1. Which of the following statements is NOT TRUE about chromosomes? Prokaryotes
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Question
1.
Which of the following statements is NOT TRUE about chromosomes?
Prokaryotes have a singel, circular chromosome
Eukaryotes have multiple, linear chromosomes.
Human cells normally 23 pairs of chromosomes.
Eukaryote chromosomes are composed of only DNA
2.
Which of the following is NOT TRUE about reproduction?
Eukaryotes life cycles include a haploid and diploid phase.
Prokaryotes reproduce asexually.
Eukaryotes can propagate by asexual or sexual reproduction.
Prokaryotes typically reproduce slower than eukaryotes.
3.
Which of the folllowing animal cells is most likely haploid?
nerve cell
muscle cell
sperm cell
liver cell
4.
When human gametes fuse, they form a _____.
Haploid egg
Diploid zygote
Haploid zygote
Triploid egg
Prokaryotes have a singel, circular chromosome
Eukaryotes have multiple, linear chromosomes.
Human cells normally 23 pairs of chromosomes.
Eukaryote chromosomes are composed of only DNA
2.
Which of the following is NOT TRUE about reproduction?
Eukaryotes life cycles include a haploid and diploid phase.
Prokaryotes reproduce asexually.
Eukaryotes can propagate by asexual or sexual reproduction.
Prokaryotes typically reproduce slower than eukaryotes.
3.
Which of the folllowing animal cells is most likely haploid?
nerve cell
muscle cell
sperm cell
liver cell
4.
When human gametes fuse, they form a _____.
Haploid egg
Diploid zygote
Haploid zygote
Triploid egg
Explanation / Answer
1. Humans have 46 chromosomes in which 44 are autosomes and two are sex chromosomes. Thus, there are 23 pairs of chromosomes in humans.
In humans, DNA is synthesized as a single continuous double strand. However, it is coiled into shorter chromosomes when DNA associates to proteins. This process is known as coiling and is very elaborate involving coiling and wrapping of DNA. Histones provide the energy for coupling process.
In this process, DNA that is negatively charged binds to positively charged histones. A short segment of DNA associates with a complex of eight histone proteins. In this complex, H2A, H2B, H3, and H4 are present as two copies. This association of DNA with the complex, forms a nucleosome. In nucleosome, 1.7 turns (or about 146 bp) of DNA wraps around the histone complex. One H1 protein (or H5 in some species) then wraps another 20 base pairs, to form two full turns around the octamer and is called linker. The final structure formed is known as a chromosome.
Thus, eukaryotic chromosomes are composed of DNA and histones. Eukaryotes chromosomes are linear and are present in multiple numbers in the cell.
On the other hand, prokaryotic chromosomes have a single circular chromosome that is called a genophore. The DNA is not present in a nucleus. Except for few prokaryotes, there are no histones in prokaryotic chromosomes.
Right answer is Eukaryote chromosomes are composed of only DNA.
2. Eukaryotes undergo sexual reproduction. Meiosis forms the male and female gametes that are haploid (n). The male and female gametes fuse to form the zygote or egg that is diploid (2n). n indicates the number of chromosomes.
Prokaryotes reproduce usually by binary fission, a type of asexual reproduction. DNA replication and segregation will take place simultaneously in this type of reproduction.
Prokaryotes have single circular chromosome. Hence, they divide faster due to less complexity. Binary fission is faster than meiosis/mitosis. They do not require recombination whereas eukaryotic require recombination for cell division. Eukaryotes also have numerous chromosomes wherein DNA is linked to histones. DNA replication is eukaryotes in nearly 2Kb/ min while the cell division in prokaryotes like E.coli takes around 20 min. Thus, prokaryotic DNA replication is faster in prokaryotes that eukaryotes.
In eukaryotes, there is sexual and asexual reproduction. Sexual reproduction occurs when the male gamete fuses with the female gamete to form the zygote. It involves meiosis. Asexual reproduction involves mitosis wherein diploid daughter cells are formed from diploid cells.
Right answer is Prokaryotes typically reproduce slower than eukaryotes.
3. Haploid cell is one that has a single set of chromosomes (n). Diploid cell has two sets of chromosomes. Sperm cell is haploid as it contains only 23 pairs of chromosomes. It is the male gamete, which is formed by meiosis. It fuses with the egg to form the diploid zygote during fertilization. The muscle, nerve, and liver cells are diploid somatic cells that have 46 chromosomes.
Right answer is sperm cell.
4. The human gametes, sperm, and egg are haploid with only one set of chromosomes. They are formed by meiosis and have 23 pairs of chromosomes. They will fuse together during to form the fertilized egg or zygote. Zygote is diploid and has 46 chromosomes.
Right answer is diploid zygote.
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