slide1
Download
Skip this Video
Download Presentation
Fig. 4-1

Loading in 2 Seconds...

play fullscreen
1 / 34

Fig. 4-1 - PowerPoint PPT Presentation


  • 85 Views
  • Uploaded on

Chapter 4 overview. Fig. 4-1. Genetic recombination : mixing of genes during gametogenesis that produces gametes with combinations of genes that are different from the combinations received from parents. Independent assortment of homologous chromosomes (Anaphase I). Genes on non-

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Fig. 4-1' - vera-giles


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Chapter 4

overview

Fig. 4-1

slide2

Genetic recombination: mixing of genes during

  • gametogenesis that produces gametes with
  • combinations of genes that are different from
  • the combinations received from parents.
  • Independent assortment of homologous
  • chromosomes (Anaphase I). Genes on non-
  • homologous chromosomes (unlinked genes)
  • assort independently.
slide4

Using a testcross

to distinguish gamete genotypes

Fig. 4-7

slide5

50% = independent

assortment

(genes are not linked)

Fig. 4-8

slide6

Genetic recombination: mixing of genes during

  • gametogenesis that produces gametes with
  • combinations of genes that are different from
  • the combinations received from parents.
  • Independent assortment of homologous
  • chromosomes (Anaphase I). Genes on non-
  • homologous chromosomes (unlinked genes)
  • assort independently.
  • Crossing over (recombination among linked
  • genes)
slide7

cis linked: both dominant alleles on the same homolog

trans linked: dominant alleles on different homologs

Fig. 4-2

slide9

Crossing over

  • Physical exchanges among non-sister chromatids;
  • visualized cytologically as chiasmata
  • Typically, several crossing over events occur within
  • each tetrad in each meiosis (chiasmata physically
  • hold homologous chromosome together and assure
  • proper segregation at Anaphase I)

p. 115

slide10

Crossing over occurs at the four-strand stage

(pre-meiotic G2 or very early prophase I)

Fig. 4-4

slide12

Crossing over

  • Physical exchanges among non-sister chromatids;
  • visualized cytologically as chiasmata
  • Typically, several crossing over events occur within
  • each tetrad in each meiosis (chiasmata physically
  • hold homologous chromosome together and assure
  • proper segregation at Anaphase I)
  • The sites at which crossing over occur are random
  • The likelihood that a crossover occurs between any
  • two particular sites (genes) is a function of the
  • physical distance between those two sites
slide13

Crossing over usually affects a minority of chromatids in a collection of meioses – recombinants are typically a minority of products

Fig. 4-9

slide15

A.H. Sturtevant (1911-3): frequency of crossing over

between two genes is a function of their distance

apart on the chromosome; created the first genetic map

number of recombinants

Recombination frequency =

total number of progeny

One map unit = one centimorgan = 1% recombinants

slide16

Rationales:

    • Crossover events are random
    • Greater separation, greater likelihood that crossover will occur
    • Map distance should be sum of smaller intervals
    • Construct entire chromosome maps by mapping intervals
    • Linear map correlates with linear chromosome

Fig. 4-11

slide17

Markers used in trihybrid testcross

in Drosophila

v = vermilion eyes (red eyes; v+are red-brown)

cv = crossveinless (cv+ wings have crossveins)

ct = cut wing (ct+ wings have regular margins)

slide18

Data from three-point testcross

v+/ v cv+/ cv ct+/ ct X v / v cv / cv ct / ct

(trihybrid) (tester)

Progeny phenotypes

v cv+ ct+ 580

v+ cv ct 592

v cv ct+ 45

v+ cv+ ct 40

v cv ct 89

v+ cv+ ct+ 94

v cv+ ct 3

v+ cv ct+ 5

1448

slide19

Steps in solving three-point testcross problem

  • Anticipate and identify eight types of products (23)
  • Identify pairs of reciprocal products
slide20

Data from three-point testcross

v+/ v cv+/ cv ct+/ ct X v / v cv / cv ct / ct

(trihybrid) (tester)

Progeny phenotypes

v cv+ ct+ 580

v+ cv ct 592

v cv ct+ 45

v+ cv+ ct 40

v cv ct 89

v+ cv+ ct+ 94

v cv+ ct 3

v+ cv ct+ 5

1448

slide21

Steps in solving three-point testcross problem

  • Anticipate and identify eight types of products (23)
  • Identify pairs of reciprocal products
  • Identify parental types as the most frequent pair of
  • products
  • Identify double crossover products as least frequent
  • pair of products
slide22

Data from three-point testcross

v+/ v cv+/ cv ct+/ ct X v / v cv / cv ct / ct

(trihybrid) (tester)

Progeny phenotypes

v cv+ ct+ 580

v+ cv ct 592

v cv ct+ 45

v+ cv+ ct 40

v cv ct 89

v+ cv+ ct+ 94

v cv+ ct 3

v+ cv ct+ 5

1448

Parental types - nco

sco

sco

dco

slide23

Steps in solving three-point testcross problem

  • Anticipate and identify eight types of products (23)
  • Identify pairs of reciprocal products
  • Identify parental types as the most frequent pair of
  • products
  • Identify double crossover products as least frequent
  • pair of products
  • Compare the parental and double crossover products
  • to deduce the order of the three gene loci
slide24

Fig. 4-12

In dco products, the central marker is displaced

relative to the parental types

slide26

Steps in solving three-point testcross problem

  • Anticipate and identify eight types of products (23)
  • Identify pairs of reciprocal products
  • Identify parental types as the most frequent pair of
  • products
  • Identify double crossover products as least frequent
  • pair of products
  • Compare the parental and double crossover products
  • to deduce the order of the three gene loci
  • Compute map distances by breaking down the
  • results for each interval
slide27

Fig. 4-12

85 + 8

1448

(0.064)

183 + 8

1448

(0.132)

RF =

slide28

Fig. 4-12

85 + 8

1448

(0.064)

183 + 8

1448

(0.132)

RF =

13.2 m.u. 6.4 m.u.

v ct cv

slide29

Interference: crossing over in one region

interferes with simultaneous crossing over in

adjacent regions

Expected frequency of dco = product of frequency crossovers in two regions

0.132 X 0.064 = 0.0084

0.084 X 1448 = 12 expected (if two sco are independent events)

slide30

Interference: crossing over in one region

interferes with simultaneous crossing over in

adjacent regions

Expected frequency of dco = product of frequency crossovers in two regions

0.132 X 0.064 = 0.0084

0.084 X 1448 = 12 expected (if two sco are independent events)

Coefficient of coincidence = observed dco / expected dco

8 / 12 = 0.667

Interference = 1 – coefficient of coincidence

1 – 0.667 = 0.333

slide31

Fig. 4-14

Tomato karyotype (n=12)

slide32

Tomato linkage map

(1952)

Fig. 4-14

ad