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How does this affect the evolution of those organisms that reproduce sexually? These variations are inherited and increase the chances of survival of an organism. How is the equal genetic contribution of male and female parents ensured in the progeny? Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete.
When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement?
Answer: Yes, variations that confer an advantage to an individual organism are inherited. The organism can survive longer in an environment and maintain its existence in the population.
Formulae Handbook for Class 10 Maths and Science. Answer: Natural selection selects the individuals having useful variations which ensure their survival in the prevailing conditions of environment. Variant individuals that can withstand or cope with prevailing environment will survive better and will increase in number through differential reproduction.
Answer: Mendel took pea plants with contrasting characteristics � tall plant and dwarf short plant. On cross pollination, he got all tall plants in F1 generation.
Then by self pollination of F1 tall plants, he produced second generation F2 consisting of tall and short plants in the ratio of 3 : 1. Answer: In a dihybrid cross made by Mendel, it was observed that when two pairs of traits or characters were considered; each trait expressed independent of the other.
Thus, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits. A man with blood group A marries a woman with blood O and their daughter has blood group O. Is this information enough to tell you which of the traits � blood group A or O is dominant? Answer: No. This is because we do not know about the blood group of all the progeny. Hence, the information is incomplete to draw any such conclusion. Answer: The females carry two X-chromosomes.
Males have one X and one Y- chromosome. Thus, female is homogametic and male is heterogametic. When a sperm carrying X- chromosome fertilises an egg, the zygote develops into female XX condition. When sperm carrying Y-chromosome fertilises an egg, the zygote develops into a male XY condition. Thus, sex is determined at the time of fertilisation. Answer: Different ways are : variation, natural selection and genetic drift isolation. Why are traits acquired during the lifetime of an individual not inherited?
Answer: Because acquired characters bring changes only in non-reproductive tissues and cannot change the genes of the germ cells. Thus, acquired traits cannot be passed to next generation. Answer: i If any natural calamity occurs and kills these small number of surviving tigers, they can become extinct resulting in the loss of some genes forever.
These both are very important for giving better survival chances to the species. What factors could lead to the rise of a new species? Answer: Genetic variations, natural selection and reproductive isolation could lead to the rise of a new species.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Answer: No, because pollination occurs on the same plant in self-pollinating plant species.
Answer: No, because asexual reproduction involves single parent or organism. Give an example of characteristics being used to determine how close two species am in evolutionary terms? Answer: Homologous organs, analogous organs and vestigial organs help to identify evolutionary relationships amongst the species.
Can the wing of butterfly and the wing of a bat be considered homologous organs? Answer: No, wing of a bat and wing of a bird cannot be considered as homologous organs because they have different basic structure. Answer: Fossils are the impression or remains of ancient life found preserved in the sedimentary rocks. Fossils are direct evidences of evolution. Fossils also help to identify evolutionary relationship between apparently different species.
They also tell about the extent of evolution that has taken place. Page Question 1. Answer: They look different because of interaction of genes with environment which results in change in their appearance. But they belong to the same species as they have same number of chromosomes and can breed among themselves. Answer: No, because different designs are the product of evolution and different species have different body design to suit or adapt to their environment.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing whfte flowers. The progeny all bore violet flowers, but almost half of them are short. An example of homologous organs is a our arm and a dogs fore-leg. Answer: d Both organs in all options have same basic structural design but have different functions and appearance.
In evolutionary terms, we have more in common with a a Chinese school-boy. Answer: a A Chinese school-bpy is also a human being. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes.
Answer: We can say that light eye colour trait is dominant because only dominant traits are expressed in the first generation. How are the areas of study � evolution and classification� inteilinked? Answer: Evolution and classification are interlinked with each other in many ways. Classification is the most important term to explain evolution.
It is based on the similarities and differences between two species or among two organisms. More closer the characteristics, the moe doser is the evolution and chances to be in the same group of classification. Thus, the classification of species is a reflection of their evolutionary relationship. Answer: Analogous organs are those organs which have different basic structural designs and developmental origins but have similar appearance and perform similar functions. Examples: Wings of an insect and wings of a bat.
Examples: Forelimbs of frog and forelimbs of human. Outline a project which alms to find the dominant coat colour in dogs. Answer: A homozygous black RB male dog and a homozygous white bb female dog is taken and given to mate and produce offspring in F1 generation.
If black colour is dominant out of every 4 dogs, 3 will be black and if white colour is dominant 3 out of 4 dogs will be white. Answer: Fossils and their study is useful to know about the species which are no longer alive.
