Genetics And Evolution

Step 1: Understanding the Concept:
Cytoplasmic male sterility (CMS) is a maternally inherited trait where a plant is unable to produce functional pollen. The term "cytoplasmic" indicates that the genes controlling this trait are located in the cytoplasm, not the nucleus.
Step 2: Detailed Explanation:
The cytoplasm of a plant cell contains organelles that have their own genomes, separate from the nuclear genome. These are the mitochondria and the chloroplasts.
Research has shown that in the vast majority of cases across different plant species, the genes responsible for causing CMS are located in the mitochondrial genome. These CMS-associated genes are often novel, chimeric open reading frames that arise from rearrangements in the mitochondrial DNA. Their expression, typically in the anther tapetum, disrupts pollen development, leading to male sterility. While chloroplast genes can sometimes influence CMS expression, the primary causative genes are almost always mitochondrial.
Step 3: Final Answer:
The genes causing cytoplasmic male sterility are generally transcribed in the mitochondria.

Step 1: Understanding the Concept:
The question asks to identify the correct characteristics of the bacterium Agrobacterium tumefaciens, which is widely used in plant biotechnology.
Step 2: Detailed Explanation:
A. It is a gram positive round shaped bacterium. This is incorrect. A. tumefaciens is Gram-negative and rod-shaped.
B. It is a gram negative rod shaped bacterium. This is correct. It is a Gram-negative, motile, rod-shaped soil bacterium.
C. It is a photosynthetic spiral bacterium. This is incorrect. It is not photosynthetic and not spiral-shaped.
D. It is also known as 'Natural genetic Engineer'. This is correct. It earned this title because of its unique, natural ability to transfer a specific segment of its DNA (the T-DNA from its Ti plasmid) into the host plant's genome.
E. It is capable of naturally transferring DNA into plant genome. This is correct. This is the mechanism by which it causes crown gall disease and is the reason it is used as a vector for creating transgenic plants.
Step 3: Final Answer:
The correct statements are B, D, and E.

Step 1: Understanding the Concept:
The question tests knowledge about the chromosome number and meiotic behavior of haploid organisms, using Arabidopsis and maize as examples. A haploid organism has a single set of chromosomes ( ).
Step 2: Detailed Explanation:
A. A haploid in Arabidopsis will have 5 chromosomes. The model plant Arabidopsis thaliana is a diploid with chromosomes. Therefore, its haploid ( ) gamete or a haploid plant would have chromosomes. (Correct)
B. Haploids are found as bivalents at metaphase-I of meiosis. A bivalent is a pair of synapsed homologous chromosomes. Since haploids have only one set of chromosomes, they lack homologous partners. Thus, bivalents cannot be formed. (Incorrect)
C. Haploids are found as univalent at metaphase-I of meiosis. In a haploid cell undergoing meiosis, each chromosome has no homolog to pair with, so it remains as a single, unpaired chromosome, which is called a univalent. (Correct)
D. The haploids in maize will have 10 chromosomes. Diploid maize (Zea mays) has chromosomes. Consequently, a haploid cell or plant will have chromosomes. (Correct)
E. The haploids in maize will have 20 chromosomes. 20 is the diploid ( ) chromosome number for maize, not the haploid number. (Incorrect)
Step 3: Final Answer:
The correct statements are A, C, and D.

Step 1: Understanding the Concept:
The question asks for the logical sequence of steps involved in the creation and establishment of a genetically modified organism.
Step 2: Detailed Explanation:
Let's arrange the steps in a logical order:
B. Identification of DNA with desired genes: The very first step is to identify and isolate the gene of interest that confers the desired trait.
C. Introduction of the DNA into the host: Once the gene is identified and isolated (often cloned into a vector), it must be introduced into the cells of the host organism. This is the transformation step.
D. Maintenance of introduced DNA in the host: After transformation, it's crucial to select the cells that have successfully incorporated the new DNA and ensure that this DNA is stable, either by integrating into the host's genome or by replicating as an episome. The host must be grown and regenerated while maintaining the new gene.
A. Transfer of DNA with desired genes to its progeny: The final goal of creating a GMO, especially in agriculture, is to have a stable line where the new trait is heritable. This means the introduced DNA must be passed on to the next generation through normal reproduction.
The correct sequence is B C D A.
Step 3: Final Answer:
The correct sequence of steps is represented by the option B, C, D, A.

Step 1: Understanding the Concept:
The question asks to identify the term for a plant that possesses half the number of chromosomes found in its normal somatic (body) cells.
Somatic cells in most plants are diploid, meaning they have two sets of chromosomes, denoted as .
Gametes (sex cells) have half this number, which is one set of chromosomes, denoted as .
Step 2: Detailed Explanation:
Let's analyze the given options:
Haploid (n): An organism or cell having a single set of unpaired chromosomes. This corresponds to half the somatic chromosome number ( ) of a diploid organism. This is the correct definition.
Monoploid (x): An organism that has the basic chromosome number of a polyploid series. In a diploid organism, the haploid number ( ) is the same as the monoploid number ( ). However, in a polyploid organism, like hexaploid wheat ( ), the haploid number is , while the monoploid number is . Haploid is the more general and accurate term for half the somatic number.
Aneuploids: Organisms with an abnormal number of chromosomes, where one or more chromosomes are either added or deleted from the normal diploid set (e.g., or ). This does not represent half the chromosome number.
Monosomics: A type of aneuploidy where one chromosome is missing from the diploid set, represented as . This is not half the somatic number.
Step 3: Final Answer:
Based on the definitions, a plant with half the somatic chromosome number is called a haploid.