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General Bio 1 for science majors > Chapter 14 > Flashcards

Chapter 14 Flashcards

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1
Q

What characteristics did Gregor Mendel study?

A

Flower color in pea plants.

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2
Q

How did Gregor Mendel discover the basic principles of heredity?

A

By breeding garden peas in carefully planned experiments.

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3
Q

What is character?

A

A heritable feature that varies among individuals, such as flower color.

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4
Q

What is a trait?

A

A variant for a character, such as purple or white color for flowers.

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5
Q

What were the advantages of using pea plants?

A

Short generation time, large numbers of offspring, and mating could be controlled. Plants could be allowed to self pollinate or could be cross pollinated.

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6
Q

What did Mendel choose to track?

A

Only characters that occurred in two distinct alternative forms.

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7
Q

What is true breeding?

A

Plants that produce offspring of the same variety when they self pollinate.

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8
Q

What is hybridization?

A

Mating two contrasting, true-breeding varieties together.

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9
Q

What is the P generation?

A

The true-breeding parents that are used for hybrids.

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10
Q

What is the F1 generation?

A

The hybrid offspring of the P generation.

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11
Q

What is the F2 generation?

A

When F1 individuals self pollinate or cross pollinate with other F1 hybrids, the F2 generation is the result.

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12
Q

What was the explanation for heredity in the 1800s?

A

The “blending” hypothesis. Mendel’s results with the pea plants were not predicted by the blending hypothesis.

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13
Q

Why did Mendel’s experiment not match the blending hypothesis?

A

When Mendel crossed contrasting, true-breeding white and purple-flowered pea plants, all of the F1 hybrids were purple. When Mendel crossed the F1 generation, many of the F2 plants had purple flowers, while some had white. Mendel discovered a ratio of about three purple flowers to one white flower in the F2 generation.

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14
Q

What did Mendel call the purple flower color?

A

He called it a dominant trait, reasoning that only the purple flower factor was affecting flower color in the F1 hybrids.

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15
Q

What did Mendel call the white flower color?

A

He called them a recessive trait, reasoning that the factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation.

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16
Q

How did Mendel discover the heritable factor?

A

Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits. We call them genes now.

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17
Q

What model did Mendel develop?

A

He developed one to explain the 3:1 inheritance pattern he observed in F2 offspring. Four related concepts make up this model, and can be related to what we now know about genes and chromosomes.

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18
Q

What is the first concept?

A

Alternative versions of genes account for variations in inherited characters. For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers.

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19
Q

What are alleles?

A

Alternative versions of a gene. Each gene resides at a specific locus on a specific chromosome.

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20
Q

What is the second concept?

A

For each character, an organism inherits two alleles, one from each parent. Mendel made this deduction without knowing about chromosomes.

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21
Q

Where can the alleles be?

A

The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s generation, or the two alleles at a locus may differ, as in the F1 hybrids.

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22
Q

What is the third concept?

A

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 appearance.

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23
Q

Why did the F1 plants have purple flowers?

A

The F1 plants had purple flowers because the allele for that trait is dominant.

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24
Q

What is the fourth concept?

A

The law of segregation. The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. Thus, an egg or a sperm gets only one of the two alleles that are present in the organism.

