12.1 Mendel's Experiments and the Laws of Probability

Who is considered the father of genetics?

Johann Gregor Mendel

What organism did Mendel primarily use for his experiments?

Garden pea (Pisum sativum)

What is the significance of Mendel's work in genetics?

He established the fundamental principles of heredity and the laws of inheritance.

What is meant by 'true-breeding' in Mendel's experiments?

True-breeding refers to plants that consistently produce offspring that look like the parent.

What are the two types of variation in traits described by Mendel?

Continuous variation and discontinuous variation.

What is continuous variation?

Variation that results from the action of many genes, leading to traits that appear blended, like human height.

What is discontinuous variation?

Variation where traits are inherited in distinct classes, such as violet versus white flowers.

What was the blending theory of inheritance?

The incorrect belief that parental traits were lost or absorbed in offspring, resulting in an intermediate appearance.

What is a monohybrid cross?

A genetic cross between two individuals that differ in one trait.

What are dominant and recessive alleles?

Dominant alleles express their traits in the presence of recessive alleles, which only express their traits when homozygous.

What is the purpose of using large sample sizes in Mendel's experiments?

To ensure that results were statistically significant and not due to chance.

What method did Mendel use to prevent self-fertilization in his experiments?

He manually removed the anthers from the flowers before they matured.

What did Mendel's experiments reveal about trait inheritance?

Traits are transmitted independently and maintain their distinctness in offspring.

When did Mendel present his findings to the Natural History Society?

In 1865.

What was the title of Mendel's published work?

Experiments in Plant Hybridization.

What was the scientific community's initial reaction to Mendel's work?

It went virtually unnoticed and was not recognized until 1900.

What role did Mendel's monastery play in his research?

It supported him in his scientific pursuits, allowing him to teach and conduct experiments.

How did Mendel's choice of pea plants benefit his experiments?

Pea plants self-fertilize, allowing for controlled breeding and clear observation of trait inheritance.

What is the significance of Mendel's laws of inheritance?

They form the basis of classical genetics and explain how traits are passed from parents to offspring.

What is the parental generation in Mendel's crosses referred to as?

P0 or parental generation one.

What is the expected outcome of a monohybrid cross involving one dominant and one recessive allele?

The dominant trait will typically be expressed in the offspring.

What is the sum rule in probability as it applies to genetics?

It states that the probability of an event occurring is the sum of the probabilities of the individual events.

What is the product rule in probability as it applies to genetics?

It states that the probability of two independent events occurring together is the product of their individual probabilities.

What did Mendel's experiments demonstrate about the blending of traits?

Traits do not blend; they remain distinct and can be passed on unchanged.

What was the impact of Mendel's work on later genetic research?

It laid the groundwork for the discovery of the chromosomal basis of heredity.

What are the plants used in first-generation crosses called?

P0, or parental generation one.

What does F1 stand for in Mendel's experiments?

The first filial generation, which are the offspring of the P0 generation.

What generation follows the F1 generation in Mendel's experiments?

The F2, or second filial generation.

What was the ratio of violet to white flowers in the F2 generation?

Approximately 3:1, with 705 violet flowers and 224 white flowers.

What did Mendel conclude about dominant and recessive traits?

Dominant traits are expressed in hybrids, while recessive traits can disappear in the F1 generation but reappear in the F2 generation.

What is a reciprocal cross in Mendel's experiments?

A paired cross where the traits of the male and female are switched in the second cross.

What characteristic did Mendel examine that involved flower color?

The contrasting traits of violet and white flowers.

How many characteristics did Mendel report in his 1865 publication?

Seven different characteristics.

What was the expected outcome of the blending theory in Mendel's flower color experiments?

Hybrid flowers would be pale violet or have equal numbers of white and violet flowers.

What was Mendel's actual finding regarding the F1 generation of flower color?

All F1 hybrids had violet flowers, indicating the white flower trait disappeared.

