Mendelian Genetics Flashcards
Allele
The alternate forms of a gene
Loci
The location of the gene on the chromosome
Genotype
The combination of alleles for a trait e.g., Rr. The collection of alleles that an individual contains (i.e., the letter ‘code’)
Phenotype
The physical appearance of a trait. It is based in genotype e.g., RR and Rr can be described as a round pea seeds; whereas rr can be described as a wrinkled pea seed
Dominant
The form of a trait that will always appear (be expressed) when an individual has an allele for it. If one dominant allele is present, then the dominant trait will be expressed (E.g: Rr or RR = round pea.)
Recessive
The form of a trait that will only appear (be expressed) if the individual has 2 alleles for it. E.g: rr = wrinkled pea
Homozygous
Describes the genotype of an individual with two alleles that are the same, e.g., RR or rr
RR = homozygous dominant round seed
rr = homozygous recessive wrinkled seed
Heterozygous
Describes the genotype of an individual with two alleles for the same gene that are different, e.g., Rr is a heterozygous round seed.
Punnett Square
A chart used by geneticists to show possible combinations of alleles in offspring. Provides a clear, simple view of the crossing of traits, especially when more than 1 trait is being examined.
Monohybrid Cross
A cross where only one trait is being tested.
Dihybrid Cross
A cross where two traits are being tested.
Autosomal inheritance – autosomal dominant vs. autosomal recessive – only definitions with genotype examples.
- Autosomal Inheritance: Inheritance of traits from genes located on the autosomes (not sex chromosomes- in humans #1- 22)
- Autosomal dominant: Occurs when the disease-causing allele is dominant and the individual has one or both copies of the allele
- Autosomal recessive: Occurs when the disease-causing allele is recessive and an individual has both copies of the allele
