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Know definitions of the words used for Meiosis, Mendel's work and Genetics

Dominant – expression that is always expressed when its gene

recessive - An expression that is expressed only when its allele is the only form of the gene present in the genotype.

incomplete dominance - Neither allele is dominant to the other, thus each is expressed in the heterozygous genotype producing an intermediate phenotype. EX. Red (RR) and White (R’R’) snapdragons produce pink (RR’).

epistasis - A condition in which one gene pair has the ability to mask or prevent the expression of another gene pair. EX. Coat color and pigment deposition in mice.

co-dominance - Inheritance characterized by full expression of both alleles in the heterozygote. Ex. Short HornCattle. Red (RR), Roan (RR’), White (R’R’)

homozygous – condition where both genes are the same (AA or aa)

heterozygous – condition where genes are different (Aa)

alleles – different forms of the same gene (Aa)

mutation – a change in the nucleotide sequence of an organism’s DNA or in the DNA or RNA of a virus

locus – location of the gene on the chromosome

gene - The unit of DNA along a chromosome that codes for a single characteristic, unit of dna that codes for a specific polypeptide

synapsis - Pairing of homologous chromosomes called

cross-over - The exchange or mixing of similar genetic material (genes) is called

chiasmata - There is a criss-crossing of the non-sister chromatids called

gene – unit of dna that codes for a specific polyeptide or characteristic

karyotype - A display of metaphase chromosomes in which homologues are paired together and photographed.

non-disjunction – an error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from eachother

pleiotrophy - The ability of a single gene pair to have multiple effects. EX. Gene for Sickle-cell Anemia.

Polyploidy – a chromosomal alteration in which the organism possesses more than 2 complete chromosome sets. It is the result of an accident of cell division

aneupliody – a chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number

monosomy – diploid cell that has only one copy of a particular chromosome instead of the normal two

trisomy – diploid cell that has three copies of a particular chromosome instead of the normal two

amneocentesis – a technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.

chorionic villus sampling – a technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.

sex chromosomes – chromosomes involved in sex determination, in man these are the X and Y chromosomes oogenesis

spermatogenesis – continuous and pro-life production of mature sperm cells in the testes.

polygenic inheritance - A characteristic that is determined by the quantitative effect of multiple pair of genes.

duplication – an aberration in a chromosome structure due to fusion with a fragment of a homologous chromosome, such that a portion of a chromosome is duplicated

translocation – an aberration in chromosome structure resulting from attatchment of a chromosomal fragment to a non homologous chromosome. In a translocation a portion of a chromosome breaks and rejoins with a non-homologous chromosome. This type of abnormality can result in an increased number of genes in a gamete or can impact coordination of a metabolic path.

deletion - A portion of a chromosome is lost from the genome, thus these genes are not present in the gamete. The lose of genes from the genotype is serious and often...
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