Mendelian Genetics

• Gregor Mendel was an Austrian monk who studied genetics.
• Genetics is the scientific study of heredity.
• Fertilization produces a new cell.
• Self-pollinating occurs when sperm cells in pollen fertilize the same flower.
• Proper breeding leads to offspring identical to the parent plant.
• Cross-pollination is the process of producing seeds with two different parents.
• A trait is a specific characteristic that varies from one individual to another.
• A gene is a sequence of DNA that codes for a protein and thus determines a trait.
• The P (parental) generation is the original pair of plants.
• The F1 (first filial) generation is the offspring of the P generation.
• Hybrids are the offspring of crosses between parents with different traits.
• The F2 (second filial) generation is the offspring of crosses between F1 generation.
• Alleles are the different forms of a gene.
• Segregation refers to the separation of alleles during gamete formation.
• Gametes are sex cells (sperm and egg).

Mendel's First Conclusion

• Biological inheritance is determined by factors (genes) passed from one generation to the next.

Mendel's Second Conclusion

• Some alleles are dominant, and others are recessive.

Mendel's Third Conclusion

• The reappearance of a trait controlled by a recessive allele indicates that the allele for that trait had been separated from the dominant allele at some point.

How Mendel Discovered Allele Segregation

• Mendel observed the reappearance of traits controlled by recessive alleles in the F2 generation.

Mendel's Experiment Crossing True-Breeding Plants

• When Mendel crossed true-breeding tall plants with true-breeding short plants, the F1 generation plants were all tall.

Principle of Dominance

• Some alleles are dominant, and others are recessive. Dominant alleles mask the effect of recessive alleles when both are present in an organism.

Probability

• Probability is the likelihood that a particular event will occur.

Alleles

• A dominant allele is the more prominent trait, represented by a capital letter (e.g., T).
• A recessive allele is the less prominent trait, represented by a lowercase letter (e.g., t).
• Homozygous organisms have two identical alleles for a particular trait (e.g., TT or tt).
• Heterozygous organisms have two different alleles for the same trait (e.g., Tt).
• Phenotype refers to physical characteristics.
• Genotype refers to genetic makeup.

Punnett Squares

• Punnett Squares are primarily used to determine gene combinations.
• The principle of probability is used to predict the average outcome of a large number of events.
• Predictions are more likely to occur with a large number of events.

Examples

Tt

• Phenotype: Tall
• Allele Type: Heterozygous

tt

• Phenotype: Short
• Allele Type: Homozygous

TT

• Phenotype: Tall
• Allele Type: Homozygous

Two-Factor Crosses

• A two-factor cross involves combining two different plants and observing two traits.

Independent Assortment

• Independent assortment describes how alleles for seed shape and seed color (or any two unlinked traits) are inherited independently of each other.

Incomplete Dominance

• Incomplete dominance occurs when one allele is not completely dominant over the other, resulting in a blended phenotype.

Codominance

• Codominance occurs when both alleles contribute to the phenotype, meaning both traits are expressed simultaneously.

Polygenic Traits

• Polygenic traits are traits controlled by two or more genes.

Punnett Square Ratio

• A Punnett Square for a dihybrid cross predicts a phenotype ratio of 9:3:3:1 in the F2 generation.

Independent Assortment Account

• Independent assortment accounts for the different combinations of traits, such as seed shape and color.

Example of Codominance

• Codominance is seen in chickens that have both black and white feathers.

Multiple Alleles

• Multiple alleles occur when there are more than two forms of a gene in a population.

Example of Polygenic Trait

• Skin color in humans is an example of a polygenic trait determined by multiple genes.

Mendel’s Principles of Genetics

• Traits separate from each other during reproduction. Traits can mix, leading to new combinations, and some traits can dominate over others.

Chromosomes

• Chromosomes are the structures that carry genes and determine many characteristics.

Chromatids

• Chromatids are the two identical copies of a chromosome that are joined together.

Homologous Chromosomes

• Homologous chromosomes are pairs of chromosomes that contain the same genes.

Tetrad

• A tetrad forms when homologous chromosomes pair up during meiosis I.

Diploid

• Diploid cells contain both sets of homologous chromosomes (2n).

Haploid

• Haploid cells contain only one set of homologous chromosomes (n).

Meiosis

• Meiosis is the process of reduction division that reduces the chromosome number in half to produce gametes.

Crossing Over

• Crossing over is the exchange of genetic material between homologous chromosomes during meiosis I.

Sperm and Eggs

• Sperm are the result of meiosis in male cells.
• Eggs are the result of meiosis in female cells.

Importance of Genetic Copies

• Each organism must inherit a single copy of every gene from each parent for Mendel’s principles to work.

Daughter Cells

• Meiosis produces four daughter cells.

Steps of Meiosis I

Prophase I

• Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Metaphase I

• Homologous chromosomes line up in the middle of the cell.

Anaphase I

• Fibers pull homologous chromosomes toward opposite ends of the cell.

Telophase I and Cytokinesis

• Telophase I: The nuclear membrane forms.
• Cytokinesis: The cell separates into two cells.

Meiosis II

• Meiosis II goes through the splitting process again to make four daughter cells, each with a haploid number of chromosomes.

Mitosis vs. Meiosis

Mitosis

• Cell Type Produced: 2 identical cells
• Number of Daughter Cells: 2
• Number of Cell Divisions: 1
• Daughter Cells: Diploid
• Purpose: Replace damaged cells.

Meiosis

• Cell Type Produced: 4 haploid cells
• Number of Daughter Cells: 4
• Number of Cell Divisions: 2
• Daughter Cells: Haploid
• Purpose: Create male and female reproductive cells.

Comparison

• Mitosis produces identical copies of cells, while meiosis produces genetically different cells.
• Mitosis results in diploid cells, while meiosis results in haploid cells.

Genetic Material

• Mitosis produces genetic copies, while meiosis produces four unique cells.

Diploid Cell Chromosomes

• A diploid cell contains both sets of homologous chromosomes.

Haploid Cell Chromosomes

• A haploid cell contains one set of chromosomes.

Homologous Chromosomes

• Homologous chromosomes are pairs of chromosomes that carry the same genes but may have different alleles. They are important in meiosis because they allow for genetic recombination through crossing over, increasing genetic variation.