In almost any biology course, the terms DNA, genes and chromosomes are used on a near daily basis. These similar and related terms are a source of confusion for many people. It is essential that students develop and use models at different scales to explain the relationship between DNA, genes and chromosomes in composing the molecular basis of heredity. Let's explore the relationship between these terms and their roles in the inheritance of traits. A chromosome, showed by the red arrow, is a structure in the nucleus of a cell that contains one long molecule of DNA that is condensed and tightly coiled around associated proteins. 0:00:51.6: Each chromosome consists of hundreds of genes that code for proteins or RNA molecules. Each cell in an organism's body contains a complete set of chromosomes. The number of chromosomes varies with the type of organism, for example, humans have 23 pairs of chromosomes. Dogs have 39 pairs and potatoes have 24 pairs. Each pair of chromosomes have genes that code for the same proteins. One chromosome in each pair was inherited from the male parent and the other from the female parent. In this way, traits of parents are passed to offspring. In mammals and fruit flies, one pair of chromosomes in an organism determines the sex, male or female of the organism. These are known as sex chromosomes. All other chromosomes are known as autosomes. Cells, except for the sex cells, contain one pair of each type of chromosome. Two X chromosomes are found in females and one X and one Y chromosome are found in males. A gene is a specific location on a chromosome consisting of a segment of DNA that codes for a particular protein or RNA molecule that has a function in an organism. Genes are cellular units of information that determine how organisms inherit characteristics from their parents. 0:02:26.3: The particular protein or RNA molecules coded by each gene determines the characteristics of the organism. DNA stands for deoxyribonucleic acid. A molecule of DNA, which comprises an organism's chromosomes is considered the code of life because it contains the instructions for building each protein that an organism needs. DNA provides the blueprint for the synthesis of proteins via the sequence of nucleotides that make up the DNA strand. Each individual organism has unique characteristics that arise because of the difference in the nucleotide sequence found in the organism's DNA. In DNA, there are four nucleotides with different nitrogenous bases, adenine, cytosine, guanine and thymine. Since DNA is a double-helix molecule, the nitrogenous base pairs with each other across from the molecule. For example, adenine pairs with thymine and guanine pairs with cytosine. 0:03:35.6: In order for DNA to remain condensed as a chromosome, eukaryotic cells organize their genetic material. DNA is wound tightly around proteins called histones, this is like thread coiled around a spool to keep it organized. The tightly organized material forms what we observe as a chromosome, the condensed genetic material in the nucleus of the cell. So, when modeling genes, DNA and chromosomes, remember that genes are the smallest part of the model, since they are segments of DNA. Chromosomes are the largest component of the model, since they represent many genes made of DNA wrapped around histone proteins.

Question

Chromosomes are made of tightly packed ________ molecules.
Responses
A DNADNA
B amino acidamino acid
C lipidlipid
Question 2
A __________ is a segment of DNA which codes for a specific trait.
Responses
A amino acidamino acid
B chromosomechromosome
C genegene
Question 3
___________ are passed from parents to offspring, determining an offsprings traits.
Responses
A chromosomeschromosomes
B nucleinuclei
C proteinsproteins

Answer 1

Based on the information provided in your text, here are the answers to the questions:

Question 1: Chromosomes are made of tightly packed A. DNA molecules.

Question 2: A C. gene is a segment of DNA which codes for a specific trait.

Question 3: A. chromosomes are passed from parents to offspring, determining an offspring's traits.