Experiments of mendel - class-X

Mendel crossed two parent plants having contrasting characters. He found that in the first filial generation, F1 generation, the dominant of the two expressed while the recessive is suppressed. Apart from this,  When the f1 generation is self crossed, in the F2 generation, these recessive characters appear again. Therefore, it is not that they have disappeared. 

Linkage is the tendency of two or more genes to inherit together as a pair and not to sort out independently.
Thus, linkage is not applicable according to Mendelian principles.
Linkgae is strictly against Law of independent assortment where Mendel explains that the characters are sorted out independently while forming gametes.

Meiosis is otherwise called as Reductional division where the ploidy level of the organism is halved. Meiosis occurs in sex cells where Law of Independent assortment is well applicable. Because during meiosis, the hereditary units are inherited independently and segregated in chromosomes. One allele of a trait segregates and moves to the chromosomes such that the offspring can acquire characters from any one parent. Thus the law of Segregation also is proved well by the process of Meiosis. The expression of phenotype very well depends on Mendel's law of dominance. The dominant character is expressed in both homozygous and heterozygous forms. Whereas recessive characters are expressed only in homozygous forms.

 According to the law of seggregation  alleles of a trait that remain together in an individual do not mix but rather keep their identity intact. They separate during gamete formation and get randomly distributed only to get paired again in the offspring’s as per the principle of probability. This results in a phenotypic trait in the 3:1 ratio in the F2 generation i.e when a heterozygous plant is crosssed. So, the correct answer is 'Law of segregation'.

• Mendel is known as 'Father of Genetics' because he had described basic laws of inheritance. 
• He was not aware of the biological mechanism of inheritance but accurately explained what actually happens when two parents having a contrasting pair of character breed, i.e, the 3:1 ratio between dominant and recessive phenotypes and 1:2:1 genotypic ratio is Mendel's contribution for which he is known as 'Father of Genetics'.

Gregor Johann Mendel first explained scientifically the explanation regarding inheritance using 7 traits in Pea plants(Pisum sativum) in 1886.

Incomplete dominance F2 phenotypic ratio is 1:2:1, and the genotypic ratio of a monohybrid F2 is also 1:2:1.

Law of segregation or law of purity of gametes holds in all situations whereas Law of independent assortment is violated in case of linkage and law of dominance is violated when codominance and incomplete dominance takes place.

Mendel's law of heredity explains that there is some factor that inherits the characters from one generation to next. To explain this  he gave 3 laws which are :
1. Law of dominance
2. Law of purity of gametes (Principle of segregation)
3. Law of independent assortment

Dihybrid cross proves the law of independent assortment. Mendel found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. This is known as Law of independent assortment. Dihybrid cross - cross between two parents that differ by two pairs of alleles (AABB X aabb). The formation of gametes is an application of this law.

Hugo DeVries (Holland), Carl Correns (Germany) and Erich Von Tschermak (Austria) were the three European geneticists who work and rediscovered Mendel's law of heredity in 1900. They expand basic principle of the Mendelian laws of inheritance in more scientific way. Thus, the correct answer is option D.

Principle of segregation: According to the principle, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance. We now know that this segregation of alleles occurs during the process of sex cell formation.

 1) J.Mendel's carried out a various experiment on garden pea in a scientific manner and gave principles which are now known Mendel's law of inheritance. The principle of segregation is also called as the law of purity of gametes is first law of Mendle. A gamete may carry either the dominant or the recessive factor but not both as we find in F11 individuals. The gametes which are formed are always pure for a particular character. This is why it is called either as the principle of segregation or law of purity of gametes. 2) As per the law of dominance, dominant characters will express in both homozygous and heterozygous conditions. Whereas, recessive characters are the characters which can express only when it is present in homozygous condition. F1generation thus, shows the mixing of characters and will not inherit as such without mixing. 3) According to Mendel's law of independent assortment, during the inheritance of two or more characters, the assortment of individual traits takes place independently during gamete formation. Thus each allele of a pair segregates independently and each gamete formed contains one allele of that trait. Thus, the correct answer is option C.

