Lesson 4: Basic Genetics

Study Notes

Gregor Mendel is considered the father of genetics. He conducted experiments with pea plants to understand inheritance.
True-breeding organisms consistently produce offspring with the same traits when self-pollinated.
Hybrids are offspring from crosses of two different true-breeding parents.
Monohybrid crosses examine the inheritance of a single trait.
Punnett squares predict the genotype and phenotype ratios of offspring.
Homozygous dominant = two dominant alleles (e.g., AA).
Heterozygous = one dominant and one recessive allele (e.g., Aa).
Homozygous recessive = two recessive alleles (e.g., aa).
The Law of Segregation states that alleles for a gene separate during gamete formation.
Alleles are different forms of a gene, which can be dominant or recessive.
Dominant alleles mask the effect of recessive alleles in heterozygotes.
Genotype refers to the genetic makeup (e.g., Aa), and phenotype refers to the physical expression of a trait (e.g., brown eyes).

Codominance: Both alleles are fully expressed in the heterozygote (e.g., AB blood type).
Incomplete dominance: A blend of traits from both alleles (e.g., red and white flowers producing pink).
Blood types (A, B, AB, O) are determined by codominant alleles (IA, IB, i) and involve multiple alleles.

X-linked traits are carried on the X chromosome; they are more common in males.
Y-linked traits are carried on the Y chromosome and are passed from father to son.

Multi-trait inheritance involves studying multiple traits simultaneously.
Dihybrid crosses examine the inheritance of two traits at once (example: AaBb x AaBb).
4 x 4 Punnett squares are often used for dihybrid crosses.
The Law of Independent Assortment states that genes for different traits segregate independently during gamete formation.
The product law determines the probability of two independent events occurring together, which is the product of their individual probabilities.
Discontinuous traits have distinct categories. Continuous traits vary over a range of phenotypes (example: height).

DNA is composed of nucleotides with a sugar, phosphate group, and nitrogenous base.
Nitrogenous bases include A, G, T, and C (Adenine, Guanine, Thymine, Cytosine).
Nucleotides are the basic building blocks of DNA.
Mutations are changes in DNA sequence, which can be point mutations or chromosomal mutations. Mutations in germ cells can be inherited.
Examples of genetic disorders include hemophilia and color blindness.
Lactose intolerance is a common condition where individuals lack the enzyme to digest lactose.
Antibiotic resistance in bacteria results from mutations that allow bacteria to survive antibiotic treatments.