Mendelian Genetics - Monohybrids (10/28-10/30)

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Pangenesis (Hint: 3)

Theory of Inheritance

Proposed by the Greek physician Hippocrates

“Seeds” produced by all parts of the body are collected in the reproductive organs then passed to the offspring at the moment of conception

Preformationism (Hint: 2)

Theory of Inheritance

Homunculus that simply develop in the womb

Homonculus

“Little man” that early microscopists thought they saw in the sperm

Blending Theory (Hint: 2)

Theory of Inheritance

Factors that control heredity traits are malleable and can blend together from generation to generation

Gregor Mendel (Hint: 3)

The father of Genetics

Austrian monk that worked with pea plants in the monastery garden

Published his findings from crossing plants in 1866 in a manuscript call Experiments in Plant Hybridization

What are the 2 Reasons for the Success of Gregor Mendel’s Experiment?

Model choice

Experimental (empirical) approach

Model Choice (Hint: 4)

Pea plants

Readily available and easy to grow

Rapid generation time and produce many offspring

A number of varieties available

Experimental (Empirical) Approach (Hint: 2)

Take detailed records of crosses

Use math to interpret results

Trait (Hint: 3)

The specific property of a character

Examples:

Round vs. wrinkled

Eye color is a characteristic and blue and brown are traits

Characteristic/Character (Hint: 3)

Morphological trait of an organism

Overarching category

Example: Seed shape/color

Gene

An inherited factor (region of DNA) that determines a characteristic

Allele

One of two or more different forms of a gene

Locus

Physical location on a chromosome occupied by a gene

Genotype (Hint: 2)

The set of alleles possessed by an individual organism

Individuals carry 2 alleles of a gene

Phenotype (Hint: 2)

The physical appearance or manifestation of a trait associated with a particular genotype

The genotype is inherited, not the phenotype

Heterozygote

2 different alleles at a locus

Homozygote

2 of the same allele at a locus

Pure/True Breeder (Hint: 3)

 Strain that produces the same trait over several generations

Homozygous for the given trait

Example: Always produces green seeds

Stamen

Male reproductive organ of a flower that produces pollen

Pistil

Female reproductive part of a flower that produces ovules

Hybridization

The mating or crossing of 2 individuals with different traits for a character

Hybrid (Hint: 2)

The offspring of such a cross

Example: Round seeds x Wrinkled seeds

Cross-Fertilization (Hint: 2)

Pollen and eggs are from different plants

Remove stamen and dust the pistil of another flower

Self-Fertilization (Hint: 2)

Pollen and eggs are from the same plant

Occurs without manipulation in peas

Monohybrid Cross (Hint: 3)

Cross 2 variants of a single characteristic (pure breeders)

How Mendel started

Example: Plant height (tall x dwarf)

P Generation (Hint: 3)

The parental cross

Cross fertilization

Use true breeding individuals (homozygous)

F₁ Generation

The result of the P generation cross

F₂ Generation

The result of crossing individuals in the F₁ generation

The Principle of Segregation (Hint: 5)

Mendel’s First Law

Each individual possesses 2 alleles for each character

Each allele separates during the formation of gametes

Each allele is separated in equal proportions (50/50)

Meiosis underlines this principle

Dominance (Hint: 3)

Used when 2 different alleles for a single character are found in the same individual

1 allele is dominant and its phenotype is expressed

The other allele is recessive and its phenotype is not expressed

Dominant (Hint: 2)

Phenotype is expressed

Capital letter

Recessive (Hint: 2)

Phenotype is not expressed

Lower case letter

Punnett Square (Hint: 2)

A grid that can be used to predict the outcome of a simple genetic cross

Originally proposed by the English geneticist Reginald Punnett

Back Cross

A cross between an F₂ genotype and either of the parental genotypes

Test Cross

An individual of unknown genotype (A_) is crossed with an individual homozygous recessive (aa) for the given trait to reveal the unknown genotype

What types of crosses did Mendel perform?

Monohybrid Crosses

What did Mendel observe for the characters in the F₁ generation?

For all 7 characters only 1 of the 2 parental traits was observed

What did Mendel observe for the characters in the F₂ generation?

Showed a 3:1 ratio of the 2 parental traits

Describe the Mendel Experiment and Results (Hint: 7)

Mendel crossed a plant homozygous for round seeds (RR) with a plant homozygous for wrinkled seeds (rr)

The two alleles in each plant separated when gametes were formed and one allele went into each gamete

Gametes used to produce heterozygous F₁ plants that had round seeds because round is dominant over wrinkled

Mendel self-fertilized the F₁ to produce the F₂ which appeared in a 3:1 ratio of round to wrinkled

Mendel also self-fertilized the F₂ to produce the F₃ seeds (Homozygous round peas produced plants with only round peas

Heterozygous plants produced round and wrinkled seeds in a 3:1 ratio;

Homozygous wrinkled peas produced plants with only wrinkled peas)