Tag: classical genetics

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Questions Related to classical genetics

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Allelic sequence variations where more than one variant (allele) at a locus in a human population is with a frequency greater than 0.01 is referred to as

  1. Incomplete dominance

  2. Multiple allelism

  3. SNP

  4. EST

  5. DNA polymorphism
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Incomplete dominance means that one allele for a trait is not completely dominant over the other one and thus the heterozygous genotype shows a combination of dominant and recessive phenotypes. Mirabilis plant shows incomplete dominance of flower colour. Multiple allelism is a condition when more than two alleles of a gene govern the trait. Human blood group inheritance is the example of multiple alleles. It is governed by three alleles namely I$^{A}$, I$^{B}$ and I$^{A}$ and I$^{B}$ show codominance while allele i is recessive to both "I$^{A}$" and "I$^{B}$". This gives total six genotypes and four phenotypes- A (I$^{A}$ I$^{A}$ and I$^{A}$i), B (I$^{B}$ I$^{B}$ and I$^{B}$i), AB (I$^{A}$ I$^{B}$) and O (ii). 

SNPs are Single nucleotide polymorphisms, a type of genetic variation among people. Each SNP refers to a difference in a single nucleotide. For example, replacement of the nucleotide cytosine (C) with the nucleotide thymine (T) in a DNA segment represents a SNP. The SNPs present between the genes serves as marker to locate disease causing genes. The SNPs present within a gene or in a regulatory region directly affect the genes function.
 EST is expressed sequence tag. It is a DNA fragment within a
coding region of a gene and is used to identify the full-length genes in gene mapping. It is derived from cDNA, i.e., DNA formed using RNA template via reverse transcription.
DNA polymorphism can be defined as a condition where more than one different normal nucleotide sequences can exist at the same locus in DNA. These two different alleles are the product of single base pair mutation, deletions, insertions etc. 

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Incomplete dominance was first discovered by

  1. Mendel

  2. Hugo de Vries

  3. Carl Correns

  4. Tschermak
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

  • Gregor Mendel was the founder of modern genetics. He performed experiments of on pea plant and established many rules of heredity, now referred to as the laws of Mendelian inheritance.
  • Hugo de Vries gave the concept of genes, rediscovered laws of heredity, introduced the term mutation and gave the mutation theory of evolution.
  • Carl Correns is known for his independent discovery of the principles of heredity and also discovered non-mendelian inheritance like cytoplasmic inheritance or cytoplasmic inheritance.
  • Tschermark developed several new disease-resistant crops. Along with Vries and Correns, he discovered Gregor's work.
So, the correct option is 'Carl Correns'.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Mendel's experiments could not explain

  1. Incomplete dominance

  2. Segregation

  3. Recessiveness

  4. Dominance

  5. Independent assortment
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mendel's laws of inheritance were based on complete dominance. Phenomena like incomplete dominance, where the heterozygote shows an intermediate phenotype, were discovered later and deviate from his original findings.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Mirabilis jalapa shows

  1. Codominance

  2. Incomplete dominance

  3. Dominance

  4. Complementary genes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Incomplete dominance is the condition when none of the factors of a gene is dominant; the phenotype of a heterozygous dominant individual is a blend of dominant and recessive traits. A monohybrid cross between two pure varieties of Mirabilis jalapa with red (RR) and white (rr) flowers gives red, pink and white colored flowers in 1:2:1 phenotypic ratio in $F _2$ generation. This is because the red color exhibits incomplete dominance over white color and the heterozygous dominant genotype (Rr) produces different phenotype from homozygous dominant (RR).  Flower color in Mirabilis jalapa is governed by a single gene. Thus, the correct answer is option B.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

A red snapdragon flower is crossed with a white snapdragon flower, and all the resulting flowers from the cross are pink. Which type of inheritance is occurring here? 

