AP Bio Chapter 14: Mendel and the Gene Idea

P Generation

parental generation, true-breeding parents

Sickle-cell disease

A recessively inherited human blood disorder in which a single nucleotide change in the β-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.

Explain epistasis.

The phenotypic expression of one gene alters that of another independently inherited gene

An event that is certain to occur has a probability of _______, while an event that is certain not to occur has a probability of ________.

-1 -0

Explain the concept of blending, and then describe how Mendel's "particulate" (gene) hypothesis was different.

-Blending Model: idea that genetic material contributed by the two parents was blended together in offspring -Particulate Model: parents pass on discrete heritable units—genes—that retain their separate identities in offspring

Explain how Mendel's crossing demonstrated the merit of experiments that covered multiple generations

-Had Mendel stopped his experiments with the F1 generation, the basic patterns of inheritance would have escaped him. -Mendel's quantitative analysis of the F2 plants from thousands of genetic crosses like these allowed him to deduce two fundamental principles of heredity: the law of segregation and the law of independent assortment

Compare and contrast codominance with incomplete dominance.

-Incomplete dominance: blending of phenotypes,. The exact phenotypes are not displayed. -Codominance: both phenotypes are present (black and white cat) -Both are the combinations of 2 different alleles.

Explain how incomplete dominance is different from complete dominance, and give an example of incomplete dominance.

-Incomplete dominance: the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele (blend of both phenotypes) -Complete dominance: the dominant allele completely covers up the recessive allele -An example of incomplete dominance is the crossing of red snapdragons with white snapdragons to produce F1 hybrids with pink flowers.

Explain how Mendel's crossing determined dominant and recessive characteristics

-The heritable factor for white flowers did not disappear in the F1 plants, but was somehow hidden, or masked, when the purple-flower factor was present. -Purple flower color is a dominant trait, and white flower color is a recessive trait.

Describe Mendel's Fourth Concept (Law of Segregation).

-The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. -Can be observed in meiosis

Explain how using pea plants allowed Mendel to control mating; that is, how did this approach let Mendel be positive about the exact characteristics of each parent?

-To achieve cross-pollination, Mendel removed the immature stamens of a plant before they produced pollen and then dusted pollen from another plant onto the altered flowers. Each resulting zygote then developed into a plant embryo encased in a seed (pea). -Mendel would always know the parentage of the young plants

Explain the three main steps in amniocentesis and the two main steps of CVS.

1. A sample of amniotic fluid can be taken starting at the fourteenth to sixteenth week of pregnancy. 2. Biochemical and genetic tests can be performed immediately on the amniotic fluid or later on the cultured cell. 3. Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping.

Achondroplasia

A form of dwarfism that occurs in one of every 25,000 people. Heterozygous individuals have the dwarf phenotype. Like the presence of extra fingers or toes, achondroplasia is a trait for which the recessive allele is much more prevalent than the corresponding dominant allele.

Huntington's Disease

A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.

Cystic Fibrosis

A human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.

Describe Mendel's First Concept.

Alternative versions of genes account for variations in inherited characters.

In probability, what is an independent event?

An event whose outcome is unaffected by what has happened on previous trials, such as in a sequence of coin tosses (random)

In sexually reproducing organisms, why are there exactly two chromosomes in each homologue?

Each somatic cell in a diploid organism has two sets of chromosomes, one set inherited from each parent.

Describe Mendel's Second Concept.

For each character, an organism inherits two alleles, one from each parent.

Why is height a good example of polygenic inheritance?

For many characters, such as human skin color and height, an either-or classification is impossible because the characters vary in the population in gradients along a continuum. Two or more genes are playing on a single phenotypic character.

Type A

Genotype: I^A I^A Enzyme adds the A carbohydrate

Type AB

Genotype: I^A I^B Enzyme adds both A and B carbohydrate codominance

Type B

Genotype: I^B I^B or I^B i Enzyme adds the B carbohydrate

Type O

Genotype: ii has neither A nor B carbohydrate

Describe Medel's Third Concept.

