Heredity and Evolution SSLC 10 Science Notes

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  • Heredity : Passing traits from parents to child.
  • Traits : Distinctly identifiable characteristics.
  • Inherited traits : Similarity of child with their parents. E.g. skin color, eye color, hair, etc.
  • Evolution : Change in frequency of inherited traits or change in frequency of genes over generations.   
  • Accumulation of variation and variation in organisms :
    • New generation inherit traits of previous generations but also shows some new variations.
    • Variation in asexually reproduced organisms : Asexually reproduced organisms are produced due to DNA copying. Error in copying causes variation that are very minor.
    • Variation in sexually reproducing organisms : Inherited genes from parents are passed to child. Child also inherits new traits on their own.
    • Advantages of variations :
      1. Adaptability : Organisms are more adaptable to its environment. E.g. Thorns in plants.
      2. Diversity : Variations brings diversity in organisms. E.g. The is diverse population of organisms in world.
  • Mendel’s Contribution :
    • Inheritance of traits in child is influenced by father’s DNA and mother’s DNA. Each DNA shows two version of of particular trait i.e. one from mother and other from father. But in actual child inherits traits from either mother or father.
    • Mendel’s Experiment: [Refer the video to understand in detail]
      1. Dominant trait: Trait whose single copy is enough to express respective character in body.
      2. Recessive trait: Traits which shows up only if both inherited traits are same.
  1. Mechanism of Heredity : [Refer the video to understand in detail]
    • DNA is information source for making proteins in the cell. DNA contains specific sections, which contains information for protein synthesis, called genes.
    • Parents pass genes that controls trait in next generation, hence, next generation have two set of genes inherited one from each parent. Genes are present in shared chromosomes. Each germ cell take one chromosomes from each parent. Hence, when male and female germ cells fuse, the new cell formed contains a pair of chromosomes. Thus, new organism will have stable DNA.
  • Sex Determination:    
    • Environmental Determination: For some organisms sex is determined by environmental conditions. The egg of loggerhead turtles produce male individual below 28℃ and females above 30℃. Snails have ability to change sex depending on their partner.
    • Genetic Determination: [Refer the video to understand in detail]
      1. Humans consist of 23 pair of chromosomes having same genes inherited from mother and father. Out of 23 pairs one pair posses sex chromosome.
      2. In males, 22 pair of chromosomes are in matched pair. 23rd pair i.e. sex chromosome consist of XY chromosome.
      3. In females all 23 pair  are in matched pair (XX)
      4. Sex determination of child.
Male Chromosome(XY) Female chromosome(XX) Sex of child
X X Female
Y X Male
  • Evolution: Change in frequency of inherited traits or change in frequency of genes over a generation is evolution.
    • Adaptability :  “Evolution that brings survival advantage to species is called adaptability.” E.g. Survival of green beetle from crow due to green plants.
    • Diversity : “Evolution which gives variety in particular species is called diversity.” E.g. Accidental survival of blue beetles among red, green and blue beetles.
    • Not an evolution : “change in body without genetic change can not be considered as evolution.”  E.g. Undernourished generation of beetles becomes healthy when plant disease is cured.   
  • Acquired and Inherited traits:
    • Traits that an organism develops during lifetime are acquired traits. E.g. Knowledge, skills, etc. acquired traits do not bring changes in DNA of germ cell. Hence they are not carried to next generation.
    • Traits that an organism inherit from parents are inherited traits. E.g. eye color,  skin color, etc. These traits are passed to next generation.
  • Speciation:  
    • Variation in organisms population in such a way that it forms two groups of individual that cannot reproduce with each other is speciation. E.g Brown bee produces red bee and black bee. If black and red bee are unable to reproduce then these are independent species.
    • Factors responsible for new species:
      1. Geographical Separation: If organisms of same species are  separated by large distance (say river) then chances of interaction is less, and over generations, reproduced species can show large variation, enough to develop into an individual species.
      2. Genetic Drift:  Organisms population may have different form of same genes are called as allele. Change in frequency of allele by chance over generations cause genetic drift.   
      3. Natural Selection: [Refer the video to understand in detail]This theory suggests survival of the fittest. According to this theory, Darwin stated that, only those individuals which have favourable variations can survive and reproduce in an environment. Those which have no favorable variations undergo declining. During industrial revolution, soot deposited on trees helped black moths to survive and reproduce while the same environment caused declining of the gray moths population. This is natural selection.
  • Evolution and Classification :
    • Evolutionary relationships are needed to be grouped. Grouping and classification is done on the basis of similarity of characteristics and behaviour.  Classification can be done in hierarchical manner. It helps to identify the common ancestor of different but   closely related species.  For example:
  • Tracing Evolutionary Relationships :
  • Similar structures performing different functions are homologous organs. E.g. limbs of human, dog, bird and whale.
  • Different structures performing similar functions are analogous organs e.g. Wings of bat and bird.
  • Tracing Evolutionary Characteristics :  
    • Fossils:  Traces of dead organisms from past are called fossils.
    • Methods of finding age of fossil :
      1. Relative method : Over period of time plant and animals gets buried over one another. Fossil found closer to earth surface are recent while fossil present  deeper are older.
      2. By Ratio of Isotopes : Age of fossil can be found by finding age of radioactive element present in the fossil.
  • Evolution by stages :
    • Evolution in organism takes place slowly from generation to generation.
    • Organs such as beak is developed during evolution which help birds for eating insects, seed, etc. But beak of birds differ with each species. Feathers  were initially evolved to provide warmth but then they were adapted for flying.
    • With the help of fossil evolutionary phase of fossil can be guessed. For  e.g. cauliflower, kohlrabi and kale plants have common ancestor i.e. wild cabbage.
  • Comparing DNA : Direct estimate of change in DNA of particular species is obtained. Comparison can be used to obtain other species with such changes, and finally derive common ancestors for both the species.
  • Can we equate evolution with progress? : Evolution means genetic change. Progress means betterness. But it is not necessary that genetic change will always provide betterness to an organism, hence we cannot equate evolution with progress.  
  • Are complex structure of body better?: Genetic changes leads to complex structure of body, but it is not necessary that complex structure are always better than the older ones. For e.g. bacteria with simple structure survives in hot springs and cold ice, but spider and chimpanzees cannot even though they have complex structure.
  • Human Evolution:
    • Human evolution can be studied with methods like excavation, time dating, studying fossil, determining DNA sequences.
    • Are different races evolved from different species?: People of different races are identified as yellow or brown or black, but biologically all  humans belong to same species called Homosapein which was originated in Africa. For better life our ancestor travelled across the planet.

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