sex- chromosomes<\/a>, also called heterosomes. The human body cells have two sex- chromosomes. A woman has two X- chromosomes while a man has one X- chromosome and one Y-chromosome.
\n
\nTherefore, an egg cell has one X- chromosome and a sperm cell has either an X- or a Y-chromosome. This means that the sex of a baby is determined by the type of sperm cell fertilizing the egg. If a egg, fused with a sperm having Y-chromosome, then the male zygote will develop and when fused with a sperm having X-chromosome then a female zygote will develop.<\/p>\n<\/p>\n
Question 3:<\/strong> A woman with normal vision marries a man with normal vision. They have a colourblind son. Her husband dies and she marries a colourblind man. Show the type of children that might be expected from this marriage and the proportion of each.
\nAnswer:<\/strong> In the first marriage of woman the son was colourblind therefore the woman is a carrier genotype of that Woman: XX
\n
\nSince the man in the second marriage was colourblind.
\nGenotype of that man: XY
\nPossible combination of this marriage.
\n<\/p>\nQuestion 4:<\/strong> What is dihybrid cross ? How did Mendel performed this cross.
\nAnswer:<\/strong> Dihybrid Cross: A cross between two parents taking into consideration alternative traits of two different characters. For example, a cross between round and yellow seed bearing plant with wrinkled and green seed bearing plant.
\n<\/p>\nQuestion 5:<\/strong> A woman had normal vision, but her father was colourblind. She marries a man, who is colourblind.
\nFind out the probability of the first child being colourblind, whether it is a boy or girl.
\nAnswer:<\/strong> That woman is heterozygous, and carrier of that trait because her father was colourblind. She marries a colourblind man, then it might be possible that her first child will be colourblind whether a son or a daughter, because mother and father both possess an inherited chromosome.
\n<\/p>\nQuestion 6:<\/strong> The karyotype (set of chromosomes) shown below is taken from a dividing cell in a certain individual.
\n(i) Is the individual male or female ? Explain your answer.
\n(ii) How would you expect (a) a female cell and (b) sperm cell to differ in chromosome composition ?
\nAnswer:<\/strong> (i) Male, because there is a Y-chromosome and an X-chromosome.
\n(ii) (a) A female would have two X-chromosomes and no Y-chromosome.
\n(b) A sperm cell would have half the number of chromosomes. 23 instead of 46. There would be only one sex-chromosome which could be either Y or X.<\/p>\nQuestion 7:<\/strong> (i) State Mendel’s law of Independent Assortment.
\n(ii) A homozygous Tall plant (T) bearing red coloured (R) flowers is crossed with a homozygous Dwarf plant (t) bearing white flowers (r):
\n(1) Give the Genotype and Phenotype of the F2<\/sub> generation.
\n(2) Give the possible combinations of the gametes that can be obtained from the F2<\/sub> hybrid.
\n(3) Give the dihybrid ratio and the phenotype of the offsprings of the F2<\/sub> generation when two plants of the F1<\/sub> generation above are crossed.
\nAnswer:<\/strong> (i) Mendel’s law of independent assortment, states that in a dihybrid cross, the alleles of one pair segregate independently of the alleles of other pair at the time of gamete formation and the gametes assort independently at the time of zygote formation. Thus, inheritance of one ; character does not interfere, the inheritance of other character.
\n
\n(1) Genotype \u2014 TtRr. Phenotype \u2014 All tall with red flowers.
\n(2) Gametes \u2014 TR, Tr, tR, tr.
\n(3) 9:3:3:1, 9 \u2014 Tall with red flowers, 3 \u2014 Tall with white flowers, 3 \u2014 Dwarf with red flowers, 1 \u2014 Dwarf with white flowers.<\/p>\nQuestion 8:<\/strong> A haemophilic man marries a carrier women. Find out the probability of their offsprings being haemophilic.
\nAnswer:<\/strong> The gene of haemophilia is present on X-chromosome. This disease is only found in males and females can only act as carriers.
\n<\/p>\nQuestion 9:<\/strong> Given below is a schematic diagram showing Mendel’s Experiment on sweet pea plants having axial flowers with round seeds (AARR) and Terminal flowers with wrinkled seeds (aarr). Study the same and answer the questions that follow :
\n
\n(i) Give the phenotype of F1<\/sub> progeny.
