Module 8 – Mendelian Genetics (Chapter 9)

Flashcards covering key concepts, vocabulary, and laws from Mendelian genetics to assist with exam preparation.

What is a trait in Mendelian genetics?

An inherited characteristic that can vary between individuals.

What does “true-breeding” mean in Mendel’s experiments?

An organism that, when self-fertilized, always passes down the same trait to its offspring.

In Mendel’s work, what is hybridization?

The intentional crossing of two different true-breeding varieties to study trait inheritance.

Define an allele.

A specific version of a gene that can produce variation in a trait.

What characterizes a dominant allele?

It masks the expression of a recessive allele in a heterozygote and determines the organism’s appearance.

When is an allele considered recessive?

When its effects are hidden in the presence of a dominant allele and expressed only in the homozygous state.

What is a testcross, and why is it used?

A cross between an individual of unknown genotype and a homozygous recessive individual to determine the unknown genotype.

In Mendel’s terminology, what do P, F1, and F2 generations represent?

P = parental generation; F1 = first filial (offspring) generation; F2 = offspring of the F1 generation.

Why does the F2 generation of a monohybrid cross often show a 3:1 phenotypic ratio?

Because dominant and recessive alleles segregate, producing three dominant-phenotype individuals for every one recessive-phenotype individual.

According to Mendel, what causes variation in inherited characters?

Alternative versions of genes, called alleles.

How many alleles for each gene does an organism inherit from its parents?

One allele from each parent.

Which allele determines an organism’s appearance when two different alleles are present?

The dominant allele.

State Mendel’s Law of Segregation.

Two alleles for a heritable character separate during gamete formation and end up in different gametes.

Differentiate homozygous and heterozygous genotypes.

Homozygous: two identical alleles for a gene; Heterozygous: two different alleles for a gene.

What is the difference between phenotype and genotype?

Phenotype is the observable physical traits; genotype is the genetic makeup that determines those traits.

Define the Law of Independent Assortment.

Alleles of different genes separate independently of one another during gamete formation.

What are multiple alleles? Give an example.

More than two allele forms for a single gene exist in a population; e.g., IA, IB, and i alleles for ABO blood type.

Contrast incomplete dominance and codominance.

Incomplete dominance produces blended intermediate traits, while codominance shows both traits fully and equally in heterozygotes.

In the ABO blood group system, which alleles are codominant and which is recessive?

IA and IB are codominant; the i allele is recessive.

What is sex-linked inheritance, and why is color-blindness more common in males?

Inheritance of traits controlled by genes on sex chromosomes (usually X). Males have only one X chromosome, so a single recessive mutation on that X expresses the trait.