Law of Independent Assortment
The alleles of different genes are distributed to the egg and sperm cells independently of each other during meiosis.
Mendel’s Second Law
Law of Independent Assortment (ONLY PARTIALLY CORRECT)
Incomplete Dominance
Heterozygous genotype results in a phenotype that is in between the two homozygous conditions
Incomplete Dominance Example
In Caucasians, curly hair (cc) combined with straight hair (ss) results in an offspring with wavy hair (sc)
Co-dominance
- A pair of non-identical alleles specify two different phenotypes
- If both non-identical alleles are inherited, both phenotypes are expressed equally
Co-dominance Example:
Blood types
- Have three (3) possible alleles: A, B and O
- O is recessive, A & B are co-dominant
Polygenetic Inheritance
Examples
Phenotype is influenced by multiple genes working together
Polygenetic Inheritance Examples
Eye color is controlled by at least 3 genes and can result in a range of different eye color phenotypes (nearly black to light blue)
Height, body size and shape are polygenic
Polygenetic Inheritance Characteristics
Tend to have a continuous range of variation in the population (more people in the middle and fewer people at the extremes) (BELL CURVE)
Heritable diseases
Our genes make us more susceptible to increased risk for conditions such as skin cancer, high cholesterol and heart diseasex
Environmental Influences
Interdependence between genes & the environment
Epigenetics (2)
Study of how traits can be changed or passed down without changing the DNA sequence itself.
Looks at how genes are turned “on” or “off” by factors like environment, lifestyle, or age.
Epigenetics Examples
- Environmental factors can modify the DNA without changing the nucleotide sequence
- Adding a methyl (-CH3) group to DNA regions or changing the way DNA is wound around histones
Linked Alleles DEF
Many alleles for different traits are often inherited together because they are physically “linked” or joined on the same chromosome
However, they are NOT always inherited together - may get shuffled during crossing-over in meiosis I
The likelihood of inheriting the two alleles together is dependent on: (2)
- How close together the two alleles are on the chromosome (the closer they are, the higher the chance of them staying together)
- How often crossing-over occurs (the more cross-over the lower the chance of the alleles staying together)
Genetic Pedigrees can be used to:
- Shows typical inheritance patterns in a chart form
- Uses standard methods, definitions and symbols
- Relies on knowledge of probability and Mendelian genetics
Punnett squares help to determine ______________ expression
- phenotype