They provide evidence and missing links between two classes. They are helpful in forming a sequence of organisms in the pathway of evolution. Thus, fossils have importance in deciding evolutionary relationships. Answer: Stanley L. Miller and Harold C. Urey provided evidence regarding origin of life from inanimate matter. They assembled an atmosphere similar to that existed on early earth.
The atmosphere had molecules like ammonia, methane, hydrogen sulphide and water, but no oxygen. So, life arose afresh on earth. Explain how sexual reproduction gives rise to more viable variations that asexual reproduction. Answer: Variations occurring during sexual reproduction may be due to:.
In asexually reproducing organisms only errors during DNA copying or mutations cause variations. Since the extent of variations is much larger in sexually reproducing organisms, therefore, the chances of evolution is also much in sexually reproducing These variations enable the organisms to adapt themselves to the changing conditions and also help to face the struggle for Over the time, they and rise to new species. Answer: Genetically organisms are of types.
As the chromosomes are the bearer of genes so haploids have single set of genes. A single gene determines the expression of character. Both the father and mother contribute practically equal amount of genetic material to the child. It means that each trait can be influenced by both paternal and maternal DNA. Answer: No, many of the times the variations are not advantageous to an individual organism but still survive in a population, e.
Most of the other variations not only give survival advantage to an individual but also contribute to genetic drift. Thus, we can say that most of the variations lead to better adaptation of an organism to the changing environment. In this way, it gives survival advantage to that organism and will also survive in the coming population. The science, which deals with study of heredity and variations is called a phylogeny b embryology c genetics d palaeontology Answer: c The genetics is the study of heredity and variations and includes their occurrence, causes, benefits, disadvantages, significance, etc.
Archaeopteryx is a connecting link between a reptiles and aquatic animals b birds and insects c reptiles and birds d birds and dinosaurs Answer: c Archaeopteryx is a connecting link- between the reptiles and birds. It appears like a bird, but has other features which are present in reptiles, e. For palaeontological studies a scientist will gather the evidences from a study of homology b study of analogy c fossils d All of these Answer: d Study of homologous and analogous organs indicates the origin and modification in organisms and study of fossils indicates the age and features of an organism.
State two methods of determining the age of fossils. Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor. For example, in a family, a brother and sister are closely related and they have a recent common ancestor i. A brother and his cousin are also related but less than the sister and her brother.
This is because the brother and his cousin have a common ancestor i. With subsequent generations, the variations make organisms more different than their ancestors. This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction.
How does this affect the evolution of those organisms that reproduce sexually? In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations, whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate. Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.
However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable. Variation and Evolution: Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place.
At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species.
Thus, variation helps in the evolution of sexually reproducing organisms. In human beings, every somatic cell of the body contains 23 pairs of chromosomes.
Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have two X chromosomes and males have one X and one Y chromosome. The gamete receives half of the chromosomes.
Therefore, the male gametes have 22 autosomes and either X or Y chromosome. The female gamete, on the other hand, has 22 autosomes and X chromosome. During reproduction, the male and female gametes fuse and thus the progeny receives 22 autosomes and one X or Y chromosome from male parent and 22 autosomes and one X chromosome from the female parent.
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not? In species, variations that offer survival advantages are naturally selected. Individuals adjust to their environments with the help of these selected variations and consequently these variations are passed on to their progeny. Evolution of organisms occurs as a result of this natural selection. However, there can be some other variations, which do not offer any survival advantage and arise only accidentally.
Such variations in small populations can change the frequency of some genes even if they are not important for survival. This accidental change in the frequency of genes in small populations is referred to as genetic drift. Thus, genetic drift provides diversity variations without any survival advantage.
How does the creation of variations in a species promote survival? Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult.
For example, if the temperature of water increases suddenly, most of the bacteria living in that water would die. Only few variants resistant to heat would be able to survive. If these variants were not there, then the entire species of bacteria would have been destroyed.
Thus, these variants help in the survival of the species. However, not all variations are useful. Chapter 14 - Sources of Energy. Chapter 15 - Our Environment. Chapter 16 - Management of Natural Resources. Variations in organisms happen during reproduction, irrespective of sexual or asexual reproduction. The preceding generation imparts basic features along with some variations to the upcoming generation.
The variation is minimal in case of asexual reproduction. This is a vital part of Chapter 9 Science Class Rules of inheritance imply a common fact. This common fact is that both the parents of an offspring contribute an equal amount of genetic material or DNA.
The mechanism behind an offspring's sex determination is not the same for all organisms. In some animals, it is determined by external factors like temperature while in some organisms, it is determined through genetic factors. Traits in organisms can either be acquired or inherited in nature.
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