The law of segregation states that every individual contains a pair of alleles for each particular trait which segregate or separate during cell division for any particular trait and that each parent passes a randomly selected copy called as allele to its offspring. The offspring then receives its own pair of alleles of the gene for that trait by inheriting sets of homologous chromosomes from the parent organisms. Interactions between alleles at a single locus are termed dominance and these influence how the offspring expresses that trait. The law states that when any individuals produces gametes, the copies of a gene separate so that each gamete receives only one copy allele. A gamete will receive one allele or the other.

According to Mendel's law, the alleles separate and segregate into gametes during meiosis. 

Mendel's law of segregation : Allele pairs separate or segregate during gamete formation and randomly unite at fertilization. There are four main concepts related to this principle. They are as follows:

Mendel's law of segregation states that allele pairs separate or segregate during gamete formation and randomly unite at fertilization. Organisms inherit two alleles for each trait. When gametes are produced by meiosis, allele pairs separate leaving each cell with a single allele for each trait. When the two alleles of a pair are different, one is dominant and the other is recessive.

3:1 ratio was the important clue for Mendle to crack the law of inheritance. When he crossed the two pea plants in a scientific manner, the result obtained were in the ratio of 3:1 and he concluded that individual has two copies of a given gene that determines the trait of the offspring. He gave the law of segregation i.e., one of the two gene copies present in the individual is passed on to the gametes. Thus, the correct answer is option B. 

Mendel's law is valid only when two pure breeding contrasting characters are crossed. In that case the dominant trait will be expressed in both homozygous and heterozygous conditions. Mendel's second law is only valid for genes located in different chromosomes. For genes situated in the same chromosome, i.e., linked genes the law is not valid since the segregation of these genes is not independent.

Linkage vs. Independent Assortment:
Chromosomes contain thousands of genes. Genes that are on separate chromosomes are inherited independently of one another and are said to follow the principle of independent assortment. Remember that this principle states that an RrYy individual is expected to make equal numbers of RY, Ry, rY and ry gametes.
Genes located on the same chromosome are not free to participate in independent assortment and are called as linked genes. These genes tend to be inherited together as a unit, as you can see in the first part of this animation. In this case, the RrYy individual makes only RY and ry gametes because these alleles are present together on the parental homologs and are not separated during gamete formation.
When two genes are always inherited together in this manner, it is referred to as complete linkage. Complete linkage creates only parental gametes, meaning that the gametes that are produced are chromosome copies of the parent they came from. If all genes demonstrated complete linkage during gamete formation, then the result would be that each individual chromosome in a gamete would be either a maternal or paternal replica and the offspring would show little genetic variation from their parents. For this reason, complete linkage rarely occurs in nature and other modes of inheritance, such as crossing over, have evolved.

Genes that are on the same chromosome, or "linked", do not assort independently, but can be separated by recombination. Two genes close together on the same chromosome tend to be inherited together and are said to be linked.
Linked genes can be separated by recombination in which homologous chromosomes exchange genetic information during meiosis; this results in parental, or non-recombinant genotypes, as well as a smaller proportion of recombinant genotypes.
Geneticists can use the amount of recombination between genes to estimate the distance between them on a chromosome.

The linkage is the tendency of closely placed genes on a chromosome to stay together during inheritance; it produces more parental combination and less/no new combinations of a gene. 

Independent assortment is segregation of factors for a trait independent of other factors during gamete formation followed by their random rearrangement in progeny thereby producing both parental and new combinations. The linkage is the tendency of closely placed genes on a chromosome to stay together during inheritance; it produces more parental combination and less/no new combinations of the gene. The linkage is indirectly proportional to the distance between genes; the less the distance between the genes, the more linkage frequency between them. Genes present together on a chromosome may show linkage, if they are close enough, and do not follow independent assortment. Genes present on homologous and nonhomologous chromosomes are too far apart from each other to show linkage. The correct answer is A.

