heredity

According to the reading, an example of an animal in the F1 generation with a fur color blend of two P generation phenotypes (e.g., that is a heterozygote phenotype intermediate between the two homozygote phenotypes) is representative of:

incomplete dominance

Lethality

one allele causes death

pleiotropy

or one gene affecting multiple characteristics.

A model system is an

organism that makes it easy for a researcher to investigate a particular scientific question, such as how traits are inherited. By studying a model system, researchers can learn general principles that apply to other, harder-to-study organisms or biological systems, such as humans.

According to the reading, the idea that only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random represents:

the law of segregation

According to the sum rule,

the probability that any of several mutually exclusive events will occur is equal to the sum of the events' individual probabilities.

According to the reading, pleiotropy refers to a set of seemingly unrelated symptoms caused by:

the same genetic variant

According to the reading, traits are not always the product of a single gene.

true

Mendel's contemporaries failed to recognize the importance of his work because his findings went against prevailing (popular) ideas about inheritance.

when Mendel was doing his experiments, most biologists subscribed to the idea of blending inheritance. Blending inheritance wasn't a formal, scientific hypothesis, but rather, a general model in which inheritance involved the permanent blending of parents' characteristics in their offspring (producing offspring with an intermediate form of a characteristic). The blending model fit well with some observations of human inheritance: for instance, children often look a bit like both of their parents.

According to the reading, an exception to Mendel's Law of independent assortment occurs when (select all that apply):

genes for traits are on the same chromosome, and are located close together

Common mistakes and misconceptions

Dominant traits are not always the most common. Some people may think that dominant trait is the most likely to be found in the population, but the term "dominant" only refers to the fact that the allele is expressed over another allele. An example of this is Huntington's disease. Even though Huntington's is caused by a dominant allele, it only affects about 30,000 people in the United States. Traits are not always the product of a single gene. For example, there are at least 3 different genes that are associated with eye color in humans. In addition, there are sometimes more than two alleles for each gene. For example, there are 3 different alleles of one gene determine coat color of cats.

According to the reading, humans are an ideal model system for research.

F

According to the reading, there are typically only two alleles for each gene.

F

Mendel proposed that traits were specified by "heritable elements" called

genes

The reason for independent assortment

Homologous chromosomes are similar but non-identical, and an organism gets one member of the pair from each of its two parents. The physical basis for the law of independent assortment lies in meiosis I of gamete formation, when homologous pairs line up in random orientations at the middle of the cell as they prepare to separate. We can get gametes with different combos of "mom" and "dad" homologues (and thus, the alleles on those homologues) because the orientation of each pair is random.

According to the reading, the patterns observed in which generations proved to be most useful:

P, F1, F2

dihybrid cross.

These phenotypic categories (categories defined by observable traits) appeared in a ratio of approximately 9:3:3:1.

In most sexually reproducing organisms, each individual has two alleles for each gene (one from each parent).

This pair of alleles is called a genotype and determines the organism's appearance, or phenotype.

This is known as the law of segregation.

When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly.

According to the reading, a lethal allele could cause death before birth (non viability) or well into a person's life.

T

According to the reading, lethal alleles can be recessive or dominant.

T

If pea color and pea shape sort independently, you cannot make a prediction (e.g., have no information) about pea color if you know the pea shape.

T

Multiple genotypes can correspond with the same phenotype.

T

A test cross can be used to determine whether an organism with a dominant phenotype is homozygous or heterozygous.

In a test cross, a parent with a dominant phenotype but unknown genotype is crossed with a recessive parent. If the parent with the unknown genotype is homozygous dominant, all the resulting offspring will have at least one dominant allele. If the parent with the unknown genotype is heterozygous, 50 percent of the offspring will inherit a recessive allele from both parents and will have the recessive phenotype.

he found very similar patterns of inheritance for all seven features he studied:

One form of a feature, such as tall, always concealed the other form, such as short, in the first generation after the cross. Mendel called the visible form the dominant trait and the hidden form the recessive trait. In the second generation, after plants were allowed to self-fertilize (pollinate themselves), the hidden form of the trait reappeared in a minority of the plants. Specifically, there were always about 3 plants that showed the dominant trait (e.g., tall) for every 1 plant that showed the recessive trait (e.g., short), making a 3:1. Mendel also found that the features were inherited independently: one feature, such as plant height, did not influence inheritance of other features, such as flower color or seed shape.

There are, however, gene pairs that do not assort independently. When genes are close together on a chromosome, the alleles on the same chromosome tend to be inherited as a unit more frequently than not.

Such genes do not display independent assortment and are said to be linked.

generations

The plants used in this initial cross are called the P generation, or parental generation. Mendel collected the seeds from the P generation cross and grew them up. These offspring were called the F1 generation, short for first filial generation Once Mendel examined the F1 plants and recorded their traits, he let them self-fertilize naturally, producing lots of seeds. He then collected and grew the seeds from the F1 plants to produce an F2 generation, or second filial generation. Again, he carefully examined the plants and recorded their traits. Mendel's experiments extended beyond the F2 generation to F3, F4, and later generations, but his model of inheritance was based mostly on the first three generations (P, F1, F2).

In some cases, however, the phenotype of a heterozygous organism can actually be a blend between the phenotypes of its homozygous parents.

This type of relationship between alleles, with a heterozygote phenotype intermediate between the two homozygote phenotypes, is called incomplete dominance.

The law of segregation (Links to an external site.) lets us predict how a single feature associated with a single gene is inherited. In some cases, though, we might want to predict the inheritance of two characteristics associated with two different genes. How can we do this?

To make an accurate prediction, we need to know whether the two genes are inherited independently or not. That is, we need to know whether they "ignore" one another when they're sorted into gametes, or whether they "stick together" and get inherited as a unit.

According to the reading, Mendel's particular model of inheritance was in opposition to the prevailing idea of the time:

blending inheritance

According to the reading, an example of a flower that has both red and while petals (i.e., both alleles expressed in the heterozygote) is representative of:

codominance

Closely related to incomplete dominance is codominance, in which both alleles are simultaneously expressed in the heterozygote.

codominance

According to the reading, genes that are linked:

do not assort independently

According to the reading, prevalent or common traits in the population are always caused by dominant alleles.

false

The two probability rules that are most relevant to Punnett squares are the

product rule and the sum rule.

Mendel's law of independent assortment

states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

According to the reading, which rules will you need to apply to cacluate genotype probabilities? (Select all the apply):

sum rule product rule

According to the reading, which method can be used to determine the genotype of an organism displaying the dominant trait?

test cross

The product rule states

that the probability of two (or more) independent events occurring together can be calculated by multiplying the individual probabilities of the events.

law of independent assortment,

which states that the alleles for one gene sort into gametes independently of the alleles of another gene.