Genetics Definitions Flashcards
Genetics
The study of inheritance
Variation
The differences between organisms
Species
A group of organisms with similar characteristics who can successfully interbreed to produce fertile offspring
Mutation
A spontaneous change in a gene or chromosome and may be inherited if present in a gamete. Eg cystic fibrosis is caused by a gene mutation i.e a change in the DNA sequence coding for a particular protein.
Mutagen
An agent that cause DNA alteration eg Nuclear radiation
Incomplete Dominance
Where neither allele is expressed in the phenotype e.g in shorthorn cattle the genotype RR gives red coat, WW gives a white coat, but RW gives a roan coat.
Sex chromosomes
These are the chromosomes which determine what sex the individual will be
XX female
XY male
Sex linkage
Genes that control characteristics other than sex and are located on the sex chromosomes
Eg haemophilia and red- green colour blindness in males
Test cross
Is a cross done to determine and unknown genotype.
The individual is always crossed with the homozygous recessive.
A tall pea plant could be TT or Tt. Cross with tt to find out.
Mitosis
A process where one cell divides to give two cells, each identical to the parent cell. Its significance is that genes are passed faithfully from one generation to the next.
Meiosis
Where one cell divides to form four cells, each with half the number of chromosomes of the parent cell and likely to be all different.
Chromosomes
Long, thread like structures found in the nucleus made up of DNA and protein. They are chains of genes.
Gene
A part of a chromosome that contains instructions for controlling a single characteristic. It is a code for making protein.
Alleles
Alternative forms of the same gene
Eg T for tall and t for dwarf
Homologous chromosomes
Pairs of chromosomes which are the same length and carry genes for the same characteristics
Heterozygous
An organism that has two different genes for the same characteristic eg Tt
Homozygous
An organism that has two identical alleles for the same characteristic eg TT or tt
Genotype
The genetic makeup of an organism eg Tt or TT
Phenotype
The physical appearance of an organism eg tall stem
Dominance
A dominant allele is one that is always expressed even if the contrasting allele is present eg Tt gives a tall plant
Recessive
The recessive allele will only be expressed if the dominant allele is not present eg tt gives dwarf the recessive characteristic but Tt gives tall
