mendel's genetics
TRANSCRIPT
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Biology, Seventh Edition Solomon • Berg • Martin
Chapter 10
The Basic Principles The Basic Principles of Heredityof Heredity
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
TerminologyTerminology
•Phenotype
•Genotype
•Locus
•Allele
•Dominant allele
•Recessive allele
•Homozygous
•Heterozygous
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Mendel’s principles of inheritance• Segregation
–During meiosis, alleles for each locus segregate
• Independent assortment–Alleles of different loci distributed randomly
into the gamete–Results in recombination–Production of new gene combinations not
found in parent
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Seven characters in Mendel’s study of pea plants
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Oneof Mendel’spea crosses
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Genelociand theiralleles
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Monohybrid cross• Cross between homozygous parents• Differ at one locus
• Dihybrid cross• Differ at two loci
• Test cross• Between individual of unknown
genotype and homozygous recessive individual
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Monohybridcross in guinea pigs
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Dihybridcrossinguinea pigs
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Test cross inguinea pigs
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Genetic ratios can be expressed as probabilities• Product rule predicts combined
probability of independent events• Sum rule predicts combined probability
of mutually exclusive events
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Rulesof probability
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Segregation• Results from homologous chromosomes
separating during meiosis
• Independent assortment• Orientation of homologous chromosomes
on the metaphase plate determines how chromosomes are distributed
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Chromosomalbasis forsegregation
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Linkage• Tendency for a group of genes on same
chromosome to be inherited together
• Recombination of linked genes• Results from crossing-over in meiotic
prophase I• By measuring frequency of
recombination, can construct linkage map of chromosome
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Two-pointtest cross todetect linkagein fruit flies
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Crossing-over
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Sex chromosomes• Cells of females of many species contain
two X chromosomes• Males have single X chromosome and
single, smaller Y chromosome• Y chromosome determines male sex in
most species of mammals
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Sex determinationin mammals
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
X-linked red-green colorblindness
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Dosage compensation in female mammals
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Incomplete dominance• Heterozygote is intermediate in
phenotype
• Codominance• Heterozygote simultaneously expresses
the phenotypes of both homozygotes
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Incompletedominancein four o’clocks
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Multiple alleles in rabbits
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Geneinteractionin chickens
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Epistasis in Labrador retrievers
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
• Norm of reaction• Range of phenotypic possibilities from a
single genotype under different environmental conditions
• Example is height in human–Can be modified by factors such as diet–Genes that affect height set norm of reaction–Environment molds phenotype within norm
of reaction
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Biology, Seventh Edition CHAPTER 10 The Basic Principles of Heredity
Polygenicinheritance inhuman skinpigmentation