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Linkage. chromosome theory of inheritance. Mendelian genes have specific loci (positions) on chromosomes Chromosomes undergo segregation and independent assortment during meiosis. Figure 12.2. /. /. /. /. 1. 1. 1. 1. 4. 4. 4. 4. P Generation. Yellow-round seeds ( YYRR ).

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chromosome theory of inheritance
chromosome theory of inheritance
  • Mendelian genes have specific loci (positions) on chromosomes
  • Chromosomes undergo segregation and independent assortment during meiosis
slide3

Figure 12.2

/

/

/

/

1

1

1

1

4

4

4

4

P Generation

Yellow-round

seeds (YYRR)

Green-wrinkled

seeds (yyrr)

y

Y

r

R

r

R

Y

y

Meiosis

Fertilization

r

y

R

Y

Gametes

All F1 plants produce

yellow-round seeds (YyRr).

F1 Generation

R

R

y

y

r

r

Y

Y

Meiosis

LAW OF SEGREGATION

The two alleles for each

gene separate.

LAW OF INDEPENDENT

ASSORTMENT Alleles of

genes on nonhomologous

chromosomes assort

independently.

r

r

R

R

Metaphase

I

y

Y

Y

y

1

1

r

r

R

R

Anaphase I

Y

Y

y

y

Metaphase

II

r

R

R

r

2

2

y

Y

y

Y

y

Y

Y

y

Y

y

y

Y

r

R

R

r

r

r

R

R

yr

yR

Yr

YR

YR

F2 Generation

An F1 F1 cross-fertilization

3

3

Fertilization results in the

9:3:3:1 phenotypic ratio

in the F2 generation.

Fertilization

recombines the R and

r alleles at random.

9

: 3

: 3

: 1

linked genes
linked genes
  • Genes located on the same chromosome that tend to be inherited together
  • Do not independently assort
slide6

What statistic would you use to verify that your observed values differed from your expected values?What would be the expected values?Hmm…not 1:1:1:1;more like 1:1

slide9

% Recombinant

Frequency or

= # map units apart two genes are

you try
You try…
  • What is the frequency of recombinants?How many map units apart are the two genes?
  • 500 offspring
  • 7 grey short recombinants
  • 8 black long recombinants
linkage map
linkage map
  • a genetic map of a chromosome based on recombination frequencies
  • the farther apart two genes are, the higher the probability that a crossover will occur between them
  • therefore the higher the recombination frequency
you try1
You try…
  • Flies can have black bodies (b), vestigial wings (vg), and cinnabar eyes (cn).
  • The cross-over frequencies are listed below:
  • b-cn 7.5%
  • b-vg 17%
  • vg-cn 9.5%
  • Draw the chromosome map. Label the distance btw the genes.
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