Chapter 12 Assesment

Key Vocabulary

• Genetics – The study of heredity and variation in organisms.

• Fertilization – The process in sexual reproduction where male and female gametes unite.

• Trait – A specific characteristic of an organism.

• Hybrid – Offspring resulting from the cross of parents with different traits.

• Gene – A segment of DNA that determines a trait.

• Allele – Different forms of a gene.

• Principle of Dominance – Mendel’s principle stating that some alleles are dominant while others are recessive.

• Segregation – The separation of alleles during gamete formation.

• Gamete – A reproductive cell (sperm or egg).

• Probability – The likelihood of a particular genetic outcome.

• Homozygous – Having two identical alleles for a trait.

• Heterozygous – Having two different alleles for a trait.

• Phenotype – The physical appearance of an organism.

• Genotype – The genetic makeup of an organism.

• Punnett Square – A diagram used to predict genetic crosses.

• Independent Assortment – The principle that genes for different traits segregate independently.

• Incomplete Dominance – A genetic situation where neither allele is completely dominant.

• Codominance – A genetic scenario where both alleles are fully expressed.

• Multiple Alleles – More than two possible alleles for a gene.

• Polygenic Trait – A trait controlled by multiple genes.

• Homologous – Chromosomes that have corresponding genes.

• Diploid – A cell with two sets of chromosomes.

• Haploid – A cell with one set of chromosomes.

• Meiosis – The process of cell division that produces gametes.

• Tetrad – A group of four chromatids formed during meiosis.

• Crossing-over – The exchange of genetic material between homologous chromosomes.

Mendel’s Experiments

• Why Pea Plants?

  • Pea plants were ideal because they had distinct traits, could self-pollinate, and had a short generation time.

• True Breeding Plants

  • True breeding plants ensured Mendel could track inheritance patterns without unexpected variations.

Mendel’s Principles

1. Principle of Dominance – Some alleles are dominant, while others are recessive.

2. Law of Segregation – Alleles separate during gamete formation.

3. Law of Independent Assortment – Genes for different traits segregate independently.

Punnett Squares

Monohybrid Cross

• A cross between two organisms focusing on one trait.

• Example: Crossing a heterozygous tall plant (Tt) with another heterozygous tall plant (Tt).

Dihybrid Cross

• A cross involving two traits.

• Example: Crossing a plant with round yellow seeds (RrYy) with another plant with round yellow seeds (RrYy).

Exceptions to Mendel’s Principles

• Incomplete Dominance – Example: Red and white flowers producing pink offspring.

• Codominance – Example: A cow with both red and white fur patches.

• Environmental Influence – Traits can be affected by surroundings (e.g., temperature affecting fur color in rabbits).

Meiosis

Meiosis is a special type of cell division that occurs in organisms that reproduce sexually. Its primary function is to create gametes (sperm and egg cells) with half the number of chromosomes found in a normal body cell.

Key Features of Meiosis:

• Produces haploid cells (cells with only one set of chromosomes)

• Two rounds of division (Meiosis I and Meiosis II)

• Ensures genetic diversity through crossing-over and independent assortment

Phases of Meiosis:

• Prophase I – Chromosomes condense, homologous chromosomes pair up to form tetrads, and crossing-over occurs (exchange of genetic material).

• Metaphase I – Homologous chromosome pairs align in the center of the cell.

• Anaphase I – Homologous chromosomes are pulled apart to opposite sides. Telophase I – Nuclear membranes reform around the two sets of chromosomes, and the cell begins to divide through cytokinesis. Meiosis II – Similar to mitosis, the sister chromatids of each chromosome are separated, leading to the formation of four haploid cells by the end of the process.

• Telophase I & Cytokinesis – Two haploid daughter cells form. 5⃣ —-Prophase II – Chromosomes condense again in the haploid cells. 6⃣ Metaphase II – Chromosomes line up in the center. 7⃣ Anaphase II – Sister chromatids (duplicated chromosome copies) separate. 8⃣ Telophase II & Cytokinesis – Four haploid gametes are formed.

Why Is Meiosis Important?

• Genetic diversity: Mixing of parental genes makes each individual unique.

• Prevents chromosome doubling: Ensures offspring inherit the correct number of chromosomes.

• Allows sexual reproduction: Without meiosis, fertilization wouldn’t produce viable offspring.

Would you like to go over diagrams or practice questions related to meiosis? 😊

Phases of Meiosis

1. Prophase I – Chromosomes condense, tetrads form, crossing-over occurs.

2. Metaphase I – Homologous chromosomes align in the center.

3. Anaphase I – Homologous chromosomes separate.

4. Telophase I & Cytokinesis – Two haploid cells form.

5. Prophase II – Chromosomes condense again.

6. Metaphase II – Chromosomes align in the center.

7. Anaphase II – Sister chromatids separate.

8. Telophase II & Cytokinesis – Four haploid cells form.

Genetic Diversity in Meiosis

1. Crossing-over – Exchange of genetic material.

2. Independent Assortment – Random distribution of chromosomes.

3. Random Fertilization – Any sperm can fertilize any egg.

Comparing Mitosis and Meiosis