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Unit 5: Heredity

Lesson Overview

• Lesson 1: Meiosis and Reproduction

• Lesson 2: Mendelian Genetics

• Lesson 3: Non-Mendelian Genetics and Pedigrees

Visual Representation of Traits

• Family traits represented: EYES, HAIR, EARS

• Family members: Dad, Son, Mom

Lesson 1: Meiosis & Reproduction

Aim

• How do organisms transmit genetic information between generations?

Think-Pair-Share Question

• Question: Do you think mutations in somatic (body) cells or gamete (sex) cells are worse, and why do you think that?

Topic 5.1: Meiosis

Learning Objectives

• IST-1.F: Explain how meiosis results in the transmission of chromosomes from one generation to the next.

• IST-1.G: Describe similarities and/or differences between the phases and outcomes of mitosis and meiosis.

Definitions

• Describe: Note the characteristics of something.

• Explain: State "why" or "how" something happens (more demanding than describing).

Topic 5.2 + 5.6: Meiosis, Genetic Diversity & Chromosomal Inheritance

Learning Objectives

• IST-1.H: Explain how meiosis generates genetic diversity.

• SYI-3.C: Explain how chromosomal inheritance generates genetic variation in sexual reproduction.

Important Vocabulary

Gamete

• Haploid sex cell (e.g., sperm and egg)

Haploid

• Cell with half the normal number of chromosomes (23 in humans)

Somatic Cell

• Diploid body cell (e.g., heart cell, skin cell, lung cell)

Diploid

• Cell with a full set of chromosomes (46 in humans)

Homologous Chromosome

• Chromosome pairs with the same structure and genes (one from each parent)

Crossing Over

• Exchange of genes between homologous chromosomes

Genetic Diversity

• Variability of traits among organisms

Major Reproductive Strategies

Asexual Reproduction

• Definition: Does not require gamete production; results in genetically identical offspring through a process similar to mitosis.

  • Pros:

    • Fast reproduction; adapted offspring.

    • No mate required.

  • Cons:

    • Overpopulation; limited resources.

    • No genetic diversity.

Sexual Reproduction

• Definition: Requires meiosis and the fusion of gametes, resulting in a zygote.

  • Pros:

    • Increases genetic diversity.

    • Offspring can exhibit different traits.

  • Cons:

    • Time and energy-consuming.

    • Mate finding may be challenging.

2. Karyotypes

Definition

• Karyotype: Display of chromosome pairs ordered by size and length.

• Displays characteristics of chromosomes (e.g., homologous duplicated chromosomes).

3. Cells and Chromosomes

Eukaryotic DNA Packaging

• DNA is packaged in chromosomes, with two types:

  • Autosomes: Non-sex determining chromosomes (22 pairs in humans).

  • Sex Chromosomes: X and Y (eggs: X; sperm: X or Y).

4. Life Cycles

Definition

• Life cycle: Sequence of stages in an organism's reproductive history from conception to reproduction.

• Sexual life cycles alternate between fertilization (gamete fusion) and meiosis.

5. Meiosis

Overview

• Process creating haploid gamete cells in diploid organisms.

• Results in daughter cells with half the chromosome number of the parent.

  • Example: Humans (Diploid: 2n = 46; Gametes: n = 23).

6. Key Events in Meiosis

Unique Events

1. Prophase I: Synapsis and crossing over.

2. Metaphase I: Tetrads line up at the metaphase plate.

3. Anaphase I: Separation of homologous pairs.

10. How Does Meiosis Lead to Genetic Variation?

1. Crossing Over: Produces recombinant chromosomes.

2. Independent Assortment: Random orientation during metaphase I.

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

11. Sexual Reproduction & Genetic Diversity

• Meiosis significantly contributes to genetic diversity through:

  • Crossing over that generates new allele combinations.

  • Random sorting of chromosomes during gamete formation.

  • Random fertilization creates unique offspring.

12. Chromosomal Mutations

Consequences of Errors

• Genetic disorders from single mutated alleles or chromosomal mutations (e.g., nondisjunction).

14. Types of Chromosomal Mutations

Types

1. Deletions: Missing section of a chromosome.

2. Duplications: Section is doubled.

3. Inversions: Gene sequences are reversed.

4. Insertions: A part of one chromosome is inserted into another.

5. Translocations: Non-homologous chromosomes exchange alleles.

33. Nondisjunction

Definition

• A mutation where homologous chromosomes fail to separate properly, leading to gametes with improper chromosome numbers (e.g., trisomy, monosomy).

36. Lesson 2: Mendelian Genetics

Aim

• What are Gregor Mendel's laws of inheritance?

