Genes and Traits Flashcards
Hierarchy of DNA
DNA ↣ Chromosomes ↣ Genes ↣ Traits
→ Humans have 46 chromosomes (23 pairs of chromosomes)
↪ One complete set of 23 chromosome from father and one set of 23 chromosome from your mother
Genetics
The study of heredity and variation in an organism; how traits are passed on from generation to generation
Genes
Genetic material on a chromosome that codes for a trait.
Trait
A distinguishing characteristic of an individual (Can be inherited)
Inherited Trait
A characteristic transmitted from one generation to the next
Alleles
Variations of genes
→ You can contain two copies of each gene that are not identical (one from father and one from mother)
Example if fur colour was a gene, Orange fur colour and blue fur colour would be alleles.
Dominant Allele
A dominant allele is a trait that will be expressed regardless of the second allele.
Recessive Allele
A recessive allele is a trait that will be shown only if both parts of the allele are recessive. Dominant will always mask recessive traits.
Genotype
Specific alleles that make up a trait (Usually letters)
Phenotype
How the trait is expressed. If eye colour was the gene, Phenotypes would be blue or brown.
Homozygous Genotypes
These are Genotypes that have two of the same allele for a trait
→ Can be homozygous dominant if both alleles are dominant
→ Can be homozygous recessive if both alleles are recessive
Heterozygous
Having two different alleles for a trait
Incomplete dominance
A condition where neither of the two alleles for the same gene can completely mask each other.
↪ So the heterozygous offspring will demonstrate a phenotype that is a mix of the recessive and dominant traits
↪ Superscripts need to be used for incomplete dominance as there is no recessive or dominant trait (They are kinda equal)
Codominance
When both alleles are fully expressed.
For example a cow at codominant genes defining fur colour, thus the white and black fur colouration.
→ Superscripts are used for codominance as both genes are expressed so there is no dominant or recessive
Polygenic Traits
Traits that need more than one gene to be expressed (most traits are polygenic).
Pleiotropic Genes
Genes that affect how many other genes will be expressed.
A Note on Mendel
In 1853 an Austrian Monk set out to explain heredity and took 8 years to complete his studies using pea plants.
He used pea plants as they have a short reproductive cycle, are easy to grow, distinguishable characteristics such as short vs long stems, wrinkled vs smooth, self pollinate (both pistil and stamen in same flower) so cross-pollination was easy to perform and keep track of, easily accessible in Europe in the time period.
Purebred | Truebred
Purebred is just organisms with homozygous traits. In Mendel’s experiments these were used as the parent generation.
Carrier | Hybrid
Heterozygous traits. In Mendel’s experiments the F1 generation were hybrids.
Mendel Disapproved
Theory of blended Inheritance
Multiple Allelism
When there are more than two possible alleles for a given gene (e.g. eye color, ABO blood types), results in a larger number of possible genotypic combinations and a greater variety of phenotypes.
Inbreeding is discouraged because
It increases chances the risks of recessive gene disorders. Since people are in the same blood pool there is a high chance that two inbred partners will both carry the recessive gene.
