Question 1

What is the blending theory of inheritance?

Accepted Answer

A hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance.

Question 2

What is continuous variation?

Accepted Answer

An inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them.

Question 3

What is discontinuous variation?

Accepted Answer

An inheritance pattern in which traits are distinct and are transmitted independently of one another.

Question 4

What is a dominant trait?

Accepted Answer

A trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait.

Question 5

What is F1?

Accepted Answer

The first filial generation in a cross; the offspring of the parental generation.

Question 6

What is F2?

Accepted Answer

The second filial generation produced when F1 individuals are self-crossed or fertilized with each other.

Question 7

What is hybridization?

Accepted Answer

The process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring.

Question 8

What is a model system?

Accepted Answer

A species or biological system used to study a specific biological phenomenon to be applied to other different species.

Question 9

What is P0?

Accepted Answer

The parental generation in a cross.

Question 10

What is the product rule?

Accepted Answer

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

Question 11

What is a recessive trait?

Accepted Answer

A trait that appears "latent" or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed.

Question 12

What is a reciprocal cross?

Accepted Answer

A paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross.

Question 13

What is the sum rule?

Accepted Answer

The probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities.

Question 14

What is a trait?

Accepted Answer

A variation in the physical appearance of a heritable characteristic.

Question 15

Who was Mendel?

Accepted Answer

Johann Gregor Mendel (1822–1884) was a lifelong learner, teacher, scientist, and man of faith. As a young adult, he joined the Augustinian Abbey of St. Thomas in Brno in what is now the Czech Republic. Supported by the monastery, he taught physics, botany, and natural science courses at the secondary and university levels.

Question 16

When did Mendel discover the laws of classical genetics?

Accepted Answer

In 1856, he began a decade-long research pursuit involving inheritance patterns in honeybees and plants, ultimately settling on pea plants as his primary model system (a system with convenient characteristics used to study a specific biological phenomenon to be applied to other systems). In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local Natural History Society. He demonstrated that traits are transmitted faithfully from parents to offspring independently of other traits and in dominant and recessive patterns. In 1866, he published his work, Experiments in Plant Hybridization , in the proceedings of the Natural History Society of Brünn.

Question 17

What were the scientific beliefs about inheritance when Mendel presented his results?

Accepted Answer

Mendel’s work went virtually unnoticed by the scientific community that believed, incorrectly, that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring; this hypothetical process appeared to be correct because of what we know now as continuous variation.

Question 18

How did Mendel avoid continuous variation?

Accepted Answer

Instead of continuous characteristics, Mendel worked with traits that were inherited in distinct classes (specifically, violet versus white flowers); this is referred to as discontinuous variation. Mendel’s choice of these kinds of traits allowed him to see experimentally that the traits were not blended in the offspring, nor were they absorbed, but rather that they kept their distinctness and could be passed on.

Question 19

What was the impact of Mendel's discoveries?

Accepted Answer

In 1868, Mendel became abbot of the monastery and exchanged his scientific pursuits for his pastoral duties. He was not recognized for his extraordinary scientific contributions during his lifetime. In fact, it was not until 1900 that his work was rediscovered, reproduced, and revitalized by scientists on the brink of discovering the chromosomal basis of heredity.

Question 20

What model organism did Mendel use and why?

Accepted Answer

Mendel’s seminal work was accomplished using the garden pea, Pisum sativum , to study inheritance. This species naturally self-fertilizes, such that pollen encounters ova within individual flowers. The flower petals remain sealed tightly until after pollination, preventing pollination from other plants. The result is highly inbred, or “true-breeding,” pea plants. These are plants that always produce offspring that look like the parent. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.

Question 21

How did Mendel perform hybridizations?

Accepted Answer

Mendel performed hybridizations, which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety. To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant’s flowers before they had a chance to mature.

Question 22

Which generations were important in Mendel's crosses?

Accepted Answer

Mendel collected the seeds belonging to the P0 plants that resulted from each cross and grew them the following season. Once Mendel examined the characteristics in the F1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F1 plants to produce the F2 generation. Mendel’s experiments extended beyond the F2 generation to the F3 and F4 generations, and so on, but it was the ratio of characteristics in the P0−F1−F2 generations that were the most intriguing and became the basis for Mendel’s postulates.