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25
What does the segregation of alleles correspond to?
The distribution of homologous chromosomes to different gametes in meiosis.
26
How can possible combinations be shown?
By using a Punnett square. A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele.
27
What is a homozygote?
An organism with two identical alleles for a gene. It is said to be homozygous for the gene controlling that character.
28
What is a heterozygote?
An organism with two different alleles for a gene is a heterozygote, and is said to be heterozygous for the gene controlling that character. Unlike homozygotes, heterozygotes are not true-breeding.
29
What is a phenotype?
Physical appearance.
30
What is a genotype?
Genetic makeup.
31
Does an organism's traits reveal its genetic composition?
No. In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes.
32
What is a testcross?
To determine the genotype, breeding the mystery individual with a homozygous recessive individual, which is called a test cross. If any offspring display the recessive phenotype, the mystery parent must be heterozygous.
33
How did Mendel derive the law of segregation?
By following a single character. The F1 offspring produced in this cross were monohybrids, meaning that they were heterozygous for one character.
34
What is a monohybrid cross?
A cross between heterozygotes.
35
How did Mendel identify his second law of inheritance?
By following two characters at the same time. Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters.
36
What is a dihybrid cross?
A cross between F1 dihybrids can determine whether two characters are transmitted to offspring together as a unit or independently.
37
What is the law of independent assortment?
Mendel's second law, it states that each pair of alleles segregates independently of any other pair of alleles during gamete formation. This law only applies to genes on different, nonhomologous chromosomes or those far apart on the same chromosome.
38
What happens to genes that are located near each other on the same chromosome?
They tend to be inherited together.
39
What do Mendel's laws of segregation and independent assortment reflect?
The rules of probability that apply to tossing coins or rolling dice. When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss. In the same way, the alleles of one gene segregate into gametes independently of another gene's alleles.
40
What is the multiplication rule?
It states that the probability that two or more independent events will occur together is the product of their individual probabilities.
41
How can probability in an F1 monohybrid cross be determined?
By using the multiplication rule. Segregation in a heterozygous plant is like flipping a coin; each gamete has a 1/2 chance of carrying the dominant allele and a 1/2 chance of carrying the recessive allele.
42
What is the addition rule?
States that the probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities. The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous.
43
What is a multicharacter cross?
It is equivalent to two or more independent monohybrid crosses occurring simultaneously. In calculating the chances for various genotypes, each character is considered separately, then the individual probabilities are multiplied.
44
Are heritable characters determined by one gene?
No. The basic principles of segregation and independent assortment apply even to more complex patterns of inheritance.
45
How can inheritance of characters deviate from simple patterns?
When alleles are not completely dominant or recessive, when a egene has more than two alleles, and when a gene produces multiple phenotypes.
46
What is complete dominance?
Occurs when phenotypes of the heterozygote and dominant homozygote are identical.
47
What is incomplete dominance?
The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties.
48
What is codominance?
Two dominant alleles affect the phenotype in separate, distinguishable ways.
49
What is the relationship between dominance and phenotype?
In the case of pea shape, the dominant allele coes for an enzyme that converts an unbranched form of starch in the seed to a branched form. The recessive allele codes for a defective form of the enzyme, which leads to an accumulation of unbranched starch, and this causes water to enter the seed, which then wrinkles as it dries.
50
What is Tay-Sachs disease?
A fatal inherited disorder; a dysfunctional enzyme causes an accumulation of lipids in the brain. At the organismal level, the allele is recessive, and at the biochemical level, the phenotype (enzyme activity level) is incompletely dominant. At the molecular level, the alleles are codominant.
51
What is the frequency of dominant alleles?
One baby out of 400 in the United States is born with extra fingers or toes. This condition, polydactyly, is caused by a dominant allele, found much less frequently in the population than the recessive allele.
52
Can there be multiple alleles for genes?
Yes. Example; four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme that attaches A or B carbohydrates to red blood cells, Ia, Ib, and I.
53
What is pleiotropy?
Most genes have multiple phenotypic effects. For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle cell disease.
54
Can traits be determined by more than one gene?
Yes. In epistasis, one gene affects the phenotype of another due to interaction of their gene products. In polygenic inheritance, multiple genes independently affect a single trait.
55
What is epistasis?
