continuous and discontinuous variation | NMDCAT 2021

About This Video!
CONTINUOUSLY VARYING TRAITS
Genotype interacts with environment to produce phenotype. Phenotypic expression
of traits has two aspects:
(i) Qualitative
(ji) Quantitative
Qualitative diferences are large and more obvious, but quantitiave variations are small
and less striking. Some traits, like pea seed shape, show discontinuous qualitative
variations with two sharply distinct phenotypes, round or wrinkled; others like 4 O’clock
lower colour can have three phenotypes, red, pink and white; still others like ABO
blood group system have four qualitatively diferent phenotypes A, B, AB and O. But
many traits like height, weight, intelligence and skin colour in humans, and grain colour
in wheat exibit continuous quantitative variation over a range of many phenotypes.
endel focused on traits that showed only two qualitatively diferent phenotypes which
could be determined by just two alternate alleles of a single gene. Darwin observed small
continuous variations within individuals of a population. Such a range of phenotypic
spectrum of a trait cannot be traced to a single gene with two alleles. Even a few multiple
alleles of a single gene cannot make such a wide range of phenotypes.
MA continuously varying trait is encoded by alleles of two or more diferent gene
pairs found at diferent loci, all inluencing the same trait in an additive way. These
quantitative traits, are called polygenic traits, and their genes are polygenes. Each
polygene has a small positive or negative efect on the character. Polygenes supplement
each other and sum of positive and negative efects of all individual polygenes produce
quantitative phenotypes of a continuously Varying trait.
Wheat grains vary in colour from white to dark red. This trait shows a continuous
spectrum of colour variation. (Fig 22-10). Some grains are white, some are deep red but
most grains have shades in between from light pink to moderately dark red. Nilsson
- Ehle studied the genetics of wheat grain colour. When he crossed a true breeding
dark red grain plant with a true breeding white grain plant, all Fi grains had light red
colour, intermediate between two parental shades. It seemed as if it was a case of
incomplete dominance. But when Fi.grains were grown to mature plants and crossed
with each other, F2 grains had exactly seven shades of colour in the ratio of 1 dark red
: 6 moderately dark red : 15 red : 20 light red : 15 pink : 6 light pink : 1 white
Three diferent gene pairs, i.e. Aa, Bb, Cc at three diferent loci contribute to the wheat
grain colour. Each individual would contain six alleles for the trait. Alleles A, B and C
code for an equal amount (dose) of red pigment, which is a positive efect. But none
of a, b and c encode red pigment, which is a no (zero) dose negative efect. If all the six
alleles code for red pigment (AABBCC), the grain is dark red; when none of the six alleles
encode red pigment (aabbcc), the grain is white. When a grain has one allele for red
pigment (Aabbcc or aaBbcc or aabbCc) its colour is light pink; if it has two alleles for the
pigment (AaBbcc or aaBbCc or AabbCc) it is pink, if it has three pigment alleles (AaBbCc
or AABbcc or AabbCC), it will be light red. Similarly four alleles colour dose (AABBcc or
aaBBCC or AAbbCC) will make red and ive alleles colour dose (AABBCc or AABbCC or
AaBBCC) will produce moderately dark red grain. Thus the colour phenotype of the
grain is the sum of the individual efects of all the six alleles.Environmental factors like
light, water and nutrients also inluence the amount of grain colour. Environmental
variations make the distribution of phenotypes more smooth and continuous.

Human skin colour is also a quantitative trait which is controlled by three to six gene
pairs. The greater the number of pigment specifying genes, the darker the skin. A child
can have darker or lighter skin than his parents.
Human height is a more complex polygenic trait. The perfectly continuous variation
in range of human heights produces a smooth bell - shaped curve . A few
people are very tall or very short, but most individuals fall in the average or mean
value. This trait is controlled by many pairs of genes at diferent loci. Even multiple
alleles may be possible at each locus. More the number of alleles for shortness, the
shorter the height will be. Similarly greater the number of alleles for tallness, the taller
the height will be. Environment also has a strong inluence on height, intelligence and
skin colour in humans. Constant exposure to sun darkens skin. Poor nutrition prevents
achieving genetically determined height. Healthy and encouraging social environment
promotes intellegence.

