Question

Genes occur in pairs, or alternate forms of each other, called a. chromosomes. b. alleles. c. base pairs. d. ribosomes.

Short answer

The correct answer is b. alleles.

Step-by-step solution

Understanding Terminology

Start by going through each of the given options to understand what they mean. Chromosomes are thread-like structures that carry genes. Alleles are alternate forms of a specific gene. Base pairs are pairs of nucleotides that form the rungs of the DNA ladder. Ribosomes are cellular structures that facilitate protein synthesis.

Identifying Gene Pairing

Recall that genes can have alternate forms resulting in variability in traits. The term used to describe these alternate forms of a gene is 'alleles'. When a gene has multiple forms, each form is called an allele that resides at a specific position on a chromosome.

Selecting the Correct Answer

Based on the understanding that alleles are alternate forms of a particular gene, the correct answer is identified as option b. 'Alleles'.

Key concepts

Alleles

Alleles are different versions of a gene that occupy the same position, or locus, on a chromosome. These variations can result in different traits or characteristics in an organism. For example, the gene responsible for eye color might have alleles that result in blue, brown, or green eyes.

This is important because it introduces genetic diversity within a species.

• Alleles can be dominant or recessive.
• A dominant allele will often mask the presence of a recessive allele in determining a trait.
• For a recessive trait to be expressed, an individual usually needs two recessive alleles.

Understanding alleles allows us to predict the probability of an offspring inheriting particular traits through methods like Punnett squares and genetic crossing.

Chromosomes

Chromosomes are long, thread-like structures composed of DNA and proteins. They are found in the nucleus of cells and carry genetic information essential for cell function and reproduction. Each species has a specific number of chromosomes; for example, humans have 23 pairs.

Chromosomes ensure proper distribution of DNA during cell division and play a key role in inheritance.

• They contain genetic material in the form of many different genes.
• Each chromosome has a centromere, which is the point of attachment for the spindle fibers during cell division.
• Chromosomal abnormalities can lead to genetic disorders such as Down syndrome, which is caused by an additional chromosome 21.

Chromosomes are vital components in understanding genetics and heredity.

Nucleotide Base Pairs

Nucleotide base pairs are the building blocks of DNA. They form the "rungs" of the DNA double helix, connecting the two strands of DNA together. There are four types of nucleotide bases—adenine (A), thymine (T), cytosine (C), and guanine (G).

These bases pair specifically with each other - adenine with thymine and cytosine with guanine - due to hydrogen bonding. This specificity in base pairing is crucial for the accuracy of DNA replication and transcription.

• DNA replication relies on the separation of strands, with each parent strand serving as a template.
• The specific pairing leads to a complementary sequence which is vital for genetic consistency.
• Mutations or errors in base pairs can cause genetic diseases, affecting protein function.

Understanding nucleotide base pairs helps us comprehend how genetic information is copied and expressed.

Protein Synthesis

Protein synthesis is the process by which cells construct proteins, essential for many cellular functions. It involves two main stages: transcription and translation. During transcription, DNA is converted into messenger RNA (mRNA) in the nucleus.

Translation occurs in the ribosome, where the mRNA is decoded to synthesize a specific protein.

• Ribosomes act as the site of translation and facilitate the assembly of amino acids into proteins.
• Transfer RNA (tRNA) molecules bring the correct amino acids in sequence as per the mRNA codons during translation.
• Each set of three nucleotides, or "codon," on the mRNA specifies a particular amino acid.

An understanding of protein synthesis helps elucidate how genetic instructions are executed to create the proteins necessary for life processes.