Solved Exercise Biology (II) Q.1: Fill In the blanks. i. is the basic unit of biological information. ii. A sudden change in the structure of a gene is called. iii. is the chance of an event to occur. iv. A cross among monohybrids is a cross. v. An individual with a homozygous genotype is called. vi. Different alleles of a gene that are both expressed in a heterozygote are called. vii. When a heterozygote exceeds the phenotypic expression of both the homozygotes the phenomenon is called. viii. When a single gene affects two or more traits, the phenomenon is called. ix. A gene with multiple phenotypic effects is called. x. The phenomenon of staying together of all the genes of a chromosome is called. xi. minimizes the chances of genetic recombination. xii. is an exchange of segments between non-sister chromatids of homologous chromosomes during meiosis. xiii. All chromosomes other than sex chromosomes are called. xiv. is the maleness determining gene in man. xv. Type of diabetes mellitus is non insulin dependent. xvi. Polygenic inheritance with environment influence is called inheritance. ANSWERS: i. Gene ix. Pleiotropic ii. Mutation x. Linkage iii. Probability xi. Gene linkage iv. Monohybrid xii. Crossing over v. Homozygote xiii. Autosomes vi. Co-dominant xiv. SRY vii. Over dominance xv. II viii. Pleiotropy xvi. Multifactorial Q.2: Write whether the statement is true or false. Correct the statement if it is false. i. In grasshopper, the male has XY and the female has XX types of sex. True: In grasshopper, the male has XO and the female has XX
types of sex chromosomes. ii. Pea is normally a self fertilizing plant. True iii. iv. Dihybrids are offspring of the parents who differ in one contrasting pair of trait. True: Dihybrids are offspring of the parents who differ in two contrasting pair of trait. X linked traits pass direct from father to son. True: X linked traits pass direct from father to daughter. v. A person suffering from blue cone monochromacy can not see blue colour. True: A person suffering from blue cone monochromacy can not see red and green colour. vi. In birds and moths eggs determine sex. True vii. A homozygote forms all gametes of the same type. True viii. The allele for a sex limited trait is dominant in one sex but recessive in the other. True: The allele for a sex influenced trait is dominant in one sex but recessive in the other. ix. Pattern baldness is a sex influenced trait. True x. Carriers of haemophilia show no symptoms of disease. True Q.3 Encircle the correct answer from the multiple choices. (i) (ii) (iii) (iv) (v) When a single gene has multiple phenotypic effects, the phenomenon is called: (a) Codominance (b) Epitasis (c) Pleiotropy (d) Sex-linkage What happens when both alleles of a gene pair independently express in a heterozygote? (a) Dominance (b) Over dominance (c) Incomplete dominance (d) Codominance A heterozygote offspring quantitatively exceeds the phenotypic expression of both the homozygote parents due to: (a) Dominance (b) Incomplete dominance (c) Over dominance (d) Codominance How many gene pairs contribute to the wheat grain colour? (a) One (b) Two (c) Three (d) Four Who for the first time found white eye mutant in Drosophila? (a) Morgan (b) Bridges (c) Correns (d) de Varies
(vi) (vii) (viii) (ix) (x) (xi) (xii) Which of the following traits is transmitted directly from an affected father to only his sons? (a) Autosomal (b) X linked (c) Y linked (d) X and Y linked Which phenomenon reduces the chances of genetic recombination and variations among offspring? (a) Linkage (b) Crossing over (c) Independent assortment (d) Dominance Which of the following traits is not sex linked recessive? (a) Haemophilia (b) Colour blindness (c) Hypophosphatemic ricket (d) tfm syndrome Which of these traits zigzags from maternal grand father through a carrier daughter to a grandson? (a) Autosomal (b) X linked (c) Y linked (d) X and Y linked When a haemophilic carrier woman marries a normal man, who among her offspring may be affected: (a) All her children (b) All her daughters (c) Half of her daughters (d) Half of her sons What is the risk of a colour-blind child in a family when mother is colour blinded but father is normal? (a) 100% (b) 75% (c) 50% (d) 25% What is the risk of a colour-blind child in a family when father is colour-blind but mother is normal? (a) Zero% (b) 25% (c) 50% (d) 100% ANSWERS: i. c ii. d iii. c iv. c v. b vi. c vii. a viii. c ix. b x. d xi. c xii. a Q.4 Short Questions. i. Differentiate between: (a) Phenotype and genotype (b) Homozygous and Heterozygous (c) Autosome and sex chromosome (d) Allele and multiple allele (e) Incomplete dominance and codominance (f) Continuous and discontinuous variations (g) Gene and allele (h) Monohybrid and dihybrid (i) Dominance and epistasis (j) X-linked trait and Y-linked trait
