Options for the question have not been provided. They are as follows:
(1) DNA in muscle cells
(2) base sequences in liver cells
(3) genes in an egg cell
(4) number of chromosomes in a fetal bone cell
Answer:
(3) genes in an egg cell
Explanation:
Evolution is the change in characteristics of a species which it develops over the time. These changes can be a result of natural selection, genetic drift, founder effect etc. They are passed from one generation to another hence the alleles for them get fixed in the population.
For evolution to occur, change should take place in germ cells. Germ cells are the one which fuse to form the organisms of next generation. If there is a change in their genes, it would also appear in next generation, unlike changes in genes of somatic cells. Since egg cell is a germ cell it is the correct answer.
Epigenetics is the study of how DNA methylation and alterations to chromosomal proteins affect a gene or group of genes express themselves. For changes in a gene's expression, both of these are need.
In a biological process called DNA methylation, methyl groups are added to the DNA molecule. A DNA segment's activity can be altered by methylation without the sequence changing. DNA methylation usually inhibits transcription of genes when it occurs in a gene promoter.
Epigenetics literally translates to "along with changes in genetic sequence." Any procedure that modifies gene activity without altering DNA sequence and results in modifications that can be passed on to daughter cells is now included in the term. Is called Epigenetics.
Learn more about Epigenetics here
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Bird skeletons are very delicate, and therefore, difficult to be preserved. The bones of the birds are soft. The small animals are very prone to physicochemical as well as biological decay. This is why the fossil record of bird is incomplete and well-preserved fossils of birds are rare to find, except at a few unusual sites.
