Mapping Our Genes



Q1:- Explain the following terms.
1. Inheritance: - The mechanism by which the character are passed on from one generation to next.
2. Heredity: - The transmission of traits, physical or mental, from parent to offspring is known as Heredity.
3. Genotype: - The genetic composition of an individual is known as Genotype.
4. Phenotype:-Phenotype is the appearance of any detectable characteristic feature of any individuals. Ex-Color of flower (Red, White etc)
5. Monohybrid Cross: - When a cross involves only one pair of character or traits, then that cross is called Monohybrid cross.
6. Dihybrid Cross: - When a cross involves two pair of character or traits, then that cross is called Dihybrid Cross.
7. Dominant: - This term used for a genetic traits which expressed itself even in the process of recessive traits.
8. Recessive: - This term used for genetic traits which cannot expressed itself in the presence of dominant traits.
9. Homozygous: - When both the genes are same in a genotype then it is called Homozygous.
10. Heterozygous: - When both the genes are different in a genotype then it is called as Heterozygous.
Q 2:- Explain the terms Inheritance and variation. What is the relationship between Inheritance and variations?
Ans:
1.      It is the mechanism by which the characters are passed on for one generation to the next.
2.      Variations are the changes occur between parents offspring in next generation.
3.      During Inheritance the variation are passed from parents to the offspring.
4.      Tiny and very few variations are produced during asexual reproduction because only one parent is involved in reproduction.
5.      More variation is produce during sexual reproduction because in this two parents are involved.
6.      Hence these variations are passed from one generation to next through the Inheritance.


Q3:- Describe the Mendel’s work in genetics?                                                                                 
OR
 Who was Mendel? What was his contribution to the field of genetic?
Ans:
1. Gregor John Mendel was an Augustinian priest and scientist.
2. He worked on the inheritance of traits in pea plants by doing various experiments.
3. By experiment he shows that the inheritances of these traits follow particular laws.
4. These laws are now called as Mendel’s Law of heredity.
5.  He discovers the concept such as Dominant and recessive characters, monohybrid and Dihybrid cross homozygous and heterozygous etc.
6. His worked has formed the foundation of modern science of genetics.  So he is called the father of genetics.
Q.4 Explain Mendel’s Monohybrid cross using an example of pea plants.
Ans:-
 1) The crossing of only one pair of contrasting characters or traits is known as Monohybrid cross.
2) He crosses two plants having only one pair of contrasting character. For ex: Red and white flowered pea plants.
3) Red and white flowered pea plant was used as parent for crossing so they are said to be P1 Generation.
4) After crossing these plants he obtained progeny of only red flowers. This is called F1 generation.
5) By this result red flower is considered as a dominant character because it expressed itself in F1 generation and white color flower considered as a recessive character as it is not expressed in F1 generation.
6) When two such red flowers are crossed with each other. Then it known as P2 generation.
7) By crossing such plants they yields 3 red flower plants & 1 white flower plant in F2 generation.
8) In F2 generation one red flowered plant has both RR genes .so it is called homozygous dominant trait.
9) Two red flowered plants have R & r genes so they are called heterozygous.
10) One white flowered plant has both rr genes it is called homozygous recessive trait.

Gamete
R
r
R
RR(Red)
Rr(Red)
 r
Rr(Red)
rr(White)
                                                                                                          
 --F2 generation  
Phenotypic ratio: 3 Red: 1White
Genotypic ratio: 1:2:1                                                                                                    


Q.5 which were the seven pairs of contrasting traits in pea plants that were studied by Mendel?
Sr.No.
Characters
Dominants traits
Recessive traits
1.
Seed shape
Round
Wrinkled
2.
Seed color
Yellow
Green
3.
Flower color
Violet
White
4.
Pod shape
Full
Constricted
5.
Pod color
Green
Yellow
6.
Flower position
Axial
Terminal
7.
Stem height
Tall
Dwarf

