AP Biology Unit 5 Recap: Heredity

Overview

Unit 5 focuses on heredity, the transmission of traits from one generation to the next.
Importance of passing down genetic information to perpetuate life.

Meiosis vs. Mitosis
- Mitosis: Cell division for growth/repair, produces exact copies (asexual reproduction).
- Meiosis: Produces gametes (sperm and eggs), enables genetic variation (sexual reproduction).
- Meiosis results in haploid cells, mitosis in diploid.
Genes and Chromosomes
- Genes: Segments of DNA encoding traits.
- Humans: 23 pairs of chromosomes. Gametes carry 23 individual chromosomes.

Genetic Variation: Crucial for evolution and survival.
Process of Meiosis
- Two divisions: Meiosis I & II.
- Meiosis I: Homologous chromosomes split, results in two haploid cells with duplicated chromosomes.
- Meiosis II: Sister chromatids separate, results in four haploid cells.
Mechanisms Creating Variation
- Independent Assortment: Random separation of homologous chromosomes.
- Crossing Over: Exchange of genetic material between nonsister chromatids in tetrads.
- Random Fertilization: Any sperm can fertilize any egg, creating diverse gene combinations.

Basic Genetics
- Study of heredity and genetic variation.
- Gregor Mendel: Father of genetics, studied inheritance using pea plants.
- Introduced concepts of dominant and recessive traits.
Mendel's Four Concepts
- Alternative versions of genes (alleles) account for variations.
- Organisms inherit two alleles per gene, one from each parent.
- Dominant alleles determine phenotype.
- Alleles segregate independently during gamete formation.
Punnett Squares: Tool to predict genotypic and phenotypic ratios.

Incomplete Dominance: Heterozygous phenotype is a blend (e.g., red x white = pink flowers).
Codominance: Both alleles are fully expressed (e.g., AB blood type).
Pleiotropy: One gene affects multiple phenotypes.
Polygenic Inheritance: Traits controlled by multiple genes (e.g., skin color, height).
Epistasis: One gene affects the expression of another gene.
Mitochondrial Inheritance: Genes inherited only from mother.
Sex-linked Genes: Located on sex chromosomes, show different inheritance patterns.
Linked Genes: Genes located on the same chromosome, tend to be inherited together.

Phenotype is influenced by both genetics and environment.
Phenotype Plasticity: Individuals with the same genotype can exhibit different phenotypes in different environments.
Examples include temperature-determined sex in reptiles and UV exposure affecting skin color.

Mechanisms Generating Variation
- Separation and independent assortment of chromosomes.
- Crossing over and random fertilization.
Genetic Disorders
- Caused by mutations in alleles or chromosomal changes.
- Examples include sickle cell anemia, cystic fibrosis, Down syndrome.
- Aneuploidy: Abnormal number of chromosomes due to nondisjunction.

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