Blog rss

Mastering the Genetic Code (Biology Class XII)

Meritnation|Mar 14th, 2014 09:00am

Untitled drawing (5) (1)

 

Genetics is one of the most difficult but interesting subjects in biology. A good understanding of genetics requires knowledge about the structure and function of cell, cell division and reproduction. Here are a few tips on how to master this subject.

  • The unit, Genetics and Evolution amounts to 18 marks in the biology paper.
  • This unit consists of three chapters namely; Principles of Inheritance and Variation (Chapter 5), Molecular Basis of Inheritance (Chapter 6) and Evolution (Chapter 7).
  • Figure out the critical aspects of genetics and try to perfect them.
  • An analysis of previous years question papers shows that many questions are asked as it is from the NCERT textbooks.
  • The table given below shows the exact question numbers of the questions in the question papers and the page numbers in the textbook where the answers to these questions are available.
Marks Chapter 5 Chapter 6 Chapter 7
Q. No. Pg. No Q.No Pg. No Q.No Pg.No 2009 Set 1
1
2
3 24 88 22 106-107 25 133
5 29 100
1 1 130 2009 Set 2
2
3 6(OR)6

88

77
5
1 3 111 2 130 2009 Set 3
2
3
5 8 (OR) 76 8 105
1 4 112 6 127 2010 Set 3
2 17 76
3 19 84 20 24 131
5 30 89 30 (OR) 136
1 7 112 2011 Set 1
2 7 99
3 20
22		 75,76, 77,
89		 21 97
5 29 (OR)
29		 134,135,
141
1 7 112 2011 Set 3
1
2 9 106
3 21 106
5
Cross Phenotypic Ratio Genotypic Ratio
Monohybrid Cross 3:1 1:2:1
Dihybrid Cross 9:3:3:1 4:2:2:2:2:1:1:1:1
Incomplete Dominance 1:2:1 1:2:1
  • Constructing a Punnett square is an essential part of solving problems based on Mendelian genetics.
  • In order to understand Punnett square, let us consider the given example.
Let us now understand the cross involved,
XHXh  x  XhY
Gametes: XH, Xh  and Xh, YPunnett Square: The gametes of the parents are taken on the horizontal and the vertical columns, here is the Punnett square for the given cross.
screenshot1Therefore, the probability that the male child will be affected is 25% while 50% of their total progeny would be affected.In case of a dihybrid cross:

  • The Punnett square for the F2 generation in a dihybrid cross consists of 16 boxes.
  • Each square gets one parent at the top and the left.
  • Choose the parental genotype in such a way that the cross obtained possesses a set pattern.
  • For example, let us take a cross between seed colour and seed shape.
  • Yellow colour and round shape is dominant over green colour and wrinkled shape.
  • Therefore, the cross would be

1112

  • Here you can note that there is a set pattern;
  • The original homozygous parental genotype occupies the first and the last boxes.
  • The hybrids, heterozygous for both the traits are formed along the diagonal.
  • The rest of the boxes are occupied by the hybrids that are either heterozygous for seed shape or seed colour.

Questions on Pedigree Analysis:

  • Pedigree analysis questions are usually asked on the inheritance of diseases such as sickle cell anaemia, haemophilia and colour blindness.
  • The inheritance pattern of such diseases involves the understanding of these traits as to whether they are sex-linked or autosomal.
  • The inheritance of sex-linked disorders differ in males and females while in case of autosomal disorders, there is no distinction in males and females.
  • The inheritance of autosomal disorders depends on whether the trait is dominant or recessive. Here are some examples of sex-linked and autosomal disorders.
  • The given table enlists some common genetic diseases.
  • Here is an example of a question on pedigree analysis.
2009 Set 1(Delhi Region): Question 24
Haemophilia is a sex-linked recessive disorder of humans. The pedigree chart given below shows the inheritance of haemophilia in one’s family. Study the pattern of inheritance and answer the question given.
pedigree-chart(a)Give all the possible genotypes of the members 4, 5 and 6 in the pedigree chart.
(b)A blood test shows that the individual 14 is a carrier of haemophilia. The member numbered 15 has recently married the member numbered 14. What is the probability that their first child will be a haemophilic male?
Answer:
(a) 4 − Carrier female with genotype X*X
5 − Affected male with genotype X*Y
6 − Normal male with genotype XY
Here, X* represents the trait for haemophilia.
(bThere is a 25% probability that their first child will be a haemophilic male.
  • For questions on processes, try to give your answers in points or flow charts and then elaborate on them if the question asks for it.
  • Try to support your answers with suitable diagrams.
  • Now let us take a look at the chapter-wise important topics in this unit.
Chapter / Marks
 1 2 3 and 5
Principles of Inheritance
and Variation

Mendelian ratios

 Mendelian crosses
Laws of Mendel Codominance
Test cross Incomplete dominance
Linkage
Sex Determination, Male and female Heterogamety
Mendelian and chromosomal disorders
Molecular Basis of Inheritance Genetic code – start and stop codons

Base complementarity
Rule

 Griffith’s experiment,
Hershey and Chase Experiment
Messelson and Stahl
experiment
Splicing Splicing Replication
histone proteins and
DNA packaging		 Post-transcriptional
Modifications (capping, Tailing)		 Transcription, translation
Mutation Features of the genetic code
Structure of tRNA
lac operon
Goals and features of HGP
DNA Fingerprinting
Evolution Origin of life Convergent and
Divergent Evolution		 Adaptive radiation
Homologous and
Analogous organs		 Natural selection and
Saltation		 Natural selection and
Saltation
Human evolution Hardy-Weinberg Principle
Human evolution

Follow these simple tips to achieve great marks in the exam.

