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In: Biology

Not all genes display Mendelian inheritance, or X-linked inherence. Eye color is a polygenetic trait. Outline...

Not all genes display Mendelian inheritance, or X-linked inherence. Eye color is a polygenetic trait. Outline how polygenic characteristics are inherited. What are the ratios of inheritance for eye color? Write an in-depth paragraph explaining your answer.

Expert Solution

The polygenic inheritance is inheritance or transmission of traits or character which is controlled by more than 2 genes, this gene is called polygene. This inheritance also called a quantitative trait. There is no gene is dominant over another so they share equal expression so the intermediate trait observed in new progeny. It's like incomplete dominance where a variety of traits observed in new generation depends on how many genes are involved

If 2 genes are involved i.e dihybrid cross the phenotypic ratio of F2 will be 1:4:6:4:1 here 5 different traits are observed & if 3 genes are involved or trihybrid cross the phenotypic ratio will be 1:6:15:20:15:6:1 here 7 different traits observed.

Let's take an example

Eye colour is controlled by 16 different genes determined by the amount of melanin present in the iris so it becomes complicated. The Black and dark brown eyes have more melanin than hazel or green eyes while blue eyes do not have melanin. Consider 2 genes i.e in dihybrid cross gene 1 has B allele for Black colour eye and b is recessive for blue colour. Gene 2 has allele G for green colour and g is recessive for light hue colour, if we cross BbGg with BbGg i.e self cross

BbGg x BbGg

Gametes are BG, Bg, bG, bg.

By punnet square

	BG	Bg	bG	bg
BG	BBGG	BBGg	BbGG	BbGg
Bg	BBGg	BBgg	BbGg	Bbgg
bG	BbGG	BbGg	bbGG	bbGg
bg	BbGg	Bbgg	bbGg	bbgg

We get in F2

1 Black eyes: (BBGG)
4 Dark Brown eyes: (BBGg), (BbGG)
6 Light Brown eyes: (BbGg), (BBgg), (bbGG)
4 Green eyes: (Bbgg), (bbGg)
1 Blue eyes: (bbgg)

Presence of all dominant produces black eyes

Presence of at least 3 dominant alleles produces dark brown eyes

Presence of at least 2 dominant alleles produces light brown eyes

Presence of one dominant allele produces green eyes

And all recessive allele produces blue eyes.

Hopes u understand

gladiator answered 2 years ago

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