Topic 5.3: Mendelian Genetics

Learning Objective

• IST-1.I: Explain the inheritance of genes and traits per Mendel’s laws.

39. Common Ancestry

Key Points

• DNA/RNA carries genetic information.

• Genetic code shared by all living organisms.

• Gregor Mendel's principles studied through pea plants.

43. Pea Plant Traits

Experimental Design

• Mendel observed two forms of traits (e.g., color, seed shape).

• Used true breeding plants for controlled experiments.

46. Testcross

Purpose

• Determine unknown genotype by crossing with homozygous recessive.

• Indications of dominance/homozygosity from offspring ratios.

47. Principles of Heredity

Fundamental Principles

1. Law of Segregation: Alleles of the same trait separate during gamete formation.

2. Law of Independent Assortment: Genes for different traits segregate independently.

51. Mendel’s Model

Explanation of 3:1 Phenotypic Ratio

1. Alternative alleles represent variations in characteristics.

2. Organisms inherit two alleles for a gene (one from each parent).

3. Dominance defined by observable traits.

4. Law of segregation reinforces allelic separation during gamete formation.

56. Dihybrid Crosses

Explanation

• Crosses involve two traits, following the law of independent assortment.

66. Laws of Probability

Key Concepts

• Multiplication Rule: Probability of independent events combined through multiplication (e.g., coin tosses, offspring outcomes).

• Addition Rule: Probability of mutually exclusive events.

71. Pedigrees

Definition

• Family trees representing inheritance patterns of specific traits.

74. Pedigree Patterns

Genetic Inheritance

• Autosomal Dominant: Affected individuals cannot have unaffected offspring.

• X-Linked Dominant: Significant representation of affected daughters from affected fathers.

76. Non-Mendelian Genetics

Overview

• Deviations from Mendelian inheritance due to:

  • Multiple genes and varying dominance.

  • Genes on sex chromosomes and tight chromosomal linkage.

81. Multiple Genes

Impact on Traits

• Epistasis: Phenotypic expression can affect another gene.

• Polygenic Inheritance: Multiple genes contribute to a single phenotype.

86. Sex-Linked Genes

Characteristics

• Genes located on sex chromosomes (X-linked and Y-linked).

• Different inheritance patterns for males and females.

90. X-Inactivation

Overview

• Mechanism for gene dosage regulation in females through inactive X chromosomes forming Barr bodies.

92. Genetic Recombination

Definition

• Production of offspring with new gene combinations from parents.

96. Linked Genes

Definition

• Genes located close on a chromosome that tend to assort together, often violating independent assortment.

100. Goodness of Fit Test

Purpose

• Chi-square tests consistency between observed and expected results in genetic experiments.

115. Practice Problem Example

Seed Color Genetics

• Observed ratios of yellow to green seeds used to test fit with expected ratios using chi-square analysis.

Independent assortment occurs during Meiosis I, specifically in Metaphase I. This is when homologous chromosomes line up at the metaphase plate in pairs. The orientation of each pair is random, leading to the independent segregation of maternal and paternal chromosomes into gametes. This process contributes to genetic variability in the offspring as different combinations of chromosomes are possible during gamete formation.

Barr Bodies: Barr bodies are inactivated X chromosomes found in the somatic cells of female mammals. This mechanism is a form of dosage compensation that equalizes gene expression between males (who have one X chromosome) and females (who have two X chromosomes). The inactivation occurs early in embryonic development, resulting in a random selection of which X chromosome will be inactivated in each cell, leading to a mosaic pattern of X-linked traits in females.

DNA Insertion of Insulin Gene into Bacterial Molecule: When a section of DNA coding for the insulin hormone is inserted into a bacterial plasmid (a small circular DNA molecule found in bacteria), it allows the bacteria to produce insulin through a process known as recombinant DNA technology. This process involves the following steps:

1. Gene Cloning: The insulin gene is isolated and inserted into the plasmid using restriction enzymes.

2. Transformation: The recombinant plasmid is introduced into competent bacterial cells through transformation, allowing the bacteria to take up the plasmid.

3. Expression: Once inside the bacterial cell, the plasmid’s insulin gene can be transcribed and translated into insulin protein.

4. Harvesting: The bacteria can be cultured in large numbers to produce significant amounts of insulin, which can then be harvested and purified for medical use.

This method enables the production of human insulin in large quantities more efficiently than extracting it from animal sources, ensuring a consistent supply for diabetes treatment.

Traits typically do not come from a single gene; instead, they are often influenced by multiple genes and their interactions, a phenomenon known as polygenic inheritance. This means that many traits, such as skin color, height, and weight, are determined by the combined effects of several genes, each contributing to the overall phenotype. Additionally, environmental factors can also interact with these genes to further influence the expression of traits.