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Section 3.2

Section 3.2 . Traits and Inheritance. VOCABULARY. Gene: One set of instructions for an inherited trait. Allele: One of the alternative forms of a gene that governs a characteristic, such as hair color. Phenotype: An organism’s appearance or other detectable characteristic.

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Section 3.2

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  1. Section 3.2 Traits and Inheritance

  2. VOCABULARY • Gene: One set of instructions for an inherited trait. • Allele: One of the alternative forms of a gene that governs a characteristic, such as hair color. • Phenotype: An organism’s appearance or other detectable characteristic. • Genotype: The entire genetic makeup of an organism; also the combination of genes for one or more specific traits. • Probability: The likelihood that a possible future even will occur in any given instance of the event.

  3. Thanks Mendel!  • Mendel’s experiments told us that there must be two sets of instructions for each characteristic: • The first-generation plants carried the instructions for both the dominant and recessive trait. • Today, scientists call the instructions for an inherited trait genes. Each parent gives one set of genes to the offspring. Therefore, the offspring have a set of the same gene for every characteristic (one from each parent). • The different forms of a gene (often considered dominant and recessive) are known as alleles (dominant showed as a CAPITAL letter and the recessive as a lowercase letter).

  4. Phenotype, Genotype, & Punnett Squares • An organisms appearance is known as it’s PHENOTYPE. • Inherited alleles form an organism’s GENOTYPE, or the genetic makeup of an organism. • When two of the same allele are present (PP or ppfor flower color), this is known as a HOMOZYGOUS. • When the allele differ (Ppfor flower color), this is known as HETEROZYGOUS. • A Punnett square is used to organize possible combinations of offspring from particular events.

  5. Heredity and Probability • Each parent has two alleles for each gene. When these alleles are different (Pp), offspring are equally likely to receive either allele (50% chance). • The mathematical chance that something will happen is known as probability. This can be written as a fraction or percentage. • To find the probability that you will toss two heads in a row, multiply the probability of tossing the first head (1/2) by the probability of tossing the second head (1/2). Therefore, the probability of tossing two heads is ¼.

  6. Since Mendel . . . • Mendel uncovered the basic principles of how genes are passed from one generation to the next. • Incomplete dominance: Sometimes one trait is not completely dominant over another. Rather, each allele has its own degree of influence. Example: snapdragon flower (red + white = pink because both alleles of the gene have some degree of influence). • Sometimes a gene can influence more than one trait (white tiger and blue eyes). • Sometimes many genes work together to influence traits (the color of your skin, eyes, and hair). In this case, different combinations of alleles result in different shades of skin, eye, and hair color. • The environment also influences traits. For example, a healthy diet may play a role in allowing you to reach the full potential height.

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