Chapter 15 : The Chromosomal Basis Of Inheritance Flashcards

1
Q

Chromosome Theory of Inheritance

A

Genes occupy specific positions on chromosomes, and it’s the random alignment of pairs of homologous chromosomes at the metaphase 1 and the separation of homologs in anaphase 1 that result in independent assortment and segregation of alleles in gamete formation.

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2
Q

The normal phenotype found most commonly in nature; represented by what

A

Wild type; a superscript

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3
Q

Alternative traits, assumed to have arisen as mutations

A

Mutant phenotypes

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4
Q

Females are XX, and produce eggs that each have an X chromosome. What are males?

A

Males are XY, and produce two kinds of sperm, each with either an X or a Y chromosome

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5
Q

Whether the gonads of an embryo develop into tested or ovaries depends on the presence or absence of what gene

A

SRY gene

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6
Q

Where is the SRY gene found

A

On the Y chromosome

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7
Q

Genes located on either sex chromosome are called :

A

Sex-linked genes

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8
Q

Approximately how many genes are located on the Y chromosome, and where are about half of these genes expressed?

A

78; in the testis

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9
Q

Approximately how many genes are located on the X chromosome?

A

1,100

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10
Q

From where do males inherit X-linked alleles

A

The mother

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11
Q

Where do daughters inherit X-linked alleles

A

Both parents

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12
Q

What condition is a result of a lack of a key muscle protein

A

Duchenne muscular dystrophy

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13
Q

What trait is characterized by excessive bleeding due to the absence of one or more blood-clotting proteins

A

Hemophilia

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14
Q

After X inactivation, the other X chromosome is contracted into the Barr body. Where is this located?

A

Inside the nuclear membrane

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15
Q

Both males and females having an equal dosage of most X-linked genes is a result of what

A

X inactivation

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16
Q

Is the selection of which X chromosome to be inactivated planned or a random event

A

Random event in embryonic cells

17
Q

Genes located near eachother on the same chromosome tend to be inherited together. What are these called

A

Linked genes

18
Q

Offspring with combos of traits that are different from those of either P generation parent is a result of what

A

Genetic Recombination

19
Q

What is a genetic map

A

An ordered list of genes on a chromosome

20
Q

Recombination frequency

A

Percentage of recombinant offspring produced in a genetic cross

21
Q

What did A.H. Sturtevant suggest about recombination frequencies

A

That they reflect the relative distance between genes

22
Q

Is the probability of crossing over occurring greater or lesser if the genes are farther apart

23
Q

When does nondisjunction occur?

A

When a pair of homologous chromosomes does not separate properly in meiosis 1, or when sister chromatids do not separate in meiosis 2.

24
Q

Sometimes a gamete receives either two copies or no copies of a chromosome. What is this a result of?

A

Non disjunction

25
A nontypical number of a particular chromosome
Aneuploidy
26
What is the chromosome number if a zygote is trisomic for that chromosome?
2n+1
27
What is the chromosome number if a zygote is monosomic for that chromosome?
2n-1
28
A chromosomal alteration in which an organism has more than two complete chromosomal sets (like triploidy or tetraploidy)
Polyploidy
29
Chromosome fragments that are lost
Deletion
30
When chromosome fragments join to a sister chromatid
Duplication
31
When chromosome fragments break off, join a sister chromatid, and rejoin the original chromosome in the reverse orientation
Inversion
32
When chromosome fragments break off, join a sister chromatid, then join a nonhomologous chromosome
Translocation
33
What is the difference between an organism with a trisomy and a triploid organism?
Trisomy means there is an extra chromosome (2n+1), but a triploid organism has a whole nother complete set of chromosomes.
34
What is Down syndrome also known as?
Trisomy 21