If the two alleles at a locus differ, then one, the dominant allele, determines the organism's appearance, the other, the recessive allele has no noticeable effect on the organism's appearance.

Explain the difference between a monohybrid cross and a dihybrid cross.

Monohybrid cross: A cross between two organisms that are heterozygous for the character being followed, one trait being examined Dihybrid cross: A cross between two organisms that are each heterozygous for both of the characters being followed, measuring 2 traits

Explain what is meant when a gene is said to have multiple alleles.

Most genes exist in more than two allelic forms, for example, ABO blood groups.

Explain why dominant alleles are not necessarily more common than recessive alleles in the gene pool.

Natural selection determines how common an allele is in the gene pool

What are the strengths and weaknesses of each fetal test?

Strength of amniocentesis: In addition to fetal cells, amniotic fluid is also collected. Amniotic fluid can be used to detect additional enzymatic or developmental problems not detectable from the karyotype. Weakness of amniocentesis: Cells must be cultured for several weeks before karyotyping, and the test cannot be performed until the fourteenth to sixteenth week. Strength of CVS: These cells proliferate rapidly enough to allow karyotyping to be carried out immediately, and CVS can be performed as early as the eighth to tenth week. Weakness of CVS: No amniotic fluid is collected with this technique.

What is pleiotropy? Explain why this is important in diseases like cystic fibrosis and sickle-cell disease.

The ability of a single gene to have multiple effects. In humans, pleiotropic alleles are responsible for multiple symptoms associated with certain hereditary diseases, such as cystic fibrosis and sickle-cell disease.

State the addition rule and give an original example.

The addition rule states that the probability that any two or more mutually exclusive events will occur is calculated by adding their individual probabilities.

State the multiplication rule and give an original example.

The multiplication rule states that to determine this probability, we multiply the probability of one event by the probability of the other event. For example, by the multiplication rule, the probability that both coins will land heads up is ½ × ½ = ¼.

Using the terms norm of reaction and multifactorial, explain the potential influence of the environment on phenotypic expression.

The outcome of a genotype lies within its norm of reaction, a phenotype range that depends on the environment in which the genotype of expressed. For some characters, such as the ABO blood group system, the norm of reaction has no breadth whatsoever. Other characteristics, such as a person's blood count of red and white cells, varies quite a bit, depending on such factors as the altitude, the customary level of physical activity, and the presence of infectious agents. Genetics refers to such characters as multifactorial, meaning that many factors, both genetic and environmental, collectively influence phenotype.

What is the probability that a couple will have a girl, a boy, a girl, and a boy in this specific order?

The probability is 1/16.

Explain how Mendel's crossing refuted bleeding

The reappearance of white-flowered plants in the F2 generation was evidence that the heritable factor causing white flowers had not been diluted or destroyed by coexisting with the purple-flower factor in the F1 hybrids. The trait had been hidden.

Explain the symptoms of phenylketonuria, and describe how newborn screening is used to identify children with this disorder.

The symptoms of phenylketonuria include an inability to metabolize the amino acid phenylalanine, causing severe mental intellectual disability. Some genetic disorders, including phenylketonuria, can be detected at birth by simple biochemical tests that are now routinely performed in most hospitals in the United States

Describe what you think is important to know medically about the behavior of recessive alleles.

Thousands of genetic disorders are known to be inherited as simple recessive traits. These disorders range in severity from relatively mild, such as albinism (lack of pigmentation, which results in susceptibility to skin cancers and vision problems) to life-threatening, such as cystic fibrosis.

Alternate versions of the same gene, like purple and white flower color, are termed ________.

alleles

F1 Generation

first filial generation

Quantitative variation usually indicates _______________.

polygenic inheritance

F2 Generation

second filial generation

Explain Mendel's law of independent assortment.

when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production