Heredity

Chapter 20 part 2

Genetic terms

• Trait - is a feature of an organism, i.e. hair colour

• Locus - a fixed position on a chromosome, such as the position of a gene. Akin to the physical address of that gene

• Allele - alternative forms of the same gene that exist in the population. Red flowers vs. white flowers.

• Wild type - is the typical form of an organism, strain, gene, or characteristic as it occurs in nature. Wild type refers to the most common phenotype in the natural population.

• Mutant - is an individual, organism, or new genetic character arising or resulting from an instance of mutation, which is a sudden structural change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not found in the parental type.

• Dominant - refers to the allele that causes a phenotype that is seen in a heterozygous genotype. Every person has two copies of every gene, one from mother and one from father. If a genetic trait is dominant, a person only needs to inherit one copy of the gene for the trait to be expressed.

• Recessive - refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele) and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father. If a genetic trait is recessive, a person needs to inherit two copies of the gene for the trait to be expressed. Thus, both parents have to be carriers of a recessive trait in order for a child to express that trait. If both parents are carriers, there is a 25% chance with each child to show the recessive trait.

• Homozygous - A homozygote's cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. When an organism is referred to as being homozygous for a specific gene, it means that it carries two identical copies of that gene for a given trait on the two corresponding chromosomes (e.g., the genotype is AA or aa). Such a cell or such an organism is called a homozygote.

• Heterozygous - a gene or trait if it has different alleles at the gene's locus for each homologous chromosome. Such an organism must be either diploid, have two homologous chromosomes in each cell, or polyploid, having more than two homologous chromosomes. In diploid organisms, the two different alleles were inherited from the organism's two parents. These different alleles contain different genetic codes. One allele may override the other, or they may both be expressed in a trait simultaneously.

• Phenotype - observable characteristics of an organism produced by the organism's genotype interacting with the environment.

• Genotype - genetic constitution of an organism.

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The Master - Mendel

• Gregor Mendel (July 22, 1822 - January 6, 1884) Born in Heizendorf, Austria, was an Augustinian abbot who is often called the "father of modern genetics" for his study of the inheritance of traits in pea plants. Mendel showed that the inheritance of traits follows particular laws, which were later named after him.

• Visit these links to learn more if you like;– http://en.wikipedia.org/wiki/Gregor_Mendel– http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.html

• Learn about his actual experiments here;– http://anthro.palomar.edu/mendel/mendel_1.htm

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LEARN ABOUT THE EXPERIMENTS ON AN

INTERACTIVE WEBSITE HERE...• Highly recommended that you try this yourself

• http://sonic.net/~nbs/projects/anthro201/exper/