Mendelian Genetics

Flashcards covering key concepts from Chapter 3: Mendelian Genetics, including Mendel's experiments, laws of inheritance, modern terminology, probability in genetics, chi-square analysis, and pedigree analysis.

Who was Gregor Mendel and when did he publish his research on pea plants?

Gregor Mendel was a scientist who published his research with peas (Pisum sativum) in 1866, providing the first insights into trait inheritance.

What did Gregor Mendel refer to as 'particulate unit factors,' and what are they known as today?

Mendel referred to 'particulate unit factors,' which are now known as genes.

What field of genetics was established by correlating chromosome behavior during meiosis to Mendel's principles of inheritance?

The field of transmission genetics.

List four reasons why Mendel's choice of garden peas (Pisum sativum) was effective for his inheritance studies.

Peas are easy to grow, have true-breeding strains, allow controlled matings (self-fertilization or cross-fertilization), grow to maturity in one season, and have observable characteristics with two distinct forms.

When was Mendel's work rediscovered, and what did it establish a basis for?

Mendel's work was rediscovered at the turn of the twentieth century and established the basis for the transmission of hereditary traits, known as transmission genetics.

What is a monohybrid cross?

A monohybrid cross involves crossing parents that were true breeding for a single pair of contrasting traits.

What are the P1 and F1 generations in a monohybrid cross?

The P1 generation refers to the original parents, and the F1 generation consists of their offspring.

How is the F2 generation produced?

The F2 generation results from selfing (self-fertilizing) the F1 offspring.

What was the significance of Mendel's 'particulate unit factors' (genes)?

They served as the basic units of heredity, passed unchanged from generation to generation, determining various traits expressed by each individual plant.

What are Mendel's first three postulates?

1. Unit factors in pairs: Genetic characters are controlled by unit factors existing in pairs. 2. Dominance/recessiveness: In a pair of unlike unit factors, one is dominant and the other is recessive. 3. Segregation: The paired unit factors segregate (separate) independently during gamete formation.

In modern terminology, what are Mendel's units of inheritance called, and what are their alternative versions?

Mendel's units of inheritance are called genes, and their alternative versions are called alleles.

Define genotype and phenotype.

Genotype is the genetic (allelic) makeup of an individual for a specific trait (e.g., DD, Dd, dd), while phenotype is the physical expression of that genetic makeup (e.g., tall and dwarf).

Distinguish between a homozygous genotype and a heterozygous genotype.

A homozygous genotype has identical alleles (e.g., DD, dd), whereas a heterozygous genotype has two different alleles (e.g., Dd).

What is the typical phenotypic ratio observed in the F2 generation of a monohybrid cross?

In the F2 generation, 3/4 of the plants exhibit the same trait as the F1 generation (dominant), and 1/4 exhibit the contrasting trait that disappeared in the F1 generation (recessive).

What is a Punnett square used for?

A Punnett square allows the genotypes and phenotypes resulting from a cross to be easily visualized.

What is the purpose of a testcross for a single character?

A testcross is used to determine whether an individual displaying the dominant phenotype is homozygous or heterozygous for that trait, by crossing it with a homozygous recessive individual.

What is a dihybrid cross?

A dihybrid cross (two-factor cross) is a cross between individuals from true-breeding strains that differ in two pairs of contrasting traits.

What is the characteristic phenotypic ratio observed in the F2 generation of a dihybrid cross?

The F2 generation of a dihybrid cross typically shows a 9:3:3:1 ratio.

What is Mendel's fourth postulate?

Mendel's fourth postulate, independent assortment, states that during gamete formation, segregating pairs of unit factors assort independently of each other.

What is the product law of probabilities and how is it used in genetics?

The product law states that when two independent events occur simultaneously, the combined probability of the two outcomes is equal to the product of their individual probabilities of occurrence. It's used to calculate the frequencies of F2 phenotypes where traits assort independently.

What is the calculated probability of producing an individual with the genotype AaBbCCdd from a cross of two heterozygotes (AaBbCcDd x AaBbCcDd)?

The probability is (1/2 Aa) * (1/2 Bb) * (1/4 CC) * (1/4 dd) = 1/64.

What is the sum law of probabilities and when is it applied?

The sum law states that the probability of obtaining an outcome that can be achieved in two or more different ways is equal to the sum of the individual probabilities of all such events. It's applied when calculating the likelihood of a specific phenotype that can result from multiple genotypic combinations.

What is the chromosomal theory of inheritance?

The chromosomal theory of inheritance proposes that genetic material is contained within chromosomes, which are transmitted from generation to generation.

Define locus in the context of genetics.

The locus is the specific location of a gene on a given chromosome.

What is chi-square (χ2) analysis used for in genetics?

Chi-square analysis evaluates the influence of chance on genetic data, helping to determine if observed deviations from expected results are due to random fluctuations or a real genetic difference.

What is a null hypothesis in chi-square analysis?

A null hypothesis assumes that data will fit a given ratio, implying no real difference between the measured and predicted values, and that any apparent difference is attributed purely to chance.

What does degrees of freedom (df) represent in chi-square analysis, and how is it calculated?

Degrees of freedom (df) accounts for the number of categories being analyzed; it is calculated as n - 1, where n is the number of different categories into which each datum point may fall.

How are pedigree charts used in human genetics?

Pedigree charts show a family tree with respect to a given trait, revealing patterns of inheritance of that trait in humans.

In a pedigree, how are females, males, and individuals of unknown sex represented?

Females are represented by circles, males by squares, and individuals of unknown sex by diamonds.

How are generations designated in a pedigree, and how are sibs typically arranged?

Generations are designated by Roman numerals. Sibs (siblings) are placed from left to right in order of birth.

What do shading and a dot within a symbol indicate in a pedigree?

Shading indicates the expression of the phenotype (affected individual), while a dot indicates a heterozygous carrier who does not express the trait.

How are identical (monozygotic) and fraternal (dizygotic) twins represented in a pedigree?

Twins are indicated by diagonal lines stemming from a common vertical line. In identical twins, the diagonal lines are linked by a horizontal line, whereas fraternal twins lack this connecting line.

What is a proband in a pedigree?

The proband (p) is the individual for whom the pedigree was constructed, often the first affected individual identified in a family.

What are key characteristics of autosomal recessive traits in a pedigree?

Autosomal recessive traits typically skip generations and appear equally in both sexes. Affected individuals may have unaffected parents who are carriers.

What are key characteristics of autosomal dominant traits in a pedigree?

Autosomal dominant traits almost always appear in each generation. Affected individuals generally have at least one affected parent, and they appear equally in both sexes.