Question

7) In humans, brown eyes (B) are a simple dominant trait over blue eyes (b). What is the genotype of a brown-eyed woman who has a blue-eyed child? A)bb -B)Bb С)ВВ D)BBB E) BbBb 8) The ability to roll the edges of the tongue upward in a U-shape is inherited as a dominant allele at a single gene locus, Which of the following genotypes would produce an individual that can roll their tongue? A)TT only B)Tt only C) only D)TT or TP E)TI or 11 9) What genotypic ratio would result from a cross between two individuals who are both heterozygous for a trait? A)100% homozygous dominant B)100% homozygous recessive C)50% homozygous dominant, 50% homozygous recessive D)25% homozygous dominant, 50% heterozygous, 25% homozygous recessive E)50% homozygous dominant, 50% heterozygous 10) In which kind of monohybrid cross would you expect to find a phenotypic ratio of 3:1 among the offspring? A)heterozygous x heterozygous B)homozygous recessive x homozygous recessive Chomozygous dominant x homozygous dominant D)homozygous recessive x homozygous dominant E)homozygous dominant x heterozygous 11) In a test cross, an organism with a dominant phenotype, but unknown genotype, is crossed with an organism that is A)homozygous dominant. B)heterozygous. C)homozygous recessive. D)heterozygous dominant. E)monohybrid dominant.

Answer 1

Ans 7) given that, brown eyes is Dominant over blue eyes.

Brown eyes = B

Blue eyes = b

Genotype of brown-eyed woman = BB or Bb

As brown eye is Dominant over Blue. As this woman had a child who has Blue eyes (recessive trait), then it is possible only when the parents are carriers of the recessive allele. So, accordingly the genotype of woman is Bb.

case 1: woman-BB ; man-bb

	B	B
b	Bb	Bb
b	Bb	Bb

If they are Homozygous then they will get a hybrid and phenotye is Dominant i.e. brown eyes of all progenies.

Case 2: woman BB ; man = BB

	B	B
B	BB	BB
B	BB	BB

ALL dominant i.e . brown eyed.

Case 3: woman- BB ; man- Bb

	B	B
B	BB	BB
b	Bb	Bb

All brown eyes but 2 heterozygous and 2 Homozygous.

Case 4: woman- Bb ; man- Bb

	B	b
B	BB	Bb
b	Bb	bb

in this case they can have Blue eyed child. So, woman as well as man are heterozygous dominant Bb.

Answer is option B.

Ans 8) rolling tongue is Dominant trait. Let it's allele be

Dominant = T

Recessive= t

Genotypes that are able to produce a rolling tongue are TT and Tt. As T is Dominant over t, so tongue rolling will be expressed phenotypically in heterozygous condition also.

Answer is option D, TT and Tt.

Ans 9) when 2 individuals are heterozygous for a trait then genotypic ratio will be:

Let dominant allele= D

Recessive allele= d.

Heterozygous parents be Dd and Dd.

Dd X Dd

	D	d
D	DD	Dd
d	Dd	dd

Genotypic ratio = 1:2:1

Or 1/4*100= 25% Homozygous dominant (DD)

2/4*100=50% heterozygous dominant (Dd and Dd)

1/4*100=25% Homozygous recessive (dd)

Answer is option D.

Ans 10) monohybrid cross that will give phenotypic ratio 3:1 of offspring is :

Heterozygous dominant parents

Dominant allele= H

Recessive allele= h

Cross between Hh X Hh

	H	h
H	HH	Hh
h	Hh	hh

Phenotypic ratio= 3:1

3 = dominant; HH,Hh and Hh

1= recessive; hh.

Answer is option A. Heterozygous X Heterozygous.

Ans 11) test cross -- it is kind of cross in which a Homozygous recessive is crossed with a phenotypically dominant individual. It helps in determining the genotype of the dominant individual. If it is Homozygous dominant or heterozygous dominant.

So, answer to the question; in a test cross, an organism with dominant phenotye, but unknown genotype is crossed with an organism that is Homozygous recessive.

Answer is option C.

Thank you...

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