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PROFESSIONAL LEARNING COMMUNITY MODEL FOR ENTRY INTO TEACHING SCIENCE
A professional learning community of STEM educators, scientists, and engineers
http://plcmets.pbworks.com/
PLCMETS Inquiry Resources Collection:
Heredity and Genetics
Current TEKS:
7.10 C: distinguish between dominant and recessive traits and recognize that inherited traits of an
individual are contained in genetic material
Future TEKS:
7.14 A: define heredity as the passage of genetic instructions from one generation to the next
7.14 C: recognize that inherited traits of individuals are governed in the genetic material
Scope & Sequence:
Aldine: Grade 7, 4th six weeks
Cy-Fair: Grade 7, 5th 6 weeks
Big Ideas:
Heredity is the transmission of traits from one generation to the next. The transmission of
traits is carried on by genes. A gene is a discrete unit of hereditary information consisting of a
specific nucleotide sequence in DNA (or RNA in some viruses). Alleles are alternative versions of
a gene, and account for variations in inherited characteristics. A character is a heritable feature,
while traits are the possible expressions of a character. Thus, flower color is an example of a
character, while a purple or white flower is an example of a trait. Genome is a term that describes
the complete complement of an organism's genes i.e. an organism's genetic material.
A gene in a sequence of DNA
http://pennstatehershey.org/healthinfo/graphics/images/en/9344.jpg
Genetics is the scientific study of heredity and heritable variation. Genotype is the genetic
makeup of an organism. All organisms carry some genes that are not expressed, but are part of our
genetic makeup. The phenotype of an organism is the physical and physiological traits that
characterize it, meaning the traits we observe by just looking at the organism. The genotype is
what comprises our genes, while the phenotype is what we see. Organisms can carry recessive
traits that are not expressed in the phenotype, but are in the genotype nevertheless. Homozygous is
a term that describes having two identical alleles for a given trait. Heterozygous is a term that
describes having two different alleles for a given genetic character. Dominant allele is the allele
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PROFESSIONAL LEARNING COMMUNITY MODEL FOR ENTRY INTO TEACHING SCIENCE
A professional learning community of STEM educators, scientists, and engineers
http://plcmets.pbworks.com/
fully expressed in a heterozygote. Recessive allele in a heterozygote is an allele that is completely
masked by the dominant allele in the phenotype. Codominance is a phenotypic situation in which
the two alleles affect the phenotype in separate, distinguishable ways. This means both alleles are
expressed. In lay terms, the coloring of an organism looks mixed i.e. crossing a red carnation with
a white carnation yielding a pink carnation.
A Punnett Square is a diagram used in the study of inheritance to show the results of random
fertilization. A Punnett square shows the possible combinations of alleles in a two allele character.
The dominant allele in a Punnett square is denoted by a capital letter, and recessive alleles are
represented with lowercase letters. In the case below, the dominant trait is yellow over the
recessive green trait. The diagram below shows that offspring from a homozygous recessive green
plant (yy) crossed with a heterozygous yellow plant (Yy) yields a 50% chance that the offspring
with either be yellow (heterozygous dominant) or green (homozygous recessive). Punnett squares
becoming increasingly larger as the number of genes controlling a particular trait increase. This is
seen in the case of human eye color, which is believed to be controlled by multiple genes.
A Punnett Square
http://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Punnett_Square.svg/600px-Punnett_Square.svg.png
Case Study:
Palominos: An Equine Case Study of Codominance Palomino is a term that describes a horse of
a golden colored coat with a white mane and tail. A palomino can occur when a chestnut colored
horse is crossed with a cremello colored horse. This is an example of codominance; where two
genes are equally expressed instead of one being dominant and one being recessive.
Chestnut Colored Horse
Cremello colored horse
X
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Palomino colored Horse
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PROFESSIONAL LEARNING COMMUNITY MODEL FOR ENTRY INTO TEACHING SCIENCE
A professional learning community of STEM educators, scientists, and engineers
http://plcmets.pbworks.com/
Good Questions for Research:
What are other examples of codominance?
Should we expect to see palomino horses in Nature, why or why not?
What type of allele is expressed with a cremello, dominant or recessive, and why?
What might result from crossing a cremello colored horse to a different color, like bay?
How does a cremello compare with albino colorations in genes, health effects, etc.?
Not So Good Questions for Research:
Is this an example of codominance?
Simulated Research Activity:
Simulation: What color eyes would your children have? - This website allows a user to input your
family's history of eye color and predict what your children's eyes are or will be.
URL: http://museum.thetech.org/ugenetics/eyeCalc/eyecalculator.html
Short Videos You May Find Useful:
The Genetic Work of Gregor Mendel - 4:51 min. video from HowStuffWorks.com explaining the
work on the genetics of pea plants by Gregor Mendel including how he established tallness as a
dominant allele
URL: http://videos.howstuffworks.com/hsw/6013-genetics-the-genetic-work-of-gregor-mendelvideo.htm
Codominance - 5:37 min. video from YouTube that reviews Punnett Squares of crosses of red and
white carnations
URL: http://www.youtube.com/watch?v=GQiloijO-OU
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