Cellular Reproduction and Patterns of Inheritance: Study Guide for BIO 110 Exam 4

Cellular Reproduction

Types of Reproduction

Reproduction is the biological process by which new organisms are generated. There are two main types:

• Asexual reproduction: Offspring are produced from a single parent without the fusion of gametes. The offspring are genetically identical to the parent. Example: Binary fission in bacteria.

• Sexual reproduction: Offspring are produced by the fusion of gametes from two parents, resulting in genetic variation among offspring. Example: Fertilization in animals and plants.

Binary fission is a form of asexual reproduction in prokaryotes, where the cell divides into two genetically identical daughter cells.

Genetic variation arises primarily from sexual reproduction due to the combination of genetic material from two parents.

Cell Division in Prokaryotes vs. Eukaryotes

• Prokaryotes: Divide by binary fission, a simple process involving DNA replication and cell splitting.

• Eukaryotes: Divide by mitosis (for somatic cells) and meiosis (for gametes), involving complex steps and organelles.

Cell Cycle Events

The cell cycle consists of interphase and the mitotic phase:

• Interphase: The cell grows and prepares for division. Subdivided into:

  • G1 phase: Cell growth

  • S phase: DNA replication

  • G2 phase: Preparation for mitosis

• Mitosis: Division of the nucleus, includes:

  • Prophase: Chromosomes condense, spindle forms

  • Prometaphase: Nuclear envelope breaks down, spindle attaches to chromosomes

  • Metaphase: Chromosomes align at the cell's equator

  • Anaphase: Sister chromatids separate and move to opposite poles

  • Telophase: Nuclear envelopes reform, chromosomes decondense

• Cytokinesis: Division of the cytoplasm

  • Cleavage furrow: In animal cells, pinching of the cell membrane

  • Cell plate: In plant cells, formation of a new cell wall

Key Terms in Cell Division

• Sister chromatids: Identical copies of a chromosome connected at the centromere

• Daughter cell: The result of cell division; genetically identical in mitosis, different in meiosis

• Homologous chromosomes: Chromosome pairs, one from each parent, similar in shape and gene content

• Karyotype: The complete set of chromosomes in a cell, arranged by size and shape

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers

Meiosis and Genetic Variation

Meiosis is the process by which gametes are produced, resulting in four genetically unique daughter cells.

• Phases of meiosis: Meiosis I and II, each with prophase, metaphase, anaphase, and telophase

• Crossing over: Exchange of genetic material between homologous chromosomes during prophase I

• Chiasma: The site where crossing over occurs

• Importance: Increases genetic diversity

Cancer and Cell Cycle Regulation

• Density-dependent inhibition: Normal cells stop dividing when crowded; cancer cells ignore this signal

• Characteristics of cancer cells: Uncontrolled division, do not follow cell cycle rules

• Benign tumor: Non-invasive, does not spread

• Metastasis: Spread of cancer cells to other parts of the body

Down Syndrome

• Cause: Nondisjunction leading to an extra chromosome 21 (trisomy 21)

• Characteristics: Distinct facial features, intellectual disability, increased risk of certain health issues

Patterns of Inheritance

Key Genetic Terms

• Pangenesis/Pangenes: Early theory that particles from all parts of the body are passed to offspring (now disproven)

• True-breeding: Organisms that produce offspring identical to themselves when self-fertilized

• P, F1, F2 generations: Parental, first filial, and second filial generations in genetic crosses

• Hybrid: Offspring of two different true-breeding parents

• Homozygous: Having two identical alleles for a gene

• Heterozygous: Having two different alleles for a gene

• Genotype: Genetic makeup of an organism

• Phenotype: Observable traits of an organism

• Alleles: Different forms of a gene

• Locus: Location of a gene on a chromosome

Mendel’s Experiments

• Plants used: Pea plants (Pisum sativum)

• Preventing random pollination: Controlled pollination by removing stamens and manually transferring pollen

• Experimental process: Crossed true-breeding plants, observed traits in F1 and F2 generations

• Results: Traits segregate according to predictable ratios

Genetic Laws and Ratios

• Law of independent assortment: Genes for different traits segregate independently during gamete formation

• Phenotypic ratio from a dihybrid cross: Typically 9:3:3:1

Solving Genetic Probability

• Rule of addition: Probability of either of two mutually exclusive events occurring

  • Formula: $P(A \text{ or } B) = P(A) + P(B)$

• Rule of multiplication: Probability of two independent events both occurring

  • Formula: $P(A \text{ and } B) = P(A) \times P(B)$

Types of Inheritance

• Incomplete dominance: Heterozygotes show intermediate phenotype (e.g., pink flowers from red and white parents)

• Codominance: Both alleles are fully expressed (e.g., AB blood type)

• Pleiotropy: One gene affects multiple traits

• Polygenic inheritance: Multiple genes contribute to a single trait (e.g., skin color)

Chromosome Theory and Linked Genes

• Chromosome theory of inheritance: Genes are located on chromosomes, which segregate during meiosis

• Linked genes: Genes located close together on the same chromosome, inherited together

• Sex-linked genes: Genes located on sex chromosomes (X or Y), often show unique inheritance patterns

Genetic Disorders and Their Inheritance

• Dominant genetic disorders: Less common because affected individuals are more likely to be eliminated from the population

• Recessive genetic disorders: Parents can be carriers (heterozygous) and unaffected, but pass the allele to offspring

• Sickle cell disease: Caused by a mutation in the hemoglobin gene, leading to abnormal red blood cell shape

Environmental Effects on Phenotype

• Phenotype can be influenced by environmental factors such as nutrition, temperature, and exposure to chemicals

Sex Chromosomes and Sex-linked Traits

• Male: XY chromosomes

• Female: XX chromosomes

• Recessive X-linked traits: More common in males because they have only one X chromosome; a single recessive allele will cause the trait

Table: Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of divisions	1	2
Number of daughter cells	2	4
Genetic identity	Identical to parent	Different from parent
Function	Growth, repair	Gamete production
Crossing over	No	Yes (prophase I)

Table: Types of Genetic Inheritance

Type	Description	Example
Complete dominance	One allele masks the other	Purple vs. white flowers in peas
Incomplete dominance	Intermediate phenotype	Pink snapdragons
Codominance	Both alleles fully expressed	AB blood type
Pleiotropy	One gene affects multiple traits	Sickle cell disease
Polygenic inheritance	Multiple genes affect one trait	Skin color

Example: In a dihybrid cross between two heterozygous pea plants (RrYy x RrYy), the phenotypic ratio is 9:3:3:1 for the four possible trait combinations.

Additional info: The study guide covers foundational concepts in cellular reproduction and Mendelian genetics, essential for understanding inheritance and genetic variation in biology.