Patterns of Genetic Inheritance

What is heredity and who discovered the fundamental principles of genetics?
Describe the difference between an allele, a gene, and a chromosome.
Describe the difference between genotype and phenotype, with examples.
Describe the difference between a recessive and dominant allele.
Describe the difference between a homozygous and heterozygous allele.
What is a monohybrid and dihybrid cross?
What is the expected phenotype ratio for a monohybrid and dihybrid cross?
What is an autosomal genetic disorder? Explain how they work.
What is a pedigree? What does it show?
Describe polygenic inheritance and pleiotropy.
Explain co-dominance and incomplete dominance.
Describe sex-linked inheritance, specifically X-linked disorders, and provide examples.
Know how to perform a monohybrid cross and identify parental genotypes, phenotypes, gametes, and the possible children's phenotypes, genotypes, and ratios.

Heredity: The transmission of traits from one generation to the next.
Genetics: The scientific study of heredity.
Gregor Mendel: An Austrian monk who discovered the fundamental principles of genetics during the 1860s, referred to "heritable factors".

Gene: A segment of DNA located at a specific position (locus) on a chromosome that encodes for a trait.
Allele: A variant form of a gene that arises by mutation and is found at the same place on a chromosome.
Chromosome: A long DNA molecule that contains genetic information.
Character: A heritable feature, such as flower color or seed shape, that varies among individuals.
Trait: Each variant of a character (e.g., purple or white flower color).

Diploid cell: A cell containing two complete sets of chromosomes, one from each parent.
Haploid gametes: The result of meiosis, where allele pairs separate, resulting in gametes that contain only one allele for each gene.

Genotype: The genetic composition (alleles) of an individual.
Phenotype: The observable physical or biochemical characteristics of an individual, determined by the genotype.
The relationship: Genotype influences phenotype, but environmental factors can also play a role.
Examples: For a gene with two alleles (A and a), possible genotypes include AA, Aa, and aa, leading to different phenotypes based on dominance.

Hexagonal grid for crosses: Used to calculate the probabilities of all possible genotypes and phenotypes of offspring.
Alleles classified: Dominant (mask expression of recessive alleles, written as capital letters) vs. recessive (expressed only in homozygous form).

Homozygous Dominant (AA): Both alleles are dominant.
Homozygous Recessive (aa): Both alleles are recessive.
Heterozygous (Aa): One dominant and one recessive allele.
Example: Eye color with alleles for normal pigmentation (A) and no pigmentation (a).

One-Trait Cross: Cross between two parents focusing on one trait.
- Example: Two parents without freckles (ff) producing children (all ff, no freckles).
- Homozygous Dominant and Homozygous Recessive Cross: FF (man with freckles) x ff (woman without freckles) results in all Ff (all children have freckles).

Gametes arrangement: Each side of the Punnett square represents gametes from the parents.
Expected Genotypic Ratio: 1:2:1 from a monohybrid cross.
Expected Phenotypic Ratio: 3:1 (3 dominant to 1 recessive) from a monohybrid cross.

Definition: A genetic cross examining two traits.
Example: FfSs (heterozygous for freckles and short fingers) crossing with ffss (homozygous for no freckles and long fingers).
- All offspring: FfSs (all heterozygous).
Expected Phenotypic Ratio for Dihybrid Cross: 9:3:3:1 (phenotypes expressed).

Example: Two heterozygous parents for freckles (Ff) and fingers size (Ss) crossing with phenotypes for no freckles and long fingers (ffss)
- Gamete combinations: Use FOIL method to determine possible gametes.

Genetic disorders can be passed down through dominant or recessive alleles.
Autosomal Dominant Disorders: Only one copy of the mutated gene is necessary for the condition to manifest; can be inherited from just one affected parent.
Autosomal Recessive Disorders: Requires two copies of the mutated gene for the condition to manifest.

Cystic Fibrosis
- Chromosome 7 affected.
- Primarily found in Caucasians, gene therapy is showing promising results.
Sickle-cell Disease
- Common in African Americans, leads to anemia, pain, jaundice, and other issues.
- Treatments: medications, blood transfusions, possibly marrow transplants.
Marfan Syndrome
- Affects connective tissues, managed through beta-blockers and various surgeries.
Huntington's Disease
- Late onset (30-40 years), progressive symptoms lead to life expectancy of 15-20 years post-onset.

Polygenic Inheritance: Traits controlled by multiple genes; examples include height and skin color.
Pleiotropy: One gene influences multiple phenotypic traits; for example, Marfan syndrome affects various systems in the body.

Incomplete Dominance: Results in a phenotype that is intermediate between two parental phenotypes.
- Example: Familial hypercholesterolemia.
Codominance: Both alleles are fully expressed in the phenotype.
- Example: ABO blood type (I^A and I^B together producing type AB blood).

Chromosomes: Human beings have 23 pairs, where sex chromosomes differ between the sexes: XX for females, XY for males.
X-linked Disorders: Traits associated with alleles on the X chromosome often have a recessive pattern and predominantly affect males.

Example 1: Color Blindness: Affects males more severely as they possess only one X chromosome.
Example 2: Hemophilia: Caused by the absence of essential clotting factors (Factor VIII and IX).

Pedigrees typically illustrate inheritance patterns, using squares for males and circles for females to depict affected individuals across generations.

Fragile X Syndrome: Characterized by a range of developmental issues and is the most common inherited cause of intellectual disabilities.
Hemophilia: Identified by bleeding issues due to lack of clotting factors; manageable through treatments.