www.smarteducations.org 1

Heredity

Q. What does variation in reproduction mean?

Ans. Variation in reproduction refers to the differences in traits between

individuals of the same species. Variation can be caused by sexual

reproduction, inaccuracies during copying of DNA(mutations), or

environmental factors.

Ans. If a trait A exists in 10% of a population of an asexually reproducing

species and a trait B exists in 60% of the same population, trait B is likely to

have arisen earlier because it is found in most of the population which is

only possible when it gets more time to spread.

Q. How does the creation of variations in a species promote survival?

Ans. The creation of variations in a species promotes survival because

variations enable some organisms of a species to withstand any sudden

changes in the environment.

Q. What does heredity mean?

Ans. Passing on of traits from parents to their offspring(children) is known

www.smarteducations.org 2

Ans. Gregor Johann Mendel was the first one to keep count of individuals

exhibiting a particular trait in each generation.This helped him to arrive at

the laws of inheritance.

Q. What does monohybrid cross mean?

Ans. Monohybrid cross is a process of crossing for only one trait.

Q. What does dihybrid cross mean?

Ans. Dihybrid cross is a process of crossing for two traits.

Q. What does homozygous mean?

Ans. Homozygous means having two same versions of a gene. For example

(TT), (RR), (YY) etc.

1. Law of dominance

2. Law of segregation

3. Law of independent assortment

Q. What does allele mean?

Ans. An allele is a variant of a gene, or a different version of a DNA

sequence at a specific location on a chromosome:

Q. What does the Law of dominance mean?

Ans. In a sexual reproduction, an organism has two sets for one

characteristic, one of its paternal and one of its maternal but only one trait

appears in the organism and the other does not appear and there are no

www.smarteducations.org 3

and the disappeared trait is known as recessive trait.

Q. What does the Law of segregation mean?

characteristic but during the formation of gamete one set of each parent is

received thus the formed gamete has again the two sets for one

Q. What does the Law of independent assortment mean?

gamete, the allele a gamete receives for one gene doesn't affect the allele

it receives for another gene.

a short plant, produced progeny by crossing them, and calculated the

percentages of tall or short progeny. In the first place, there were no

halfway characteristics in this first- generation, or F1 progeny – no

‘medium-height’ plants. All the plants were tall. This meant that only one of

the parental traits was seen, not some mixture of the two. So the next

question was, were the tall plants in the F1 generation exactly the same as

the tall plants of the parent generation? Mendelian experiments test this by

getting both the parental plants and these F1 tall plants to reproduce by

self-pollination. The progeny of the parental plants are, of course, all tall.

However, the second-generation, or F2, progeny of the F1 tall plants are

independently?

www.smarteducations.org 4

inherited independently; he crossed two pea plants with contrasting traits,

such as a plant with (round yellow) seeds and a plant with (wrinkled green)

seeds. All seeds in the F1 generation were round and yellow. But The F2

phenotypic ratio of 9 (round yellow):3 (round green):3 (wrinkled yellow):1

(wrinkled green).

Q. A man with blood group A marries a woman with blood group O and

their daughter has blood group O. Is this information enough to tell you

Ans. This information is not enough to tell us which of the traits – blood

group A or O – is dominant. Because in both cases their daughter’s blood

group may be O.

progeny from the two may be (AO) or (OO). Thus in the case of (OO)

daughter’s blood is O in spite of O being recessive.

Case2:- Let blood group O be dominant then the gene set of the

man must be (AA) , the woman’s may be (OO) or (AO) and the produced

progeny from the two may be (AO) or (OO). Thus in the case of (AO) or

(OO) daughter’s blood is O because A is recessive.

Q. What are the factors on which sex of an organism is determined?

Ans. The factors on which sex of an organism is determined :-

1. Environmental factors such as temperature.(in crocodile, turtle, some

Some organisms can change their sex during their lifespan. For example :-

www.smarteducations.org 5

Ans. There are a total 46(23 pairs) chromosomes in humans, which

contain genetic materials and are present in the nucleus of a cell. They are

of two types :- autosome and sex chromosome.

characteristics like body weight, length etc. In humans the number of

autosomes is 44 (22 pairs) and are the same for male and females.

determine sex of an organism. In humans, males and females have

different sex chromosomes. Male has (XY) and female has (XX).

Q. How is the sex of the child determined in human beings?

Ans. The sex of a child in human beings is determined by sex

chromosomes of the parents. Male has (XY) sex chromosomes and

(XY) zygote is formed which is a male. Thus All children

will inherit an X chromosome from their mother

regardless of whether they are boys or girls. Thus, the

sex of the children will be determined by what they inherit

from their father.

Ans. The traits involved in the experiment are:-

Flower Color: Violet (W) is dominant over white (w).

www.smarteducations.org 6

short. This suggests that the genetic make-up of the tall parent can be

depicted as (TtWW). (Tt) for tallness because half of the progeny were

short and (WW) for color because all the progeny bore violet flowers.

Q. A study found that children with light-coloured eyes are likely to have

whether the light eye colour trait is dominant or recessive? Why or why

not?

Light eye color (c) and dark eye color (C) .

Case1:- Let light eye colour be dominant then the gene set of the parents

must be (cc) or (Cc), and the produced progeny from the two must be (cc)

Thus in this case also the child has light eye colour.

So in both cases, it is possible that the child has light eye colour. Hence it

can’t be said whether the light eye colour trait is dominant or recessive.

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

Ans. To find the dominant coat colour in dogs we must cross the dogs of a

homozygous coat colour. Let say black male dog (BB) and brown female

dog (bb). If all the progeny are Black then Black is the dominant coat colour

and if all the progeny are Brown then Brown is the dominant coat colour.

offspring thus the offspring also has a full set of chromosomes.

www.smarteducations.org 7