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Biology: Genetics > Chapter 5: Chromosome Mapping in Eukaryotes > Flashcards

Chapter 5: Chromosome Mapping in Eukaryotes Flashcards

1
Q

What are the units of transmission in meiosis?

A

Chromosomes, NOT genes

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2
Q

What are linked genes?

A

Linked genes are genes that are likely to be inherited together because they are physically close to one another on the same chromosome.

Chromosomes have the potential to recombine, If genes are close together, the chances of being recombined are higher than if they are far away from each other.

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3
Q

The frequency of crossing over on a single chromosome is proportional to…

A

Distance between them

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4
Q

What does crossing over result in?

A

Recombination

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5
Q

What do chromosome maps indicate?

A

The relative location of genes on a chromosome

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6
Q

Meiotic Consequences: independent assortment

A

No linkage exhibited

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7
Q

Meiotic Consequences: Linkage without crossing over

A

Complete linkage

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8
Q

Meiotic Consequences: Linkage with crossing over

A

Generates recombinant gametes

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9
Q

What is complete linkage?

A

0% recombination

Parental combinations of alleles always segregate together into the same gamete

Extremely rare

For this to occur, the alleles at the two loci are physically attached to the same chromatid and will nearly always segregate together into the same gamete.

No crossing over between two genes

Produces parental nonrecombinant gametes

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10
Q

What is crossing over?

A

-Occurs between two nonsister chromatids
-Both parental and recombinant (crossover) gametes are produced

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11
Q

What is the linkage ratio?

A

Complete linkage between two genes due to close proximity

-Results in unique F2 phenotypic ration results

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12
Q

What is a linkage group?

A

-Genes on the same chromosome are part of a linkage group

-Number of linkage groups should correspond to haploid number of chromosomes

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13
Q

Chiasmata

A

-Synapsed chromosomes in meiosis wrap around each other
-CHIASMATA: the point at which two non homolog pairs touch when crossing over

-X shaped intersections with points of overlap
-Points of genetic exchange

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14
Q

The percentage of offspring resulting from recombinant gametes depends on distance between two genes on ________ chromosome

(same or different?)

A

Same

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15
Q

Two genes that are located close to each other along a chromosome are less likely to have a ____________

A

Chiasma

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16
Q

Sturtevant (this is the name of the scientist dude)

A

-He compiled data from crosses
-Recombination frequencies between linked genes are ADDITIVE

17
Q

Frequencies of exchange is an estimate of relative ….

A

distance between two genes

18
Q

Map unit (mu)

A

1 percent recombination between two genes on a chromosome

Also called the centi-Morgan (cM)

RELATIVE distances, not EXACT

19
Q

Single Crossover (SCO)

A

-Occurs between two nonsister chromatids
-Recombination is observed in 50 percent of gametes
-In genes that are 50 cM apart, crossing over can be expected between 100 percent of tetrad

20
Q

When a single crossover event takes place in the tetrad stage, what gametes are produced?

A

-Two noncrossover (parental) gametes are produced

-two crossover (recombinant) gametes are produced

21
Q

What are single crossovers used to determine?

A

the distance between two linked genes

22
Q

What are double corssovers, and what do they help determine?

A

-It is the double exchanges of genetic material

-Used to determine the distance between THREE linked genes

-In this case, genes must be heterozygous for two alleles

23
Q

What are the three criteria for three-point mapping?

A

-Parent must be heterozygous for all three genes under consideration

-Phenotypic class must reflect the genotype of gametes of parents

-Sufficient number of offspring must be produced for a representative sample

24
Q

What is a Three-point cross?

A

-Determining the distance and order of three genes on one chromosome (doing it at three genes at a time)

25
Q

Noncrossover F2 phenotypes occurs…

A

in the greatest proportion of offspring

26
Q

Double crossover (DCO) phenotypes occurs…

A

in the smallest proportion

27
Q

Reciprocal Classes of phenotypes

A

-F2 phenotypes compliment each other
-Derived from heterozygote
-Have wild type and mutant for all three genes

??

28
Q

Determining gene sequence: two methods?

A

Method 1: based in the three possible arrangements of genes

Method 2: uses three possible arrangements as basis, BUT it also considers the double-crossover event

29
Q

There are a large number of mutants in organisms like…

These organisms allow for ….

A

-Drosophila
-Maize
-Mice

Allows for the construction of extensive chromosome mapping

30
Q

What are DNA markers ?

What are the earliest examples of DNA markers?

A

-Short segments of DNA with known sequence and location

-Useful landmarks for mapping

-Earliest examples of DNA markers:
-RFLPs and microsatellites

Another example: Single-nucleotide polymorphisms

31
Q

What are RFLPs (what does it stand for, etc.)?

A

-Restriction fragment length polymorphisms

-polymorphic sites
-generated when specific DNA sequences are recognized and cut by restriction enzyme

32
Q

What are microsatellites?

A

-Short repetitive sequences
-Found throughout the genome

33
Q

What are single-nucleotide polymorphisms? provide an example of what they screen?

A

-Found throughout the genome
-Used by geneticists to identify and locate related genes
-Used to screen for diseases
Example: Cystic fibrosis

34
Q

What is cystic fibrosis? Give a description and relate it to DNA markers

A

-Gene located by using DNA markers

-Life-shortening autosomal recessive exocirne disorder

-Gene causing disorder found on chromosome 7

35
Q

During which phase in meiosis does crossing over take place in?

A

Prophase I of meiosis

36
Q
A

Biology: Genetics (7 decks)

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