12 Class

Describe the different types of choromosomes.

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Chromosomes exhibit diverse structures classified into four types based on the centromere’s position: 1. Metacentric: In metacentric chromosomes, the centromere is centrally located, resulting in arms of nearly equal length. This configuration gives the chromosome a characteristic ‘V’ shape during anaphase. 2. Sub-metacentric: Characterized by a centromere positioned away from the middle, sub-metacentric chromosomes have … Read more

What is cris-cross inheritance? Explain with suitable example.

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Criss-cross inheritance is a pattern where genes are transmitted from father to daughter and then to her son, meaning from male to female and subsequently from female to male (grandson). In simpler terms, it is described as the transfer of genes from a grandfather to his grandson through his daughter. 1) The inheritance pattern of color … Read more

With the help of neat labelled diagram, describe the structure of chromosome.

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1. Chromosomes represent the densely packed form of DNA, facilitated by histone proteins H1, H2A, H2B, H3, and H4, visible during metaphase in cell division. 2. Eukaryotic chromosomes have two arms, termed p-arm and q-arm, with a central constriction called the centromere where spindle fibers attach during cell division. 3. The centromere’s location categorizes chromosomes … Read more

In the answer for inheritance of X-linked genes, Madhav had shown carrier male. His answer was marked incorrect. Madhav was wondering why his marks were cut. Explain the reason.

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Males, with a single X and a Y chromosome, cannot be carriers for X-linked recessive disorders, as they lack another X chromosome to mask the expression of such genes. In females, having two X chromosomes allows them to be carriers without displaying physical traits, as one X can compensate for the recessive gene on the … Read more

What is parthenogenesis? Explain the haplo-diploid method of sex determination in Honey bee.

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Parthenogenesis is a form of asexual reproduction where embryos develop from unfertilized female gametes. Examples include honey bees, Aphis, wasps, and ants. The haplo-diploid method of sex determination in  honey bee are:  In honeybees, sex determination operates through haplodiploidy. Three distinct types of individuals emerge:Diploid queens (2n = 32), fully functional females originating from fertilized … Read more

Define test cross and explain its significance.

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A cross between F1 offspring and its homozygous recessive parent is called a test cross. Significance of testcross 1. Genotype Identification: Test cross helps determine the genotype of a plant expressing dominant traits, revealing whether it is homozygous or heterozygous. 2. Understanding Genetic Composition: It is a valuable tool for discerning the genetic makeup of plants, … Read more

Explain with suitable example an independent assotrment.

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Referred to as Mendel’s Second Law by Correns, The Law of Independent Assortment states that alleles from two pairs of traits segregate independently during gamete or spore formation. Subsequently, they undergo random rearrangement during fertilization, giving rise to both parental and novel trait combinations. Two crucial events occurs The independent separation of alleles for two … Read more

What is dihybrid cross? Explain with suitable example and checker board method.

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A dihybrid cross occurs when two pairs of alleles are involved, resulting in a phenotypic ratio of 9:3:3:1 in the F2 generation, known as the dihybrid ratio. For example, When we mate a true-breeding pea plant with round and yellow seeds with another true-breeding pea plant having wrinkled and green seeds, the offspring in the … Read more

Explain the chromosomal theory of inheritance.

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The Chromosomal Theory establishes chromosomes as carriers of genetic material and puts forth the following principles: Hereditary traits are transmitted through gametes, the reproductive cells formed by the parents (sperms and ova), acting as a link between parents and offspring.  Chromosomes within the nucleus of gametes serve as the vehicles for transmitting all hereditary characteristics. … Read more