Lethal gene, Biology

Assignment Help:

LETHAL GENE (2:1 Instead of 1 : 2 : 1 or 3 : 1)

(i)         All the genes present in an organism are not useful, but some of them show harmful effects and sometimes may cause death or lethality. Such factors or genes which cause death or lethality in an organism are called lethal gene or factors.

(ii)         These lethal factors are fortunately present in recessive state and thus cause death only in homozygous condition. In heterozygous condition, they may cause structural changes.

(iii)        Lethal factors were first of all reported in mice body colour by a French geneticist, L. Cuenot (1905). According to him, yellow mice never show true breeding and when yellow mouse is crossed with another yellow mouse, produce yellow and brown in the ratio of 2 : 1 (not 3 : 1). Yellow mouse is never present in homozygous condition.

(iv)        In the following example, 'Y' is a dominant gene for body colour but is recessive for lethality and when recessive genes come in homozygous condition, death is caused (i.e; YY - dies).

1213_lethal genes.png

(v)         Lethal factors in case of plants were reported first of all in Snapdragons (Antirrhinum majus) by E. Baur (1907). (vi) In Snapdragons (Antirrhinum majus), yellow leaved (golden leaved) or 'aurea' variety never breeds true. When aurea variety is crossed with aurea, aurea and green are produced in the ratio of 2 : 1 (not 3 : 1) i.e. aurea is always heterozygous (Gg).

1469_lethal genes1.png

(vii)        Here again 'G' is dominant gene for yellow colour but is simultaneously recessive for lethality and when recessive gene come in homozygous condition, death is caused (i.e; GG - dies). 

Thus lethal factors cause modification of 3 : 1 ratio into 2 : 1.


Related Discussions:- Lethal gene

Role of protein in metabolism, ROL E OF PROTEIN - Main organic comp...

ROL E OF PROTEIN - Main organic component of body. Unit is amino acid. Polymer of amino acids. Amino acids combine to each other by peptide bond. Formation of bone, t

Explain about the macro minerals, Explain about the Macro Minerals? Pre...

Explain about the Macro Minerals? Previously we learnt about the structure, properties, deficiencies/toxicity and recommended dietary intakes of several vitamins. In this unit,

General reproduction, write about the asexual reproduction in mucor

write about the asexual reproduction in mucor

Define tests to measure flexibility component in the humans, Define Tests t...

Define Tests to Measure Flexibility Component in the Humans? The flexibility component measures the elasticity or range of motion around a joint. This component of physical fi

Explain cardiac type of tapvc, Explain Cardiac Type of TAPVC (Draining into...

Explain Cardiac Type of TAPVC (Draining into Coronary Sinus) ? Initial steps of the operation are the same as described earlier. The right atrium is opened and the roof of the

Asexual reproduction in animals, Asexual Reproduction in Animals Repro...

Asexual Reproduction in Animals Reproduction may be referred as production of true copies. Most of the animals that are quite familiar to us generate male and female gametes (

Biology, excretory organs of different animals from protozoa to mammals

excretory organs of different animals from protozoa to mammals

Sex, How can I fuck my girlfriend without taking out cum?

How can I fuck my girlfriend without taking out cum?

Explain antiarrhythmic drugs, Explain Antiarrhythmic Drugs? Amiodarone ...

Explain Antiarrhythmic Drugs? Amiodarone may be considered in VT/VF that is refractory to shock. It might be given if the third shock is not successful. The dose is 300 mg IV i

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd