AP BIO CH 14,15

ch14#6,9,13,25,28,32,36 ch15#2,3,8,13,22,27,

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Name and describe three human sex-linked disorders

1. hemophilia: A human genetic disease caused by a sex-linked recessive allele, resulting in the absence of one or more blood-clotting proteins; characterized by excessive bleeding following injury 2. color blindness: A mild disorder almost always inherited as an X-linked allele 3. Duchenne muscular dystrophy: A human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue

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

define linkage map?

A linkage map is a genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.

In pea plants, T is the allele for tall plants, while t is the allele for dwarf plants. If you have a tall plant, demonstrate with a test cross how it could be determined if the plant is homozygous tall or heterozygous tall.

A testcross always involves crossing the unknown phenotype with an individual that is homozygous recessive for the trait in question. In this case, a homozygous tall plant crossed with a homozygous recessive dwarf will yield all tall offspring. A heterozygous tall plant crossed with a dwarf will yield an offspring ratio of one tall plant to one dwarf plant. The presence of dwarf plants indicates that the previously unknown tall plant is heterozygous.

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

Explain Mendel's law of independent assortment

Each pair of alleles segregates independently of each other pair of alleles during gamete formation.

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

define epistasis.

Epistatis is a type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene

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

Genetic recombination is the process during which linked genes become unlinked. What do geneticists call the offspring that show these new combinations?

Geneticists call the offspring that show these new combinations recombinant types, or recombinants for short.

Explain genomic imprinting

Genomic imprinting occurs during gamete formation and results in the silencing of a particular allele of certain genes. Because these genes are imprinted differently in sperm and eggs, the zygote expresses only one allele of an imprinted gene that is inherited from either the female or the male parent. The imprints are then transmitted to all body cells during development

Determine the following for blood groups: Genotype; Phenotype (blood group)

IAIA or IAi; A IBIB or IBi; B IAIB; AB ii; O

Compare and contrast codominance with incomplete dominance

In codominance, the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways, such as in the human MN blood group, determined by the codominant alleles for two specific molecules located on the surface of red blood cells, the M and N molecules. In incomplete dominance, the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele; neither allele is completely dominant, and the F1 hybrids have a phenotype somewhere between those of the two parental varieties.

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

Incomplete dominance is the situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele. Complete dominance is the situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable. An example of incomplete dominance is the crossing of red snapdragons with white snapdragons to produce F1 hybrids with pink flowers.

What are linked genes? Do linked genes sort independently?

Linked genes are genes located close enough together on a chromosome that they tend to be inherited together; no, but rather are transmitted as a unit. It is important to note that as Morgan's experiments illustrated, some mechanism (later discovered to be "crossing over") occasionally breaks the linkage between specific alleles of genes on the same chromosome.

List at least three reasons the fruit fly is an excellent subject for genetic studies

List at least three reasons the fruit fly is an excellent subject for genetic studies

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?

Mendel could always be sure of the parentage of new seeds because he removed the immature stamens of a plant before they produced pollen. He then dusted pollen from another plant onto the altered flowers, which resulted in zygotes developed into plant embryos.

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 (or the self-pollination of a heterozygous plant) Dihybrid cross: A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters)

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

Dominant alleles are not necessarily more common than recessive alleles in the gene pool. Explain why this is true.

Natural selection determines how common an allele is in the gene pool. For example, having six fingers (polydactyly) is dominant to five fingers, but the presence of six fingers is not common in the human gene pool.

Define the following terms. a. P generation b. F1 generation c. F2 generation

P generation: Parent generation F1 generation: First filial generation F2 generation: Second filial generation

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

Pleiotropy is 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.

What is the SRY gene? Where is it found, and what does it do?

SRY refers to the Sex determining Region of Y, a gene found on the Y chromosome that is required for the development of testes.

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

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

The blending concept is genetic material contributed by the two parents mixes in a manner like mixing blue and yellow paint to make green. It predicted that over many generations, a freely mating population would produce a uniform population of individuals. But the gene hypothesis said parents pass on discreet heritable genes that retain their separate identities in offspring.

