Genetics Test Cross Quiz

Mendelian Genetics

• Gregor Mendel (1822-1884) is credited with establishing the fundamental laws of inheritance. He conducted experiments with pea plants (Pisum sativum).
• Mendel's work was groundbreaking, but it wasn't recognized until the 20th century.
• Between 1856 and 1863, Mendel cultivated and tested 28,000 pea plants. 
• He observed that offspring retained traits of their parents.
• Mendel is considered the "Father of Genetics."
• Mendel's experimental garden is located in the Czech Republic.

Particulate Inheritance

• Physical traits are inherited as "particles."
• Mendel didn't know that these particles were chromosomes and DNA.

Genetic Terminology

• Trait: A characteristic passed from parent to offspring.
• Heredity: The passing of traits from parent to offspring.
• Genetics: The study of heredity.

Types of Genetic Crosses

• Monohybrid cross: A cross involving a single trait (e.g., flower color).
• Dihybrid cross: A cross involving two traits (e.g., flower color and plant height).

Punnett Square

• A tool used to predict possible genotypes and phenotypes of offspring.
• In a simple example, the parents are heterozygous for a yellow-pea allele (Yy).
• The genotype ratio is 1:2:1.
• The phenotype ratio is 3:1 (yellow peas to green peas).

Designer "Genes"

• Alleles: Two forms of a gene (dominant and recessive).
• Dominant: A stronger gene expressed in a hybrid; represented by a capital letter (e.g., R).
• Recessive: A gene expressed less frequently; represented by a lowercase letter (e.g., r).

More Terminology

• Genotype: The gene combination for a trait (e.g., RR, Rr, rr).

• Phenotype: The physical feature resulting from the genotype (e.g., red or white flowers).

• Example: In flowers, the genotype RR (or Rr) results in a red phenotype, and the genotype rr results in a white phenotype

• The possible combinations include: RR, Rr, and rr, leading to the phenotypes: Red, Red, and White, respectively. 

Genotypes

• Homozygous: A gene combination involving two dominant or two recessive genes. Examples: RR or rr. Also called pure.
• Heterozygous: A gene combination involving one dominant and one recessive allele. Example: Rr. Also called hybrid.

Genes and Environment

• Genes and the environment influence characteristics.

Mendel's Pea Plant Experiments

• Pea plants were readily suited for Mendel's studies.

Why Peas?

• Can be grown in a small area.
• Produce a large number of offspring.
• Produce pure offspring when self-pollinated.
• Can be artificially cross-pollinated.

Reproduction in Flowering Plants

• Pollen contains sperm, produced by the stamen.
• The pistil contains eggs, housed in the ovary.
• Pollen carries sperm to the eggs.
• Self-fertilization can occur in the same flower.
• Cross-fertilization occurs between flowers.

Mendel's Experimental Methods

• Hand-pollinated flowers using a paintbrush.
• Stamen snipping to prevent self-pollination.
• Covering flowers with bags.
• Traced traits through several generations.

How Mendel Began

• Self-pollination.
• Fertilization.
• Germination.

Eight Pea Plant Traits

• Seed shape (round or wrinkled).
• Seed color (yellow or green).
• Pod shape (smooth or wrinkled).
• Pod color (green or yellow).
• Seed coat color (gray or white).
• Flower position (axial or terminal).
• Plant height (tall or short).
• Flower color (purple or white).

Table 11.1: Pea-Plant Characters Studied by Mendel

• This table lists the dominant and recessive traits Mendel studied in pea plants.

Mendel's Experimental Results

• Ratios of dominant to recessive traits observed.

Did the Observed Ratio Match the Theoretical Ratio?

• The observed results were similar to the expected results but showed a possible statistical discrepancy.

Generation "Gap"

• Parental (P) generation: The parent generation in a breeding experiment.
• First filial (F₁) generation: The first-generation offspring in a breeding experiment.
• Second filial (F₂) generation:  The second-generation offspring in a breeding experiment.

Following the Generations

• Cross 2 Pure Plants produces all hybrids.
• Cross 2 Hybrids produces 3 tall and 1 short plants.

Monohybrid Crosses

• A cross involving a single trait.

P₁ Monohybrid Cross

• Example using seed shape

P₁ Monohybrid Cross Review

• Summary of basic monohybrid cross.

F₁ Monohybrid Cross

• Example involving round seeds.

F₁ Monohybrid Cross Review

• Summary of the F₁ monohybrid cross involving two heterozygotes.

F₂ Monohybrid Cross (1st)

• Example dealing with round seeds.

F₂ Monohybrid Cross (2nd)

• Example dealing with wrinkled seeds crossed with round seeds. 

F₂ Monohybrid Cross Review

• Summary involving homozygous and heterozygous crosses.

Practice Your Crosses

•  These notes suggest reviewing P₁, F₁, and both F₂ crosses for characteristics other than seed shape.

Mendel's Laws

• Results from the monohybrid crosses.
• Heritable factors (genes).
• Phenotype is based on genotype. 
• True breeding individuals are homozygous (both alleles).

Law of Dominance

• Principle pertaining to contrasting traits in pure parents.
• All offspring are heterozygous. 
• Example: RR x rr yields all Rr (round seeds).

Law of Segregation

• Alleles separate during gamete formation.

Applying the Law of Segregation

• Examples presented in the form of a problem or question with solutions.

Law of Independent Assortment

• Alleles for different traits are inherited independently.

Dihybrid Cross

• A breeding experiment for two traits.

Dihybrid Cross

• Example of a dihybrid cross for seed shape and seed color.

Test Cross

• Mating between an individual of unknown genotype and a homozygous recessive individual.
• Examples concerning eye color, traits, and the expected results.

Summary of Mendel's Laws

• Summary of the laws in the context of parent crosses and offspring.

Incomplete Dominance and Codominance

• Incomplete dominance.

Incomplete Dominance

• F₁ hybrids are intermediate between parental phenotypes.
• Example: Red flower crossed with white flower. 

Incomplete Dominance 

• F₁ hybrid characteristics

Incomplete Dominance

• Parental generation diagram illustrated.

Codominance

• Two alleles expressed equally in heterozygous individuals.
• Example: A blood type.

Codominance Problem

• Example involving Type B male and Type A female cross.

Another Codominance Problem

• Example of male Type O and female Type AB cross.

Codominance Question

• Example with blood types, parents' genotypes, and phenotypes.

Codominance Answer

• Analysis, demonstrating possible genotypes and phenotypes of the parents.

Sex-linked Traits

• Traits located on sex chromosomes (X and Y).
• XX genotype in females, XY in males.
• Many sex-linked traits are carried on the X chromosome.

Sex-linked Traits

• Example involving eye color in fruit flies.

Sex-linked Trait Problem

• Example cross of a red-eyed male and white-eyed female. 

Sex-linked Trait Solution

• Solution containing the possible offspring in the cross.

Female Carriers

• How females can be carriers whereas males produce the phenotype more often.

Genetic Practice Problems

• An illustrative example.

Breed the P₁ Generation

• Example with tall and dwarf pea plants.

Solution

• Detailed solution to the tall vs dwarf cross.

### Breed the F₁ Generation

• Example of tall vs tall pea plants

### Solution

• Detailed breakdown of the cross.

Test your knowledge on test crosses and monohybrid crosses in genetics. This quiz covers fundamental concepts like phenotypic ratios and gamete production. Perfect for students studying Mendelian genetics and plant breeding.