Chapter 5: Chromosomes & Inheritance

Asexual Reproduction

The creation of genetically identical offspring by a single parent, without the participation of gametes (sperm and egg).

Cell Division

The reproduction of a cell.

Cell Theory

The theory that all living things are composed of cells and that all cells come from other cells.

Egg

A female gamete.

Fertilization

The union of a haploid sperm cell with a haploid egg cell, producing a zygote.

Sexual Reproduction

The creation of genetically distinct offspring by the fusion of two haploid sex cells (gametes: sperm and egg), forming a diploid zygote.

Zygote

The fertilized egg, which is diploid, that results from the union of haploid gametes (sperm and egg) during fertilization.

Centromere

The region of a chromosome where two sister chromatids are joined and where spindle microtubules attach during mitosis and meiosis. The centromere divides at the onset of anaphase during mitosis and anaphase II of meiosis.

DNA

The genetic material that organisms inherit from their parents; a double-stranded helical macromolecule consisting of nucleotide monomers with deoxyribose sugar, a phosphate group, and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T). See also gene.

Genes

A unit of inheritance in DNA (or RNA, in some viruses) consisting of a specific nucleotide sequence that programs the amino acid sequence of a polypeptide. Most of the genes of a eukaryote are located in its chromosomal DNA; a few are carried by the DNA of mitochondria and chloroplasts.

Sister Chromatids

One of the two identical parts of a duplicated chromosome. While joined, two sister chromatids make up one chromosome; chromatids are eventually separated during mitosis or meiosis II

Cell Cycle

An ordered sequence of events (including interphase and the mitotic phase) that extends from the time a eukaryotic cell is first formed from a dividing parent cell until its own division into two cells.

Cytokinesis

The last stage of the cell cycle during which the cytoplasm is divided and distributed to two new offspring cells.

Interphase

The subset of the cell cycle in eukaryotes during which the cell is not dividing and is going about its usual activities.

Mitosis

The division of a single nucleus into two genetically identical daughter nuclei. Mitosis and cytokinesis make up the mitotic phase of the cell cycle.

Mitotic Phase

The phase of the cell cycle when mitosis divides the nucleus and distributes its chromosomes to the daughter nuclei and cytokinesis divides the cytoplasm, producing two daughter cells.

Small Intestine

The longest section of the alimentary canal. It is the principal site of the enzymatic hydrolysis of food molecules and absorption of nutrients.

Anaphase

A stage of mitosis during which sister chromatids split apart, separate from each other, and move to opposite sides of the cell.

Metaphase

A stage of mitosis during which duplicated chromosomes line up at the center of the cell with each chromosome attached to the mitotic spindle.

Prophase

A stage of mitosis during which duplicated chromosomes condense and the mitotic spindle forms.

Telophase

The final stage of mitosis during which chromosomes uncondense and new nuclei form at the two poles of a cell.

Mitotic Spindle

A spindle-shaped structure formed of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis and meiosis. (A spindle is shaped roughly like a football.)

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Cell Plate

A membranous disk that forms across the midline of a dividing plant cell. During cytokinesis, the cell plate grows outward, accumulating more cell wall material and eventually fusing into a new cell wall.

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Cleavage

(1) Cytokinesis in animal cells and in some protists, characterized by pinching in of the plasma membrane. (2) In animal development, the succession of rapid cell divisions without cell growth, converting the animal zygote to a ball of cells.

Cleavage Furrow

The first sign of cytokinesis during cell division in an animal cell; a shallow groove in the cell surface near the old metaphase plate.

Clones

As a verb, to produce genetically identical copies of a cell, organism, or DNA molecule. As a noun, the collection of cells, organisms, or molecules resulting from cloning; also (colloquially), a single organism that is genetically identical to another because it arose from the cloning of a somatic cell.

Nuclear Tranplantation

A technique in which the nucleus of one cell is placed into another cell that already has a nucleus or in which the nucleus has been previously destroyed. The cell is then stimulated to grow, producing an embryo that is a genetic copy of the nucleus donor.

Reproductive Cloning

Using a somatic cell from a multicellular organism to make one or more genetically identical individuals.

Stem Cells

A relatively unspecialized cell that can give rise to one or more types of specialized cells.

Threrapeutic Cloning

The cloning of human cells by nuclear transplantation for therapeutic purposes, such as the replacement of body cells that have been irreversibly damaged by disease or injury. See also nuclear transplantation; reproductive cloning.

