Learning Objectives

• Define a chromosome and learn about its basic parts and structure.

• Explain how DNA, genes, and chromosomes are all related to each other.

• Differentiate between diploid and haploid cells and provide examples of each type.

• Describe how a karyotype can be used to determine an organism's biological sex.

Key Vocabulary

Chromosome

A coiled, threadlike structure of DNA that carries genetic information within the cell's nucleus.

Gene

A segment of DNA on a chromosome that codes for a specific protein, influencing a trait.

Diploid

A cell containing a complete set of paired chromosomes, with one from each parent.

Haploid

A cell, like a sex cell, that contains a single set of unpaired chromosomes.

Karyotype

An organized visual profile of a person's chromosomes, used to check for chromosomal abnormalities.

What Are Chromosomes?

• A chromosome is a thread-like structure inside the cell nucleus.

• It is made of DNA tightly coiled around proteins.

• Chromosomes carry genetic information in the form of genes.

• Humans have 23 pairs, inheriting one set from each parent.

The Structure of a Chromosome

• A chromosome has two identical copies called sister chromatids.

• A central point called the centromere joins the sister chromatids.

• The centromere divides the chromosome into a short and long arm.

Genes on Chromosomes

• A gene is a specific segment of DNA with protein-making instructions.

• These proteins determine your physical traits, making genes the units of heredity.

• Each gene has a specific position on a chromosome called a locus.

• Homologous chromosomes are pairs carrying the same genes, one from each parent.

Diploid vs. Haploid Cells

• Diploid cells (2n) have a full set of chromosomes in pairs.

• Most of your body’s somatic cells, like skin cells, are diploid.

• Haploid cells (n) have half the number of chromosomes, with no pairs.

• Gametes, or sex cells like sperm and eggs, are haploid.

Karyotypes and Sex Determination

Female Karyotype (XX)

• The sex chromosomes are the final pair shown in a karyotype.

• A biological female has two X chromosomes that are similar in size.

• This final pair is written as XX in a female karyotype.

Male Karyotype (XY)

• Sex chromosomes determine if an individual is biologically male or female.

• A biological male has one X chromosome and one smaller Y chromosome.

• This final pair is written as XY in a male karyotype.

Common Misconceptions about Chromosomes

Summary

• Chromosomes are condensed DNA structures that carry genes determining our traits.

• Human diploid body cells have 46 chromosomes, while haploid sex cells have 23.

• A duplicated chromosome consists of two sister chromatids joined by a centromere.

• A karyotype is a visual map of chromosomes used to determine sex.