CHROMOSOME CONNECTION Life Science: Natural World

CHROMOSOMES Genes are located on chromosomes. Similarities between organisms are due to similarities in the information found on chromosomes.

CHROMOSOMES We can determine genetic similarities among organisms by comparing chromosomes.

EVOLUTIONARY GENETICS Species that are more closely related anatomically, should have more similar chromosomes. length of the chromosome the location of the centromere banding patterns centromere

GIEMSA STAINING Giemsa (gē-em-sa) stain produces dark banding on chromosomes called G bands. Dark bands are where the chromosomes are methylated (constricted by methyl groups). Light bands are where the chromosomes are not condensed. Figure 1 Human Chromosome #1

CHROMOSOME ADDRESSES The centromere divides the chromosome into two arms. The “p” arm of a chromosome is the shorter arm. The long arm is represented by "q". Figure 1 Human Chromosome #1 An address such as 1q2.4 can be used to identify any band of a chromosome. The 1 represents the chromosome number. The q represents the arm. The 2 represents the region. The 4 represents the band The “p” stands for petite. The “q” is used for the long arm, simply because it follows "p" in the alphabet

RELATED CHROMOSOMES The probability that two different chromosomes would independently have identical banding patterns by chance is basically zero. Comparing bullet marks: “Numerous studies show that CHROMOSOME SIMILARITY is a good measure of GENETIC RELATEDNESS. The probability that two different chromosomes would independently have identical banding patterns by chance is essentially zero.” “Detailed studies provide clear evidence that any IDENTICAL CHROMOSOMES in two different species INDICATES COMMON ANCESTRY just as surely as identical scratch patterns on two bullets indicate that both came from the same gun.” (Wallace, 1966).

CHROMOSOMAL MUTATIONS Recall that mutations that may affect chromosomes are Deletion, Duplication, Inversion, and Translocation. The following human and chimpanzee chromosomes differ only in that there are additional dark bands at the ends of the chimpanzee chromosomes.

CHROMOSOMAL MUTATIONS An inversion is a segment of a chromosome that is reversed in the order of the bands. A pericentric inversion contains the centromere and has break points in both arms.

Primate Chromosome Cladogram See this lesson: “The Chromosome Connection” at www.BecomingHuman.org Access via ENSI lesson: “Comparison of Hominoid Chromosomes”