\n(ii) Give the phenotypes of F2<\/sub> progeny produced upon by the self-pollination of F1<\/sub> progeny.
\n(iii) Give the phenotypic ratio of F2<\/sub> progeny.
\n(iv) Name and explain the law induced by Mendel on the basis of the above observation.
\nAnswer:<\/strong> (i) Axial round
\n(ii) Axial round, axial wrinkled, terminal round, terminal wrinkled.
\n(iii) 9:3:3:1
\n(iv) Law of independent assortment: When there are two pairs of contrasting characters, the distribution of factors of each pair in the gametes is independent of the distribution of other pair of characters.<\/p>\nQuestion 10:<\/strong> (a) Given below is a schematic diagram showing Mendel’s Experiment on sweet pea plants having axial flowers with round seeds (AARR) and terminal flowers with wrinkled seeds (aarr). Study the same and answer the questions, that follow :
\n
\n(i) Give the phenotype of F1<\/sub> progeny.
\n(ii) Give the phenotypes of F2<\/sub> progeny produced upon by the self-pollination of F1<\/sub> progeny.
\n(iii) Give the phenotypic ratio of F2<\/sub> progeny.
\n(iv) Name and explain the law induced by Mendel on the basis of the above observation.
\nAnswer:<\/strong> (a) (i) Axial round
\n(ii) Axial round, axial wrinkled, terminal round, terminal wrinkled.
\n(iii) 9:3:3:1
\n(iv) Law of independent assortment: When there are two pairs of contrasting characters, the distribution of factors of each pair in the gametes is independent of the distribution of other pair of characters.<\/p>\nExplain the Terms<\/span><\/h3>\nQuestion:<\/strong>
\n1. Heredity
\n2. Variation
\n3. Dominance
\n4. Linkage
\n5. Mutation
\n6. Crossing-over
\n7. Heterosome
\n8. Recessive character
\n9. Genotype
\n10. Alleles
\nAnswer:<\/strong> 1. Heredity:<\/strong> The process of transmission of parental characters to the progeny through the generations.
\n2. Variation:<\/strong> Occurrence of differences in progeny of same parents and individuals of same species.
\n3. Dominance:<\/strong> The character expressed in first generation when any two individuals of contrasting characters breed is dominant and the phenomenon is called dominance.
\n4. Linkage:<\/strong> The phenomenon of inheritance of a group of genes together through some generations.
\n5. Mutation:<\/strong> Any change brought about into the genetic composition through external or internal factors.
\n6. Crossing-over:<\/strong> The phenomenon of the exchange of genetic material between two non\u00acsister chromatids.
\n7. Heterosome:<\/strong> Chromosome found in reproductive cell and which are responsible for the sex of a child.
\n8. Recessive character:<\/strong> The character which remains hidden in F1<\/sub> generation and expressed in the second-generation in the ratio of 1:2:1.
\n9. Genotype:<\/strong> The genetic composition of any organism is called genotype.
\n10. Alleles:<\/strong> Alleles are the alternative forms of the same gene. For example, tallness and dwarfness are the two alternative forms of a gene for height and are called alleles. Similarly, attached ear lobes and free ear lobes are alleles for the type of ear lobes.<\/p>\nName the Following<\/span><\/h3>\nQuestion:<\/strong>
\n1. The study of heredity and variation.
\n2. Cells having a single set of chromosomes.
\n3. The genetic composition of an organism.
\n4. Pairs of chromosomes, present in human egg cells.
\n5. Number of chromosomes present in human gametes.
\n6. The diploid number for cell of man.
\n7. Chromatids where Recombination of characters occurs.
\n8. A specific part of chromosome that determine hereditary characteristics.
\n9. The pattern of arrangement of genes along a chromosome.
\n10. Pair of genes responsible for a particular characteristic.
\n11. The type of gene, which in the presence of a contrasting allele is not expressed.
\nAnswer:<\/strong>
\n1. Genetics
\n2. Haploid
\n3. Genotype
\n4. 23
\n5. 23
\n6. 46
\n7. Non-sister chromatids
\n8. Gene
\n9. Linearly
\n10. Alleles
\n11. Recessive<\/p>\nGive Technical Terms<\/span><\/h3>\nQuestion:<\/strong>
\n1. Transmission pf characters through generations.
