Genetics

General BiologyMs. LichtenwaldGenetics

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.

Goals

By the end of this lesson, you should meet the following Michigan Merit Curriculum course requirements for Genetics and Inherited Traits:

DefinitionsChromosome: 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.

Dominance

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 their offspring.

The two alleles inherited is the genotype of a specific trait.

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?

S s T t

Genotypes

Heterozygous: Homozygous:

B b bB bB

Click on each letter to see the difference between heterozygous

and homozygous genotypes.

Phenotypes

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.

SS Ss ss

The phenotype is the physical trait coded by the alleles in the genotype.

EXAMPLE

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.

ccCc X

C c

c

c

Cc

Cc

cc

cc

Genotypic ratio:2-Cc, 2-cc 1:1

Phenotypic ratio:2-dominant, 2-recessive

1curly:1straight = 1:1

The Monohybrid Cross

Click here to watch a detailed video to see how a

Punnett square is filled.

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.

CcCc X

Set up the cross to

determine the

phenotypic ratio.

Click on the correct phenotypic ratio of

attached to free ear lobes for this monohybrid cross.

1:3 = 1 attached to 3 free2:2 (or 1:1) = 2 attached to 2 free

3:1 = 3 attached to 1 free

0:4 = 0 attached to 4 free

4:0 = 4 attached to 0 free

Punnett Square Practice

Click here to be directed to a website do practice a few

more monohybrid crosses.

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.

Try Again!

Correct!

Works CitedContent:

Carter, J.S. (1996). Genetics Practice Problems. Retrieved December 2, 2009, from http://biology.clc.uc.edu/Courses/Bio105/geneprob.htm National Institutes of Health. National Human Genome Research Institute. “Talking Glossary

of Genetic Terms.” Retrieved November 30, 2009, from http://www.genome.gov/glossary/State of Michigan. Michigan Merit Curriculum Course/Credit Requirements. 2009. Print. 38.Zerobio (Video). (2006). Genetics: monohybrid cross [Web]. Retrieved from http://www.zerobio.com/videos/monohybrid.html

Images:

"Buttons." Flaming Text. Web. 4 Nov 2009. <http://www2.flamingtext.com/>.Farabee, M.J. (Artist). (2001). Introduction to genetics [Web]. Retrieved from http://www.agen.ufl.edu/~chyn/age2062/OnLineBiology/OLBB/www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenintro.html

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