(k) (l) (m) Sex limited and sex influenced trait Dominant trait and recessive trait Wild type and mutant PHENOTYPE The form of appearance of a trait is called phenotype. GENOTYPE The genetic constitution underlaying a single trait or set of traits is called genotype. HOMOZYGOUS The condition in which the alleles of a gene pair in an organism are identical is called homozygous. HETEROZYGOUS The condition in which the alleles of a gene pair in an organism are not identical is called heterozygous. AUTOSOME Any eukaryotic chromosome that is not a sex chromosome is called autosome. Same sort of autosomes are present in both male and female of a species. SEX CHROMOSOME Chromosome other than autosome is called sex chromosome. Different sort of sex chromosomes are present in both male and female of a species. ALLELE Partner of a gene pair occupying the same gene locus is called allele. MULTIPLE ALLELE More than two alternate forms of a gene which arise by gene mutation are called multiple alleles. INCOMPLETE DOMINANCE The dominance in which the phenotype of the heterozygote is intermediate between phenotypes of the two homozygotes is called incomplete dominance. CO-DOMINANCE The dominance in which there are different alleles of a gene and that both alleles are expressed in a heterozygous condition is called codominance. CONTINUOUS VARIATION The variation is which there are many genes and all genes are present in different combinations within individuals of a population is called continuous variation. DISCONTINUOUS VARIATION Variation showing clear cut difference among individuals with no intermediates between them is called discontinuous variation.
GENE The basic unit of biological information is called gene. MONOHYBRID A hybrid for one trait is called monohybrid. ALLELE Partner of a gene pair occupying the same gene locus is called allele. DIHYBRID A hybrid for two traits is called dihybrid. DOMINANCE The physiological effect of an allele over its partner allele on the same gene locus is called dominance. EPISTASIS The phenomenon in which an effect caused by a gene or gene pair at one locus interferes with or hides the effect caused by another gene or gene pair at another locus is called epistasis. X-LINKED TRAIT A trait whose gene is present on X- chromosome is called X-linked trait. Y-LINKED TRAIT A trait whose gene is present on Y- chromosome is called Y-linked trait. SEX LIMITED TRAIT The trait which is limited to only one sex due to anatomical differences is called sex limited trait. E.g. Genes for milk yield in dairy cattle affects only cows. SEX INFLUENCED TRAIT The trait which occurs in both males and females but is more common in one sex is called sex influenced trait. E.g. Pattern baldness. DOMINANT TRAIT A trait which expresses itself in F 1 generation is called dominant trait. RECESSIVE TRAIT A trait which hides over itself in F 1 generation is called recessive trait. WILD TYPE A normal gene or individual found in natural population is called wild type. ii. Ans. iii. Ans. MUTANT An organism carrying a gene that has undergone a mutation is called mutant. What is a gene pool? All the genes/alleles found in a breeding population at a given time are collectively called the gene pool. Was pea a lucky choice for Mendel? What would have happened if he had studied an eighth character? Yes, pea was a lucky choice for Mendel. The pea has 14 chromosomes. Only seven characters can be present separately on each 7 homologous
