1. Multiple Choice Questions :(1 Mark each)
(l) Phenotypic ratio of incomplete dominance in Mirabilis jalapa.
(a) 2 : 1 : 1 (b) 1 : 2 : 1 (c) 3: 1 (d) 2: 2
(2) In dihybrid cross, F 2 generation offspring show four different phenotypes while the genotypes are ……
(a) six (b) nine (c) eight (d) sixteen
(3) A cross between an individual with unknown genotype for a trait with recessive plant for that trait is………..
(a) back cross (b) reciprocal cross
(c) monohybrid cross (d) test cross
(4) When phenotypic and genotypic ratios are the same, then it is an example of …………….
(a) incomplete dominance (b) complete dominance
(c) multiple alleles (d) cytoplasmic inheritance
(5) If the centromere is situated near the end of the chromosome, the chromosome is called………….
(a) Metacentric (b) Acrocentric (c) Sub-Metacentric (d) Telocentric
(6) Chromosomal theory of inheritance was proposed by…………..
(a) Sutton and Boveri (b) Watson and Crick
(c) Miller and Urey (d) Oparin and Halden
(7) If the genes are located in a chromosome as p-q-r-s-t, which of the following gene pairs will have least probability of being inherited together?
(a) p and q (b) r and s (c) s and t (d) p and s
(8) Find the mis matched pair :
(a) Down's syndrome = 44 + XY
(b) Turner's syndrome = 44 + XO
(c) Klinefelter's syndrome = 44 + XXY
(d) Super female = 44 + XXX
(9) A colourblind man marries a woman, who is homozygous for normal colour vision, the probability of their son being colour blind is……….. .
(a) 0% (b) 25% (cl 50% (d) 100%
Q. 2. Very Short Answer Questions: (1 mark
each)
1) Give Reasons or Explain the Statements
(a) Test cross is back cross but back cross is not necessarily a test cross.
Ans-( i) Test cross is the cross between F 1 hybrid and homozygous recessive parent.
(ii) Back cross is the cross of offspring with any one of the parents, either dominant or recessive .
(iii) There fore, test cross can be a back cross but back cross cannot be a test cross.
(b) Law of dominance is not universal. ADs.
Ans-( i) There are many traits in many organisms which show dominance. For example, widow's peak in human beings is a dominant trait. Yellow seed colour and round seed shape are dominant traits in pea plant.
(ii) However, there are characters which areeither co-dominant, such as genes for human blood group A and B or incompletely dominant as in flower colour of Mirabilis jalapa.
(iii) Therefore the law of dominance is not universally applicable.
Q.2.Define the following terms
(a) Dihybrid cross : A cross between par differing in two heritable traits is dihybrid cross.
(b) Homozygous: An indiVidual possessing • identical alleles for a particular trait is called homozygous or pure for that trait. E.g. IT for tallness and tt for dwarfness
(c) Heterozygous: An individual possessing contrasting allele for a particular trait is called heterozygous. E.g. Tt showing tallness
(d) Test cross: The cross of F1 progeny homozygous recessive parent is called a cross.
(3)What are allosomes?
Ans. Allosomes are the chromosomes which decide the sex of an organism .
(4 ) What is crossing over?
Ans. Crossing over is the process of forming n recombinations by interchanging and exchanging non-sister chromatid the homologous chromosomes
(5) Give one example of autosomal recessive disorder.
Ans. Thalassemia is an example of autosomal recessive disorder.
(6) What are X-linked genes?
Ans. Genes located on the non-homologou region of X chromosome are called X-linked genes.
(7) What are holandric traits?
Ans. Genes located on the non-homologous region of Y chromosome are called V-linked genes. The traits due to such genes are called holandric traits which are seen only in male sex
(8) Give an example of chromosomal disorder caused due to non-disjunction of autosomes.
Ans-Down's syndrome is an example of chromosomal disorder caused due to nondisjunction of autosomes. .
(9) Give one example of complete sex linkage. .
Ans. Sex linkage can be complete X linkage an complete Y linkage. X linkage is haemophiIia and Y linkage is hypertrichosis.
(2)Why law of segregation is also called the law of purity of gametes?
i)Mendel's law of segregation is also called ,Law of purity of gametes because, during formation of gametes, the alleles separate or segregate from each other and only one allele enters a gamete.
ii) The separation of one allele does not affect other allele Since single allele enters a gamete means gametes will be pure for a trait.
iii)E.g. The contrasting characters such as tall (T) and dwarf (t) present in F1 hybrid (Tt) segregate during the formation of gametes.
iv)Owing to this two types of gametes T and t are formed which are pure for the characters which they carry.
v) Example :Tt (F1 hybrid)= (T) and (t) gametes .
