Genetics SAC 1B Flashcards
Diploid
Cells with two sets of chromosomes (2n), one set derived from each parent. In humans the diploid number is 46
haploid
Cells with one set of chromosomes (n). These cells are produced by meiosis. In humans the haploid number is 23
Gene
A section of DNA that codes for a protein, basic unit of heredity.
Allele
Alternative form of a gene
Genotype
genetic makeup of an individual, wither in relation to a trait, or a set of traits. e.g. FF, Ff, ff
Phenotype
The physical, biochemical, physiological expression of the genotype. It is influenced by the environment
recessive
2 identical alleles must be present to observe the trait
autosomal
gene is located on an autosome
sex-linked
gene is located on the sex chromosome
heterozygous
2 different alleles. e.g, Ff
homozygous
2 identical alleles. e.g. FF or ff
complete dominance (dominant trait)
one allele completely masks the effect on another allele. Dominant traits are observed if only one copy of the affected allele is present.
co dominance
both alleles are expressed in a heterozygous therefore a third phenotype is observed.
multiple alleles
where there are more than two alleles for a particular gene in the population, but only 2 can ever be present in an individual. E.g. blood groups
continuous variation
many intermediate forms of the trait, which follow a normal distribution. E.g. height in humans
discontinuous variation
descrete, non-overlapping classes of phenotypes.
monogenic inheritance
trait determined by one gene with two or more alleles.
polygenic inheritance
trait determined by many genes.
Pedigree
graphic representation using standard symbols showing the pattern of occurrence of an inherited trait in a family.
Monohybrid crosses
a cross in which alleles of only one gene are involved.
Test cross
a mating (set up by humans) where an individual with the dominant phenotype is crossed/ mated with an individual with the recessive trait.
Why are test crosses used?
they can determine whether the parent with the dominant trait is homozygous or heterozygous, by observing the ratio of dominant to recessive traits in the offspring.
