Chapter 9, Problem 23A

Summary Introduction

To write:

When would a chromosome consist of two identical sister chromatids.

Introduction:

Cells reproduce by a cycle of growing and dividing called the cell cycle. There are three main stages of a cell cycle; interphase, mitosis and cytokinesis.Chromosomes are the structures that contain the genetic material that are passed from generation to generation of cells. Chromatin is the relaxed form of DNA in the cell’s nucleus.

Answer to Problem 23A

A chromosome consist of two identical sister chromatidsduring prophaseof mitosis.

Explanation of Solution

There are four stages in mitosis; prophase, metaphase, anaphase and telophase. Prophaseis the first and longest stage of mitosis. During this stage the chromatin tightens and condenses into chromosomes. Chromosomes are shaped like an X. Each half of this X chromosome is called sister chromatid. Sister chromatids are the structures that contain identical copies of DNA. The sister chromatids are attached at the center with a structure called centromere.