(3) Write Short note onPleiotropy
(1) When a Single gene controls two or more different traits, it is called a pleiotropic gene and the phenomenon is known as pleiotropy or pleiotropism.
(2) The pleiotropic ratio is always 1 : 2 instead of normal 3 : 1.
(3) Sickle-cell anaemia is caused by the gene. HbS. The healthy or normal gene which is dominant is HbA.
(4) The heterozygotes or carriers Le., HbAlHbs show anaemia as there is deficiency of haemoglobin due' to Sickling of RBCs. Abnormally low concentration of oxygen car. cause Sickling of RBCs.
(5) The homozygotes possessing the recessive gene HbS die because of fatal anaemia because the gene for Sickle-cell anaemia is lethal in homozygous condition and causes sickle-cell trait in heterozygous carrier.
(6) Thus a Single gene produces two different expressions.
(7) When two carriers are married they will produce normal carriers and Sickle-cell anaemic children in the ratio of 1 : 2 : 1.
(8) Out of these three children sickle-cell anaemic child Will die leaving the ratio 1 : 2 instead of 3 : 1.
(4) What are the reasons of Mendel's success .
Ans. Reasons for Mendel's success:
(1) Mendel planned his experiments carefuly and these experiments consisted of larg sample.
(2) He always recorded the results of number of plants of each type and their ratios.
(3) The contrasting characters that he chose were easily recognizable.
(4) The seven pairs of contrasting characters that he selected were under control of a Single factor each.
(5) They were present on separate chromosomes and were transmitted from one generation to the next.
(6) Mendel studied and introduced concept of dominance and recessiveness
(5) "Father is responsible for determina tion of sex of child and not the mother Justify.
(1) Human male is heterogametic, i.e. produces two different types of sperms.
(2) One is bearing X chromosome along with 22 autosomes and the other is Y be sperm with 22 autosomes.
(3) Mother is homogametic producing all similar types of ova, bearing X chromosome along with 22 autosomes
(4) If 22 +X bearing sperm fertilise an egg ,female child is formed while 22 + Y bearing sperm fertilizes an egg, male child is form
(5) Thus sex of the child is dependent upon type of sperm that father gives, there fore, is said that father is responsible determination of sex of a child and not mother.
(6) What is linkage? How many linkage groups do occur in human being ?
( i) Linkage is defined as the tendency of genes to be inherited together because are present in the same chromosome Linkage group is group of genes situated on a chromosome.
(ii) Humans have 23 linkage groups because they have 23 pairs of chromosomes. .
(7) Write Notes on PKU. =Phenylketonuria (PKU): -
i) PKU means phenylketonuria which is an autosomal recessive inborn error .
ii)It is an inborn metabolic disorder caused due to recessive autosomal genes.
iii)When recessive genes are present in homozygous
condition, phenylalanine hydroxylase enzyme is not produced.
iv) This enzyme is essential for conversion of amino acid phenylalanine into tyrosine.
v)Due to absence of this enzyme, phenylalanine is not converted into tyrosine.
vi)Hence, phenylalanine and it derivatlves are accumulated in blood and cerebrospinal fluid (CSF).
vii)It affects development of brain and causes mental retardation.
viii)Excess phenylalanine is excreted in urine; hence this disease is called phenylketonuria. .
ix) PKU is caused by mutations in the PAH gene on chromosome no. 12
x)Autosomal recessive raits appear in both sexes with equal frequency. These traits tend to skip generations.
(l) Chromosomal theory of inheritance was put forth by Sutton and Boveri after studying parallel behaviour of genes and chromosomes during meiotic division.
(2) Chromosomal theory identifies chromosomes as the carrier of genetic material.
(3) All the hereditary characters are transmitted by gametes. Nucleus of gametes, i.e. sperms and ova of the parents contain chromosomes which transmit the heredity to offspring.
(4) Chromosomes are found in pairs in somatic or diploid cells.
(5) During gamete formation, homologous chromosomes pair and segregate independently at meiosis .
(6) The diploid condition is converted into haploid condition. Thus each gamete contains 0 one chromosome of a pair.
(7) During fertilization, the union of sperm egg restores the diploid number chromosomes.
(10)Observe the given pedigree chart and answer the following questions
(a) Identify whether the trait is sex-linked or autosomal.
Ans-The above pedigree show (X-linked) trait. Since criss-cross in heritance is seen in the trait, it must be sex- inheritance
(b) Give an example of a trait in human beings which shows such a pattern of inheritance.
Ans-Such trait and its inheritance can be seen in colourblindness.
