Chapter 14: Mendel and the Gene

Who was Gregor Mendel?

Scientist who discovered basic principles of inheritance using pea plants.

What is genetics?

The study of heredity and how traits are passed from parents to offspring.

What is the chromosome theory of inheritance?

Genes are located on chromosomes and passed during meiosis.

What is heredity?

Transmission of traits from parents to offspring.

What is a trait?

Any observable characteristic of an organism.

Why did Mendel use pea plants?

Easy to grow, short generation time, many offspring, controllable mating.

What is a model organism?

A species used to study biological processes.

What is a polymorphic trait?

Trait with two or more common forms.

What is self-fertilization?

A plant fertilizes itself.

What is cross-fertilization?

Pollen from one plant fertilizes another plant.

What is a pure line?

True-breeding organisms that produce identical offspring.

What is a hybrid?

Offspring from two different pure lines.

What is the parental (P) generation?

The original parents in a cross.

What is the F1 generation?

First generation offspring.

What is the F2 generation?

Offspring from F1 individuals.

What is a monohybrid cross?

A cross involving one trait.

What happened in Mendel's F1 generation?

Only dominant trait appeared.

What happened in the F2 generation?

Recessive trait reappeared.

What was the F2 ratio?

3:1 (dominant to recessive).

What is a dominant trait?

Trait that appears in heterozygotes.

What is a recessive trait?

Trait hidden in heterozygotes.

What is particulate inheritance?

Traits are passed as discrete units (genes), not blended.

What is a gene?

A hereditary unit that determines a trait.

What are alleles?

Different versions of a gene.

What is genotype?

Genetic makeup of an organism.

What is phenotype?

Observable traits.

What is the principle of segregation?

Alleles separate during gamete formation.

What is homozygous?

Two identical alleles.

What is heterozygous?

Two different alleles.

What is a Punnett square?

A diagram used to predict offspring genotypes.

What is a testcross?

Cross with a homozygous recessive to determine genotype.

What is a dihybrid cross?

Cross involving two traits.

What is independent assortment?

Genes for different traits are inherited independently.

What is the typical dihybrid ratio?

9:3:3:1.

Where are genes located?

On chromosomes.

What is a locus?

Location of a gene on a chromosome.

What are sex chromosomes?

X and Y chromosomes.

What is sex linkage?

Genes located on sex chromosomes.

What is X-linked inheritance?

Trait controlled by gene on X chromosome.

What is linkage?

Genes close together on the same chromosome tend to be inherited together.

Can linked genes separate?

Yes, through crossing over.

What is crossing over?

Exchange of DNA between homologous chromosomes.

What does crossing over cause?

Genetic recombination.

What determines crossing over frequency?

Distance between genes.

What is multiple allelism?

More than two alleles exist for a gene.

Example of multiple alleles?

ABO blood types.

What is complete dominance?

One allele fully masks another.

What is codominance?

Both alleles are expressed.

What is incomplete dominance?

Heterozygote shows intermediate phenotype.

What is pleiotropy?

One gene affects multiple traits.

What is epistasis?

One gene masks another gene's effect.

Do genes alone determine traits?

No, environment also influences phenotype.

Example of gene-environment interaction?

PKU disease affected by diet.

What are quantitative traits?

Traits that vary continuously (like height).

What causes quantitative traits?

Multiple genes and environmental factors.

What is a pedigree?

A family tree used to track inheritance.

What is an autosomal trait?

Trait on non-sex chromosomes.

Autosomal recessive traits?

Require two recessive alleles.

Autosomal dominant traits?

One dominant allele is enough.

X-linked recessive traits?

More common in males.

X-linked dominant traits?

Affect both sexes but differ in inheritance.

Y-linked traits?

Passed from father to son.

Why is Mendel important?

He established the basic rules of inheritance used in genetics today.