Question

A multicellular organism develops from a zygote that undergoes both cell division and differentiation as it grows into an adult. What explains the fact that cells are able to differentiate into adult cells with different structures and functions even though they all have the same DNA?

Option 1: External and internal cues trigger different genes to turn on and off in different cells.
Option 2: The cell nucleus controls the expression of genes based on a pre-determined sequence.
Option 3: Chromosomes are keyed to be expressed only in some cells but not in others.
Option 4: Cells randomly express different genes during development.

Answer 1

Cells in a multicellular organism differentiate into diverse structures and functions through gene regulation, where external and internal cues, as well as transcription factors, direct specific genes to be expressed while others are turned off.

Step-by-step explanation:

The different structures and functions of adult cells, despite containing the same DNA, can be explained by the fact that cells differentiate by expressing different subsets of genes. This differentiation is akin to actors reading only their part from a complete movie script. External and internal cues are instrumental in triggering which genes are turned on and off in different cells, leading to the variety of specialized cell types observed in a multicellular organism.

Transcription factors play a pivotal role in this process, binding to DNA and promoting or inhibiting the transcription of genes, thus guiding the differentiation. The specificity of gene expression is also influenced by the cells' embryonic environment, which provides chemical signals to direct cell differentiation.

Therefore, option 1: External and internal cues trigger different genes to turn on and off in different cells, is the correct explanation for cell differentiation in a multicellular organism.