Ch.14 genetics
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Transcript of Ch.14 genetics
Genetics
Chapter 14
Gregor Mendel
• Father of Genetics
• Used peas to study heredity
Vocabulary
• Heredity: passing of traits from parent to offspring
• Genetics: study of heredity
• True-breeding: self-pollinating plant always produces the same offspring
• Allele: alternative versions of a gene
More Vocabulary
• Dominant: A
• Recessive: a
• Homozygous: AA or aa
• Heterozygous: Aa
Law of Segregation
• Separation of alleles into separate gametes
• 50% chance that one allele will go into a gamete
Test Cross
Law of Independent Assortment
Incomplete Dominance
Multiple Alleles
Epistasis
• A gene at one locus alters the expression of a gene at another locus.
• Example: – Black coat (B) is
dominant to brown (b)– Pigment color (C) is
dominant to no pigment color (c)
Polygenic Traits
• Additive effect of multiple genes on a single phenotype
• Results in normal distribution
• Examples: skin color, height
Effect of Environment on Phenotype
More acidic soil Less acidic soil
Pleiotropic Effects
Pedigree Analysis
Pedigree
Male
Female
Heterozygous
Shows trait
Probabilities
Aa aaChild will have recessive trait?
aa
Chance of “a” allele from dad?
1/2
Chance of “a” allele from mom?
2/2 (1)
Total
1/2 x 1 = 1/2
Recessive characteristicsInheritance pattern
•Trait tends to skip generations
Dominant characteristics
•Trait does not skip generations•Occurs frequently within a family
Sex linked characteristics•Tend to occur more in males than in females
•Color-blindness •Hemophilia
X-linked Recessives: More commonly seen in Males
• Why?• Males only need one recessive
allele to see trait.• E.g. Color-blindness
• XC – 92 % of alleles• Xc – 8 % of alleles
Females Males
92%
8%
(0.92)(0.92) = 85%
2x (0.92)(0.08) = 15%
(0.08)(0.08) = 0.64%
XCXC
XCXc
XcXc
XCyXcy
Problem:
A woman with normal vision whose father was color-blind marries a color-blind male. What percent of the couple’s sons will be color-blind?
1. All
2. 75%
3. 50%
4. 25%