Dominant Traits

Q.

A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because

1. tallness is the dominant trait

2. shortness is the dominant trait

3. tallness is the recessive trait

4. height of pea plant is not governed by gene ‘T’ or ‘t’

Q.

Explain with an example, how genes control the charcteristics (or traits) .

Q. If a normal man marries a woman who is carrier for haemophilia, then what is the probability that their son will be haemophilic?

1. 25%
2. 50%
3. 75%
4. 100%

Q.

Outline a project which aims to find the dominant coat color in dogs.

Q.

Two pairs (A & B) of rabbits were crossed as gien below:

(a) can you tell which coat colour (black or white) is dominant?
(b) Is the coat colour sex linked?

Q.

How is the sex of a newborn determined in humans?

Q.

In humans , if gene B gives brown eyes and gene b gives blue eyes. What will be the colour of eyes of the persons having the following combination of genes ?

(a) Bb (b) bb (c) BB

Q.

A red-haired woman marries a brown-haired man , and all the children are brown haired. Explain this genetically.

Q.

Fill in the following blanks with suitable words :

(a) Genes always work in ............ .

(b) In pea plants , the gene for dwarfness is ........... whereas that for tallness is ............. .

(c) Most people have ....... earlobes but some have ....... earlobes.

(d) A human gamete contains ........ chromosomes whereas a normal body cell has ....... chromosomes in it.

(e) All races of man have ...... blood groups.

(f) The ....... chromosomes for a ........ are XX whereas that for a .......... are XY.

Q.

Is human eye color incomplete dominance?

Q.

(a) E is the gene for brown eye colour and e is the gene for blue eye colour. Which gene is (i) recessive, and (ii) dominant?

(b) Both father and mother have the genes Ee in their cells. What colour are their eyes?

(c) Which combination of genes in the zygote will produce children with blue eyes?

(d) Which combination of genes in the zygote will produce children with brown eyes?

Q.

Pure-bred pea plants A are crossed with pure- bred pea plants B. It is found that the plants which look like A do not appear in $F_1$ generation but re-emerge in $F_2$ generation. Which of the plants A and B are : (i) tall, and (ii) dwarf ? Give reason for your answer.

Q.

Question 7
Outline a project which aims to find the dominant coat colour in dogs.

Q.

Question 2
Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be

(a) double fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilisation

Q.

Question 44
Study the following cross and showing self-pollination in F1, fill in the blank and answer the question that follows.
$\begin{array}{cccc}Parents& RRYY& x& rryy\\ & Round,yellow& & wrinkled,green\\ F1-& RrYy& x& ?\\ & Round,yellow& & \end{array}$

Q.

A plant has two varieties, one with red petals and the other with white petals. When these two varieties are cross-pollinated, all the offsprings have red petals ?

(a) Which gene is dominant ?

(b) Choose suitable letters to represent the two genes.

Q.

Which of the following represent tall plants and which represent short plants (or dwarf plants) ?

(a) Tt (b) tt (c) TT

Give reason for your choice (The symbols have their usual meaning).

Q.

Question 34
Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive.
(i) yellow seed (ii) round seed (iii) green seed (iv) wrinkled seed.

Q. Some humans are able to roll their tongue, while others are not. Two parents (both tongue-rollers) have four children, all of whom are not tongue-rollers. Which of the following statements hold true regarding this?
(i) The allele for tongue-rolling is dominant
(ii) The probability that their next child will be a tongue-roller is 0.5.
(iii) The probability that their next child will not be a tongue-roller is 0.75.
(iv) Both parents have one allele for tongue-rolling and one allele for non-tongue-rolling.

1. (i) and (iii) only
2. (i) and (iv) only
3. (ii) and (iii) only
4. (ii) and (iv) only

Q.

Which of the following is best suited for codominance.

1. Both are recessive

2. Both are dominant

3. One is recessive

4. One is dominant

Q.

A plant with two 'small' genes breeds with a plant with two 'tall' genes to prooduce :

(a) small plants and tall plants in the ratio 1 :3 (b) all small plants

(c) all tall plants (d) tall plants and small plants in the ratio 3 : 1

Q.

What is incorrect in the following mendelian traits:

Character Dominant Recessive

1. Height Tall Dwarf

2. Seed colour Green Yelllow

3. Flower Position Axillary Terminal

4. Flower colour Voilet White

Q.

A cross between a tall plant (TT) and short plant (tt) resulted in pregeny that were all tall plants because :

(a) tallness is the dominant trait (b) shortness is the dominant trait

(c) tallness is the recessive trait (d) height of plant is not governed by gene T or t

Q. Some humans are able to roll their tongue, while others are not. Two parents (both tongue-rollers) have four children, all of whom are not tongue-rollers. Which of the following statements hold true regarding this?
(i) The allele for tongue-rolling is dominant
(ii) The probability that their next child will be a tongue-roller is 0.5.
(iii) The probability that their next child will not be a tongue-roller is 0.75.
(iv) Both parents have one allele for tongue-rolling and one allele for non-tongue-rolling.

1. (i) and (iv) only
2. (ii) and (iii) only
3. (ii) and (iv) only
4. (i) and (iii) only

Q. The _________ character is expressed in the hybrid progeny.

1. dominant
2. recessive
3. co-dominant
4. epistatic

Q.

Which of the following are called 'carriers' of heredity?

1. Nucleus

2. Chromosomes

3. RNA

4. Nucleolus

Q.

How is the sex of a newborn determined in humans?

Q. The dominant allele is identified by a lower case letter.

1. True
2. False

Q. A trait in an offspring of sexually reproducing organisms is influenced by:

1. DNA of only male gamete
2. Both male and female gametes
3. Neither male nor female gamete
4. DNA of only female gamete

Q. Dominant character masks the ................. characters.

1. Recessive
2. Parental
3. Dominant
4. All of the above