  1. Incomplete dominance

  2. Codominance

  3. Sex-linked inheritance

  4. Pleiotropy

  5. Polygenic inheritance
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A. When F1 hybrid exhibit a mixture or blending of characters of two parents, it is called incomplete dominance. For example, in snapdragon one parent is homozygous for red flowers (AA) and the other is homozygous for white flowers (aa). No dominance is present and the heterozygous F1 flowers are pink. The 1: 2: 1 ratio of red, pink and white flowers in the F2 progeny is shown by appropriate colouring.
B. In codominance, both alleles of a pair express themselves fully in F1 hybrid. For example, in cattles when a cattle with red coat is crossed with the cattle having white coat, the F1 hybrid possess roan appearance. In roan appearance, the red and white hairs occur in patches but no hairs have intermediate colour of red and white.
C. Sex chromosomes are primarily concerned with the determination of sex, but these do carry the genes also for other characters. Such characters whose genes are located on the sex chromosomes are known as sex-linked characters. The genes which govern these sex-linked characters are known as sex-linked genes and their inheritance is known as sex-linked inheritance. For example, colour blindness in humans.
D. Pleiotropy is the condition in which one gene produces many effects. In other words, a pleiotropic gene produces a major phenotypic trait and also, it influences some other phenotypic traits.
E. Polygenic inheritance is the condition when many genes control the inheritance of one trait or character. Such genes are called polygenes and show quantitative inheritance. For example, kernel colour of wheat and skin colour in humans.
So, the correct answer is 'Incomplete dominance'.
Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Incomplete dominance is also called

  1. Intermediate inheritance

  2. Blending inheritance

  3. Partial dominance

  4. All the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Incomplete dominance occurs when neither allele is completely dominant over the other, resulting in a phenotype that is a blend or intermediate between the two parents. Thus, it is often called intermediate inheritance.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Mendel did not propose

  1. Dominance

  2. Incomplete dominance

  3. Segregation

  4. Independent assortment
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A.Law of dominance – When two contrasting alleles for a character come together in an organism, only one is expressed and another one is not expressed. Expressed character is called Dominant character and the character which is not expressed is called Recessive character

B.Incomplete dominance – Expression of new phenotypes in the progeny, other than the parents is called Incomplete dominance

C.Segregation – This law states both parental alleles of F1 generation separate and are expressed phenotypically in F2 generation

D.Independent assortment – When a cross is made between two individuals different from each other in two or more characters, then the inheritance of one character is independence of the inheritance of another character

So, the correct answer is ‘Incomplete dominance’

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Phenotypic and genotypic ratio in $F _2$ generation in incomplete dominance is

  1. 1 : 2 : 1 and 1 : 2 : 1

  2. 3 : 1 and 1 : 2 : 1

  3. 9 : 6 and 3 : 1

  4. 9 : 3 : 3 : 1 and 1 : 2 : 1 : 4 : 1 : 1 : 2 : 1 : 2 : 1.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Appearance of new phenotypes or intermediate phenotypes, other than parental phenotypes in progeny  is incomplete dominance. In this, In the F2 generation, 1 red flowered plants(RR), two pink flowered plants(Rr), 1 white flowered plants(rr) are formed. So, the phenotypic and genotypic ratio is 1:2:1.

So, the correct option is ‘1:2:1 and 1:2:1’.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

A plant having 24 cm long internodes is crossed with a plant having 12 cm long internodes. The hybrids have 18 cm long internodes due to

  1. Multiple allelism

  2. Complete dominance

  3. Recessive dominance

  4. Incomplete dominance
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Appearance of new phenotypes or intermediate phenotypes, other than parental phenotypes in progeny  is incomplete dominance. A plant having  24cm long internodes is crossed with plant having 12cm long internodes. In the hybrids 18cm long internodes appear. It is due to blending of characters. So, it is called Incomplete dominance or blending inheritance.

So, the correct option is ‘Incomplete dominance’.

Multiple choice botany classical genetics incomplete dominance deviation from mendelism inheritance

Which one is exception to Mendel's principle of dominance?

  1. Wild Pea

  2. Mirabilis

  3. Garden Pea

  4. Maize
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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 Law of dominance, Law of segregation, Law of Independent assortment. These laws are exceptional in some cases like incomplete dominance, co-dominance, etc.

So, the correct option is ‘Mirabilis’.