MOLECULAR BASIS OF INHERITANCE

In continuation with preparation for Board 2020, let's practise some objective questions from Chapter 6,

 Molecular Basis of Inheritance

These questions will also be very useful for NEET preparation.

OBJECTIVE QUESTIONS

1. The ________________ biomolecule is a characteristic feature of an organism.
2. If the amount of haploid DNA in a human child is 3.3×10⁹bp, the amount of DNA in a normal human adult would be ________________.
3. The _______________ pyrimidine is present in both m RNA & tRNA but not in DNA.
4. The N bases are attached to __ C of deoxyribose sugar while the PO₄ are present on ____ C.
5. The __________________________ technique helped Wilkins & Franklin to study the structure of DNA.
6. The law of complementarity of N bases was given by ______________
7. Stability of double strand of DNA is due to stacking of bases & ____ bonds.
8. Central dogma of molecular biology was given by _________________.
9. The circumference of a sphere is 2.2 m. what would be the number of base pairs of DNA required to encircle the sphere once?
10. The protein involved in packing of DNA of eukaryotes but absent in DNA of prokaryotes is _____________
11. The ‘beads’ in “beads on String” structure is made of ____________, which is further made of __________
12. Euchromatin is active _______________, but heterochromatin is not.

Do not forget to leave comments, queries and doubts. All the Best

PRETEST: Principles of Inheritance & vaiation (Part 1)

Hello!

Starting with Unit 2.

Here are the pretest questions based on first 8 pages of Chapter 5. In my book (i.e. 2019-20 publication available online) the page numbers are 67-75. In terms of Topic; End of 5.2 (Inheritance of One Gene)

Read the pages carefully; and try to answer the questions. see how many you can answer.

The key points of this portion are already on blog, but I would request you not to refer them, and focus solely on book reading.

1.       Branch of Biology that deals with inheritance & variations _________

2.       ___________ is the basis of heredity.

3.       The major cause of variation is ______________; which has been used by humans for selective breeding.

4.       Experiments conducted by Mendel involved ___________ of true breeding Pea plants, which involved the technique of ___________.

5.       What was the advantage of taking large sampling size in Mendel’s experiment?

6.       Define true breeding lines.

7.       F₁ & F₂ in crossing stands for ___________ & _________.

8.       The ratios obtained by Mendel in F₁ & F₂ of monohybrid cross respectively was _________ & ____________.

9.       Factors of Mendel are equivalent to _______, and are units of inheritance required for expression of particular trait.

10.   T & t represent two forms of a __________, known as __________ which control expression of a trait.

11.   TT & Tt produce the same phenotype.

                                             i.            Capital T represents ________, small t represents _______.

                                           ii.            What conclusion was drawn by Mendel on the basis of this?

12.   The type of cell division that occurs during gamete formation is _____. Here only one _______ of a pair is passed in to a gamete.

13.   Graphical representation to calculate the probability of occurrence of different types of Genotypes in a cross is known as ___________.

14.   Self Pollination of a dwarf plant will give tall and dwarf in the ratio _:_.

15.   An organism exhibiting a recessive phenotype for tallness will have the following genotypes _________.; while an organism exhibiting a dominant phenotype for tallness will have the following genotypes _______________.

16.   Test cross is crossing tall (dominant phenotype) plant with ________ plant.

17.   Mendel gave ___ (no.) laws on the basis of monohybrid crosses; they are ___________ & _____________.

18.   _______ flower position & _______ flower colour in pea is dominant.

19.   The two seed related characters chosen by Mendel were ______ & _________.

The total number of true breeding

Chapter 5: Principles of Inheritance & Variation (Part 1)

Inheritance: Process by which character are passed from parents to progeny. Basis of heredity
            Term Genetics: Bateson

Heredity: Transmission of Characters

Variation: Degree by which progeny differs from parents. Cause: Sexual rep

Exploited by humans for developing high yielding var of plants & animals. E.g. Sahiwal cows from wild cows by artificial selection & domestication.

Mendel: On basis of hybridization exp on garden peas (Pisum sativum -14 chr) for 7 yrs Work rediscovered 34 yrs later by DeVries, Correns & Tschermak Unique features of Mendel’s research: ·       Applied math & statistics to study biology ·       Large sample size ·       Continuous experiments on successive generations

•     Studied visible traits with contrasting characters

Father of Genetics: Mendel Checkpoint: At this point it is very important to review few terms: ·        Gene vs Allele ·        Homozygous vs Heterozygous ·        Dominant vs Recessive ·        Genotype Vs Phenotype Make sure that you know them all clearly & confidently before proceeding ahead.

