3. Heredity and Evolution

Based on notes

Genetics

The study of gene structure and action and the pattern of transmission of traits from parent to offspring

Nucleus

A organelle found in all eukaryotic cells - contains chromosomes (nuclear DNA)

Deoxyribonucleic acid (DNA)

The double-stranded molecule that contains the genetic code - main component of chromosomes

Ribonucleic acid (RNA)

A molecule similar in structure to DNA - three different single-stranded forms of RNA are essential to protein synthesis

Cytoplasm

Consists of a semi-fluid material and contains numerous structures involved in cell function

Cells

the basic units of life in all living things

Multicellular forms

plants, insects, birds, and mammals - composed of billions of cells

Prokaryotes

single-celled organisms ex. bacteria

Eukaryotic cells

structurally more complex cells that are found in multicellular organisms

Proteins

Three-dimensional molecules that serve a wide variety of functions through their ability to bind to other molecules

Protein synthesis

The assembly of chains of amino acids into functional protein molecules - the process is directed by DNA

Two types of cells

somatic cells and gametes

Somatic cells

cellular components of body tissues, such as muscle, bone, skin, nerves, heart, and brain

Gametes

Reproductive cells (eggs and sperm in animals) developed from precursor cells in ovaries and testes

Zygote

A cell formed by the union of an egg and a sperm cell - contains the full complement 46 chromosomes - can turn into an organism

Molecule

A structure made up of two or more atoms - can combine with others to make up more complex structures

Nucleotides

Basic units of the DNA molecule, composed of a sugar, a phosphate unit and one of four DNA bases

Enzymes

Specialized proteins that initiate and direct chemical reactions in the body

Complementary

Referring to the fact that DNA bases form base pairs in a precise manner. Ex, adenine - thymine

Hemoglobin

A protein molecule that occurs in red blood cells and binds to oxygen molecules

Hormones

Substances (usually proteins) that are produced by specialized cells and travel to other parts of the body, where they influence chemical reactions and regulate various cellular functions

Proteins are made up of chains of smaller molecules

amino acids

Amino Acids

20 different acids which make up proteins

Gene

A sequence of DNA bases that specifies the order of amino acids in an entire protein, a portion of a protein, or any functional product

Mutation

A change in DNA - bases or chromosome numbers

Regulatory genes

Genes that code for the production of proteins that can influence the action of other genes - active only during certain stages of development

Homeobox (Hox) genes

An evolutionarily ancient family of regulatory genes. They direct the segmentation and patterning of the overall body plan during embryonic development

Chromosomes

Structures, composed of DNA and protein, found only in the nuclei of cells

Centromere

The constricted portion of a chromosome - after replication, the two strands of a double-stranded chromosome are joined at the centromere

Autosomes

All chromosomes except the sex chromosomes

Sex chromosomes

The X and Y chromosomes - The Y chromosome determines if it’s a male or not

Mitosis

Simple cell division -the process by which somatic cells divide to produce two identical daughter cells

Meiosis

Cell division in specialized cells in ovaries and testes - meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes

Recombination

The exchange of DNA between paired chromosomes during meiosis - also called crossing over

Clones

A clone is an organism that is genetically identical to another organism - the term may also be used to refer to genetically identical DNA segments and molecules

Principle of segregation

Genes (alleles) occur in pairs because chromosomes occur in pairs - Ex. During gamete production, the members of each gene pair separate

Recessive

Describing a trait that is not expressed in heterozygotes; also refers to the allele that governs the trait (homozygous)

Dominant

Describing a trait governed by an allele that can be expressed in the presence of another, different allele (heterozygous)

Locus (.pl., loci)

The position on a chromosome where a given gene occurs

Alleles

Alternate forms of a gene

Homozygous

Having the same allele at the same locus on both members of a chromosome pair

Heterozygous

Having different alleles at a particular locus on the members of a chromosome pair

Genotype

The genetic makeup of an individual

Phenotypes

The observable or detectable physical characteristics of an organism

Mendelian traits

Characteristics that are influenced by alleles at only one genetic locus - Ex. blood types, genetic disorders - sickle-cell anemia etc

Antigens

Large molecules found on the surface of cells - toxic foreign substances that attack blood cells

Codominance

The expression of both alleles in heterozygotes - neither allele is dominant or recessive - both influence the phenotype

Human Genome Project

An international effort that has mapped the entire human genome

Variation

Inherited differences among individuals - the basis of all evolutionary change

Allele frequency

In a population, the percentage of all the alleles at a locus accounted for by one specific allele

Population

Within a species - a community of individuals where mates are usually found

Gene flow

Exchange of genes between populations

Gene pool

The total complement of genes shared by the reproductive members of a population

Genetic drift

Evolutionary changes - changes in allele frequencies-produced by random factors - result of population size

Founder effect

A type of genetic drift in which allele frequencies are altered in small populations that are taken from, or are remnants of, larger populations

Directional change

The nonrandom change in allele frequencies caused by natural selection - change is directional - frequencies of alleles consistently increase or decrease (they change in one direction)