\n2. Differences occurring within offsprings of the same progeny.
\n3. Cell organelle directly involved in genetics.
\n4. Cell which determines the sex of a baby.
\n5. A virus with DNA as heredity material.
\n6. The hereditary unit, which is responsible for inheritance.
\n7. Transmits characteristics from parents to offsprings.
\n8. The individual having similar pair of genes.
\n9. The individuals having dissimilar pair of genes.
\n10. The ratio of offspring on F2 generation in a dihybrid cross.
\n11. A single egg was fertilized by a single sperm. But twins derived from that egg were born. What is the name of such type of twins ?
\n12. A twin consisting of a brother and a sister were bom to a lady. What is the name of such a type of twins ?
\n13. Name a genetic disease in which a person cannot distinguish red and green colour.
\nAnswer:<\/strong>
\n1. Heredity
\n2. Variation
\n3. Nucleus
\n4. Sperm cell
\n5. Retro virus e.g. HIV
\n6. Gene
\n7. Genes
\n8. Homozygous
\n9. Heterozygous
\n10. 9 : 3 : 3 : 1
\n11. Identical or monozygotic twins
\n12. Non-identical or fraternal twins
\n13. Colour blindness<\/p>\nFill in the Blanks<\/span><\/h3>\nComplete the following sentences with appropriate words :<\/strong>
\n1. The chromosomal theory of inheritance was proposed by Sutton<\/span> and Boveri<\/span> in 1902.
\n2. Gene<\/span> is the hereditary unit.
\n3. In mammals, the female is homozygous while the male is Heterozygous<\/span>.
\n4. A chromosome is composed of 50<\/span> % DNA and 50% histone<\/span>.
\n5. Gregor John Mendel<\/span> is the Father of Genetics.
\n6. The number of chromosomes in human is pairs\/46<\/span>.
\n7. The physical expression of genes is called Phenotype<\/span>.
\n8. The small differences among individuals are called Variations<\/span>.
\n9. The dissimilar pairs of genes present in an individual are known as Heterozygous<\/span>.
\n10. Autosomes<\/span> chromosomes do not take part in sex determination.
\n11. Alleles<\/span> are the alternative forms of a gene producing different effects.
\n12. 9 : 3 : 3 : 1<\/span> is the ratio of dihybrid cross.
\n13. A character that is supressed is Recessive<\/span>.
\n14. Upon Fertilization<\/span> the diploid condition is restored.<\/p>\nTrue & False<\/span><\/h3>\nMention, if the following statements are True or False. If false rewrite the wrong statement in its correct form:<\/strong>
\n1. Most genetic diseases in man are recessive in character. (True)<\/strong>
\n2. DNA has a double helical structure. (True)<\/strong>
\n3. Genes are responsible for genetic characters. (True)<\/strong>
\n4. Linkage is a permanent feature of few genes. (True)<\/strong>
\n5. Mutation can be brought about artificially. (True)<\/strong>
\n6. A female is responsible for the sex of the progeny. (False, Male is responsible for the sex of progeny.)<\/strong>
\n7. Mendel experimented upon plants of Oryza sativa. (False, Mendel experimented plants of Pisum sativum.)<\/strong>
\n8. Male act as carrier for colourblindness. (False, Female acts as carrier for colour blindness.)<\/strong>
\n9. Females are more affected by sex-linked genetic disorders. (False, Males are more affected by sex linked genetic disorders.)<\/strong>
\n10. Colour blindness is a Y-linked character. (False, Colour blindness is a X-linked character.)<\/strong>
\n11. Haemophilia exhibits X linked inheritance. (True)<\/strong>
\n12. A colourblind male cannot distinguish any colour. (False, A colour blind male cannot distinguish red and green colour.)<\/strong>
\n13. Cancer is a genetic disorder. (False, Cancer is not a genetic disorder.)<\/strong><\/p>\nState the Function<\/span><\/h3>\nWrite the functional activity of the following structures:<\/strong><\/p>\n\n\n\nName<\/strong><\/td>\nFunction<\/strong><\/td>\n<\/tr>\n\n | |