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

X inactivation maintains the proper gene dosage How is the X chromosome inactivated?

The selection of which X chromosome will form the Barr body occurs randomly and independently in each embryonic cell present at the time of X inactivation

What other organelle has its own genes?

These are extranuclear genes.

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.

In humans, how has that term (sex linked gene) been historically modified?

Typically, the sex-linked traits are actually X-linked genes.

What is a Barr body? Why do human females show a Barr body in their cells?

a dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome. Female mammals, including humans, inherit two X chromosomes—twice the number inherited by males; females show a Barr body in their cells so that the cells of females and males have the same effective dose (one copy) of most X-linked genes

define sex-linked gene

a gene located on either sex chromosome that doesn't have to do with gender characteristics. expression of genes depend on the gender of the individual

Explain each of the following terms: a. aneuploidy b. monosomy c. trisomy d. polyploidy

a. A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number. Trisomy 21 (Down syndrome) is an aneuploidy b. Refers to a diploid cell that has only one copy of a particular chromosome instead of the normal two. Turner syndrome is a human monosomy; the female has only one X chromosome. c. Refers to a diploid cell that has three copies of a particular chromosome instead of the normal two. Trisomy 21 is trisomic for chromosome 21 d. A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division

define a. deletion b. duplication c. inversion d. translocation

a. A deficiency in a chromosome resulting from the loss of a fragment through breakage b. An aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated c. An aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a reverse orientation to the chromosome from which it originated d. An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome

Students are expected to have a general knowledge of the pattern of inheritance and the common symptoms of a number of genetic disorders. Provide this information for the disorders listed below. a. cystic fibrosis b. sickle-cell disease c. achondroplasia d. Huntington's disease

a. 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. b. 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. c. 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 d. 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.

Mendel's Four Concepts Description of Concepts: Describe the: a. 1st concept b. 2nd concept c. 3rd concept d. 4th concept (law of segregation)

a. Alternative versions of genes account for variations in inherited characters. b. For each character, an organism inherits two copies of a gene, one from each parent c. 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. d. The two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes.

For each of the following human aneuploidies, give the sex of the individual as well as any physical manifestation of the syndrome. a. XXY; sex? physical traits? b. XXX; sex? physical traits? c. XO; sex? physical traits? d. XYY; sex? physical traits?

a. klinefelter syndrome; male; female characteristics b. trisomy x; female; no unusual physical features other than being slightly taller than average; at risk for learning disabilities; fertile c. Turner syndrome: phenotypically female, but sterile due to lack of maturation in sex organs; secondary sex characteristics developed with estrogen replacement; normal intelligence d. male; Normal sexual development; taller than average stature

Explain how Mendel's simple cross of purple and white flowers did the following: a. refuted blending b. determined dominant and recessive characteristics c. demonstrated the merit of experiments that covered multiple generations

a. 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 b. Mendel reasoned that 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. In Mendel's terminology, purple flower color is a dominant trait, and white flower color is a recessive trait c. Analyzing thousands of genetic crosses from F2 plants allowed him to deduce two fundamental principles of heredity: the law of segregation and the law of independent assortment

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

alleles

What occurs in nondisjunction?

an error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.

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

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

What is the chromosome theory of inheritance?

genes have specific loci along chromosomes, chromosomes segregate and assort independently

define map unit

map unit is a unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency

Although you inherited one chromosome of each pair from your mother and your father, you have inherited a group of genes from your mother only. What genes are these?

mitochondrial DNA

Quantitative variation usually indicates ______________________________.

polygenic inheritance.

When does crossing over occur?

prophase 1

State the addition rule and give an original example.

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

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

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

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

Which of these events (aneuploidy, monosomy, trisomy, or polyploidy) results in Down syndrome? What are four characteristics of Down syndrome?

trisomy 1. Characteristic facial features 2. Short stature 3. Correctable heart defects 4. Developmental delays