Genetics is all about how traits get passed down from parents to kids. It's like a blueprint for life, with genes as the building blocks. Understanding how genes work helps us predict what traits offspring might inherit.

Sometimes inheritance follows simple rules, but other times it's more complex. Factors like dominant and recessive genes, sex-linked traits, and mutations can shake things up. This diversity in inheritance patterns makes genetics fascinating to study.

Mendelian Inheritance

Genotypes to phenotypes relationship

• Genotype genetic makeup of an organism consists of alleles alternative forms of a gene
• Phenotype observable physical or biochemical characteristics determined by expression of alleles
• Dominant alleles (uppercase letters like A) mask expression of recessive alleles only one dominant allele needed for trait expression
• Recessive alleles (lowercase letters like a) only expressed when no dominant allele present two recessive alleles needed for trait expression
• Homozygous dominant (AA) and homozygous recessive (aa) genotypes result in corresponding dominant and recessive phenotypes
• Heterozygous genotype (Aa) results in dominant phenotype due to dominance of A allele over a allele

Punnett squares for genetic prediction

• Monohybrid cross mates individuals differing in one trait
• Create Punnett square by determining parent genotypes, drawing 2x2 grid, writing alleles of one parent across top and other parent along left side, and filling in possible offspring genotypes
• Genotypic ratio proportion of each genotype in offspring (1 AA : 2 Aa : 1 aa)
• Phenotypic ratio proportion of each phenotype in offspring (3 dominant : 1 recessive)
• Punnett squares predict probability of offspring genotypes and phenotypes based on parent genotypes

Purpose of test crosses

• Test cross determines genotype of individual with dominant phenotype by crossing with homozygous recessive individual
• Heterozygous (Aa) individual produces 1:1 ratio of dominant to recessive phenotypes in offspring when test crossed
• Homozygous dominant (AA) individual produces all dominant phenotype offspring when test crossed
• Perform test cross by:
  1. Crossing unknown genotype individual with homozygous recessive individual
  2. Observing offspring phenotypes
  3. Determining genotype based on offspring phenotypes

Non-Mendelian Inheritance

Mendelian vs non-Mendelian inheritance

• Mendelian inheritance follows principles of dominance, segregation, independent assortment
• Non-Mendelian inheritance deviates from these principles includes incomplete dominance and sex-linked traits
• Incomplete dominance neither allele completely dominant heterozygous individuals have intermediate phenotype (red RR and white WW flowers produce pink RW flowers)
• Sex-linked traits genes located on sex chromosomes (X and Y) males have one X and one Y, females have two X
• X-linked recessive traits more common in males who only need one recessive allele to express trait (color blindness, hemophilia)

Genetic Material and Inheritance

Heredity and genes

• Heredity is the passing of traits from parents to offspring
• Genes are segments of DNA that code for specific traits
• Genes are located on chromosomes, which are structures in the cell nucleus
• Chromosomes contain the genetic material (DNA) that is inherited

Mutations and inheritance patterns

• Mutations are changes in the DNA sequence that can alter genes
• Mutations can lead to new alleles and affect inheritance patterns
• Different inheritance patterns include:
  • Autosomal dominant
  • Autosomal recessive
  • X-linked dominant
  • X-linked recessive