BIO101 Unit 13
Meiosis, Organismic Reproduction
& Genetics
Glossary
alleles
one member of a pair of genes that occupy a specific position on a specific chromosome that affect the same trait.
asexual reproduction
Type of reproduction that usually requires only one parent and only one sex cell.
binary fission
a type of asexual reproduction which occurs when a unicellular organism divides into two unicellular organisms by mitosis.
blastocyst
early stage of human embryonic development that consists of a hollow fluid-filled ball of cells that implants in the uterus wall of the female.
blastula
hollow ball of cells occurring during the first stages of animal embryonic development prior to the gastrula stage; 23 to 32 cells big.
budding
A type of asexual reproduction which occurs when a new organism grows directly off an adult.
cleavage
rapid cellular divisions that occur during the first stages of animal development; usually occurs without cytoplasmic increases or cellular enlargement.
conjugation
The type of sexual reproduction when there is a temporary union between two individuals in which genetic material is exchanged; usually this occurs between two unicellular organisms.
dominant allele
A gene which is always expressed when present.
diploid
the normal number of chromosomes; (2n) twice the number of chromosomes found in a gamete.
egg
female sex cell; also referred to as ovum.
ectoderm
the outer germ layer of the gastrula stage that gives rise to the nervous system, epidermis layer of the skin, and lining of the oral cavity and the rectum.
endoderm
the inner layer of the gastrula stage that gives rise to the lining of the digestive, urinary and respiratory systems.
fertilization
union of the sperm nucleus and the egg nucleus which creates the zygote with a diploid number of chromosomes.
gamete
a haploid sex cell; the egg or sperm which contain one-half the normal number of chromosomes; the egg unites with a sperm to form the zygote during fertilization.
gastrula
an early cleavage stage of embryonic development between 32 and 64 cells big which results in the formation of the three germ layers: ectoderm, mesoderm and endoderm.
gene locus
the position that a given gene occupies on a chromosome.
genetics
The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms
genotype
the combination of alleles (genes) located on homologous chromosomes that determines a specific characteristic or trait.
gonads
an organ that produced gametes; testes produce sperm, and the ovary produces eggs.
haploid
one-half the normal number of chromosomes; (n) sex cells are haploid cells.
heredity
the biological process whereby genetic factors are transmitted from one generation to the next; the total of inherited attributes; the transmission of traits from ancestor to descendant.
Inheritance
the process of genetic transmission of characteristics from parents to offspring; the sum of characteristics genetically transmitted from parents to offspring.
meiosis
the cellular division process that results in the production of sex cells; this process is a reduction division because the number of chromosomes in the sex cells is reduced by one-half.
mesoderm
the middle layer of the gastrula stage that gives rise to the muscles, skeleton and urinary, circulatory and reproductive systems.
monohybrid cross
a one-trait genetic cross; a genetic cross involving only one characteristic such as hairline.
morula
ball like cleavage stage of embryonic development resembling a mulberry 8 to 16 cells big.
oogenesis
production of eggs in females by the process of meiosis.
phenotype
The observable physical characteristics of an organism, as determined by the organisms genetic makeup; the expression of a specific trait, such as hair color or blood type, based on genetic makeup of an organism.
recessive allele
A gene or allele which is only expressed in the absence of a dominant gene (allele).
regeneration
a type of asexual reproduction which occurs a piece of an organism will develop into a new organism.
sperm
male sex cell.
spermatogenesis
production of sperm in males by the process of meiosis.
syngamy
a type o sexual reproduction between two unicellular organisms that temporarily fuse to exchange genetic material.
zygote
a fertilized egg; a diploid cell formed by the union of egg and sperm.