chromosomes. The eighth character will be linked to any one of these seven characters. Had Mendel studied eighth character, it would have been linked to any other seven traits. So the alleles of this trait would not segregate independently. Therefore, Mendel was unable to prove his law of independent assortment. iv. What is a test cross? Why did Mendel devise this cross? Ans. The cross which is used to determine the genotype of an individual showing dominant phenotype is called test cross. Mendel devised test cross to test the genotype of an individual showing a dominant phenotype. v. What would happen if alleles of a pair do not segregate at meiosis? How would it affect the purity of gamete? Ans. If alleles of a pair do not segregate at meiosis, the gamete can have extra chromosomes or lesser chromosomes. It would affect the purity of gametes because when these gametes would fuse with normal gamete, they would produce abnormal individual (like in Down's syndrome and Turner s syndrome etc). vi. If the alleles do not assort independently, which type of combination is missing in the progeny? Ans. The progeny would not have recombinant individuals. vii. Why has each gamete equal chance of getting one or the other allele of a pair? Ans. The alleles are present on different chromosomes. Every chromosome assorts independently. So each gamete has equal chance to get one or the other allele of the gene. viii. Does the dominant allele modify the determinative nature of its recessive partner? What sort of relationship do they have? Ans. The dominant allele does not modify the determinative nature of recessive partner. It only hides the affect of the recessive allele. The recessive allele can express itself in a later cross. ix. Which type of traits can assort independently? Ans. The traits which are present on different homologous chromosomes and are not linked to each other can assort independently. x. Why does the blood group phenotype of a person remain constant throughout life? Ans. The blood group phenotype is controlled by genes, that why it remains constant throughout life. xi. Ans. xii. Ans. What is a universal blood donor? The person who can donate blood to any person having any blood group is called universal blood donor. The blood group O is universal blood donor. How can ABO-incompatibility protects the baby against Rhincompatibility? Sometime ABO-incompatibility protects the baby against Rhincompatibility. If O - mother conceives A + or B + baby, any fetal A or B type RBC entering the mother s blood are quickly destroyed by
her anti-a or anti-b antibodies, before she can form anti-rh antibodies. xiii. Which type of genes do not obey law of independent assortment? Ans. Linked genes do not obey law of independent assortment. xiv. How can linked genes be separated from each other? Ans. Linked genes can be separated from each other by crossing over. xv. What is multifactorial inheritance? Ans. Polygenic inheritance with environmental influence is called multifactorial inheritance. xvi. What is MODY? Ans. About 2-5% of type-ii diabetics get the disease early in life before 25 years of age. It is called maturity onset diabetes of the young (MODY). xvii. Can a child have more intelligence (IQ score) than his parents? Ans. Intelligence is controlled by polygenes. Moreover, environment also affects it. Therefore, a child can have more intelligence than his parents. Q.5 Extensive questions. i. What is incomplete dominance? Explain it with examples. ii. Define Mendel's law of segregation. Explain it with an example. iii. Define Mendel's law of independent assortment. Explain it with an example. iv. Define probability. Derive 9:3:3:1 F 2 ratio of independent assortment through product rule. v. What is codominance? Explain the phenomenon of codominance with an example. vi. Define multiple alleles. Describe multiple allelic blood group system of man. vii. What id Rh factor? Describe the genetic basis of Rh-blood group system of man. viii. What is erythroblastosis foetalis? Discuss this adverse affect of Rh incompatibility. Also suggest a therapy to avoid Rh sensitization of an Rh - mother married to an Rh + man. ix. Define epistasis. Explain epistatic gene interaction with examples. x. What is a pleiotropic gene? Discuss pleiotropy with examples. xi. What are polygenes? Explain polygenic inheritance. xii. What is crossing over? Define recombination frequency and explain its significance. xiii. What are sex-chromosomes? Discuss the chromosomal patterns of sex determination in organisms. xiv. Compare chromosomal determination of sex between Drosophila and humans. xv. Define gene pool. Explain the concept of gene pool in a sample population. xvi. What is sex linkage? Explain T.H. Morgan s study of sex-linkage in Drosophila.
xvii. xviii. xix. Compare the pattern of inheritance of an X-linked dominant trait with an X-linked recessive trait in humans. Explain diabetes mellitus and its genetic basis. Discuss the genetics of colour blindness or haemophilia.