Mendelian Genetics II: Dihybrid Crosses, Laws of Inheritance, and Probability

Vocabulary flashcards covering Mendel's laws of inheritance, dihybrid crosses, standard Mendelian ratios, probability rules, and meiotic mechanisms.

Dihybrid cross

A breeding experiment involving crosses between two true-breeding lines that differ for two distinct traits (for example, $RRYY \times rryy$).

Law of Segregation (Mendel's First Law)

The law stating that during gamete formation (sperm or egg), the alleles for each gene segregate from each other so each gamete carries only one allele for each gene, with pairing restored at fertilization.

Law of Independent Assortment (Mendel's Second Law)

The law stating that alleles for different traits separate independently of one another during gamete formation, such that the segregation outcome of one allele does not affect that of another.

Law of Dominance (Mendel's Third Law)

The law stating that some alleles are dominant while others are recessive, and an organism with at least one dominant allele will express the dominant phenotype, masking the recessive allele.

Multiplication rule (AND rule)

A probability rule stating that the probability of two independent events occurring simultaneously is the product of their individual probabilities ($p(A \text{ and } B) = p(A) \times p(B)$).

Addition rule (OR rule)

A probability rule stating that the probability that any one of several mutually exclusive events will occur is the sum of their individual probabilities ($p(A \text{ or } B) = p(A) + p(B)$).

Probability scale

A quantitative measurement ranging between $0$ and $1$, where $0$ indicates an event will never happen, $1$ indicates it will always happen, and intermediate values represent uncertainty (such as $0.5 = 50\%$).

$9:3:3:1$ ratio

The expected phenotypic ratio produced in the $F_2$ generation from a dihybrid cross of two heterozygous individuals ($AaBb \times AaBb$).

$3:1$ ratio

The expected phenotypic ratio resulting from a monohybrid cross between two heterozygous individuals ($Aa \times Aa$).

$1:2:1$ ratio

The expected genotypic ratio resulting from a monohybrid cross between two heterozygous individuals ($Aa \times Aa$).

$1:1$ ratio

The expected phenotypic or genotypic ratio produced by a monohybrid testcross between a heterozygote and a homozygous recessive individual ($Aa \times aa$).

$1:1:1:1$ ratio

The expected phenotypic or genotypic ratio resulting from a dihybrid testcross between a double heterozygote and a double homozygous recessive individual ($AaBb \times aabb$).

Meiotic basis of independent assortment

The physical separation event in anaphase I of meiosis wherein each pair of homologous chromosomes separates independently, causing non-homologous genes to assort independently into gametes.

Phenylketonuria (PKU)

An inherited genetic disorder identified in genetic problem-solving as being transmitted via an autosomal recessive pattern.

Myotonic dystrophy (MD)

An inherited genetic disorder identified in genetic problem-solving as being transmitted via an autosomal dominant pattern.