Diploid

Containing two sets of chromosomes (pairs of homologous chromosomes) in each cell, one set inherited from each parent; referring to a 2n cell.

Gametes

A sex cell; a haploid egg or sperm. The union of two gametes of opposite sex (fertilization) produces a zygote.

Haploid

Containing a single set of chromosomes; referring to an n cell.

Homologous Chromosomes

The two chromosomes that make up a matched pair in a diploid cell. Homologous chromosomes are of the same length, centromere position, and staining pattern and possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism’s father, the other from the mother.

Karyotype

A display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere position.

Life Cycle

The entire sequence of stages in the life of an organism, from the adults of one generation to the adults of the next.

Somatic Cells

Any cell in a multicellular organism except a sperm or egg cell or a cell that develops into a sperm or egg; a body cell.

Meiosis

In a sexually reproducing organism, the process of cell division that produces haploid gametes from diploid cells within the reproductive organs.

Crossing Over

The exchange of segments between chromatids of homologous chromosomes during prophase I of meiosis.

Down Syndrome

A human genetic disorder resulting from a condition called trisomy 21, the presence of an extra chromosome 21; characterized by heart and respiratory defects and varying degrees of mental retardation.

Nondisjunction

An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.

Trisomy 21

A human genetic disorder resulting from a condition called trisomy 21, the presence of an extra chromosome 21; characterized by heart and respiratory defects and varying degrees of mental retardation.

Alleles

An alternative version of a gene.

Character

A heritable feature that varies among individuals within a population, such as flower color in pea plants.

Dominant Allele

In a heterozygote, the allele that determines the phenotype with respect to a particular gene.

Genetics

The branch of biology that is the scientific study of inheritance.

Genotype

The genetic makeup of an organism.

Heredity

The transmission of traits from one generation to the next.

Heterozygous

Having two different alleles for a given gene.

Homozygous

Having two identical alleles for a given gene.

Phenotype

The expressed traits of an organism.

Recessive Allele

In heterozygotes, the allele that has no noticeable effect on the phenotype.

Traits

A variant of a character found within a population, such as purple flowers in pea plants.

F1 Generation

The offspring of two parental (P generation) individuals. F1 stands for first filial.

Genetic Cross

A mating of two sexually reproducing individuals.

Law of Segregation

A general rule of inheritance, first proposed by Gregor Mendel, that states that the two alleles in a pair segregate (separate) into different gametes during meiosis.

Monohybrid Cross

A mating of two organisms that are heterozygous for one character.

P Generation

The parent individuals from which offspring are derived in studies of inheritance. P stands for parental.

Punnett Square

A diagram used in the study of inheritance to show the results of random fertilization.

Testcross

The mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character.

Dihybrid Cross

A mating of two organisms that are each heterozygous for two characters.

Law of Independent Assortment

A general rule of inheritance, first proposed by Gregor Mendel, that states that when gametes form during meiosis, each pair of alleles for a particular character segregate (separate) independently of each other pair.

Carrier

An individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder.

Mutant Trait

The phenotypic trait that is less commonly observed in natural populations; the opposite of the wild-type trait.

Pedigree

A family tree representing the occurrence of heritable traits in parents and offspring across a number of generations.

Wild-Type Trait

The trait most commonly found in nature.

Codominant

A form of genetic inheritance in which a heterozygous individual displays the traits of both alleles.

Incomplete Dominance

A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa).

Multiple Alleles

The existence of more than two common versions of a gene. For example, the gene that determines human blood type (ABO) comes in three common varieties.

Pleiotropy

The control of more than one phenotypic character by a single gene.

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Polygenic Inheritance

The additive effect of two or more genes on a single phenotypic character.

Linked Genes

Genes located close enough together on a chromosome that they are usually inherited together.

Recombinant Chromosomes

Chromosomes that contain DNA sequences derived from two parents chromosomes, making them a patchwork of regions derived from both parent chromosomes.

Autosomes

A chromosome not directly involved in determining the sex of an organism; in mammals, for example, any chromosome other than X or Y.

Sex Chromosomes

A chromosome that determines whether an individual is male or female; in mammals, these are the X and Y chromosomes.

Sex-Linked Genes

A gene located on a sex chromosome.