Q.6 What is dihybrid cross? Explain with a suitable example?
Ans: - 1) The cross contains two pairs of contrasting characters is known as a dihybrid cross
2) Mendel selected two pairs of contrasting characters (i.e. seed shape & seed color) Round & Yellow seed with wrinkled & green seed.
3) The character of round & yellow seed are dominant while wrinkled & green seeds are a recessive character.
4) In P1 generation a plant with round & yellow seed crossed with a plant having wrinkled & green seed RRYY (round & yellow) & rryy (wrinkled &green)
5) Each pairs of genes separate (segregates) from each other.
6) RRYY parent produced RY type of gametes and rryy parent produced ry types of gametes.
7) In the F1 generation all offspring produced show genotype RrYy and there phenotype yellow and round.
8) The F1 generation produced four different types of gametes viz. RY, Ry, rY, and ry.
9) By crossing these four male gamete and four female gamete 16 different combinations are produced.
Gametes
RY
Ry
rY
ry
   RY
RRYY
(Round yellow)
RRYy
(Round yellow)
RrYY
(Round yellow)
RrYy
(Round yellow)
   Ry
RRYy
(Round yellow)
RRyy
(Round green)
RrYy
(Round yellow)
Rryy
(Round green)
   rY
RrYY
(Round yellow)
RrYy
(Round yellow)
rrYY
(wrinkled yellow)
rrYy
(Wrinkled yellow)
    ry
RrYy
(Round yellow)
Rryy
(Round green)
rrYy
(Wrinkled yellow)
Rryy
(Wrinkled green)

10) The phenotypic ratio was – 9:3:3:1
Round Yellow - 9
Round green   - 3
Round Yellow - 3
Wrinkled green -1
This ratio is called Dihybrid Ratio.
* Que:- 7) With the help of diagram (Punett  square ) show a Mendelian experiment where tall pea plant bearing red flowers is cross with a short pea plant bearing white flowers, Write both the phenotypic and genotypic ratio for F2 generation.
Ans: - 1) Tall pea plant bearing red flower
              Tallness- Dominant character
              Shortness- Recessive character
               Red color of flower -Dominant.
               White color flower –Recessive
            2) Therefore genes for character mentioned in the question are
Tallness- TT
Shortness- tt
Red flower- RR
White flower-rr
 (Male)                        X                          (female)
Tall (TT)                                                Short (tt)
Red flower (RR)                                   white flower (rr)
TTRR               X            ttrr  
Gametes           -TR                   X            tr
F1 generation    - TtRr (Tall red)
P2 generation    -Cross between TtRr    X    TtRr
Gamete
TR
Tr
tR
tr
TR
TTRR
(Tall red)
TTRr
(Tall red)
TtRR
(Tall red)
TtRr
(Tall red)
Tr
TTRr
(Tall red)
TTrr
(Tall white)
TtRr
(Tall red)
Ttrr
(Tall white)
tR
TtRR
(Tall red)
TtRr
(Tall red)
ttRR
(short red)
ttRr
(short red)
tr
TtRr
(Tall red)
Ttrr
(Tall white)
ttRr
(short red)
ttrr
(short white)
 In F2 the ratio obtained was   9:3:3:1
Tall Red           -          9
Tall white         -          3
Short red          -          3
Short white         -        1
Phenotypic ratio -        9:3:3:1
Genotypic ratio              -1:1:2:2:4:2:2:1:1

Q8. How is sex determined in the human being?
Ans: - 1) Sex determination in human being is genetic.
2) In human being there are 46 chromosomes or 23 pairs out of which 22 pairs are outsoles 1 pairs is sex chromosomes.
3) So in human male contain 22 pair of autosomes & 1 pairs of heteromorphic sex chromosomes i.e. XY
4) In human female contain 22pair of autosome & 1 pair of homomorphism sex chromosomes i.e. XX
5) Thus all normal male are 44 + XY & normal female are 44 + XX
6) The sperm produced by male are of two types, type one contain 22 autosomes & one X chromosome &type two contain 22 autosomes & one Y chromosome   
7) The eggs produced by female are of only one type,
      22 autosomes & one X chromosome   
8) When sperm having X chromosome fertilizes the egg, female child is produced (i.e. 44 +XX)
9) When sperm having Y chromosome refrozen the egg female child is produced (i.e. 44+XY)
10) Hence sex determination in human beings totally depends on father not the mother
XY (Male)           X                XX (Female)
      X     Y                                            X     X

