Antibiotic resistance gene

Antibiotics are the medications that kill bacteria. Anti means ‘against’ and biotic means ‘life’. Antibiotic resistance gene has the ability to resist the effects of antibiotics. This gene is present in plasmid of bacteria. R plasmid are bacterial resistant plasmid that carry genes to provide resistance against the antibiotic. Antibiotics select for resistant Mutant and […]

Arabidopsis plants have 10 chromosomes (5 pairs) in their somatic cells. How many chromosomes are present in each of the following: (a) egg cell nucleus in the female gametophyte, (b) generative cell nucleus in a pollen grain, (c) fertilized endosperm nucleus, (d) fertilized egg nucleus?

  (a) Egg cells are haploid. Sperm and egg cells are haploid. Somatic cells are diploid which means they contain two sets of chromosomes that are inherited from each parent. Therefore, 5 chromosomes are present in egg cell of the female gametophyte. (b) Generative cell nucleus in a pollen grain of flowering plant is one […]

The mouse haploid genome contains about 2.9 x 109 nucleotide pairs of DNA. How many nucleotide pairs of DNA are present in each of the following mouse cells: (a) somatic cell, (b) sperm cell, (c) fertilized egg?

(a) In somatic cell, 5.8 ×109 nucleotide pairs of DNA are present. Somatic cells are diploid which means they contain two sets of chromosomes that are inherited from each parent. Therefore, if haploid genome contains 2.9 x 109 nucleotide pairs of DNA then somatic cells contains its double. (b) In sperm cells, 2.9 ×109 nucleotide […]

In flowering plants, two nuclei from the pollen grain participate in the events of fertilization. With which nuclei from the female gametophyte do these nuclei combine? What tissues are formed from the fertilization events?

Answer: Two nuclei from the pollen grain combine with egg and the polar nuclei from the female gametophyte and forms the sporophyte and triploid endosperm respectively. Explanation: In flowering plants, fertilization is known as double fertilization because two male nuclei from the pollen grain fuses with the egg and polar nuclei and forms diploid zygote […]

Given the way that chromosomes behave during meiosis, is there any advantage for an organism to have an even number of chromosome pairs (such as Drosophiladoes), as opposed to an odd number of chromosome pairs (such as human beings do)?

Answer: No, there is not any advantage associated with an even number of chromosomes. Explanation: In the haploid state, the offspring receives single chromosome from each parent. Therefore, it can be either odd or even number of chromosomes. Most of the organisms have an even number of chromosomes as chromosomes come in pairs from each […]

A cell of the bacterium E. Coli, a prokaryote contains one chromosome with about 4.6 million base pairs of DNA comprising 4288 protein-encoding genes. A cell of the yeast saccharomyces cerevisiae eukaryote, contains about 12 million base pairs of DNA comprising 6,268 genes, and this DNA is distributed over 16 distinct chromosomes. Are you surprised that the chromosome of a prokaryote is larger than some of the chromosomes of a eukaryote? Explain your answer

Eukaryotic chromosomes are larger than prokaryotic chromosomes because of presence of introns (non coding sequence) and more repetitive DNA. Therefore, it is surprised that the chromosome of a prokaryote such as E.coli is larger than some of the chromosomes of a eukaryote such as yeast. Yeast is an exceptional case in which genome is distributed […]

Are the synergid cells in an Arabidopsis female gametophyte genetically identical to the egg cell nestled between them.

Answer: Yes, synergid cells in an Arabidopsis female gametophyte genetically identical to the egg cell nestled between them. Explanation: Synergid cells in the female gametophyte are positioned adjacent to the egg cell and plays an important role in guiding pollen tube and fertilization. The Arabidopsis thaliana is a small flowering plant which is used as […]

In Arabidopsis, is leaf tissue haploid or diploid? How many nuclei are present in the female gametophyte?

Answer: In Arabidopsis, leaf tissue is diploid. Eight nuclei are present in the female gametophyte. Three nuclei are present in the male gametophyte. Explanation: The Arabidopsis thaliana is a small flowering plant which is used as a model organism. Flowers are the reproductive organs. Male and female gametes are produced through meiosis Microspores are produced […]

During meiosis, when does chromosome disjunction occur? When does chromatid disjunction occur?

Answer: Chromosome disjunction occurs during anaphase of meiosis I and chromatid disjunction occurs during anaphase of meiosis II. Explanation: Disjunction is defined as separation of sister chromatids or homologous chromosomes during cell division. Gametes are eggs and sperm cells having one set of 23 chromosomes. This is called as haploid or n gametes and fusion […]