Genetics PDF

**Genetics** - **Inherited Traits.** Traits are inherited through the passing of genes from parents to their offspring. Genes are units of heredity made up of DNA and are located on chromosomes within the cells of all living organisms. Here's a simplified overview of how traits are inherited: -...

**Genetics** - **Inherited Traits.** Traits are inherited through the passing of genes from parents to their offspring. Genes are units of heredity made up of DNA and are located on chromosomes within the cells of all living organisms. Here's a simplified overview of how traits are inherited: - **Genes and Alleles:** Each gene ha different forms called alleles. For example, a gene for eye color might have an allele for blue eyes and another for brown eyes. - **Inheritance from Parents:** Offspring inherit one allele for each gene from each parent, resulting in a pair of alleles for each trait. These alleles can be the same (homozygous) or different (heterozygous). - **Dominant and Recessive Alleles:** Alleles can be dominant or recessive. A dominant allele will express its trait even if only one copy is present, while a recessive allele only expresses its traits if both alleles in the pair are recessive. For example, if brown eye color (B) is dominant and blue (b) is recessive, an individual with alleles BB or Bb will have brown eyes, while only bb will result in blue eyes. - **Genotype and Phenotype:** The combination of alleles an individual has is called the genotype (BB, Bb, or bb). The observable is called the phenotype (brown or blue eyes). - **Mendelian Inheritance:** This basic inheritance pattern was first described by Gregor Mendel, who discovered how traits are passed down through dominant and recessive alleles. More complex patterns include incomplete dominance, codominance, polygenic inheritance (where multiple genes influence a trait), and environmental factors affecting gene expression. - **Homologous Chromosomes.** During meiosis, homologous chromosomes are randomly distributed into gametes (sperm and egg cells), which ensures genetic variation in the resulting offspring. Meiosis involves two key processes that contribute to this randomness: 1. **Independent Assortment:** During metaphase I of meiosis, homologous pairs of chromosomes line up at the cell's equator. The orientation of each pair is random, meaning that any combination of maternal and paternal chromosomes can be segregated into the gametes. This random distribution results in numerous potential combinations of chromosomes in the gametes. 2. **Crossing Over (Recombination):** In prophase I of meiosis, homologous chromosomes can exchange segments of genetic material through a process called crossing over. This further increases genetic diversity by creating new combinations of alleles on each chromosome. These randomly assorted chromosomes, each carrying different alleles, are then passed to the next generation when gametes fuse during fertilization. This randomness ensures that offspring inherit a unique mix of genes from both parents, contributing to genetic variation within a population. - **Breakdown of Terms.** **Genes** - **Definition:** A gene is a specific segment of DNA that codes for a particular protein or function, ultimately influencing a trait of characteristics in an organism. - **Function:** Genes are responsible for the inheritance and expression of traits, such as eye color, hair texture, and blood type. **Alleles** - **Definition:** Alleles are different versions or forms of a gene. Each gene can have multiple alleles that contribute to variations in a particular trait. - **Example:** For a gene that determines eye color, one allele might code for blue eyes while another allele might code for brown eyes. - **Relationship to Genes:** While a gene is a broader concept referring to a location on a chromosome that influences a trait, alleles are the specific variations of that gene. **Homologs (Homologous Chromosomes)** - **Definition:** Homologs refer to pairs of chromosomes that are similar in size, shape, and genetic content. One chromosome of each homologous pair comes from the mother, and the other comes from the father. - **Characteristics:** Although homologous chromosomes carry the same genes in the same order, they can have different alleles for those genes. For example, a pair of homologous chromosomes may both carry a gene for eye color, but one may carry an allele for brown eyes while the other carries an allele for blue eyes. - **Role in Meiosis:** Homologous chromosomes pair up during meiosis and undergo processes like crossing over, which increases genetic diversity in the resulting gametes. This difference helps clarify that while genes are the fundamental units of heredity, alleles represent the variation that lead to different traits, and homologs are chromosome pairs that facilitate genetic recombination and assortment during meiosis. - **Inheritance Patterns** 1. **Complete Dominance** (Simple Dominance, Mendelian Inheritance) [Complete dominance - Definition and Examples - Biology Online Dictionary[1,920 × 1,080]](https://www.biologyonline.com/dictionary/complete-dominance) 2. **Codominance** 3. **Incomplete Dominance** 4. **Multiple Alleles**  5. **Polygenic** polygenic trait definition and examples - **Mendel's Two Laws of Inheritance.** 1. **Mendel's Law of Segregation (1^st^ Law):** This law states that each individual has two alleles for each gene (one from each parent), and these alleles segregate (separate) during gamete formation. As a result, each gamete receives only on allele. This explains why offspring inherit one genetic allele from each parent, leading to the formation of a new pair in the offspring. 2. **Mendel's Law of Independent Assortment (2^nd^ Law):** This law states that alleles for different genes are distributed to gametes independently of one another. This means that the inheritance of one trait (flower color) does not influence the inheritance of another trait (seed shape), provided the genes for these traits are located on different chromosomes or are far apart one the same chromosome. Together, these laws form the basis of classical genetics, explaining how traits are passed from parents to offspring through predictable patterns. - **Mendel's Discovery of Inheritance.** 1. **Chose Pea Plants:** He worked with pea plants because they had clear, simple traits and were easy to breed. 2. **Controlled Breeding:** He carefully controlled which plants mated with each other. 3. **Counted Results:** He kept detailed records and counted the number of plants with different traits. 4. **Studied One Trait at a Time:** He started by looking at one trait at a time (like flower color) to see how it was passed down. 5. **Used Large Numbers:** He used a lot of plants in experiments to get reliable results. These methods allowed Mendel to see clear patterns in how traits were inherited, leading to his two key laws of inheritance.