XX          XX                             XY           XY

Q. 9 Give scientific reasons –
1) In sexual mode of reproduction greater diversities are generated.
Ans: - a) In asexual mode of reproduction two only one parent are involve.
b) But in sexual mode of reproduction two different parents are involve.
c) So there are two different types of DNA copies.
d) That DNA copies pass with their nuclei at the time of fertilization of gamete. 
e) The process of meiosis at the time of gamete formation, also produces variation, hence in sexual mode of reproduction greater diversities are generated.


2) Phenotypic and genotypic ratios are different.
Ans: a) The Phenotype is the appearance of any detectable characterstic features of an individual.
b) It is the character which one can actually see.
c) Genotype is the gene composition of the individual.
d) It is the character which we cannot see.
e) Phenotypically all the individual can look same but genotypically some may be homozygous and some may be Heterozygous.
f) Thus we can say that F1 plants are phenotypically similar to P1 generation but genotypically different.
h) Thus the phenotypic ratio is 3:1.
i) The genotype ratio is 1:2:1.
j) Thus it can be conclude that phenotypically there are two types of F2 plants.
i) Genotypically there are three homozygous, and heterozygous.

3) In human being the gametes from the male parents decide the sex of the body.
Ans: a) The sex of an individual is determining d by genes inherited by it from its parents.
b) From male parent two different gametes are formed- i.e. one containing 22 autosomes and a single X- chromosomes and other containing 22 autosomes and single Y- chromosomes.
c) From female parent all gametes are of same type containing 22 autosomes and a single X- chromosome.
d) So the sex of the baby will be dependent upon which kind of sperm is fertilizing the egg.
e) If X- bearing sperm fertilized the egg, a female child is developed. Whereas if Y- bearing sperm fertilized the egg. A male child is developed.
4) Why children remember their parents.
Ans: a) In mammals child born due to sexual reproduction.
b) During sexual reproduction mixing of gametes takes place.
c) Gametes i.e. the sperm from father and the egg from mother containing nucleus and haploid chromosomes number.
d) In fertilization    these two haploid gametes fused with each other and form diploid zygote from which child is developed.
e) The chromosomes contain genetic information in the form of DNA molecules and this DNA passed from parent to children, so they resemble their parents.
*Q. 10:- Fill in the blanks.
*1) In ____________ mode of reproduction the offspring are with minor differences.
*2) Both the parents contribute equal amount of____________ material of the offspring.
*3) Dominants character masks the ________Characters.
4) Sex determination in human being is ____________
5) Mendel’s experiment was based on a number of visible_______ characters of pea plants.
6) In a few organisms, the _______ factor decides the sex.
Ans: 1-Asexual. 2- Genetic.  3- Recessive.  4- Genetical.  5- Contrasting. 6- Envoirmental.
Q.11:- Match the columns:
      A                                                                                         B
1. Dominant                                                                        a) Can express only when alone
2. Recessive                                                                        b) Contain two similar genes
3. Homozygous                                                                  c) Contain two different genes
4. Heterozygous                                                                 d) Express in spite of the presence of other gene.
Ans: 1- d, 2- a, 3- b, 4- c.
Q.12:- Answer the following in one sentence:
1) What is a chromosome?
Ans: Single long thread of DNA which is present as an independent piece is called chromosomes.
2) What is gene?
Ans: The fragment of DNA that provides complete information about one protein is called gene.

3) How many pairs of autosomes are present in human beings?
Ans: There are 22 pairs of autosomes in human beings.
4) How many sets of genes are present in each gametes?
Ans: In each gamete there is only one set of genes.
5) Why do organisms that reproduced asexually have only minor differences?
Ans: During asexual reproduction very minor differences are produced due to small inaccuracies in the DNA copying.
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