[@sabahameed5974]

Great sir🤟✌🏻👍🏻👍🏻👍🏻

[@NZ-yk1lc]

Mashallah grt👌

[@BEATaminofficial]

Thanku sir USS biology have tough english to be understood Your explanation is wonderful😌😌

[@marachand1430]

Unique method of teaching

[@cotmajor6045]

Thank u, sir, it is the best video on the internet on this topic very helpful

[@ALIACADEMYAR7]

Dear Share this channel link with friends. Ta k ap bh duay le sky🙂

[@amirsohail5108]

Great sir mashallah

[@ayatullah3520]

I was in confusion but when I heard your this lecture I understood many more .thank you sir

[@mirtabinda517]

Walaykum asalam waramatullahi wa barakatuhu

[@amritkulana695]

ANALYSIS OF CONTINUOUS VARIATION........?

[@fotomoon123]

You amazing sir

[@IbrahimMughal-jm4np]

"Jo buht asan or simple sa topic hy" Yh ni bola sir ap ny 😄😃

[@usamarajpot7991]

Sir ye topic to Bohut lamba hai book par or ap ne Bohut short karvaya hai to hum bas yahi kare agar ye paper me ajae

[@asifamunir8681]

Its outstanding Amazing

[@Dhruvkumar-ty2vy]

Love from india... Sir..!! 🥰🥰🥰🥰

[@samanrehmanrehman9499]

Brilliant❤

[@kmemon6892]

Well explained ❤

[@rasheedraja603]

Very helpful

[@shaikhanis1097]

Great sir you are great

[@aamirbilal9857]

Thank Very good video

[@sairachandio8004]

Zabardast sir

[@sairachandio8004]

Sir Allah aap ko kamyab kry

[@Shahwaizsukhera-kb7zu]

Which everyone can easily understand 😊 Ammmmmmazing sir💞

[@Champ-wd9fg]

Heavy sir g

[@yarjan8876]

keep doing good work dear

[@sakhawatshahkhalil]

Amazing👍👍

[@mehsankhan3272]

Kindly post more videos regarding MCAT Your lectures are helpful!

[@ALIACADEMYAR7]

Dear all lectures are uploaded

[@ALIACADEMYAR7]

Check Playlist

[@umeriqbal9126]

Thumbs up👍👍👍

[@kisazehra1223]

Thank you very much sir

[@zabithayat1381]

Grt

[@pallabisaha9709]

Thanks sir

[@habiburrehman5265]

Sir evolution continuous variations sa ati ha ??

[@Manab-4980]

Well.....💓

[@abdullahabdulghaffar7938]

WELL EXPLAINED

[@shivikadubey2606]

Thank you sir

[@pritidebnath9239]

Thank you sir ☺️

[@nuzhathussain787]

sir horse skin color continuous or discontinuous?i

[@fatimamughal3986]

Okay sir

[@yousafxaiofficial9347]

Well explained thank you sir

[@aanandsah8820]

Clear

[@kratikasaini2728]

Vry helpful sir😊

[@farzanakhan9558]

Amazing lecture

[@Shahwaizsukhera-kb7zu]

Brilliant lacture❤

[@areebanoor2050]

🆗 done ✅

[@nakage_official]

"Light White"

[@shoaibkhanji2887]

Asslamualikum warahmatullah e wabarakatu

[@MBBSLOVER786]

Good

[@simrano6209]

Sir kindaly upload botany lecture

[@abdullahbhai8636]

Done sir

[@kinzahafeez5504]

Done ✅

[@hafizasadiakanwal3705]

done sir

[@Rehanhyder331]

❤

[@cupcake7453]

Thank u sir🤩🤩

[@ayshatahir8644]

👍👍👍👍

[@rohabshakil7223]

Done sir ✅

[@afeidkhankhan5867]

Asslamoalikum sir ! What means quantitative variation and qualilative variation? Sir.......................%?

[@uqbasyeda2991]

SIR G I HAVE DONE

[@pakturkian604]

❤❤❤❤

[@keithlanrosiellanza]

kederi

[@mariyamjutt9967]

Awlaa

[@bestknowledgepoint.6885]

❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤

[@SonamKumari-lq3kx]

Sir continuous ke spelling m N nhi h

[@user-rc7vf1nq7w]

Lecture pr focus kro N pr ni

[@sami400ullah]

Thank you sir

[@mominasaeed5296]

Done sir

[@simrano6209]

Sir kindaly upload botany lecture

[@ALIACADEMYAR7]

Kon se tooics

[@simrano6209]

I m from azad kashmir

[@simrano6209]

Introduction to plant systematic