According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual but the only dominant trait is expressed and recessive one is masked by the presence of dominant allele. Incomplete dominance and co-dominance are the exception to the law of dominance. Law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. Segregation of chromosomes of a homologous pair during meiosis followed by their distribution to gametes singly ensures its universal acceptance without any exception. Law of independent assortment tells about segregation and distribution of factors governing two different traits. The tendency of closely placed genes on a chromosome to stay together during inheritance i.e. linkage and therefore no independent assortment make the linked traits exception to the law of independent assortment. According to the principle of a unit factor, each character is governed by a pair of the discrete unit, called factor or genes. Multiple alleles serve as an exception to this rule. Thus, the correct answer is option B.

• According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; the allele/factor that can express itself in a heterozygous individual is called as a dominant trait. The other factor whose effect is masked by the presence of a dominant factor is called recessive factor. It does not tell about gametes.
•  The law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. 
• Thus each gamete receives one allele for a trait and two types of gametes are formed; 50% gametes carry factor for dominance and 50% carry the recessive factor. 
•  Law of independent assortment tells about segregation and distribution of factors governing two different traits; not about segregation of factors of one trait. 
• The principle of unit factor tells about the presence of two alternative forms of a gene governing each character of organisms. 

• According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; only dominant trait is expressed, irrespective of the presence of both factors, in a heterozygous individual. It does not tell about the reappearance of the missing trait in $F _2$ generation. 
• The law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. 
• Thus each gamete receives one allele for a trait and two types of gametes are formed; 50% gametes carry factor for dominance and 50% carry the recessive factor. 
• Random fusion of these gametes leads to the presence of both recessive and dominant individuals in $F _2$ generation. Law of independent assortment tells about segregation and distribution of factors governing two different traits; not about segregation of factors of one trait. 
• Incomplete dominance is the condition when none of the factors of a gene is dominant and the phenotype of a heterozygous dominant individual is a blend of dominant and recessive traits. It affects the phenotype of $F _1$ individuals, not that of $F _2$. Thus, the correct answer is option B.

The Principle of Independent Assortment states that two or more characters are inherited when the responsible gene separate independently from one another when reproductive cells develop. During meiosis, the pairs of homologous chromosome divide in half and form the haploid cell. This separation of chromosomes is random. After meiosis, each haploid cell of the offspring contain mixture of genes from the organism's mother and the father.

The principle of segregation is also called as the law of purity of gametes. A gamete may carry either the dominant or the recessive factor but not both as we find in F$ _1$ individuals. The gametes which are formed are always pure for a particular character. This is why it is called either as the principle of segregation or law of purity of gametes. Thus, the correct answer is option C.

DNA is the unit of heredity and determines the genetic traits of organisms. Inheritance of genetic traits from parent to offspring is ensured by processes of meiosis and syngamy. Meiosis is the process of cell division that reduces the number of chromosomes and thus, the DNA content to half in the resultant daughter cells i.e. gametes. Fusion of male and female gametes during syngamy restores the DNA content in the resultant offspring. Thus, each offspring consists of half paternal and half maternal DNA which in turn determines its traits. Thus, the correct answer is option C.

Law of inheritance was proposed by Gregor Mendel and was known as Mendels law of inheritance. He was the first to introduce that characteristic of parents can be in cooperated in the offsprings of the next generation. Therefore, (d) is the correct answer.

Mendel proposed the law of inheritance of traits from the first generation to the next generation. Law of inheritance is made up of three laws: Law of segregation, law of independent assortment and law of dominance. Therefore, (D) is the correct answer.

Mendel explained that one or more traits can be inherited from the parents individually and can be transmitted to the next generation. Mendels law of inheritance says that at least one trait is inherited by the progeny from the parent. Therefore, (a) is the correct answer.

 In experiments performed by Mendel all the genes showed independent assortment, in which genes separate from each other independently and there was no sign of any linked gene so he could not explain the concept of linkage, because he never observed it .

Law of segregation states that alleles for genes segregate from each other whether it is for tall (TT) or dwarf (tt) so that the gamete carries one allele for each gene, whereas law of dominance states that the phenotype which is expressed is the dominant character and other is recessive, since there are both tall & dwarf plants, this means that both characters are expressed . 

