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Biology Exam 3 > Chapter 15 > Flashcards

Chapter 15 Flashcards

1
Q

What is the chromosomal theory of inheritance?

A

States that Mendelian genes have specific loci (positions) on chromosomes and chromosomes undergo segregation and independent assortment.

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2
Q

How did Morgan’s work with Drosophila enhance Mendel’s findings?

A

Morgan’s work accounted for Mendel’s laws of segregation and independent assortment and added to it by working out the effects of sex-linked traits and linked genes.

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3
Q

Why are fruit flies a good experimental model for genetic studies?

A
  • They produce many offspring
  • A generation can be bred every two weeks
  • They have only four pairs of chromosomes
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4
Q

What notation did Morgan use to indicate wild type and mutant type?

A

He used lower case letters to represent traits and a superscript plus sign to represent the dominant, wild type traits

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5
Q

Why did he use a different notation from regular dominant/recessive traits?

A

The traits he was studying were generated in his lab, and not natural traits

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6
Q

Describe the sex chromosomes of fruit flies.

A

Female are XX and males are XY

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7
Q

Compare the genes of an X and a Y sex chromosome.

A

They have a few genes in common, but the X has hundreds of genes that aren’t found on the Y and the Y has many genes not found on the X.

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8
Q

Sex chromosomes for grasshoppers

A

female has two copies of the sex chromosome, males have one

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9
Q

Sex chromosomes for chickens

A

ZW system where the females have ZW and the males have ZZ

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10
Q

Sex chromosomes for bees

A

females are diploid, males are haploid

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11
Q

Describe sex-linked genes.

A

A gene that is located on either sex chromosome

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12
Q

How do sex-linked genes affect gene expression?

A

For a recessive X-linked trait to be expressed: A female needs two copies of the allele (homozygous), A male needs only one copy of the allele (hemizygous); X-linked recessive disorders are much more common in males than in females

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13
Q

How are sex-linked genes different from linked genes?

A

Linked genes are genes located on the same chromosome that tend to be inherited together and are found on the autosomes

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14
Q

Describe the cross that Morgan performed with red-eyed and white-eyed flies.

A

Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type)

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15
Q

What was the outcome of Morgan’s experiment?

A

The F1 generation all had red eyes; The F2 generation showed the 3:1 red: white eye ratio, but only males had white eyes

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16
Q

How did Morgan’s experiment support the concept of sex-linked genes?

A

Morgan determined that the white-eyed mutant allele must be located on the X chromosome

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17
Q

Describe x-linked traits.

A

Genes on the X chromosome

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18
Q

Are x-linked traits more commonly expressed in males or females?

A

Males

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19
Q

Why can mothers, but not fathers, pass x-linked genes to their sons?

A

Because fathers give a Y to their sons, but mothers give an X

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20
Q

What is X inactivation?

A

the X chromosomes in each cell are randomly inactivated during embryonic development

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21
Q

What is a Barr body? Is this found in females, males, or both?

A

It is a condensed, inactive X. It is found in females.

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22
Q

How does X inactivation lead to calico cats?

A

Female cats are a mosaic of the black and orange alleles that are found on their X chromosomes

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23
Q

What traits did Morgan cross to study linked genes?

A

body color and wing size

24
Q

How does the inheritance pattern of linked genes differ from the inheritance pattern described by Mendel?

A

Rather than having a 9:3:3:1 ratio from a dihybrid cross and recombination of the parental phenotypes, it will have a 3:1 ratio, and only the parental phenotypes

25
Describe Morgan’s cross to study linked genes.
Morgan crossed flies that differed in traits of body color (gray (wild type) vs black (mutant)) and wing size (normal (wild type) vs vestigial (mutant))
26
What were the genotypes and phenotypes of P and F1 generations in Morgan’s cross?
P = b+b+vg+vg+; gray body, normal wings x bbvgvg; black body, vestigial wings; F1 = b+bvg+vg; gray body, normal wings x bbvgvg; black body, vestigial wings
27
How did Morgan use a test cross to determine whether the genes for the traits were linked?
Morgan found that body color and wing size are usually inherited together in specific combinations (parental phenotypes); He noted that these genes do not assort independently, and reasoned that they were on the same chromosome
28
What is genetic recombination?
Production of offspring with combinations of traits differing from either parent; Mendel observed that combinations of traits in some offspring differ from either parent; Offspring with a phenotype matching one of the parental phenotypes are called parental types; Offspring with nonparental phenotypes (new combinations of traits) are called recombinant types, or recombinants.
29
How did genetic recombination affect Morgan’s test cross?
Morgan discovered that genes can be linked, but incompletely because some recombinant phenotypes were observed; He proposed that a process (crossing over) must occasionally break the physical connection between genes on the same chromosome
30
What are some of the mechanisms of genetic recombination?
Crossing over, independent assortment, random fertilization
31
What is a linkage map?
A genetic map - ordered list of the genetic loci along a particular chromosome based on recombination frequencies
32
What does a linkage map tell us about the likelihood of crossing over occurring?
the farther apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency
33
Describe nondisjunction.
Genes that are far apart on the same chromosome can have a recombination frequency near 50%
34
What is aneuploidy?
results in an abnormal number of a particular chromosome
35
How does aneuploidy relate to a monosomy or trisomy of the chromosomes?
A monosomic zygote has only one copy of a particular chromosome; A trisomic zygote has three copies of a particular chromosome
36
How does aneuploidy affect an organism?
Some types of aneuploidy appear to upset the genetic balance less than others, resulting in individuals surviving to birth and beyond; These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of aneuploidy
37
What is polyploidy?
a condition in which an organism has more than two complete sets of chromosomes
38
How does polyploidy relate to triploidy and tetraploidy of the chromosomes?
Triploidy (3n) is three sets of chromosomes; Tetraploidy (4n) is four sets of chromosomes;
39
How does polyploidy affect plants?
common in plants; can lead to the production of a new species
40
How does polyploidy affect animals?
Uncommon in animals; often detrimental to the animal involved
41
How does deletion affect inheritance?
Deletion removes a chromosomal segment
42
How does duplication affect inheritance?
Duplication repeats a segment
43
How does inversion affect inheritance?
Inversion reverses the orientation of a segment within a chromosome
44
How does translocation affect inheritance?
Translocation moves a segment from one chromosome to another
45
What causes Down’s syndrome?
Down’s syndrome is an aneuploid condition that results from three copies of chromosome 21
46
What causes Klinefelter’s syndrome?
Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals
47
What causes Turner’s syndrome?
Turner's syndrome, or monosomy X, produces X0 females, who are sterile and is the only known viable monosomy in humans
48
Drosophila melanogaster
the scientific name of the fruit fly used by Morgan
49
Wild type
the natural phenotype of fruit fly
50
Mutant type
phenotypes developed in the lab by Morgan
51
Double mutant
has a mutant allele for two genes
52
Hemizygous
has one copy of an allele due to the gene being on the X and Y chromosomes
53
Recombinants
recombinants - offspring with nonparental phenotypes
54
Genetic map
an ordered list of the genetic loci along a particular chromosome
55
Centimorgan
a genetic map unit that represents a 1% recombination frequency
56
cytogenetic map
the visual appearance of a chromosome when stained and examined under a microscope
57
Recombination frequency
frequency of producing non-parental phenotype combinations

Biology Exam 3 (6 decks)

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