Mendel

Who was Johann (Gregor) Mendel and why was he able to conduct his experiments?

Mendel was a monk who had access to a monastery garden; peas grew relatively fast for the time, and he could study many different characteristics.

What did Mendel observe about pea offspring?

He saw offspring that could look different from their parents, and some characteristics would disappear and later reappear.

What is true breeding?

A strain that always passes down a certain phenotypic trait to its offspring.

Control

What is a reciprocal cross?

A cross between the male of one strain and the female of another strain, and then the reverse cross.

Mendel’s Crossings Summarized

[P] True breed round and wrinkled

[F1] Self cross with offspring of [P] - PpxPp

[F2] 3:1 ratio, wrinkled reappeared.

What is blended inheritance?

The idea that random traits from parents combine or mix to produce inherited traits; the all-round F1 generation disproved this idea.

What pattern did Mendel observe from the F2 results?

A predictable pattern developed, leading Mendel to assume that some particle of inheritance must pass to offspring.

What did Mendel conclude about genetic characters that control phenotypes?

They must exist in pairs because otherwise the recessive wrinkled phenotype could not disappear in F1 and reappear in F2.

What idea of chromosome number did Mendel develop?

The idea of diploid (2n), meaning two particles of inheritance are passed to an offspring.

What is dominance in Mendel's model?

Any offspring with the dominant R allele has the round phenotype, so the dominant allele masks the recessive phenotype.

What is a test cross?

A cross between an individual with an unknown genotype and a completely recessive individual (rr); the offspring phenotype is used to determine the unknown parent's genotype.

What is a gene?

A discrete particle of inheritance represented by a DNA sequence that generates a protein and contributes to phenotype.

What is an allele?

An alternative form of a gene, such as R or r.

What is a locus?

The physical location of a gene on a chromosome.

What are loci?

The physical locations of two or more genes on a chromosome.

What is a genotype?

The combination of alleles an individual has, such as RR, Rr, or rr.

What is a phenotype?

The physical appearance of a trait, such as round or wrinkled seeds.

What is a homozygote?

An individual having the same alleles, such as RR or rr.

What is a heterozygote?

An individual having different alleles.

What is Mendel's Third Law?

The idea of dominance: the trait from one allele masks the trait of another allele.

What is a monohybrid cross?

A mating between two individuals involving alleles at a single locus, such as R on one chromosome crossed with r on one chromosome.

What is Mendel's First Law?

The Law of Segregation of Alleles: every diploid individual has two alleles for a trait; during gamete formation, the alleles separate, and offspring randomly receive one allele from each parent.

What is a dihybrid cross?

A cross involving two different traits or two loci; the notes give GgFf × GgFf as a self-cross and a homozygous recessive test cross.

What is Mendel's Second Law?

The Law of Independent Assortment: during gamete formation, when two or more alleles are inherited, individual alleles assort independently, giving different traits an equal opportunity of occurring.

How does independent assortment apply to a dihybrid cross?

The alleles for different traits assort independently during gamete formation, allowing combinations of traits to occur.