GENETICS TERMINOLOGY - A GLOSSARY

1. haploid - the condition of having only one set of chromosomes per cell (n)

2. diploid - the condition of having two sets of chromosomes per cell (2n)

3. gamete - a haploid (n) sex cell in plants and animals (egg or sperm)

4. zygote - diploid (2n) cell resulting from the union of two gametes in sexual reproduction

5. chromatin - the complex of DNA, RNA and proteins that makes up uncondensed eukaryotic chromosomes.

6. chromosome - structures within the nucleus of eukaryotic cells composed of chromatin and visible at cell division (condensed chromatin).

7. homologous chromosomes - chromosomes that are similar in morphology (shape and form) and genetic constitution. In animals one set comes from the father and the other from the mother.

8. chromatids - one of the two halves of a duplicated chromosome

9. centromeres - specialized constricted region of a chromatid, that contains the kinetochore; sister chromatids are joined at the centromere during cell division

10. recombination - exchange of genetic material between chromosomes

11. crossover - the breaking and rejoining of homologous (non-sister) chromatids during early prophase I of meiosis, resulting in recombination

12. synapsis - the pairing of homologous chromosomes during prophase I of meiosis.

13. disjunction - separation of homologous chromosomes (or sister chromatids) during anaphase.

14. genotype - the genetic make-up (the assemblage of alleles) of an individual.

15. phenotype - the physical or chemical expression of an organismís genes.

16. gene - a discrete unit of hereditary information that usually specifies a protein; a region of DNA (locus) located on a chromosome that specifies a trait (characteristic).

17. alleles - genes governing variations of the same characteristic (trait) that occupy corresponding positions (loci) on homologous chromosomes; alternative forms of a gene.

18. dominant allele - an allele that is always expressed when present, regardless of whether the organism is homozygous or heterozygous for that gene.

19. recessive allele - an allele that is only expressed when the organism is homozygous for that allele and not expressed when heterozygous (when paired with a dominant allele).

20. homozygous - possessing a pair of identical alleles for a particular locus (gene).

21. heterozygous - possessing a pair of unlike alleles for a particular locus (gene).

22. carrier - a heterozygous individual not expressing a recessive trait but capable of passing it on to its offspring.

23. parent generation (P) - the generation that supplies gametes to the filial generation.

24. filial generation (F,) - the generation that receives gametes from the parental generation.

25. hybrid - an offspring resulting from the mating between individuals of two different genetic constitutions.

26. dihybrid cross - a genetic cross that takes into account the effect of alleles at two separate loci (two different genes).

27. monohybrid cross - a genetic cross that takes into account the effect of alleles at a single locus (single gene).