The identical twins are alike and they are produced from the same zygote. They have the same genome and so, the genes are alike. Due to these, the girls will have the same phenotypic appearance. There will be differences in the random repeats region which do not code for any protein. The mitochondrial DNA will be same as they have been inherited from the same mother. However, the mitochondrial genes are not involved in the phenotype expression. 

Gregor Johann Mendel was born in Heizendorf, of Austria. He conducted hybridization experiments on garden pea and first explained the principles of inheritance. Finally, he postulated Law of Inheritance. So he is regarded as Father of Genetics.

So, the correct option is ‘Laws of inheritance’.

Law of segregation and Law of independent assortment are based on the mechanism of meiosis, because these principles show segregation of characters and independent movement of characters.

So,
the correct option is ‘Meiosis’.

Meiosis (a type of cell division) is the cytological basis for Mendel's laws of segregation and independent assortment.

• Mendelian factors or genes, as well as chromosomes, are present in pairs.
• According to this Mendelian concept, inheritance of a trait depends on the passing-on of units. 
• For any given trait, an individual inherits one gene from each parent so that the individual has a pairing of two genes.

• The trait is a distinguishable feature of a character and its detectable variant. For example, tallness and dwarfness. 
• The hybrid plant possesses a heterozygous condition in which genotype have both contrasting alleles such as Tt in the hybrid plant. T represents tallness and t represents dwarfness.
•  Dominant character tallness (T) can be expressed in both conditions such as homozygous (TT) and heterozygous condition (Tt) but recessive character dwarfness (t) can be expressed only in homozygous (tt) condition and thus unable to express in hybrid plants.

• Segregation literally means separation. In Mendelian genetics, in a given plant or animal each character is governed by two alleles, one coming from the father and one coming from the mother.
•  At the time of gamete formation both the alleles, of each gene, separate from each other and go to separate gametes. 
• Thus, each gamete will be having only one allele from each pair of the allele, e.g., for tallness if we denote two alleles in a plant as Tt then that plant can form two possible gametes one having T and the other having t allele.

In case of pea plant, two types of tall plants are possible- one homozygous and other heterozygous. In case a homozygous, tall pea plant is crossed with a homozygous dwarf pea plant, then all the off springs are tall, i.e., dwarf character masked and is not shown by any of the offspring but next when two of the progeny heterozygous tall pea plants are crossed the dwarf character reappears, even when this time none of the parent was dwarf. The characters are passed on from one generation to the other by gametes. Hence, it is clear that gametes remain pure between generation the gamete with alleles for dwarfness is not disturbed or polluted or altered between generations and even when the F$ _1$ plants were phenotypically tall the allele for dwarfness remained pure and were passed on to F$ _2$ plants.

• Segregation means separation. In classical Mendelian genetics, it is assumed that each individual has two alleles which code for each character. 
• One allele comes from the father and the other from the mother. These two alleles separate from each other during gamete formation. 
• Thus, each gamete contributes a single allele for each character during zygote formation.

The Mendelian principles which were discovered in 1865 and 1866 were discovered again by Hugo de Vries, Tsechermark and Correns independently.

Mendel's law of genetics is applicable only in plants which reproduce sexually. In Mendelian genetics he explains about the independent assortment which results in the formation of gametes which has the contrasting characters from both male and female parents. It will be expressed according to its zygosity and dominant traits. if the recessive trait is present in its homozygous form, the character will be expressed. At the same time, dominant character will be expressed in both homozygous and heterozgous forms. Pisum sativum which Mendel chose was a sexually reproducing plant.

Pea plant has 2n= 14. Mendel chose 7 characters the genes for which are present on 7 different chromosomes. The presence of different chromosomes allowed genes for two traits to assort independently during dihybrid cross and recombinant progeny, as well as parental progeny, is produced. If he had chosen eight characters, genes for any two characters must be present on the same chromosome and would exhibit linkage and the law of independent assortment is violated. Law of dominance explains the appearance of a dominant trait by heterozygous genotype and law of segregation tells about segregation of alleles of heterozygous genotype during gamete formation. Law of purity tells about the presence of a single allele of a gene in gametes. Thus, the correct answer is option C.