What does the term 'trait' refer to in Mendel's experiments?

A variation in the physical appearance of a heritable characteristic.

What were the results for the flower position trait in Mendel's experiments?

100 percent axial in F1, with 651 axial and 207 terminal in F2, resulting in a ratio of 3.14:1.

What was the outcome for plant height in Mendel's experiments?

100 percent tall in F1, with 787 tall and 277 dwarf in F2, resulting in a ratio of 2.84:1.

What was the result for seed texture in Mendel's experiments?

100 percent round in F1, with 5,474 round and 1,850 wrinkled in F2, resulting in a ratio of 2.96:1.

What was the outcome for seed color in Mendel's experiments?

100 percent yellow in F1, with 6,022 yellow and 2,001 green in F2, resulting in a ratio of 3.01:1.

What were the results for pea pod texture in Mendel's experiments?

100 percent inflated in F1, with 882 inflated and 299 constricted in F2, resulting in a ratio of 2.95:1.

What was the outcome for pea pod color in Mendel's experiments?

100 percent green in F1, with 428 green and 152 yellow in F2, resulting in a ratio of 2.82:1.

What did Mendel propose about the genetic composition of plants?

Plants possess two copies of each trait, with each parent transmitting one copy to the offspring.

What is the significance of the trait reappearing in the F2 generation?

It indicates that traits remain separate and are not blended in the F1 generation.

What does the observation of a recessive trait indicate?

The organism lacks any dominant versions of that characteristic.

What ratio did Mendel repeatedly obtain in his crosses?

A 3:1 ratio.

How is empirical probability calculated?

By dividing the number of times an event occurs by the total number of opportunities for the event to occur.

What is theoretical probability?

It is calculated by dividing the number of times an event is expected to occur by the number of times it could occur.

What does a probability of one indicate?

The event is guaranteed to occur.

What does a probability of zero indicate?

The event is guaranteed not to occur.

In Mendel's experiments, what was the probability of obtaining round seeds in the F1 generation?

One in the F1 offspring of true-breeding parents.

What was the expected probability of F2 offspring having round seeds?

Three out of four (75%).

What does the product rule of probability state?

The probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event.

Give an example of applying the product rule using a die and a penny.

The probability of rolling a two (1/6) and flipping heads (1/2) is (1/6) x (1/2) = 1/12.

What does the sum rule of probability apply to?

It applies to two mutually exclusive outcomes that can occur by more than one pathway.

How do you calculate the probability of one coin showing heads and another showing tails?

By summing the probabilities of the two cases: [(PH) × (QT)] + [(QH) × (PT)].

What is the probability of obtaining one head and one tail when flipping a penny and a quarter?

1/2.

What is necessary for accurate probability calculations in genetics?

Working with large sample sizes to avoid deviations caused by chance.

What did Mendel's large quantities of pea plants allow him to do?

Calculate the probabilities of traits appearing in the F2 generation.

How did Mendel's discoveries impact predictions of offspring traits?

They allowed accurate predictions of offspring traits even before fertilization.

What is the significance of the 3:1 ratio in Mendel's experiments?

It reflects the inheritance pattern of dominant and recessive traits.

What is meant by 'independent transmission of characteristics' in Mendel's work?

Different characteristics, like seed color and texture, are transmitted independently and can be analyzed separately.

What is an example of a genetic event in Mendel's experiments?

The production of round seeds by a pea plant.

What is the relationship between the product rule and independent events?

The product rule applies when calculating the probability of independent events occurring together.

What does the term 'mutually exclusive events' refer to?

Events that cannot occur at the same time.

What is the probability of having both dominant traits in the F2 progeny of a dihybrid cross?

It is the product of the probabilities of having each dominant trait.

What does the term 'dihybrid cross' refer to?

A genetic cross involving two traits.

What is the importance of the laws of probability in genetics?

They help predict the inheritance patterns of traits.