SR.GENETICS.3A

BIOLOGY CURRICULUM 2006

KARYOTYPES – Я - US

INTRODUCTION

Some parents want to be surprised about the gender of their new baby. Others prefer to know the gender in advance to help make preparations such as room decorations and clothing colors. Through a process called karyotyping, much information can be learned about the developing baby such as gender and chromosomal disorders.

A karyotype is a picture in which the chromosomes of a cell have been stained so that the banding pattern of the chromosomes appears. Cells in metaphase of cell division are stained to show distinct parts of the chromosomes. The cells are then photographed through a microscope, and the photograph is enlarged. The chromosomes are cut from the photograph and arranged in pairs according to size, arm length, centromere position, and banding patterns (see

Figure 1). Karyotypes have become of increasing importance to genetic counselors as disorders and diseases have been traced to specific visible abnormalities of the chromosomes.

OBJECTIVE

After completing this lab, you will be to analyze a karyotype in order to explain how chromosome number affects an individual’s traits.

MATERIALS

scissors

glue stick or tape

one of six possible chromosome spreads

PROCEDURE

Interpreting a Karyotype

Examine the completed human karyotype in Figure 2 and answer the questions below.

  1. Describe how the chromosomes are arranged. Be as specific as possible.
  1. How many chromosomes are present? Is this the normal number for a human?
  1. What is the gender of this individual? Justify your answer.

Scenario

You are the director of a genetics counseling center and currently have a caseload of six expectant couples. The expecting parents have come to you, to tell each of them the gender of their unborn child so that they might be better prepared for the birth. They also wish to know if their babies have any chromosomal disorders such as Down Syndrome. Using Figure 2 as a guide, construct and analyze the karyotype of one of the six unborn children.

  1. Record the spread number on the karyotype form.
  1. Cut out individual chromosomes. It is acceptable to have a small oval or rectangle of white paper around the chromosome, as in Figure 3.
  1. Arrange the chromosomes in pairs, using Figure 2 as a guide.
  1. Glue or tape the pairs of chromosomes in their appropriate locations on the karyotype form.
  1. Answer the analysis questions below.

ANALYSIS

  1. What is the gender of the unborn child? Justify your answer.
  1. How many chromosomes does the baby have?
  • Is this the normal number of chromosomes?
  • If no, how is the child’s number of chromosomes different from the normal number?
  1. A child inherits the wrong number of chromosomes due to an error in which of the following processes? (Circle the correct answer.)

Justify your answer.

  1. mitosis
  2. meiosis
  3. fertilization
  4. metabolism
  1. On a separate piece of paper, write a letter to the parents of this child to let them know the following information:
  2. gender of the child
  3. if there is a chromosomal disorder present
  4. how you determined that a disorder was or was not present
  5. the name of the disorder, if applicable
  6. a description of the characteristics associated with the disorder, if applicable

EXTENSION

After reviewing your initial report, the couple has a few more questions about their unborn baby’s traits. They wish to know more about their child’s physical features such as eye color, hair color, and height. Based on your knowledge of karyotype analysis, how would you respond?

KARYOTYPE FORM

SPREAD # ______

1