• According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; only dominant trait is expressed, irrespective of the presence of both factors, in a heterozygous individual.
•  It does not tell about the reappearance of the missing trait in $F _2$ generation. The law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. 
• Thus each gamete receives one allele for a trait and two types of gametes are formed; 50% gametes carry factor for dominance and 50% carry the recessive factor. Random fusion of these gametes leads to the presence of both recessive and dominant individuals in $F _2$ generation. 
• Law of independent assortment tells about segregation and distribution of factors governing two different traits; not about segregation of factors of one trait. Incomplete dominance is the condition when none of the factors of a gene is dominant and the phenotype of a heterozygous dominant individual is a blend of dominant and recessive traits. 
• It affects the phenotype of $F _1$ individuals, not that of $F _2$. Thus, the correct answer is option B.

Gregor Johann Mendel, an Austrian Monk, discovered the principles of heredity through the experiments on the pea plant. Mendel conducted hybridization experiments on garden peas for seven years and proposed the laws of inheritance in living organisms. They are the Law of dominance, Law of segregation, Law of Independent assortment.

So, the correct option is ‘Three’.

Gregor Johann Mendel, an Austrian Monk. He discovered the principles of heredity through the experiments on the pea plant. Mendel conducted hybridization experiments on garden peas for seven years and proposed the laws of inheritance in living organisms. They are Law of dominance, Law of segregation, Law of Independent assortment. He is regarded as Father of Genetics.

So,
the correct option is ‘Mendel’,

He chose garden pea that was easy to grow and to hybridise artificailly.

The plant reproduce well and grows to maturity in a single season.

Mendel then chose to follow seven visible features(unit characters), each represented by two contrasting forms or traits.

Mendel was fortunate in choosing a diploid plant because diploid organisms contain only two sets of chromosomes.

A singe alteration in a trait was therefore demonstrated by a visible differences between varieites.

He restricted his examination to one or very few pairs of contrasting traits in each experiment.

He also kept accurate quatitative records, a necessity in genetic experiments.

In his experiments, no appearance of recombinations and linkage.

So,
the correct option is ‘He did not encounter the linkage’.

The blending theory state that the inheritance of traits from two parents produces offspring with characteristics that are intermediate between those of the parents.

The incorrect pair here is the contrasting feature of the pod shape is "Elongated/constricted" which should be smooth/constricted in reality.

The Law of Segregation is considered the first law of inheritance, describing how alleles separate during gamete formation. The Law of Dominance is often taught first, but historically, segregation is the fundamental principle derived from the monohybrid cross.

In 1990, three scientists (Correns, de Vries and Von Tschermak) independently rediscovered Mendel's results on the inheritance of character.

Answer is A.

A dihybrid cross involves the inheritance of two traits. Mendel's experiments with dihybrid crosses demonstrated the Law of Dominance (b) and the Law of Independent Assortment (f).

Main reasons for the success of Gregor Mendel: 

Mendel chose seven pairs of contrasting traits, the gene for each of which is present on seven different chromosomes of pea plant. Due to the presence on different chromosomes, Mendel's trait followed independent assortment during meiosis and produced the expected parental and recombinant phenotypes. If genes of these traits would have present together showing linkage, Mendel would not have got the expected results. Repeating the experiment, keeping records and use of statistical analysis were the secondary factors; major being the chosen traits not showing linkage. 

Mendel was lucky because he used pea plant i.e. Pisum sativum, they are bisexual, they had pure breeding varieties with observable characters, & each character is regulated by one type of gene, whether it is tall, dwarf, round or wrinkled etc. It was an ideal choice for him.

Mendel was successful in formulating the laws of inheritance whereas his predecessors were not because of the following reasons.

He selected only pure breeding varieties of pea for his experiments.

He took one or two characters at one time while his predecessor often studied all the traits simultaneously.

He formulated theoretical explanations for interpreting his results.

