Ch 11 Intro To Genetics

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homozygous genotype

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A genotype consisting of two identical alleles of a gene for a particular trait.

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recessive allele

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The general term for an allele that is masked in the phenotype by the presence of another allele.

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alleles

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Alternate forms of the same gene. Because they are different, their action may result in different expressions of a trait.

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phenotype

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The observable or detectable characteristics of an individual organism; the detectable expression of a genotype.

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heterozygous genotype

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The term for a genotype in which there is a dominant allele and a recessive one.

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genotype

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The genetic makeup of an individual for a trait or for all of his/her inherited traits- not the observable or detectable characteristics.

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gametes

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Specialized cells involved in sexual reproduction.

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diploid

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Cell that contains both sets of chromosomes (2N)

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haploid

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Cell that contains only a single set of chromosomes (N).

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polygenic trait

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A trait that is determined by the combined effect of more than one gene. Human skin and hair color are examples. The result of this kind of inheritance is the perception of gradation in the expression of such traits.

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dominant allele

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The general term for an allele that masks the presence of another allele in the phenotype.

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Gene map

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Shows the relative location of each gene on a chromosome.

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tetrad

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Structure containing 4 chromatids, forms during meiosis.

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probability

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The likelihood that a particular event will occur.

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fertilization

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The joining of male and female reproductive cells.

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heterozygous

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A genotype consisting of two different alleles of a gene for a particular trait.

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homologous

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Term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent.

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Gregor Mendel

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A 19th century central European monk scientist who published his ideas about genetics in 1866 but largely went unrecognized until 1900, which was long after his death. He acquired his understanding of genetics mostly through pea plant breeding experiments.

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homozygous recessive

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The term for a genotype in which there are two recessive alleles.

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homozygous dominant

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The term for a genotype in which there are two dominant alleles

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Thomas Hunt Morgan

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American geneticist who worked with fruit flies, Drosophila melanogaster, discovered chromosomes.

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Crossing-over

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Process in which homologous chromosomes exchange portions of their chromatids during meiosis

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Punnett square

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A simple graphical method of showing all of the potential combinations of offspring genotypes that can occur and their probability given the parent genotypes. This system involves the use of a tic-tac-toe square. It was named after pioneer British geneticist Reginald Punnett.

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Mendelian genetics

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The general term of inheritance patterns which can be explained by simple rules of dominance and recessiveness of genes.

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codominance

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The inheritance pattern in which two different alleles for a trait are expressed unblended in the phenotype of heterozygous individuals. Type AB human blood is an example.

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incomplete dominance

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The inheritance pattern in which a trait is expressed in the phenotype of heterozygous individuals as an apparent blend or an intermediate expression. For instance, in primroses white flowers are homozygous recessive, red ones are homozygous dominant, and pink ones are heterozygous.

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genetics

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The study of gene structure and action and the patterns of inheritance of traits from parent to offspring. This is the branch of science that deals with the inheritance of biological characteristics.

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meiosis

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Division of sex cells (gametes).

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purebred

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Offspring that are the result of mating between genetically similar kinds of parents- the opposite of hybrid.

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hybrid

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Offspring that are the result of mating between two genetically different kinds of parents -- the opposite of purebred.

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Principle of Independent Assortment

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Gregor Mendel's principle of genetic inheritance stating that different pairs of genes are passed to offspring independently so that new combinations of genes, present in neither parent are ppossible. In other words, the distribution of one pair of alleles does not influence the distribution of another pair--the genes controlling different traits are inherited independently of one another.

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Principle of Segregation

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Gregor Mendel's principle of genetic inheritance stating that, for any particular trait, the pair of genes of each parent separate (during the formation of sex cells) and only one gene from each parent passes on to an offspring.

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heterozygous

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The genotype of an individual who is a carrier for a recesive allele that is not expressed in his/her phenotype.

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multiple alleles

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An inheritance pattern in which a gene has more than two alleles. The human ABO blood type system is an example. It is controlled by at least 3 alleles.

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genes

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Units of inheritance usually occuring at specific locations, or loci, on a chromosome. These units are responsible for hereditary characteristics in plants and animals.