Expression of a gene at one locus alters the phenotypic expression of a gene at a second locus. For example, in Labrador retrievers and many other mammals, coat color depends on two genes.
56
What happens in mammals and their coat colors?
One gene determines the pigment color (with allelles B for black and b for brown). The other gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair.
57
What happens if heterozygous black labs (BbEe) are mated?
You can expect the dihybrid F2 ratio of 9:3:3:1. However, a Punnett square shows that the phenotypic ratio will be 9 black to 3 chocolate to 4 yellow labs. Epistatic interactions produce a variety of ratios, all of which are modified versions of 9:3:3:1.
58
What are quantitative characters?
Those that vary in the population along a continuum.
59
What does quantitative variation indicate?
Polygenic inheritance, an additive effect of two or more genes on a single phenotype. Height is a good example of polygenic inheritance; over 180 genes affect height.
60
What is skin pigmentation in humans controlled by?
Many separately inherited genes.
61
What happens when the phenotype for a character depends on environment as well?
The phenotypic range is broadest for polygenic characters. Traits that depend on multiple genes combined with environmental influences are called multifactorial. Ex. Hydrangeas in different pH soil; basic soil will be pink flowers and acidic soil with free aluminum will be blue.
62
What does an organism's phenotype include?
All aspects of its physical appearance, internal anatomy, physiology, and behavior. An organism's phenotype reflects its overall genotype and unique environmental history.
63
Why are humans not good subjects for genetic research?
Generation time is too long, parents produce relatively few offspring, and breeding experiments are unacceptable. However, basic Mendelian genetics endures as the foundation of human genetics.
64
What do geneticists analyze in human genetics?
The results of human matings that have already occurred.
65
What is a pedigree?
A family tree that describes the inheritance of a trait across generations.
66
What can pedigrees be used for?
To make predictions about future offspring. We can use the multiplication and addition rules to predict the probability of specific phenotypes.
67
How are genetic disorders inherited?
In a recessive manner. These range from relatively mild to life threatening.
68
When do recessively inherited disorders show up?
Only in individuals homozygous for the allele.
69
What are carriers?
Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal. Most individuals with recessive disorders are born to carrier parents.
70
What is albinism?
A recessive condition characterized by a lack of pigmentation in skin and hair.
71
What happens with rare diseases?
It is unlikely that two carriers will meet and mate.
72
What is consanguineous mating?
Matings between close relatives. They increase the chance that both parents of a child carry the same rare allele. Most societies and cultures have laws or taboos against marriages between close relatives.
73
What is cystic fibrosis?
The most common lethal genetic disease in the United States (1/2500 of European descent). The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes, leading to a buildup of chloride ions outside the cell.
74
What are cystic fibrosis symptoms?
Include mucus buildup in some internal organs, and abnormal absorption of nutrients in the small intestine.
75
What happens when people inherit cystic fibrosis?
Untreated, it can cause death by age 5. Daily doses of antibiotics to stop infection and physical therapies can prolong life. In the US, more than half of those with cystic fibrosis now survive into their 40s.
76
What is sickle cell disease?
It affects 1/400 African Americans, and is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells. In homozygous individuals, all hemoglobin is abnormal.
77
What are symptoms of sickle cell disease?
Physical weakness, pain, organ, damage, and even paralysis.
78
What happens when people are heterozygous for sickle cell disease?
Usually healthy but may suffer some symptoms (also called sickle cell trait). About 1/10 African Americans have sickle cell trait, and heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous in regions where malaria is common.
79
What disorders are caused by dominant alleles?
Dominant alleles that cause a lethal disease are rare and arise by mutation. One is achondroplasia, a form of dwarfism caused by a rare dominant allele.
80
What can also affect inheritance of a disease?
The timing of onset. Huntington's disease is a degenerative disease of the nervous system, and the disease has no obvious phenotypic effects until the individual is about 35-40 yrs of age. Once the deterioration of the nervous system begins, the condition is irreversible and fatal.
81
Can diseases have genetic AND environmental components?
Yes. Heart disease, cancer, alcoholism, and many mental illnesses. Lifestyle always has a tremendous effect on phenotype.
82
What happens if both members of a couple had a sibling with a recessively inherited illness?
They are both carriers.
83
What is amniocentesis?
The liquid that bathes the fetus is removed and tested for certain genetic disorders.
84
What is chorionic villus sampling (CVS)?
A sample of the placenta is removed and tested. Other techniques like ultrasound allow fetal health to be assessed visually in utero.
85
What is PKU?
A common test for phenylketonuria, a recessively inherited disorder that occurs in 1 out of every 10,000-15,000 births in the US.

General Bio 1 for science majors (11 decks)

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