Question

14) (4 pts) Many characters in a species are quantitative; in other words, the phenotypes in a population are gradations along continuum. Human height and human skin color are good examples. Explain the genetic basis (.e., not environmental) of this range of phenotypes. in one cell in meiosis II during gametogenesis, what will be the results the completion of

Answer 1

Many characters in species are quantitative and are represented in number of phenotypes in population such examples are human height and human skin colour. These variable range of phenotypes occur due to 2 factors 1) genetic 2) environmental

Genetic basis on this kind of population showing variable characters in a species. We take example of human height. In our family we can see the variation of heights between our mother and father, their children and the siblings too differ in the heights. We phenotypically observe twins that have grown adult will also not have exactly same height they too differ in height. This occurs due to polygenic inheritance. The characters that are expressed due to multiple genes are called polygenic and type of inheritance is called polygenic inheritance.

Human height shows continuous variation and a complex inheritance pattern. These can be seen as while experimenting will a monohybrid plant like pea there are only 2 genes expressing only 2 types of plant tall or dwarf. But as we cross yellow round seed plants and green wrinkled which is dihybrid cross we get 4 different types of phenotypes but a great variation in their genotypes. And when we take a trihybrid plant the complexity grows. From here we can observe that as the number of alleles increase the complexity of genotypes and phenotypes too increases.

Human height have a great variation and this is well observed in our family , our class, etc.having people of different heights and of different genetic composition. Many times this also happens that offspring of tall parents is shorter and vice versa and different results with different individuals.

Second we talk about the human eye colour. Black and brown eye colour is most common but we would have seen individuals with blue, grey, light brown, etc eye colour individuals. So this all is also due to polygenic inheritance in which many genes are responsible for expressing a character. The effect of each gene in an individual is hard to study in these cases and is very complex. There are about 15 or 16 genes responsible for the expression of eye colour. So we can understand how complex is to study their inheritance.

Except these 2 examples human skin colour is also a result of polygenic inheritance. So let's take an example that 3 pairs of gene are responsible for human skin colour, AaBbCc and these are self crossed. Then we can see the genetic variation and their phenotype.

AA, BB, CC = Contribute more pigment

Aa, Bb, Cc = some pigment ( half of the AA, BB, CC)

aa, bb cc = no pigment

These when expressed together results into

ABC AbC ab.c abc abC Abc a Bc A Bc AABBCC AABBCC Aa BBCe AABBCAABbCe AaBbCE Aa BB CeAaBbCe ABC * AbC AABbcCAAbbCc AaBb Cc AABbCe AAbbCe Aabb CC AaBbCcAabbCc Aa bbCe aa BBcc AaBB.cc Aabb.ceaabbCuaaBBcclaaBbcu abc AABBC c ABC AABBCC AABbCe Aa BBeie AABBccAABbet AabbCe Aabbee AaBbee AABBC.AAbbCt Aa Bb e AABbeAAbbes Aa bb Ce AaBbee Aabb ke Abc Ab C Aa BbCC Aabbce 2aBbCe Ag 8blabbce aabb Cc laqBbCaaabb Cc abc Aa BBCe Aa Bb Ce 0aBBea AaBBeAa Bbae aabb Ce aa Bbefaabbec abc AabbC Aabb Ce aabbet Aa bbae Aabbee aabb Ce aa Bbce laabb.ec. Phensty pe Ratio : 1: 6: 15:20:15: 6 : 1 6. 1. 15 20

The cross results in 7 different colour individuals.

Thank you...