Lecture 12 - Mendelian Genetics

A set of practice flashcards covering Mendelian genetics, including key terminology, Mendel's laws, cross ratios, and complex inheritance patterns like codominance and polygenic inheritance.

Who is known as the Father of Genetics and what was his specialty?

Gregor Mendel ($1822$ – $1884$), an Austrian monk who studied the inheritance of traits in pea plants.

Define the term Genetics.

The branch of biology that focuses on the inheritance of traits.

Define the term Heredity.

The transmission of traits from parent to offspring; inheritance.

What is a gene?

A sequence of DNA that codes for a specific protein.

What is an allele?

A different variety of a gene.

How many pairs of chromosomes do humans have?

Humans have $23$ pairs of chromosomes ($46$ individual chromosomes).

How are human gametes produced and what is their genetic content?

Meiosis produces human gametes (egg and sperm) with just one copy of each chromosome and, thus, one copy of each gene.

What are model organisms?

Organisms that are easy to care for and can be used to make inferences about many other similar species.

List the four stages of the life cycle of the pea plant.

$1.$ Self-pollination, $2.$ Fertilization, $3.$ Germination, and $4.$ Development.

What is the first step in Mendel’s cross-pollination procedure?

Pull out the pollen-bearing stamens with tweezers so that self-fertilization is no longer possible.

Contrast Genotype and Phenotype.

Phenotype refers to the observable features of an individual (e.g., yellow seeds), while Genotype is the genetic makeup found within a particular individual (e.g., $YY$ or $Yy$).

What is a dominant allele?

An allele that determines the phenotype of a heterozygous individual, denoted with a capital letter (e.g., $Y$ or $R$).

What is a recessive allele?

An allele whose phenotype is only expressed in homozygous recessive individuals, denoted with a lowercase letter (e.g., $y$ or $r$).

Define Homozygous and Heterozygous.

Homozygous means having the same two alleles ($YY$ or $yy$); Heterozygous means having two different alleles ($Yy$ or $Rr$).

What are the phenotypic and genotypic ratios in the $F_2$ generation of a monohybrid cross?

The phenotypic ratio is $3:1$ and the genotypic ratio is $1:2:1$.

State Mendel's Law of Segregation.

Alleles of each gene segregate during the formation of gametes (meiosis), so egg and sperm carry one copy of each gene.

What is a testcross?

The crossing of a homozygous recessive individual with an individual of unknown genotype displaying a dominant phenotype.

What are the phenotypic and genotypic ratios in the $F_2$ generation of a dihybrid cross?

The phenotypic ratio is $9:3:3:1$ and the genotypic ratio is $1:2:2:1:4:2:1:2:1$.

State Mendel’s Law of Independent Assortment.

One trait does not influence the inheritance of another trait; all traits are inherited independently of one another.

Explain Incomplete Dominance.

A condition where a heterozygote exhibits an intermediate phenotype between the two homozygotes, such as pink flowers resulting from red and white snapdragons.

Define Codominance and provide an example.

A condition in which two alleles of a given gene have different phenotypic effects, with both effects present in heterozygotes; an example is Blood type.

What is Polygenic inheritance?

When the interaction of multiple genes determines the phenotype, each having a small additive effect, resulting in continuous variation (e.g., human height).

Identify the Universal Recipient and Universal Donor blood types.

Type $AB$ is the universal recipient (has $A$ and $B$ antigens, produces no antibodies); Type $O$ is the universal donor (has neither $A$ nor $B$ antigens).

Contrast Discrete and Quantitative traits.

Discrete traits exhibit distinct phenotypic forms (e.g., pea traits), while Quantitative traits exhibit phenotypic variation along a smooth, continuous scale (e.g., human height).

What is the observed distribution of quantitative traits in a population?

A normal distribution, often represented by a bell curve where values are symmetrical around the average.