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24 Cards in this Set

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Glossary
CHAPTER 9
allele
One of two or more molecular forms of a gene that arise by mutation and code for different versions of the same trait.
asexual reproduction
Any reproductive mode by which offspring arise from a single parent and inherit the genes of that parent only.
chromosome number
All chromosomes in a given type of cell. See haploidy; diploidy.
crossing over
At prophase I of meiosis, an interaction in which nonsister chromatids of a pair of homologous chromosomes break at corresponding sites and exchange segments; genetic recombination is the result.
diploidy
Presence of two of each type of chromosome (i.e., pairs of homologous chromosomes) in a cell nucleus at interphase. Compare haploidy.
egg
Mature female gamete; an ovum.
fertilization
[L. fertilis, to carry, to bear] The fusion of a sperm nucleus with the nucleus of an egg, thus forming a zygote.
gamete
[Gk. gametes, husband, and gamete, wife] Haploid cell, formed by meiotic cell division of a germ cell; required for sexual reproduction. Eggs and sperm are examples.
gene
[German pangan, after Gk. pan, all; genes, to be born] Unit of information for a heritable trait, passed from parents to offspring.
germ cell
Animal cell of a lineage set aside for sexual reproduction; gives rise to gametes.
haploidy
Presence of only half of the parental number of chromosomes in a spore or gamete, as brought about by meiosis.
homologous chromosome
One of a pair of chromosomes that are identical in size, shape, and the genes they carry, and that line up with each other at meiosis I. The X and Y chromosomes differ in these respects but still function as homologues.
life cycle
A recurring pattern of genetically programmed events from the time individuals are produced until they themselves reproduce.
meiosis
[Gk. meioun, to diminish] Two-stage nuclear division process that halves the chromosome number of a parental germ cell nucleus, to the haploid number. Basis of gamete formation (and meiospore formation).
oocyte
Type of immature egg.
oogenesis
Process by which a germ cell develops into a mature oocyte.
prophase I
First stage of meoisis I. Each duplicated chromosome starts to condense. It pairs with its homologue; nonsister chromatids usually undergo crossing over and are attached to spindle. One pair of duplicated centrioles (if present) is moved to the opposite spindle pole.
prophase II
First stage of meiosis II. Spindle microtubules attach to each chromosome and move them to spindle's equator. A centriole pair (if present) is already at each spindle pole.
sexual reproduction
Production of offspring by meiosis, gamete formation, and fertilization.
sister chromatid
Of a duplicated chromosome, one of two DNA molecules (and associated proteins) attached at the centromere until they are separated from each other at mitosis or meiosis; each is then a separate chromosome.
sperm
[Gk. sperma, seed] Mature male gamete.
spermatogenesis
Formation of mature sperm from a germ cell.
spore
A reproductive or resting structure of one or a few cells, often walled or coated; used for resisting harsh conditions, dispersal, or both. May be nonsexual or sexual, as formed by way of meiosis. Some bacteria as well as sporozoans, fungi, and plants form spores.