Foundational Genetic Terms
- genetics: study of heredity; parents pass traits in genes to their progeny
- genes: a gene is a stretch of DNA whose sequence determines the structure and functino of a specific funcional molecule (usually a protein)
- genes are located in Chromosomes, one pair of homologuous chromosomes such as gene for blue eyes and gene for gren eyes
- alleles: different genes for the same trait
- trait: eg blue eyes or brown eyes
- genome: complete set of chromosomes
- genotype: genetic constitution of an individual
- phenotype: physically observable trait of an individual
- dominant gene: gene that prevents the other gene from 'showing' (upper case letter)
- recessive gene: gene that does not 'show' even though it is present (lower case letter)
- homozygous (purebred): both genes of a pare are the same
- heterzygous: one dominant and one recessive gene
- Mendel's first law of segregation of alleles: cells contain 2 alleles of each gene. Alleles separate during gamete frmation (meiosis) and gametes only carry one copy of each gene.
- Mendel's second law of Independent Assortment: during gamete formation, genes for different traits separate independently into gametes because of random alignment of homolgues at meiosis I.
- exceptions to mendel's principles include incomplete dominance (when an offspring's phenotype is intermediate between the phenotypes of its parents) and Codominance when both alleles are expressed (eg chickens with black and white speckled feathers
- genes on teh same chromosome tend to be inherited together and are known as linked genes, crossing over produces gametes with recombinant chromosomes.
- There are also sex-linked traits and genes for these traits are located only on the X chromosome and always show up in males whether dominant or recessive because males only have 1 X chromosome. Examples of recesive sex-linked disorders are colour blindness and haemophilia
- basis for breed differences
- allows for animal selection
- genetic improvement of breeds
- determines extent of response to selection in breeding systems
Learn More
Crash Course Biology: Heredity
This Place: Mendelian Inheritance
Ted-ed: How Mendel's Pea Plants helped us understand Genetics
Practice Quiz for Mendel's Genetics
Questions
- define the first and second laws of mendelian inheritance,
- what is a sex-linked gene and what is its importance particularly regarding males?