By the end of this lesson, you should meet the following
Michigan Merit Curriculum course requirements for Genetics
and Inherited Traits:
B4.1A Draw and label a homologous chromosome pair with heterozygous alleles
highlighting a particular gene location.
B4.1B Explain that the information passed from parents to offspring is
transmitted by means of genes that are coded in DNA molecules.
B4.1C Differentiate between
dominant, recessive, codominant, polygenic, and sex-linked traits.
B4.1E Determine the genotype and phenotype of monohybrid
crosses using a Punnett Square.
Chromosome: A chromosome is an organized package of DNA found in the
nucleus of the cell.
Gene: The gene is the basic physical unit of inheritance, is passed from parents to
offspring and contains the information needed to specify traits. Genes are
arranged, one after another, on structures called chromosomes.
Allele: An allele is one of two or more versions of a gene. An individual inherits
two alleles for each gene, one from each parent.
Dominant: If the alleles of a gene are different, one allele will be expressed; it is
the dominant gene.
Recessive: If the alleles are different, the dominant allele will be expressed, while
the effect of the other allele, called recessive, is masked.
Genotype: The two alleles inherited for a particular gene. The expression of the
genotype contributes to the individual's observable traits, called the phenotype.
Phenotype: A phenotype is an individual's observable traits, such as height, eye
color, and blood type.
Homozygous: Homozygous is a genetic condition where an individual inherits
the same alleles for a particular gene from both parents.
Heterozygous: A phenotype is an individual's observable traits, such as
height, eye color, and blood type.
Trait: A trait is a specific characteristic of an organism.
A dominant trait is represented by a capital letter
while a recessive trait is represented by the
lowercase of the same letter as the dominant.
Each parent passes on one allele of each trait to
The two alleles inherited is the genotype of a
In a pea plant, the dominant allele
for height may be represented by a
capital T, for tall.
Click on the letter that represents the
recessive allele for short height?
Click on each letter to see the difference
between heterozygous and homozygous
B B Bbbb
The phenotype is the physical trait coded by the alleles in the genotype.
Spherical pea plant seeds are
dominant over dented.
Click on the alleles that
make up the genotype for a
homozygous dominant pea
plant for this trait.
The Monohybrid Cross
A Punnett square crosses the genotype of a specific trait from each parent
to show what the offspring might inherit from the parents.
The cross below shows a mother with curly hair and a father with
straight hair. Curly hair is the dominant trait.
Cc X cc
2-Cc, 2-cc 1:1 c Cc cc
1curly:1straight = 1:1
c Cc cc
The Monohybrid Cross
A heterozygous female was crossed with a heterozygous male for the trait
for ear lobe attachment. Attached ear lobes is the recessive trait.
Cc X Cc
Click on the correct
phenotypic ratio of attached
to free ear lobes for this
0:4 = 0 attached to 4 free Set up the
1:3 = 1 attached to 3 free cross to
2:2 (or 1:1) = 2 attached to 2 free determine
3:1 = 3 attached to 1 free the
4:0 = 4 attached to 0 free phenotypic
Punnett Square Practice
Click here to be directed to a
website do practice a few more
When you are done with the monohybrid cross practice
problems, return here to view terms for the next lesson.
Terms for next time!
Codominance: Codominance is a relationship between two versions of
a gene. In codominance, neither allele is recessive and the phenotypes of
both alleles are expressed.
Polygenic: A polygenic trait is one whose phenotype is influenced by
more than one gene.
Sex-linked traits: Sex linked is a trait in which a gene is located on a sex
chromosome. In humans, the term generally refers to traits that are
influenced by genes on the X chromosome.
Carter, J.S. (1996). Genetics Practice Problems. Retrieved December 2, 2009, from
National Institutes of Health. National Human Genome Research Institute. “Talking Glossary
of Genetic Terms.” Retrieved November 30, 2009, from
State of Michigan. Michigan Merit Curriculum Course/Credit Requirements. 2009. Print. 38.
Zerobio (Video). (2006). Genetics: monohybrid cross [Web]. Retrieved from
"Buttons." Flaming Text. Web. 4 Nov 2009. <http://www2.flamingtext.com/>.
Farabee, M.J. (Artist). (2001). Introduction to genetics [Web]. Retrieved from
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