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Biology Exam 3 > Chapter 15 > Flashcards

Chapter 15 Flashcards

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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
Q

Describe Morgan’s cross to study linked genes.

A

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
Q

What were the genotypes and phenotypes of P and F1 generations in Morgan’s cross?

A

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
Q

How did Morgan use a test cross to determine whether the genes for the traits were linked?

A

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
Q

What is genetic recombination?

A

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
Q

How did genetic recombination affect Morgan’s test cross?

A

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
Q

What are some of the mechanisms of genetic recombination?

A

Crossing over, independent assortment, random fertilization

31
Q

What is a linkage map?

A

A genetic map - ordered list of the genetic loci along a particular chromosome based on recombination frequencies

32
Q

What does a linkage map tell us about the likelihood of crossing over occurring?

A

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
Q

Describe nondisjunction.

A

Genes that are far apart on the same chromosome can have a recombination frequency near 50%

34
Q

What is aneuploidy?

A

results in an abnormal number of a particular chromosome

35
Q

How does aneuploidy relate to a monosomy or trisomy of the chromosomes?

A

A monosomic zygote has only one copy of a particular chromosome; A trisomic zygote has three copies of a particular chromosome

36
Q

How does aneuploidy affect an organism?

A

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
Q

What is polyploidy?

A

a condition in which an organism has more than two complete sets of chromosomes

38
Q

How does polyploidy relate to triploidy and tetraploidy of the chromosomes?

A

Triploidy (3n) is three sets of chromosomes; Tetraploidy (4n) is four sets of chromosomes;

39
Q

How does polyploidy affect plants?

A

common in plants; can lead to the production of a new species

40
Q

How does polyploidy affect animals?

A

Uncommon in animals; often detrimental to the animal involved

41
Q

How does deletion affect inheritance?

A

Deletion removes a chromosomal segment

42
Q

How does duplication affect inheritance?

A

Duplication repeats a segment

43
Q

How does inversion affect inheritance?

A

Inversion reverses the orientation of a segment within a chromosome

44
Q

How does translocation affect inheritance?

A

Translocation moves a segment from one chromosome to another

45
Q

What causes Down’s syndrome?

A

Down’s syndrome is an aneuploid condition that results from three copies of chromosome 21

46
Q

What causes Klinefelter’s syndrome?

A

Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals

47
Q

What causes Turner’s syndrome?

A

Turner’s syndrome, or monosomy X, produces X0 females, who are sterile and is the only known viable monosomy in humans

48
Q

Drosophila melanogaster

A

the scientific name of the fruit fly used by Morgan

49
Q

Wild type

A

the natural phenotype of fruit fly

50
Q

Mutant type

A

phenotypes developed in the lab by Morgan

51
Q

Double mutant

A

has a mutant allele for two genes

52
Q

Hemizygous

A

has one copy of an allele due to the gene being on the X and Y chromosomes

53
Q

Recombinants

A

recombinants - offspring with nonparental phenotypes

54
Q

Genetic map

A

an ordered list of the genetic loci along a particular chromosome

55
Q

Centimorgan

A

a genetic map unit that represents a 1% recombination frequency

56
Q

cytogenetic map

A

the visual appearance of a chromosome when stained and examined under a microscope

57
Q

Recombination frequency

A

frequency of producing non-parental phenotype combinations

Biology Exam 3 (6 decks)

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