The Genome

CMECNE

The Chromosome – Structure and Number

Learning Objectives and CME/Disclosure Information

This activity is intended for healthcare providers delivering care to women and their families.

After completing this activity, the participant should be better able to:

1. Describe the architecture of a chromosome
2. Define aneuploidy and euploidy

Estimated time to complete activity: 0.25 hours

Faculty:

Susan J. Gross, MD, FRCSC, FACOG, FACMG
President and CEO, The ObG Project

Disclosure of Conflicts of Interest

Postgraduate Institute for Medicine (PIM) requires instructors, planners, managers and other individuals who are in a position to control the content of this activity to disclose any real or apparent conflict of interest (COI) they may have as related to the content of this activity. All identified COI are thoroughly vetted and resolved according to PIM policy. PIM is committed to providing its learners with high quality CME activities and related materials that promote improvements or quality in healthcare and not a specific proprietary business interest of a commercial interest.

Faculty: Susan J. Gross, MD, receives consulting fees from Cradle Genomics, and has financial interest in The ObG Project, Inc.

Planners and Managers: The PIM planners and managers, Trace Hutchison, PharmD, Samantha Mattiucci, PharmD, CHCP, Judi Smelker-Mitchek, MBA, MSN, RN, and Jan Schultz, MSN, RN, CHCP have nothing to disclose.

Method of Participation and Request for Credit

Fees for participating and receiving CME credit for this activity are as posted on The ObG Project website. During the period from Dec 31 2017 through Dec 31 2019, participants must read the learning objectives and faculty disclosures and study the educational activity.

If you wish to receive acknowledgment for completing this activity, please complete the post-test and evaluation. Upon registering and successfully completing the post-test with a score of 100% and the activity evaluation, your certificate will be made available immediately.

For Pharmacists: Upon successfully completing the post-test with a score of 100% and the activity evaluation form, transcript information will be sent to the NABP CPE Monitor Service within 4 weeks.

Joint Accreditation Statement

In support of improving patient care, this activity has been planned and implemented by the Postgraduate Institute for Medicine and The ObG Project. Postgraduate Institute for Medicine is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

Physician Continuing Medical Education

Postgraduate Institute for Medicine designates this enduring material for a maximum of 0.25 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Continuing Nursing Education

The maximum number of hours awarded for this Continuing Nursing Education activity is 0.2 contact hours.

Read Disclaimer & Fine Print

WHAT IS IT?

A chromosome is the structure for the efficient packaging of DNA that is found in the cellular nucleus. Humans have 23 chromosome pairs, typically one maternal and one paternal of each. The chromosome number will vary in some cases of viable aneuploidies.

Each chromosome has 2 “arms”

Short arm (petit), notated “p”
Long arm, notated “q”
Chromosomes are numbered, 1 through 23
- 1 through 22 are autosomes, and is not related to whether one is female or male
Sex chromosomes are notated X and Y
- Female Chromosome complement: 46,XX
- Male Chromosome complement: 46,XY

This illustration depicts DNA packed tightly into chromosomes, as well as a DNA molecule unwound to reveal its 3-D structure | credit: NHGRI https://www.genome.gov

When the chromosomal complement is BALANCED (any multiple of 23), it is EUPLOID

‘Balanced’ does not necessarily mean a normal chromosome complement | 69, XXY is euploid, but is considered to be a chromosomal abnormality

When the chromosomal number is NOT BALANCED, it is ANEUPLOID

Common chromosomal trisomies and monosomies are examples of aneuploidy
- Trisomy 21 / Down syndrome (47, XX, +21 [female]; 47, XY, +21 [male])
- Trisomy 13 and Trisomy 18
- Klinefelter syndrome (47,XXY)
- Turner syndrome (45,X)

Besides additional whole or missing chromosomes, chromosomes can have other structural changes, such as deletions (del), duplications (dup), insertions (ins), inversions (inv), many of which are associated with recognizable genetic syndromes, for example:

22q11.2 deletion syndrome
Wolf-Hirschhorn syndrome (WHS): results from deletion of a portion of chromosome 4p

Not all structural changes have significance

inv(9)(p11q12) and inv(9)(p11q13): common inversions involving chromosome 9 with no clinical sequelae

KEY POINTS:

Chromosomal analysis requires only a single cell, at minimum, and can be performed on tissue/tumor, blood or amniotic fluid samples
Chromosomal analysis has an important role in prenatal diagnosis, clinical diagnosis in individuals with multiple congenital anomalies and other complex clinical pictures
Karyotype is a pictorial arrangement of chromosomes, that allows for careful analysis of gross numerical or structural changes
Chromosomal microarrays are being increasingly utilized as a method to analyze chromosomes as they offer the ability to detect submicroscopic abnormalities that may go undetected with conventional karyotyping (see ‘Related ObG Topics’ below)

Learn More – Primary Sources:

GHR: Chromosomes & mtDNA

CDC: Genetic Basics

NCBI: An Introduction to Genetic Analysis: Aneuploidy

NIH: NHGRI – Chromosomes

NIH: NHGRI – Chromosome Abnormalities

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