Genetics And Evolutionary Theory

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acquired characteristics

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developed by Lamarck: traits are acquired during the lifetime of an organism can be passed on to offspring

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adaptation

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the process of adjustment of a species to its environment. there are 3 levels: acclimatization, developmental and genetic.

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albinism

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a genetic disorder that results from failure to produce the enzyme tyrosonase which is important to the manufacturing of melanin as a result the individual lacks skin pigment. it is a rare recessive trait.

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allele

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an alternative form of a gene at the same locus (position) on a chromosome

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anagenesis

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a process by which one species gradually evolves into another, with no isolation taking place

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assortative mating

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a type of non-random mating in which individuals of like phenotype (positive assortment mating)'or unlike phenotypes (negative assortment mating) mate more often than predicted under random mating conditions

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autosome

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any chromosome except for sex chromosome

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biological species

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a group of interbreeding populations that is reproductively isolated from other such group

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catastrophism

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the idea that there was a series of violent catastrophes which destroyed most living organisms. this was proposed to explain the fossil record. associates with the French paleontologist Curvier (1769-1832).

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centromere

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the constricted part of the chromosome to which the arms are attached

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chromosomal abberation

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a rearrangement or loss of a large section of the chromosome

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chromosome

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threadlike, gene-carrying body made of DNA. visible in the nucleus of the cell only during cell division

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cladogenesis

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a process by which two new daughter species originate from the parent species by isolation of their gene pools

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crossing-over

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the exchange of genetic material between homologous chromosomes during meiosis

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deme

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the smallest possible Mendelian population of a species

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diploid number

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the full complement of chromosomes in a somatic or body cell. in humans the diploid number (2n) = 46

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DNA (Deoxyribonucleic acid)

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a large and complex molecule consisting of repeated series of a base, a phosphate and a suger arranged in a double helix. Carries genetic code.

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dominant

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a trait determined by a dominant allele. an allele that prevents the phenotypic appearance of a recessive allele

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Down's syndrome

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a genetic disorder caused by the occurence of an additional autosomal chromosome - chromosome 21 (trisomy 21)

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Ellis van Creveld Syndrome

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a rare recessive genetic disorder leading to six-fingered dwarfism. common among the Amish of Pennsylvania

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Fixity of species

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the belief that species, once created, never change, ie remain fixed

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founder effect

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a type of genetic drift in which allele frequencies are altered in small populations due to the effects of sampling

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gamete

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a sex cell (spermatozoa or ovum) produced by the gonads. They have a haploid (n) chromosome count

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gene

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the section of DNA responsible for the synthesis of a polypeptide chain of an amino acid; that portion of DNA with a detectable function

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gene flow

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the transfer of gene from one population to another by migration or interbreeding

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gene pool

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the total complement of genes in a population of deme

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gene frequency

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the proportion of different genes or alleles in the population. determined by the Hardy0Weinberg formula

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genetics

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the study of the inheritance of characteristics. the principles of inheritance were first elucidated by Mendel (1822-1884)

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genetic drift

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shifts in allele frequency due to random events as a function of a small population size

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genetic screening

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testing programs to acertain individuals with genetic diseases of carriers of such diseases

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genotype

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the genetic makeup of an individual organism. the genes at one or more loci

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gradualism

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the concept that evolutionary change takes place through a series of small changes over along period of time

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haploid number

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number of chromosomes in a gamete after meiosis. in humans the haploid number (n) = 23

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Hardy-Weinberg formula

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the mathematical relationship expressing, under the conditions of random mating, the predicted distribution of genes in populations. the central theorem of population genetics

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heterozygous

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having different alleles at a given locus on a pair of homologous chromosomes

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hybrid

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offspring of a parents of two different alleles of the same trait (heterozygote)

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inbreeding

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a type of non-random mating in which blood relatives mate more often than under random mating conditions

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independent assortment

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where homologous chromosomes separate independently from one another during meiosis and are randomly assorted in gametes. (Mendel's Second Law)

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Karyotype

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a diagram of the chromosome complement contained in a single cell

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Klinfelter's Syndrome

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a genetic disorder of the sex chromosomes in which there is an extra chromosome (XXY). the individual is phenotypically male

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locus (loci)

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the position of a gene on the chromosome

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meiosis

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cell division in which the total complement (diploid number) of chromosomes is reduced by half (haploid number) in the gametes

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melanin

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a skin pigment produced from tyrosine by the enzyme tyrosinase. it is important in preventing ultra volet radiation from damaging the deeper skin tissues

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Mendelian Populations

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a group of organisms in which each member is more likely to mate with another member than with an outsider

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Mitosis

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cell division in somatic (body) cells, in which the resulting two daughter cells are identical to the parent cell

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monogenic trait

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a trait that is influenced by genes at only one locus

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multiple alleles

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a gene which has more than two alleles . a good example is the ABO blood group system (3 alleles)

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mutagen

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an agent that alters the DNA structure of a cell to produce a mutation (e.g. X-Rays)

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natural selection

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the mechanism by which evolutionary change take place, which was first articulaed by Charles Darwin (1809-1882) THe process by which the adapted members of a population increase in number at the expense of less favored individuals

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ovum(ova)

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female gamete

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phenotype

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the oservable characteristics of an individual - the product of the genotype and the environment

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point mutation

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changes in one base in the DNA sequence

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polygenic trait

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a phenotypic characteristic that is influenced by genes at more than one locus

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polymorphism

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the situation where two or more alleles at a given locus occur with frequencies greater than 1% in a population

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polytypic species

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a species whose constituent populations differ in their gene frequenies and phenotypic traits

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population

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within a species, a community of individuals where mates are usually found

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puctuated equilibrium

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the view that evolutionary rates are not constant and gradual, but occur in sudden spurtdafter periods of stasis (no change)

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punnett square

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a table that shows all of the possible genotypes that can result, at a given locus, from the mating of two individuals

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recessive

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an allele that is expressed phenotypically only in the homozygous state

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sex chromosomes

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the chromosome that determine the sex of an individual. The X and Y chromosomes in mammals

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sex ratio

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the ratio of male to female individuals in a population. the primary sex ratio is the predicted ratio. Primary sex ratio: 1:1 Secondary sex ratio (observed ratio at birth, usually more males than females)

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somatic cells

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body cells that divide by mitosis

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speciation

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the process by which the gene pool of a species splits permanently and irreversibly to produce one or more species

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spermatozoa

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male gamete

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Turner's syndrome

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a genetic disorder of the sex chromosomes, in which there is only a single X chromosome (XO) The individuals are phenotypically female

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Uniformitarianism

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a concept maintaining that the Earth's processes in the past were caused by the same physical principles acting today. GEological processes were the result of natural popularized by Lyell (1797-1875)

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zygote

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the fertilized egg produced by the fusion of the male and female gametes