Lecture 4 Bio

Blending Hypothesis

Traits from parents blend together in offspring like mixing paint.

Particulate Hypothesis

Parents pass discrete hereditary units (genes) that retain their identity.

Gregor Mendel

Discovered the basic principles of inheritance.

Pollination

Transfer of pollen from the anther (male) to the stigma (female).

Fertilization

Fusion of male and female gametes inside the ovule.

True-breeding

Organisms that produce offspring with the same trait when self-fertilized.

F1 generation

Offspring from crossing two true-breeding parents.

Monohybrid cross

A cross that examines one trait.

Genotype

The genetic makeup of an organism (PP, Pp, pp).

Phenotype

The observable trait (purple flower).

Dominant allele

An allele expressed in the heterozygous condition.

Recessive allele

Only expressed when two copies are present.

Mendel’s Principle of Segregation

The two alleles for a gene separate during gamete formation and reunite at fertilization.

Pedigree

A family tree used to track inheritance of traits across generations.

Dihybrid cross

A cross examining two traits simultaneously.

Test cross

Crossing an individual with unknown genotype with a homozygous recessive.

Polygenic inheritance

A trait controlled by multiple genes.

Pleiotropy

One gene influences multiple traits.

Incomplete dominance

Heterozygote shows an intermediate phenotype.

Codominance

Both alleles are fully expressed in the heterozygote.

Multiple alleles

More than two allele types exist for a gene.

Environmental effects on genes

Environment influences gene expression.

Epistasis

One gene affects or masks the expression of another gene.

What two basic ideas about heredity existed before the 20th century?

Traits are inherited within species and passed from parents to offspring.

What phenotypic ratio appears in F2 of a monohybrid cross?

3:1 (dominant : recessive).

What genotypic ratio appears in F2?

1:2:1 (AA : Aa : aa).

What is a character?

A heritable feature (ex: flower color).

What is a trait?

A specific form of a character (ex: purple flowers).

What is a gene?

A segment of DNA that determines a trait.

How many genes for a character does an individual have?

Two (one from each parent).

Do alleles blend?

No. They remain separate.

What does homozygous mean?

Two identical alleles (AA or aa).

What does heterozygous mean?

Two different alleles (Aa).

What is the F2 generation?

Offspring from self-fertilizing the F1 generation.

What is self-fertilization?

A plant fertilizes itself using its own pollen.

What is cross-pollination?

Transfer of pollen between different plants.

Why was the Blending Hypothesis incorrect?

Traits do not permanently blend; they remain separate and can reappear in later generations.

Why does segregation occur?

Alleles separate during meiosis.

What is a dominant pedigree pattern?

Trait appears in every generation.

What is a recessive pedigree pattern?

Trait can skip generations.

What is the F2 phenotypic ratio of a dihybrid cross?

9 : 3 : 3 : 1

What does the Principle of Independent Assortment state?

Alleles of different genes separate independently during gamete formation.

Why perform a test cross?

To determine if a dominant phenotype is homozygous or heterozygous.

Why is Mendel’s model considered an oversimplification?

Most traits involve multiple genes or complex interactions.

Example of polygenic inheritance?

Human height.

Example of mutliple alleles?

ABO blood types.

Example of environmental effects?

Temperature-dependent fur color in Siamese cats

Example of incomplete dominance?

Red + white flowers → pink.