Q. 5. Long Answer Questions
(1) What is dihybrid cross? Explain with suitable example and checker board method.
( i) A cross between parent differing in two heritable traits is called dihybrid cross .or A cross which involves two pairs of alleles is called a dihybrid cross. ( ii) A phenotypic ratio of 9: 3 : 3 : 1 obtained in the F 2 generation of a dihybrtd cross is called a dihybrid ratio.
(iii) For example, when we cross a pea plant bearing round and yellow seeds with a wrinkled and green seeds we get pea plants bearing round and yellow seeds in the F 1 generation.
(2) Explain with suitable example independent assortment.
Ans.(i) states that when two parents differing from each other in two or more pairs of contrasting characters are crossed, then the inheritance of one pair of characters is independent of that of the other pair of characters.
(ii) For example, when we cross a pea plant bearing yellow round seed(YYRR) with a pea plant bearing green wrinkled seed (yyrr),
(iii) we get in F 1 generation is yellow round seeds(YyRr). When F 1 generation are selfed, 9: 3 : 3 : 1 ratio was obtained in F 2 generation 9 pea plants bearing yellow round seeds,3 pea plants bearing yellow wrinkled seeds, 3 pea plants bearing green round seeds, and 1 pea plant bearing green wrinkled seeds.
(v) Results : The offspring of F 1 generation will be in the proportion of ratio is 9 : 3 : 3 : 1 in F 2 generation.
9- pea plants bearing yellow round seeds,
3 - pea plants bearing yellow wrinkled seeds,
3- pea plants bearing green round seeds,
1 -pea plant bearing green wrinkled seeds
(vi) From the results of the above cross, it is obvious that the character of yellow colour of the seed in no way is linked with the round shape of the seed.. This is due to the fact that in the above cross, the two pairs of characters segregate independently. In other words, there is independent assortment of characters during inheritance.
(3) Define test cross and explain its significance.
Definition of test cross : A cross between F 1 offspring and its homozygous recessive parent is called a test cross.
Significance of test cross:
(1) Test cross can be used to find out the genotype of any plant which shows dominant characters.
(2) In the plant is homozygous or heterozygous can be understood by performing test cross.
(3) Test cross is used to introduce useful recessive traits in the hybrids of self pollinated plants.
(4) Test cross is quicker method to improve the variety of crop plants .
(5) it is useful for breeders and geneticists.
(6) Test cross can be used for verifying the laws of inheritance
(4) What is parthenogenesis? Explain the . haplodiploid method of sex determinationin honey bee.
(a)Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur Without fertilization by sperm.
In some insects like honey bees,parthenogenesis means.development of an embryo from an unfertilized egg cell.
(b) In honey bee,
(I) Sex determination is by haplodiploid system.
(2) Sex is determined by the number of sets of shromosomes received by an individual.
(3) The egg which is fertilized by sperm, becomes diploid and develops into female.
(4) The egg which is not fertilized develops by parthenogenesis and develops into a male.
(5) The queen and worker bee therefore contain 32 chromosomes. The drone, I.e. male bears 16 chromosomes.
(6) The sperms are produced by mitosis while . eggs are produced by meiosis
(10) In the answer for inheritance of X-linked genes, Madhav had shown carrier male. His answer was marked incorrect. Madhav was wondering why his marks were cut. Explain the reason.
Ans. (i) Males can never be carriers. They have Single X and other Y chromosome.
(ii) In X linked inheritance, the genes are present on the non-homologous region of X chromosome.
(iii) Males do not have other X and hence if the genes are present on his X chromosome, they Will not be suppressed in them.
(iv) The Y chromosome does not have dominant gene to hide this expression as there is no homolorous region .
(v) But in case of females, there are double . X chromosomes and hence if X-linked gene is recessive, the other X can hide the expression of such X-linked gene.
(vi) So, she becomes a carrier Without showing any physical characters. She is physically normal and does not suffer from such X-linked recessive disorder.
(vii) So, Madhav Will get his answer wrong due to incorrect concept
(6) With the help of neat labelled diag describe the structure of chromosome.
( 1) A chromosome is best visible metaphase, when it is highly condensed.
(2) Chromosome shows two called sister chromatids are held together at centromere called primary constriction.
(3) Primary constriction has disc shaped plate called kinetochore. This plate is useful f attachment of spindle fibres at the time cell division.
(4) Additional narrow constrictions are seen in some chromosom which are known as nucleolar organizer.
(5) They help in the formation of nucleolus secondary constriction (i) there is nucleo organising region. Secondary constriction(ii) shows attachment of satellite body SAT body.