All the Best!

Team Meritnation

Related Posts

Tags In this Post :

Add Comment Total Comments (28)

  • 1. poornima  |  April 2nd, 2015 at 3:34 pm

    thnx for this also provide for physics chemistry also

  • 2. Lupita Fader  |  November 6th, 2014 at 1:26 pm

    Well it was quite a excellent post.Thanx for writing such an info here.I really hope you’re going to keep on enlightening people in future also,with the help of this kind of beneficial info.Continue the excellent task.

  • 3. Ophelia  |  June 10th, 2014 at 3:03 am

    Thanks for one’s marvelous posting! I genuinely enjoyed reading it, you’re a
    great author.I will be sure to bookmark your blog and may
    come back in the future. I want to encourage you to continue your
    great job, have a nice day!

  • 4. harsimran narula  |  June 14th, 2013 at 9:35 pm

    Thanks alot…

  • 5. pooja  |  April 15th, 2013 at 1:36 pm

    thanks for these points.

  • 6. Udddhav pradhan  |  April 6th, 2013 at 12:31 pm

    thanks a lot for these tips
    please provide for ecosystem too

  • 7. r4i sdhc 3ds  |  March 25th, 2013 at 10:06 am

    Nice…thanks for this.

  • 8. sirisha  |  March 24th, 2013 at 11:05 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 9. sirisha  |  March 24th, 2013 at 11:05 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 10. sirisha  |  March 24th, 2013 at 11:05 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 11. sirisha  |  March 24th, 2013 at 11:05 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 12. sirisha  |  March 24th, 2013 at 11:05 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 13. sirisha  |  March 24th, 2013 at 11:04 pm

    thank u so much for your valuable tips.please post some suggestions about physiotherapy.

  • 14. sirisha  |  March 24th, 2013 at 11:01 pm

    thank u so much , that u have said that how to prepare. also post some suggestions about physiotherapy.

  • 15. scrapebox  |  March 23rd, 2013 at 1:18 am

    I was just looking for this info for a while. After 6 hours of continuous Googleing, finally I got it in your site. I wonder what is the lack of Google strategy that don’t rank this type of informative sites in top of the list. Generally the top sites are full of garbage.

  • 16. LAKSHMI S DAS  |  March 14th, 2013 at 1:43 am

    THANK YOU SO MUCH.. YOUR EXPERT TIPS HAD HELPED ME A LOT IN CHEMISTRY EXAM….. KINDLY POST SOME TIPS FOR MATHEMATICS ALSO

  • 17. wonders  |  March 13th, 2013 at 8:04 pm

    wonderful… 🙂

  • 18. Saroj  |  March 13th, 2013 at 2:15 pm

    Sir, Please provide us short detail about these experiments because many times long questions were asked from these experiments named:
    1)Metthew Meselson and Frenklin Stahl Experiment
    2)Hershey-Chasey Experiment
    3)Frederick Griffith’s experiment
    (from chapter- Molecular Basis Of Inheritance)
    4)Miller’s Experiment (form Evolution)

    It would be very helpful if you do so..
    Thanks!

  • 19. Musthafa  |  March 13th, 2013 at 1:26 pm

    Please provide tips for maths it will be helpful too thanks for chem wonderfull job

  • 20. Musthafa  |  March 13th, 2013 at 1:24 pm

    Please provide tips for maths it will be helpful too thanks for chem

  • 21. kirtisingh  |  March 13th, 2013 at 10:36 am

    please help in neet entrance exam rivision notes

  • 22. Shikhar  |  March 13th, 2013 at 7:38 am

    Though I’m not a biology student, I am thankful to Meritnation for providing us with such tips and summary of the courses. It has helped me a lot in Chemistry.
    Please update the blog with tips for mathematics Mathematics also.

    Regards,
    Shikhar

  • 23. Catherine  |  March 13th, 2013 at 3:25 am

    You guys are the best I will definitely recommend all my juniors to use this website ….but it would be better if you guys would give more tips on otherchapter
    Anyway thankyou very much 🙂

  • 24. Sherly  |  March 13th, 2013 at 12:08 am

    plz provide some tips on maths also……becoz maths+computer science students hv maths next….

    thanks

  • 25. roshni  |  March 12th, 2013 at 9:02 pm

    thank you very much.
    you’re guidelines are helping me very much

  • 26. himanshu  |  March 12th, 2013 at 8:46 pm

    thanks a lot for these tips
    please provide for ecosystem too
    🙂

  • 27. Akanksha Payal  |  March 12th, 2013 at 7:31 pm

    thnx alot……….!!!!!!!!!!
    but plz provide for biotechnology also

  • 28. archana  |  March 12th, 2013 at 6:45 pm

    pls give some tips 4 unit 1 also

Comment

*
*
*
Some HTML allowed:
<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>