Genetics General Biology Ms. Lichtenwald Genetics

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:

Definitions 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.

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?

Genotypes Heterozygous: Homozygous: BbbBbB 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.  The phenotype is the physical trait coded by the alleles in the genotype.

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 Cc c c cc Genotypic ratio: 2-Cc, 2-cc 1:1 Phenotypic ratio: 2-dominant, 2-recessive 1curly:1straight = 1:1

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 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 free 2:2 (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.here 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.

Works Cited Content: 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 Print. 38. Zerobio (Video). (2006). Genetics: monohybrid cross [Web]. Retrieved from Images: "Buttons." Flaming Text. Web. 4 Nov Farabee, M.J. (Artist). (2001). Introduction to genetics [Web]. Retrieved from pa.edu/faculty/farabee/BIOBK/BioBookgenintro.html pa.edu/faculty/farabee/BIOBK/BioBookgenintro.html Return to the beginning