He used statistical methods and law of probability for analyzing results, etc.,

So,
the correct explanation is ‘He studied one clear-cut character at a time’.

Mendel’s work(monohybrid cross & dihybrid cross) did not receive any recognition, remained unnoticed, and unappreciated for several years due to the following reasons:

Communication was not easy in those days and his work could not be widely publicized.

His concept of stable, unblending and discrete units or factors for various traits did not find acceptance from the contemporaries.

His approach of using mathematics and statistical analysis to explain biological phenomena was totally new and unacceptable to many biologists. He could not provide any physical proof for the existence of factors. In 1900, three scientists Hugo de Vries, Carl Correns, and Erich von Tschermark, worked independently on Mendel’s work, proved whatever explained by Mendel on inheritance is true. It is called Rediscovery of Mendel’s laws.

He chose garden pea that was easy to grow and to hybridise artificailly.

The plant reproduce well and grows to maturity in a single season.

Mendel then chose to follow seven visible features(unit characters), each represented by two contrasting forms or traits.

Mendel was fortunate in choosing a diploid plant because diploid organisms contain only two sets of chromosomes.

A singe alteration in a trait was therefore demonstrated by a visible differences between varieites.

He restricted his examination to one or very few pairs of contrasting traits in each experiment.

He also kept accurate quatitative records, a necessity in genetic experiments.

In his experiments, no appearance of recombinations and linkage.

So, the correct option is ‘Traits chosed by him had genes far
apart so that linkage was absent’.

Mendel’s work was rediscovered by Hugo de Vries, T.Correns, and Carl Correns independently in 1900.

So,
the correct answer is ‘1900’.

Mendel's seven traits were: flower color, flower position, stem height, pod shape, pod color, seed shape, and seed color. Categorizing these: flower (2), pod (2), and seed (2), with stem height as the remaining one.

The correct answer will be '7 pairs of true breeding varieties' that was used by Mendel for his experiments on pea plant.

The colour based contrasting traits studied by Mender in pea plant were pod colour,  i.e., green (dominant) and yellow (recessive), flower colour, i.e., violet (dominant) and white (recessive) and seed colour, i.e., yellow (dominant) and green (recessive). 

Mendelian inheritance is a type of biological inheritance that follows the laws originally proposed by Gregor Mendel in 1865 and 1866 and rediscovered in 1900.

Mendel’s law of inheritance were rediscovered by Hugo de vries, Tschemark, Correns. Hugo de vries republished the Mendel’s work in ‘Flora’.

So,
the correct option is ‘De vries’.

Carl Erich Correns was a German botanist and geneticist, who is notable primarily for his independent discovery of the principles of heredity, and for his rediscovery of Gregor Mendel's earlier paper on that subject, which he achieved simultaneously but independently of the botanists Erich Tschermak von Seysenegg. He also converted Mendel’s conclusions into principles of heredity.

So, the conclusion is ‘Carl correns’.

Erich Tschermak was an Austrian agronomist who developed several new disease-resistant crops, including wheat-rye and oat hybrids. He independently rediscovered Gregor Mendel's work on genetics. He was a plant breeder, and his hybridization experiments were done with the idea of improving crops using the laws of heredity.

So, the correct option is ‘Austria’.

Hugo de Vries, Holland botanist and geneticist, is the author of the mutation theory of evolution. His work led to the rediscovery and establishment of Mendel's laws. He made his first notable contributions to science in the 1880s in the field of plant physiology.

So, the correct option is ‘Holland’.

Carl Erich Correns was a German botanist and geneticist, who is notable primarily for his independent discovery of the principles of heredity, and for his rediscovery of Gregor Mendel's earlier paper on that subject, which he achieved simultaneously but independently of the botanists Erich Tschermak von Seysenegg and Hugo de Vries, and the agronomist William Jasper Spillman.

So, the correct option is ‘German’.

Mendel’s laws of inheritance was rediscovered by Hugo de Vries, Carl Correns, and T.Schemark independently.

So,
the correct option is ‘Von Tschemark’.