Chapter 3 Basic Principles of Heredity - Practice Flashcards

Question-and-answer flashcards covering Mendel's principles, terminology, crosses, probability, and chi-square concepts from the lecture notes.

What organism did Mendel use as his genetic model system in his experiments?

Pisum sativum (garden pea), chosen for fast generation time, large progeny, and seven easily observed traits.

Name two characteristics that made Mendel's approach effective.

A proper experimental model and a mathematical analysis of results (plus easily observed, unambiguous traits and predictive hypotheses).

When were Mendel's results published, and when did they become widely known?

Published in 1866; rediscovered and popularized about 44 years later (around 1910).

Define a gene.

An inherited factor that helps determine a trait; encoded in DNA.

Define an allele.

One of two or more alternative forms of a gene.

Define a locus.

Specific place on a chromosome occupied by an allele.

Define genotype.

The set of alleles possessed by an individual organism.

Define a heterozygote.

An individual possessing two different alleles at a locus.

Define a homozygote.

An individual possessing two of the same alleles at a locus.

Define phenotype.

The appearance or manifestation of a characteristic.

What is the difference between a locus and an allele?

A locus is the location on a chromosome; an allele is a version of the gene at that locus.

State Mendel's Principle of Segregation.

Each diploid organism has two alleles for a trait; these alleles segregate during gamete formation, and each gamete receives one allele.

What is the concept of dominance?

When two different alleles are present, the trait encoded by the dominant allele is observed in the phenotype.

What is a monohybrid cross?

A cross between two true-breeding parents that differ in a single trait.

What is a backcross?

A cross between the F1 and either parent.

What is a testcross?

A cross between an unknown genotype and a true-breeding recessive (homozygous recessive).

What is a Punnett square used for?

A visual tool to visualize a genetic cross and predict outcomes.

What phenotypic ratio results from a simple monohybrid cross Aa × Aa?

3:1 (dominant phenotype to recessive phenotype).

What genotypic ratio results from Aa × Aa?

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

What is the difference between a backcross and a testcross (clarified)?

Backcross is to either parent; a testcross is to a known homozygous recessive.

What does 'true breeding' mean in Mendel's experiments?

A line that produces uniform offspring for a trait across generations; homozygous for that trait.

What does the dihybrid cross illustrate?

The principle of independent assortment (Mendel's Second Law) for two traits.

What is meant by independent assortment?

Alleles at different loci segregate independently of one another during gamete formation.

How can dihybrid cross outcomes be predicted when traits assort independently?

Multiply the single-locus ratios to obtain the overall phenotypic proportions.

What is a branch diagram used for in dihybrid crosses?

A visual tool to determine phenotypes and expected proportions for a dihybrid cross (e.g., Rr Yy × Rr Yy).

What is the dihybrid testcross and its purpose?

A cross between a dihybrid (Rr Yy) and a homozygous recessive (rr yy) to reveal the genotype of the dihybrid individual.

What is chi-square goodness-of-fit used for in genetics?

Determines the probability that the difference between observed and expected progeny is due to chance.

What does a chi-square table provide?

Critical values for the chi-square distribution to assess significance at given degrees of freedom (P).

What is the Multiplication Rule in genetics?

To find the probability of two independent events both occurring (AND) by multiplying their probabilities.

What is the Addition Rule in genetics?

To find the probability of either of two mutually exclusive events occurring (OR) by adding their probabilities.

In binomial probability, what do p and q represent?

p is the probability of one event; q is the probability of the alternative event; p + q = 1.

What is the form (p + q)^n used for in genetics?

Calculates the probability distribution for the number of times an event occurs in n trials (offspring).

What is the effect of crossing over on a monohybrid cross’s expected ratio?

In a simple monohybrid cross, crossing over does not affect the 1:2:1 genotype ratio if genes are not linked; crossing over is more relevant for linked genes.

What is a Punnett square?

A grid used to predict the genotypes and phenotypes of offspring from a cross.