11. In mice the yellow allele is dominant over the white allele, but lethal in t

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11. In mice the yellow allele is dominant over the white allele, but lethal in the homozygous 1 state. Several yellow mice are crossed and 108 offspring are produced. How many of these should be yellow? 12. The ability to taste PTC, a bitter tasting chemical, is determined by a dominant allele Albinism is caused by the recessive allele in the homozygous state. Two tasters, normally pigmented, have an albino son and a non-taster, normally pigmented daughter. What is the probability that their son is a taster? 13. If an individual has the genotype AABbDdee what possible gametes could they produce? 14. In wheat red color is produced when the dominant alleles R and B are both present. Brown color is produced when only one of the dominant alleles is present. Homozygous recessives are white. What is the genetic term for this type of cumulative effect? What is the phenotype and ratio of the F, and F2 generations of a cross between a brown (Rrbb) plant and brown (rBB) plant? 1

Explanation / Answer

11.

Genotype of yellow mice: XYXW

lethal

XYXW

XWXW

From above table it is clear that 2 / 3 i.e. 66.6 % will be yellow mice.

Thus number of yellow mice out of 108 mice = 108 x 66.6 / 100 = 72

12.

Let’s, say XP represents allele for ability to taste PTC

Xp represents allele for inability to taste PTC

Xa represents allele for albinism

XA represents allele for normal pigmentation

According to the phenotype of daughter and son, the genotype of parents will be

XPXpXaXA (female) X XPXAY (male)

XPXA

XPXA XPXA

XPXAY

XPXa

XPXa XPXA

XPXaY

XpXA

XpXA XPXA

XpXAY

XpXa

XpXa XPXA

XpXaY

So, from above chart it is clear that only one albino son is non-tastier, so probability is 3 tastier : 1 non-tastier.

For daughters, there are 3 tastier normal pigmented : 1 non-tastier normal pigmented.

13.

AABbDdee or ABDe / Abde

(Note: gametes must have one allele for each gene; keep the alleles for the same gene together and put the dominant allele (capital letter) first for each gene)

Gametes produced: ABDe (4), ABde (4), AbDe (4), Abde (4). Total 16 gametes and 4 different types of gametes are produced.

Just perform crossing over between alleles one above line and one below line which normally is observed during meiosis I during gametogenesis.

14.

Rrbb X rrBB

Gametes produced by Rrbb: Rb, rb ; Gametes produced by rrBB: rB

RrbB

rrbB

Phenotype of F1: Red (50 % or 8 / 16) and brown (50 % or 8 / 16)

A cross between red and brown will produce F2 generation

Genotype of red: RrbB ; Gametes produced: Rb, RB, rb, rB.

Genotype of brown: rrbB ; Gametes produced: rb, rB

Rrbb

RrbB

RrBb

RrBB

rrbb

rrbB

rrBb

rrBB

Red phenotype: 6 / 16

Brown phenotype: 8 / 16

White phenotype: 2 / 16

Red : brown : white = 6 : 8 : 2 = 3 : 4 : 1

The effect represents Polygenic inheritance (one characteristic is controlled by two or more genes)

lethal

XYXW

XWXW

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11. In mice the yellow allele is dominant over the white allele, but lethal in t

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