Chapter 12 Demonstrating genetic principles using the garden pea

1
Chapter 12 Demonstrating genetic principles
using the garden pea
2
Genetics background

• Phenotype Physical appearance
• Genotype Genes that control a trait
• Homozygous 2 alleles are the same
• Heterozygous 1 allele each
• Dominant Only 1 dominant gene needs to be
  present for that trait to show
• Recessive Both alleles must be recessive for it
  to show

3
Monohybrid cross

• Phenotype
• I Yellow, dominant
• i Green, recessive
• P1 II, yellow
• P2 ii, green
• F1Ii, yellow
• F2 1 II2 Ii 1 ii

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Is it true?

• What is Chi-Square analysis?
• Chi-square
• S((observed expected)2 / expected)
• Degrees of freedom
• number of phenotypes - 1
• Monohybrid 1 (use Yates correction factor)
• Dihybrid 3

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Calculate chi-square for monohybrid 1

• Chi-square for I- ((41.25-41)-0.5)2/41.250.0015
• Chi-square for ii ((14-13.75)-0.5)2/13.750.0045
• Degree of freedom 1
• Go to chi-square table
• probability of observed outcome is between
  0.8-0.99, accept hypothesis. They obey laws of
  segregation.

6
Calculate chi-square for monohybrid 2

• Chi-square for R- ((41.25-41)-0.5)2/41.250.067
• Chi-square for rr ((14-13.75)-0.5)2/13.750.55
• Degree of freedom 1
• Go to chi-square table
• probability of observed outcome is between
  0.5-0.2, accept hypothesis. They obey laws of
  segregation.

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Phenotype ratio of dihybrid cross

• P1 AABB
• P2 aabb
• F1 AaBb
• F2
• 9 A-B-
• 3 A-bb
• 3 aaB-
• 1 aabb

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Calculate chi-square for dihybrid 1
9
Calculate chi-square for dihybrid 2

• Chi-square for I-R-
• (23-25.88)2/25.88 0.32
• Chi-square for I-rr (7-8.63)2/8.630.31
• Chi-square for iiRr (14-8.63)2/8.633.35
• Chi-square for iirr (2-2.88)2/2.880.27
• Sum of Chi - Square 4.24
• Degree of freedom 3
• Go to chi-square table
• probability of observed outcome is between
  0.5-0.2, accept hypothesis they obey laws
  independent assortment.

10
Six morphological traits of pea

• I-i yellow (I) green (i) cotyledon color
• R-r smooth (R) wrinkle (r) seed
• Tl-tl Tendrils (Tl) terminal leaflets (tl)
• Td-td presence (Td) absence (td) foliar
  dentation
• St-st normal (St) reduced (st) stipules
• Le-le normal height (Le) dwarf (le)

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What you need to do

• Calculate chi-square for all six traits for
  monohybrid cross to see whether they obey 31
  ratio
• Calculate chi-square for st-tl, tl-r, st-r for
  dihybrid cross to see whether they obey 9331
  ratio
• If they dont obey 9331 ratio, these two genes
  may be linked together. That means, they are on
  one chromosome
• Write a lab report on this!