A karyotype is a picture of all the chromosomes of a cell.  Karyotyping is one of many techniques that allow us to look for several thousand possible genetic diseases in humans. 

Below is an actual karyotype photograph of a human somatic (body) cell.  Because humans are diploid organisms, chromosomes are present in two identical copies.  This human karyotype has 22 pairs of somatic chromosomes and 1 pair of sex chromosomes.

 

 

Today you and your partner will be creating your own karyotypes.  Then, you will be using these karyotypes to produce a baby!  A karyotype baby that is. 

 

Part One 

1. For each trait in Table 1 and 2 below, first determine your phenotype.  For example for “eye color”, determine if you have the dominant phenotype (not blue eyes) or the recessive phenotype (blue eyes).
2. Then, determine your genotype that produced your phenotype.  For example, if you have blue eyes, there is only one genotype – ee.  If you don’t have blue eyes, then your genotype can be homozygous (EE) or heterozygous (Ee).  Flip a coin to determine which one – heads is homozygous, tails is heterozygous. 
3. Once you have determine your genotype, write the genotype underneath the appropriate chromosome on your karyotype worksheet.  For example, if your genotype was Ee for eye color, then you would write (chromosome 2):

     E      e

4.  Continue in this manner for each trait in Tables 1 and 2.  See Appendix 2 to help you identify each trait.  Table 2 consists of various genetic diseases.  See Appendix 1 for a brief description of each of these diseases.  You must assume that you are carrying a recessive, or hidden version of each disease.  As a matter of fact, we all carry 6-9 lethal, but recessive (hidden) genes.   

TABLE 1

Trait	Chromosome for Gene Location	Dominant Phenotype	Possible Dominant Genotypes	Recessive Phenotype	Recessive Genotype
Eye color	2	not blue	EE or Ee	blue	ee
widow's peak	4	peak	PP or Pp	no peak	pp
cheek dimples	5	dimples	DD or Dd	not dimples	dd
face freckles	9	freckles	FF or Ff	no freckles	ff
mid-digital hair	10	hair	HH or Hh	no hair	hh
Hitchhiker's thumb	17	straight	TT or Tt	curved	tt
ear lobes	21	free	LL or Ll	attached	ll
tongue rolling	22	ability	RR or Rr	no ability	rr
cleft chin	16	cleft	YY or Yy	no cleft	yy

TABLE 2

Trait	Chromosome for Gene Location	Genotype
skin cancer	1	Cc
cystic fibrosis	7	Qq
albinism	11	Aa
xeroderma pigmentosa	15	Xx
lung cancer	3	Nn
PKU (phenylketonuria)	12	Gg
Muscular Dystrophy	X sex chromosome	Mm (girls only)

 

Part Two 

1. Color the chromosomes on you karyotype ALL ONE COLOR. Have your partner color his/her karyotype A DIFFERENT COLOR.
2. Cut out each of your chromosomes.
3. Flip a coin to determine which allele you will pass on to your baby.  For example.  If you don’t have blue eyes and have a genotype of Ee, heads will tell you to pass on the “E” allele to the baby.  Tails will tell you to pass on the “e” allele to the baby. 
4. Now, provide a list of your child’s genetic makeup.  List the trait (phenotypes) and the genotypes that your child inherited from you and your partner. 
5. YOU WILL HAND IN YOUR TRAIT LIST (WITH GENOTYPES) OF YOUR CHILD, YOUR CHILD’S KARYOTYPE, AND THE ANSWERS TO THE QUESTIONS BELOW (ON A SEPARATE SHEET).

 

 

WRAP-UP QUESTIONS

1. Were there any traits that you and your partner both had, but your child did not?  Explain how this could happen.

 

2. Is it possible for both parents to have attached earlobes and their baby have free earlobes?  Why or why not?

 

3. Did your child inherit any of the genetic diseases in Table 2?  If so, which one(s)?

 

4. If you found out your child had PKU, or phenylketonuria, what could the child do to live a normal life?  Be specific. 

  

5. If you have a family history of skin cancer, what advice could you give your child to help prevent the occurrence of this disease?

 

  Scoring Guide

Three components of the “Genetic Traits and Human Karyotypes” activity will be collected on Friday, February 2, 2007.  The following is how you will be scored for this activity. 

 

1. Stayed on task -                                                                                         10 points

Student was working on the activity and exhibited

proper behavior (e.g., no throwing of supplies) during

the entire class period

 

 

2.  Baby’s trait list -                                                                                       15 points

            Student handed in a completed list of their baby’s

traits and the genotype for each trait.  Each student

must hand in their own trait list!

 

3.  Baby’s karyotype -                                                                                   15 points

            The group handed in their baby’s karyotype – properly

“filled in” with the parent chromosomes.  Only one baby

karyotype need be handed in for each group.

 

4.  “Wrap-up Question” responses -                                                             50 points

            Student handed in completed responses to the 5 “wrap-up

questions”.  Responses must be in complete sentences. 

 

 

 

  

 Appendix 1

 

Skin cancer is a malignant growth on the skin, which can have many causes, including repeated severe sunburn or long-term exposure to the sun.  Prevention includes reducing sun exposure, wearing sunscreen, and wearing protective clothing when outdoors.

 

Cystic fibrosis (CF) is a common hereditary disease that affects the entire body, causing progressive disability and early death. Difficulty breathing is the most common symptom and results from frequent lung infections, which are treated, though not always cured, by antibiotics and other medications. 

 

Albinism is characterized by a lack of pigment in the eyes, skin and hair (or more rarely the eyes alone).  Albinism is a condition that cannot be "cured" or "treated", but small things can be done to improve the quality of life for those affected. It is vital that people with albinism use sunscreen. Treatment of the eye conditions consists of visual rehabilitation.

 

Xeroderma pigmentosum, or XP, is a genetic disorder of DNA repair in which the body's normal ability to remove damage caused by ultraviolet (UV) light is deficient. This leads to multiple basaliomas and other skin malignancies at a young age. In severe cases, it is necessary to avoid sunlight.  The most important part of managing the condition is reducing exposure to the sun.

 

Lung cancer is the malignant transformation and expansion of lung tissue, and is the most lethal of all cancers worldwide.  Eliminating tobacco smoking is a primary goal in the fight to prevent lung cancer and is the most important preventative tool in this process.

 

Phenylketonuria is a human genetic disorder that can cause brain damage and progressive mental retardation. If the condition is diagnosed early enough, an affected newborn can grow up with normal brain development, but only by eating a special diet low in phenylalanine for the rest of their life. This requires severely restricting or eliminating foods high in phenylalanine, such as breast milk, meat, chicken, fish, nuts, cheese and other dairy products. Starchy foods such as potatoes, bread, pasta, and corn must be monitored. Many diet foods and diet soft drinks that contain the sweetener aspartame must also be avoided, as aspartame is metabolized into several constituent chemicals, including phenylalanine.

 

Muscular Dystrophy is characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue. There is no known cure for muscular dystrophy. Inactivity (such as bed-rest and even sitting for long periods) can worsen the disease. Physical therapy and orthopedic instruments (e.g., wheelchairs, standing frames) may be helpful.

 

   

Appendix 2.