handed colling, while Individuals will exihibit left handed individuals, those produces typical 3:1
ratio(right handed : left handed in F3)
The reciprocal cross (♂️ right handed DD X ♀️ left handed dd), on the other hand, right handed
coiling in F1 as well as F₂ But on F3, a 8:1 ratio is optained as was cross at the previous. Thus inheritance
coiling of limnaea cell show......
1) Differences between Fi from receprocal cross(2) No segregation in F₂ (3)Appearence of typical F₂,
F3 generation.
The 3:1 ratio is clearly indicates the coiling of cells is governed by single nuclear gene. But the
segregation of this nuclear gene appeared to be delayed by one generation. In fact, the effect of the
segregation of nuclear gene Dd is normal and occurs in the F₂ generation itself. But the phenotypic effects
of this segregation are visible only one generation after the actual segregation of the alleles. These is
because the direction of colling. in this snail is determined by the plan or the direction of the first meiotic
division of the zygote, which is determined by some substances already present in the egg.
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