1992 Woodrow Wilson Biology Institute
Too often when teaching heredity, teachers do not emphasize that whole chromosomes (linkage groups) are inherited from parents. Students often think they inherit separate genes. Mendel's Law of Independent Assortment is only applicable if genes are on separate chromosomes. If genes are linked on the same chromosome, the probability of inheriting both those genes increases. Students are also taught that they have half of each parent's chromosomes, twenty-five percent of each grandparent's chromosomes, etc. This exercise will visually present the mode of inheritance of chromosomes through three generations, demonstrating the percent of chromosome inheritance from a grandparent as being a matter of chance.
To visually demonstrate the concept that chromosomes (linkage groups) are inherited, and not individual genes.
To familiarize students with the procedure of locating gene loci.
To understand the concept of homologous chromosomes and crossing-over.
To increase understanding of the use of karyotypes and their analysis.
To demonstrate the following genetic concepts: dominance, recessive-ness, homozygous, heterozygous, genotype, phenotype, complete and domi-nance, polygenic inheritance, sex-linkage, probability, gene loci, karyo-typing, and Mendel's laws of Segregation and Independent Assortment.
To understand the relationship between genes on a chromosome and the resulting phenotypes.
Time Allotment: 2 to 3 class periods. Some activities may be completed at home.
This hands-on activity is highly adaptable. It can be used as an introduction to many genetic concepts, or as a reinforcement to concepts already introduced in class. I recommend terms and concepts such as dominant, recessive, homozygous, heterozygous, genotype, phenotype, complete and incomplete dominance, sex linkage, linkage groups, crossing-over, polygenic inheritance, homologous chromosomes, Punnett squares, karyotypes, and Mendel's Laws of Segregation and Independent Assortment should first be introduced to insure the smooth continuance of this model. This activity is an excellent application and it reinforces all the terminology and concepts listed.
I have included the reference numbers from McKusick's Mendelian Inheritance in Man. These will be helpful if further studies include research of the etiology of each condition.
Answers to the application questions are included on the student worksheet.
|1 (11700)||Rh blood type|
|85% Rh+ phenotype|
|Fragile, hyperflex skin|
|3 ** (with 6)||Acne (2 Locus model)|
N=active allele for acne
|NNNN = severe|
NNNn = moderate
NNnn = mild
Nnnn = very mild
nnnn = none
|4 (143100)||Huntington's disease|
|mid-life neurologic decline|
|6 **(with 3)||Acne|
|6 (222100)||Diabetes mellitus, insulin dependent|
|7 (219700)||Cystic Fibrosis
|1/20 Caucasian carriers|
|9||ABO blood group|
IA, IB, i
|10 **||Short/long index finger
male - dominant
|11 (141900)||Sickle Cell hemoglobin|
|HbAHbS=sickle cell trait|
HbSHbS=sickle cell anemia
P = normal
p = PKU
(see 14, 16, 18)
A = active
a = inactive
B = active
b = inactive
|15 (272800)||Tay Sachs|
T = normal
t = Tay Sachs
|death usually within 2 years|
C = active
c = inactive
M = Marfans
m = normal
|20,000 affected in USA|
15% new mutation
N = normal
n = Neurofibromatosis
D = active
d = inactive
|18 (137589)||Tourette Syndrome
T = Normal
t = Tourette
|19 (143890)||Familial Hypercholesterolemia|
F = affected
f = normal
|300-500 Cholesterol levels|
|X (303700)||Xcb, XN = Colorblindness / Normal||Xq28|
|8% Caucasian males|
|X (306700)||Xh, XN = Hemophilia / Normal||Xq28|
|X (310200)||Xdmd, XN = Duchene
Muscular Dystrophy / Normal
|Testis determining factor|
Dr. John Q. Frothingham III was a very respected, wealthy man from a socially prominent family. He was the head of a major genetics research laboratory in the East. He felt an intense duty to continue his family name and genetic background. At the age of 55, he died in a plane crash. He had stipulated that his estate would go to any males who would carry on his family name and gene pool. His daughter Alice is married with a son and a daughter. His son Gerald is 34 and still single. Dr. Frothingham's second wife Christine is 12 weeks pregnant and her amniocentesis procedure confirmed that her child is male.
Should Alice's son receive the entire estate? Should Reginald receive his share of the estate? Should Alice or her daughter receive any of the estate?
Does Dr. Frothingham have a son with his second wife? Does the fetus have a right to a part of the estate?
If you were a close personal friend of Dr. Frothingham, a colleague at work, and named executor of his will, what would you suggest to follow Dr. Frothingham's intentions as he had meant for them to be carried out?
The haploid human genome contains 23 chromosomes, containing a total of about 50,000 to 100,000 genes. Each chromosome has a few hundred to several thousand genes, depending upon its length and the size of the genes. Chromosomes are arranged on a karyotype form by size, position of centro-mere, and banding patterns.
The largest chromosomes are placed first and sequentially become smaller, except for the X and Y chromosomes. Chromosomes which are metacentric have the centromere (which binds the two replicated chromosomes together) in the middle, submetacentric chromosomes have the centromere off-center, and acrocentric chromosomes have the centromere close to one end. The shorter arms of the chromosomes are called the p- petite arms and are positioned on the top in a karyotype. The longer arms are the q arms. The locus (location on a chromosome) for each gene is represented by the chro-mosome number, which arm it occurs on, the section number, and the gene position. In the illustration, the cystic fibrosis gene is indicated as 7q31. This reading indicates its position is on the seventh chromosome, the q or longer arm, section 3, gene position 1.
|Special thanks for original ideas to:||Gordon
Lawrence Central High School
McKusick, V.A. Mendelian Inheritance in Man . (9th ed.). Baltimore: The Johns Hopkins University Press, 1990.
O'Brien, S.J. (Ed.). Genetic Maps Locus Maps of Complex Genomes (5th ed.). Book 5 Human Maps. Cold Spring Harbor, NY: Cold Spring Harbor Press, 1990.
Offner, S. "A Plain English Map of the Human Chromosomes." The American Biology Teacher Feb (1992) 87-91.