(6) Each chromatid is made up of chromatids called chromonemata. chromonema consists of a long, unbranchec slender, highly coiled DNA thread. This double stranded DNA molecule extends throughout the length of the chromosome.
(7) The ends of the chromatid arms are call telomeres.
(7) What is criss-cross inheritance? Explain suitable example.
Criss-cross inheritance is the type of inheritance in which the genes are passed from father transmits the disorder to his grandson through his carrier daughter. The inheritance of characters from the father to his grandson through his daughter is called criss-cross inheritance.
a)Inheritance of Colour blindness show criss-cross pattern.
(I) Colour blindness is a sex-linked disorder in which the person concerned cannot dtstingutsh between red and green colours.
(2) It is recessively X-linked disorder, which is expressed in males. It is rarely seen in females.
(3) The genes for normal vision are dominant whereas those for colour blindness are recessive.
1) Marriage between colour blind maIe with normal female, will produce normal visioned male and female offspring in F1.The sons have normal vision but daughter will be carrier for the disease.
2) Marriage between carrier female (daughter) and normal male will produce female offsprings with normal vision but half of them will be carriers for the disease.
Result- ( 1) Normal female with Colour blind male: Such cross produces 50% carrier daughters and 50% normal sons.
(2) Carrier female with normal male: Such a cross produces 25% normal daughters, 25% normal sons. 25% carrier daughters and 25% colour blind sons.
(3) Colour blind father transmits the disorder to his grandson through his carrier daughter. The inheritance of characters from the father to his grandson through his daughter is called criss-cross inheritance
(8) Describe the different types of chromosomes.
A)Chromosomes are classified into the following four types according to the position of the centromere in them :
1)Metacentric : In this chromosome, the centromere is situated in the middle of the chromosome. The two arms of the chromosome are equal. It appears 'V -shaped during anaphase.
1)Sub-metacentric : In this chromosome, the centromere is situated some distance away from the middle. Due to this, one arm of the chromosome is shorter than the other. It appears 'L:-shaped during anaphase.
3)Acrocentric : In this chromosome, die centromere is situated near the end of the chromosome. One arm of the acrocentric chromosome is very short while the other is long making it appear like : J -shaped during anaphase.
4)Telocentric : In this chromosome, the centromere is situated at the tip of the chroomosome. Telocentric chromosome has only one arm thus it appears rod-shaped.
B)Based on the functions. chromosomes are divided into two types 1)Autosomes are somatic chromosomes which decide the body characters. 2)Allosomes are chromosomes which decide the sex of the individual.
9. Multiple Choice Questions :(1 Mark each)
(1) If a heterozygous tall plant is crossed with a homozygous dwarf plant, the proportion of dwarf progeny will be ………
(a) 100 per cent (b) 75 per cent
(c) 50 per cent (d) 25 per cent
(2) The recombination of characters dihybrid cross is related to ………
(a) law of dominance (b) incomplete dominance
(c) co-dominance (d) independent assortment
(3) Which of the following is not X-linked disorder?
a) Haemophilia (b) Night-blindness
c) Hypertrichosis (d) Myopia
(4) Which of the following is also called bleeder's disease?
a) Anaemia (b) Thrombocytopenia
c) Polycythemia (d) Haemophilia
(5) The word chroma means ……..
(a) a part of nucleus (b) a part of chromosome
(c) Colour (d) filamentous body
(6) On what basis are the chromosomes usually classified?
(a) On the basis of their function
(b) On the basis of their length
(c) On the basis of the position of the centromere
(d) On the basis of their number
(7) A mature Woman has.............. linkage groups.
(a) 44 (b) 22 (c) 46 (d) 23
(8) If centromere is situated in the middle of the chromosome, it is called
(a) metacentric (b) acrocentric
(c) submetacentric (d) telocentric
(9) If a haemophilic woman marries a normal man,
(a) all their children will be normal.
(b) all their sons will be haemophilic.
(c) all their daughters will be haemophilic.
(d) 50% sons and 50% daughters will be haemophilic.
(10) Which of the following traits studied by Mendel in garden pea is a dominant trait?
(a) Terminal flowers.
(b) Inflated pod.
(c) Green colour of seed.
(d) Yellow colour of pod.
1)Female heterogamety is observed in.
Answer: Birds.
2) In sickle-cell anaemia, the amino acid, glutamic acid is substituted by in the beta chain of haemoglobin. Answer: Valine.
.4) What are true-breeding lines that are used to study inheritance pattern of traits in plants?
Answer: A true-breeding line is one that has undergone continuous self-pollination/inbreeding and shows stable inheritance and expression of a trait for several generations.