Mendel's Procedure: Artificial/cross pollination using true breeding plants

Selected 14 true breeding plants similar in all respects except 1 contrasting character
Inheritance of one Gene: Monohybrid Cross; Only one allelic pair considered

Dihybrid Cross: Two allelic pairs considered.

Laws of Inheritance: 3  Law of Dominance: In a hybrid where both contrasting alleles present, only 1 factor/allele expresses itself, this is known as dominant allele. The other – recessive               In F2: dominant : recessive:: 3:1  Principle of segregation: When a pair of contrasting characters present in an organisms, the characters do not mix together, simply stay together. They are separated at the time of gamete formation, so that each gamete will have allele for only 1 contrasting trait.              Also k/a Law of Purity of Gametes

• Principle of Independent Assortment: Genes of different characters present together in a plant are not inherited together. They are inherited independent of each other.

A father produces two types of gametes, while a mother produces only 1 type. Which of Mendel’s law is justified by this? State if there are any situations which under normal circumstances show exception to this law.

Cause of Dominance: When one of the alleles in a heterozygous individual is non-functional, i.e. either is not transcribed, or does not produces a functional protein. That allele is recessive. The other functional allele is dominant.

Dominance is relative

Reciprocal Cross: two crosses with same characters taken in to consideration but with reversing the sexes.

Back Cross: Cross of F1 progeny with either of the parent

Test Cross: Crossing of F1 progeny with homozygous recessive parent. Used to determine whether an individual with dominant trait is homozygous or heterozygous. During Test Cross:

All Tall: Homozygous                                                   Tall: Dwarf=1:1 Heterozygous

When Aa is crossed with aa, what is the genotype and ratio of various genotypes in progeny? Can you give a name for this type of cross?

Reasons for Mendel’s Success:        Self-Fertilizing, easy to grow plant        Diploid plant        7 visible features Focused on few contrasting characters, 1 or 2 at time Kept accurate quantitative records

Post Mendel studies revealed interactions between genes.

Post Mendelism: Mendel stated ‘factors’ (genes) to be discrete units inherited independently of each other.

Gene Interactions of 2 types: Intragenic (Interallelic): between two alleles, present on same gene locus on two homologous chromosomes. E.g. Incomplete Dominance, Codominance, Multiple Alleles.

Intergenic (Non-Allelic): two or more independent genes present on same or different chromosomes. E.g. epistasis, duplicate genes, complementary genes.

Incomplete Dominance: Dominant gene does not completely express itself in heterozygotes. E.g. Mirabilis jalapa, P: Dom-Red, Rec- White F1: Pink

F1 genotypic ratio & Phenotypic ratio: 1:2:1

Codominance: Alleles expressed equally in F1.  E.g. Coat colour in Cattle. P: Black Coat & White Coat F1: Neither black/white, but fur with both white & black in patches (roan coat colour)

Genotypic & Phenotypic 1:2:1

Multiple Alleles: More than 2 alleles for a gene. Located at same locus, in different organisms in a population. At a time one organism has only 2 forms of these alleles, & a gamete has only one form (??)

e.g. Blood Groups in humans

Blood Groups: ABO type – discovery: Dr. Karl Landsteiner) Gene I; 3 alleles IA, IB, IO Any 2 forms present in a person; so the genotype combinations can be:__________, _________, _________, _________, _________, ___________ (Total 6) IA& IB Are codominant, while  IO is recessive to  IA& IB On this basis work out the phenotypes from the genotypes you’ve listed above

Thus ABO blood gp is an example of Codominance & Multiple Allelism Cause of Blood Gps: The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene I.

Pleiotropism: when one gene controls more than 1 phenotype.  E.g ·       Sickle Cells anaemia: Gene controls shape of RBC, & O2 carrying efficiency ·       B gene in Pea seeds: 2 forms B, b Phenotype 1 ü  BB: large starch grains, more efficient starch synthesis ü  Bb: intermediate size starch grains ü  bb: small starch grains, less efficient starch synthesis             Phenotype 2 ü  BB: round seeds ü  Bb: round seeds ü  Bb: wrinkled seeds

Can you tell the difference in expression pattern of the two phenotypes ??

Polygenic Inheritance: Poly ______; Genic: _______ Character expression controlled by many genes 3 or more genes have a cumulative effect on a particular character. Each dominant allele expresses a part of the trait. Full trait expression when all dominant alleles present. e.g. Kernel colour in wheat (2 pairs of genes) Height in humans (10 or more pairs of genes)

(interestingly shortness is dominant; so more the number of dominant alleles; shorter the person will be). Further height is also influenced by many environmental factors.