Question 23

Which garden pea characteristics did Mendel study?

Accepted Answer

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. The characteristics included plant height, seed texture, seed color, flower color, pea pod size, pea pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet.

Question 24

How many plants did Mendel use in his research?

Accepted Answer

To fully examine each characteristic, Mendel generated large numbers of F1 and F2 plants, reporting results from 19,959 F2 plants alone. His findings were consistent.

Question 25

What were Mendel's results for self-crossed reproduction on flower color?

Accepted Answer

First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical.

Question 26

What were Mendel's results from crossing plants with different flower colors?

Accepted Answer

Mendel would apply the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait in the F1 generation had completely disappeared.

Question 27

What were Mendel's results from self-crossing the F1 plants?

Accepted Answer

He would allow the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait.

Question 28

What were Mendel's results for garden pea characteristics other than flower color?

Accepted Answer

For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1.

Question 29

What were Mendel's conclusions?

Accepted Answer

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

Question 30

How did Mendel use probability in his research?

Accepted Answer

In his experiment, Mendel demonstrated that the probability of the event “round seed” occurring was 100 percent in the F1 offspring of true-breeding parents, one of which has round seeds and one of which has wrinkled seeds. When the F1 plants were subsequently self-crossed, the probability of any given F2 offspring having round seeds was now 75 percent. Using large numbers of crosses, Mendel was able to calculate probabilities and use these to predict the outcomes of other crosses.

Question 31

What relationships between traits did Mendel discover in his research?

Accepted Answer

Mendel demonstrated that the pea-plant characteristics he studied were transmitted as discrete units from parent to offspring. Mendel also determined that different characteristics, like seed color and seed texture, were transmitted independently of one another and could be considered in separate probability analyses. The characteristics of color and texture did not influence each other.

Question 32

How can rolling a die and flipping a coin be used to illustrate the product rule?

Accepted Answer

Imagine that you are rolling a six-sided die (D) and flipping a penny (P) at the same time. The die may roll any number from 1–6 (D#), whereas the penny may turn up heads (PH) or tails (PT). The outcome of rolling the die has no effect on the outcome of flipping the penny and vice versa. There are 12 possible outcomes of this action, and each event is expected to occur with equal probability. Of the 12 possible outcomes, the die has a 2/12 (or 1/6) probability of rolling a two, and the penny has a 6/12 (or 1/2) probability of coming up heads. By the product rule, the probability that you will obtain the combined outcome 2 and heads is: (D2) x (PH) = (1/6) x (1/2) or 1/12 (table above). Notice the word “and” in the description of the probability. The “and” is a signal to apply the product rule.

Question 33

How can flipping coins be used to illustrate the sum rule?

Accepted Answer

Imagine you are flipping a penny (P) and a quarter (Q). What is the probability of one coin coming up heads and one coin coming up tails? This outcome can be achieved by two cases: the penny may be heads (PH) and the quarter may be tails (QT), or the quarter may be heads (QH) and the penny may be tails (PT). Either case fulfills the outcome. By the sum rule, the probability of obtaining one head and one tail can be calculated as [(PH)×(QT)] + [(QH)×(PT)] = [(1/2)×(1/2)] + [(1/2)×(1/2)] = 1/2

Question 34

What is an allele?

Accepted Answer

A gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes.

Question 35

What are autosomes?

Accepted Answer

Any of the non-sex chromosomes.

Question 36

What is codominance?

Accepted Answer

In a heterozygote, complete and simultaneous expression of both alleles for the same characteristic.

Question 37

What is a dominant lethal inheritance pattern?

Accepted Answer

Inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age.

Question 38

What is a genotype?

Accepted Answer

The underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism.

Question 39

What does it mean to be hemizygous?

Accepted Answer

Presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant.

12: Mendel's Experiments and Heredity Flashcards

Mendel's Experiments and the Laws of Probability, Characteristics and Traits, Laws of Inheritance

Brainscape's Knowledge GenomeTM

12: Mendel's Experiments and Heredity Flashcards

Mendel's Experiments and the Laws of Probability, Characteristics and Traits, Laws of Inheritance

Brainscape's Knowledge Genome^TM