Genes and Chromosomes (Class - XII)

Sutton and Boveri proposed chromosomal theory of inheritance in 1902.

The functional unit of a gene is called cistron.

Both bacteria and blue-green algae are prokaryotes and contain nucleoid.

Pigeon has 80 chromosomes.

F-plasmid is responsible for transfer of genetic material.

The darkly stained bodies located inside the nucleolus were named as chromosomes by Waldeyar in 1888. Chromosomes are called carriers of heredity. The chromosomes carry the genes and similarities of parents to the offsprings. Thus, these are called hereditary vehicles.

Aleucantha (radiolarian) have 1600 chromosomes. Thus, it has the maximum number of chromosomes of all the given species.

Human genomes do not have either telocentric or holocentric chromosomes.

If arms' lengths are unequal, the chromosome is said to be sub-metacentric.

Metaphase is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their most condensed and coiled stage. Thus, it is the best stage for studying mitosis.

The largest human chromosome is chromosome 1. Chromosome 1 spans about 249 million nucleotide base pairs.

Each chromosome is bounded by a membrane called pellicle. It is very thin and is formed of achromatic substance.

A holocentric chromosome is where a large number of centromeres are scattered throughout the length of the chromosome.

Telomeres provide stability to chromosomes. Telomeres are essential for protecting chromosome ends and ensuring chromosome stability.

A chromosome consists of two chromatids at metaphase.

A nucleolar organiser region contains genes for coding 18S and 28S ribosomal RNA.

The balbini rings of salivary gland chromosomes function in transcription of RNA.

Chromosomes 13, 14, 15, 21 and 22 are acrocentric and possess nucleolar organiser. Therefore, both (a) and (b) are correct.

TMV is a ssDNA virus.

Lamp brush chromosomes help in the formation of certain amount of yolk material in eggs.

A small chromosomal segment separated from the main body of the chromosome by secondary constriction is called satellite. In humans, it is usually associated with the short arm of an acrocentric chromosome.

Mature sperm cells largely use protamines to package their genomic DNA, most likely to achieve an even higher packaging ratio. Thus, these act as the basic unit of DNA packaging in mature sperm cells.

H1 histone is found with linker DNA. It is involved in chromatin compaction and sit at the base of the nucleosome near the DNA entry and exit binding to the linker region of the DNA.

Telomeres never form permanent association with other parts of homologous or non-homologous chromosomes. Thus, they never participate in cross over.

Roger Kornberg proposed nucleosome model in 1975 for DNA packaging.

The prophase form of chromatids are chromonemata.

According to the modern concept, gene is a functional unit of DNA.

Flow-FISH is most commonly used to quantify the length of telomeres, which are stretches of repetitious DNA (hexameric TTAGGG repeats) at the distal ends of chromosomes.

Chromosome is made up of DNA, histone protein and some chromosomal RNAs which may have a role in transcription.

Chiasmata is the part of a chromosome where crossing over has taken place.