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HumanGeneticsACTIVITY1 - Tami Port Instructor Winter 08 P-1...

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Tami Port, Instructor, Winter ’08, P-1 I. Introduction GENETICS is the study of heredity and variation. Heredity is the transmission of characters from parents to offspring, while VARIATION is the tendency of offspring to differ from their parents and each other. Inherited variation may be due to genetic recombination or mutations. Noninherited variation may be due to environmental influences such as nutrition, weather factors, crowding and pollution. II. Gamete Formation Gamete formation involves independent assortment. Every diploid cell contains pairs of HOMOLOGOUS CHROMOSOMES on which are found GENES. The genes are in pairs, and govern hereditary traits such as flower color or height in plants. The two members of a given pair of genes are known as ALLELES. During meiosis, at which time the gametes (sperm & egg) are formed, the pairs of homologous chromosomes are separated along with the genes they bear. Only one of each pair is eventually sorted into each egg or sperm. In studying genetics, it is helpful to consider one pair at a time. The following problems should help fix in your mind the concept of INDEPENDENT ASSORTMENT of gene pairs in the formation of gametes. In each of the following examples, determine how many DIFFERENT KINDS of gametes may be formed from the diploid parent cells. The LETTERS within the parent cells represent GENES for a particular trait. The capital letters A, B, D represent genes for DOMINANT TRAITS. While lower case letters a, b, d represent genes for RECESSIVE TRAITS. In examples #1, #2, and #3, fill in the gamete cell with the letter or letters which represent all the hereditary combinations. Assume that each pair of genes is located on a different pair of homologous chromosomes. NOTE: each gamete is HAPLOID and contains only ONE gene of a pair. This means ONLY ONE letter (either dominant or recessive) of each pair must be represented. Your instructor will represent the “BRACKET METHOD” for determination of gamete genotype. This in-class activity has been adapted from a laboratory exercise written by Bette Doezema, Professor at Grand Rapids Community College.
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Tami Port, Instructor, Winter ’08, P-2 Determining Genetic Makeup of Gametes Example #1 Example #2 Example #3 Parent Cells (2n) > Aa Aa Bb Aa Bb Dd Possible Gametes (n) > III. Monohybrid Cross (The recombination of gametes) When both genes of a pair of a particular trait are the same, they are said to be HOMOZYGOUS. When the gene pair consists of genes that produce contrasting effects for the trait, they are called HETEROZYGOUS. A DOMINANT gene (A, for example) of a contrasting pair (alleles Aa) is the one which expresses its effect, while the RECESSIVE gene (a) of the pair does not express its effect. The genetic combination of the gene pair is called a GENOTYPE, and is symbolized by letters (AA, Aa, or aa). The PHENOTYPE is the expressed physical characteristic described in words such as “red”, “white”, “tall”, “smooth”, etc. A MONOHYBRID CROSS involves the transmission and expression of a SINGLE PAIR of genes.
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HumanGeneticsACTIVITY1 - Tami Port Instructor Winter 08 P-1...

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