Dominant characters : In a cross, the characters which express themselves by covering the other characters are called dominant characters.
Recessive characters : In a cross those characters which are present but cannot express themselves due to the presence of dominant characters which are present but cannot express themselves due to presence of dominant characters is called recessive characters.
Allele or Allemorphs : A pair of genes controlling a pair of contrasting characters is known as allele pair.
Phenotype : The external appeareance of an organism for a cvontrasting character is called phenotypee. It is expressed in words for example: tall, dwarf etc.
Geno type: The genetic make up or genetic constitution of an organism is called genotype. It is expressed in letters for example : TT (pure tall), Tt hybrid tall, tt pure dwarf. etc
Some of the important terms in genetics are :
Allele : One of two or more alternate forms of a gene or marker at a particular locus on a chromosome.
Anticipation (genetic) :Apparent earlier age of onset and increased severity of a disease in successive generations, eg, Huntington's disease.
cDNA :Single-stranded complementary DNA, ie, a DNA molecule synthesized from a RNA template by reverse transcription of RNA.
Common disorder common variant (CDCV) hypothesis : A theory that many common diseases are caused by common alleles that individually have little effect, but in concert confer a high risk.
Complex disease : A disorder in which the cause is considered to be a combination of genetic effects and environmental influences.
Comparative genome hybridization (CGH) : CGH is a molecular-cytogenetic method for the analysis of copy number changes (gains or losses) in the DNA content of a given individual's DNA.
Compound heterozygosity : Heterozygosity for two different mutant alleles of a gene, often the case for autosomal recessive disorders.
Copy number variation (CNV) : A segment of DNA in which copy number differences have been found by comparison of two or more genomes. The segment may range from one kilobase to several megabases in size. The variation is usually due to deletion or duplication.
Genotype : The genetic constitution with respect to the alleles at one or more pairs of genetic loci under observation. The genotype of an individual is the sum total of the genetic information contained on the chromosomes, as distinguished from the individual's phenotype (idiotype).
Haploid : A single genome or set of chromosomes (eg, in human gametes, n=23), compared to the normal diploid (double) set of chromosomes (n=46)
Haplotype :A combination of alleles at closely linked gene loci that are inherited together.
Hemizygous : When one or more genes is present in only one, instead of two copies, eg, men are hemizygous for most genes on the X and Y chromosomes.
Heterozygous : Having different alleles for one or more genes in homologous chromosome segments, as opposed to being homozygous with identical alleles at these loci.
Linkage :Genetic linkage refers to the observation that two or more genes located on the same chromosome are inherited together. The ratio of being transmitted together versus being separated allows an estimate of their distance from each other (recombination fraction).