gene linkage inheritance patterns for ---two genes on the same chromosome ---genes on the sex...
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Gene LinkageGene Linkage
Inheritance Patterns for Inheritance Patterns for
---Two Genes on the Same Chromosome---Two Genes on the Same Chromosome
---Genes on the Sex Chromosomes ---Genes on the Sex Chromosomes
Sex DeterminationSex Determination
Sex ChromosomesSex Chromosomes: homologous : homologous chromosomes that differ in size and chromosomes that differ in size and genetic composition between males and genetic composition between males and femalesfemales
Human Human
ChromosomeChromosome
XX YY
SizeSize LargerLarger SmallerSmaller
Genetic Genetic
CompositionComposition
Multiple Multiple
genesgenes
unrelated unrelated
to genderto gender
Very few genesVery few genes
SRY region determines SRY region determines maleness maleness
Sex DeterminationSex Determination
Autosome:Autosome: any chromosome that is any chromosome that is not a sex chromosomenot a sex chromosome
Humans have Humans have 22 autosome pairs 22 autosome pairs and 1 pair of sex and 1 pair of sex chromosomeschromosomes
Sex Determination Sex Determination
Female Male Female Male XX x XYXX x XY
XX
YY
X XX X
XXXX XXXX
XYXY XYXY
Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring ½ Female + ½ Male½ Female + ½ Male
Sex Linked Genes Sex Linked Genes Hemophilic Male Non-hemophilic Hemophilic Male Non-hemophilic Female Female (father is hemophilic)(father is hemophilic)
XXhh
YY
XXHH X Xhh
XXHHXXhh XXhhXXhh
XXHHYY XXhhYY
Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring¼ hemophilic males + ¼ non-hemophilic males¼ hemophilic males + ¼ non-hemophilic males
¼ hemophilic females + ¼ non-hemophilic females¼ hemophilic females + ¼ non-hemophilic females
XXhhY x XY x XHHXXhh
Males are Males are hemizygous for hemizygous for traits on thetraits on the X chromosomeX chromosome
Females can beFemales can behomozygous or homozygous or heterozygous for heterozygous for traits on thetraits on the X chromosomeX chromosome
DadDadXXhhYY
XXhh
Patterns of InheritancePatterns of Inheritance
• Autosomal DominantAutosomal Dominant• Autosomal RecessiveAutosomal Recessive• Sex-Linked Dominant (X-linked) Sex-Linked Dominant (X-linked) • Sex-Linked Recessive (X-linked)Sex-Linked Recessive (X-linked)
Pedigree for An Autosomal Dominant TraitPedigree for An Autosomal Dominant Trait
Pedigree for Albinism: Pedigree for Albinism: An Autosomal Recessive TraitAn Autosomal Recessive Trait
Pedigree forPedigree for Hemophilia, Hemophilia, An X-linked Recessive Trait An X-linked Recessive Trait
Pedigree forPedigree for Colorblindness, Colorblindness, An X-linked Recessive Trait An X-linked Recessive Trait
Patterns of InheritancePatterns of Inheritance
• Autosomal DominantAutosomal Dominant
• Autosomal RecessiveAutosomal Recessive
• Sex-Linked Dominant (X-linked) Sex-Linked Dominant (X-linked)
• Sex-Linked Recessive (X-linked)Sex-Linked Recessive (X-linked)
• Mitochondrial InheritanceMitochondrial Inheritance
Linked GenesLinked Genes
Mendel’s Mendel’s experimentsexperiments
Linked GenesLinked Genes
Gene Gene locationlocation
Genes on separate Genes on separate chromosomes or far chromosomes or far apart on the same apart on the same chromosomechromosome
Genes on the same Genes on the same chromosomechromosome
Gamete Gamete typestypes
Equal numbers of all Equal numbers of all possible allele possible allele combinationscombinations
More parental More parental combinations than combinations than recombinant recombinant combinationscombinations
How Do We Study How Do We Study Gene Linkage?Gene Linkage?
Example from the Fruit FlyExample from the Fruit Fly
Red eyes, x Pink eyesRed eyes, x Pink eyes
Beige body Ebony bodyBeige body Ebony body
RRBBRRBB rrbbrrbb
F1: Red eyes, Beige bodyF1: Red eyes, Beige body RrBb RrBb
Testcross: cross to individual of Testcross: cross to individual of known genotype known genotype
F1: Red eyes X Pink eyesF1: Red eyes X Pink eyes
Beige body Ebony bodyBeige body Ebony body
RrBbRrBb rrbbrrbb
How Do We Study How Do We Study Gene Linkage? Gene Linkage?
How Do We Study How Do We Study Gene Linkage? Gene Linkage?
F2 phenotypeF2 phenotype Number of Number of OffspringOffspring
Expected for Expected for Unlinked GenesUnlinked Genes
Red eyesRed eyes
Beige bodyBeige body
398398 250250
Pink eyesPink eyes
Ebony bodyEbony body
382382 250250
Red eyesRed eyes
Ebony bodyEbony body
108108 250250
Pink eyesPink eyes
Beige bodyBeige body
112112 250250
How Do We Study How Do We Study
Gene Linkage?Gene Linkage?
If genes are linked: If genes are linked:
Red eyes, x Pink eyesRed eyes, x Pink eyes
Beige body Ebony bodyBeige body Ebony body
r br b
R BR B
F1: Red eyes, Beige bodyF1: Red eyes, Beige body
R BR B
R BR B
r br b
r br b
F1: Red eyes, Beige bodyF1: Red eyes, Beige body
How Do We Study How Do We Study
Gene Linkage?Gene Linkage?
R BR B
r br bXX
R BR B
r br b r Br B
R bR b
Four types of gametes are producedFour types of gametes are produced Parental Parental Recombinant Recombinant
Alleles are inAlleles are inCis ConfigurationCis Configuration
How Do We Study How Do We Study Gene Linkage?Gene Linkage?
F1:Red eyes X Pink eyesF1:Red eyes X Pink eyes
Beige body Ebony bodyBeige body Ebony body
R BR B
r br b
r br b R bR b r Br B
R BR B
r br b
r br b
r br b
R BR B
r br b
r br b
r br b
R bR b
r br b
r Br B
r br b
How Do We Study How Do We Study Gene Linkage?Gene Linkage?
F2 phenotypeF2 phenotype Number of Number of OffspringOffspring
Chromosome Chromosome arrangementarrangement
Red eyesRed eyes
Beige bodyBeige body
398398 RB//rbRB//rb
ParentalParental
Pink eyesPink eyes
Ebony bodyEbony body
382382 rb//rbrb//rb
ParentalParental
Red eyesRed eyes
Ebony bodyEbony body
108108 Rb//rbRb//rb
RecombinantRecombinant
Pink eyesPink eyes
Beige bodyBeige body
112112 rB//rbrB//rb
RecombinantRecombinant
Genetic Map UnitsGenetic Map Units
1% recombination = 1 map unit1% recombination = 1 map unit 108 + 112108 + 112 x 100 = 22% x 100 = 22% 10001000 These genes are located 22 map units These genes are located 22 map units
apart on the same chromosome.apart on the same chromosome.Map is drawn as: Map is drawn as:
R BR B
I 22 map units II 22 map units I
Knowing the gene distance allows us to predict the expected percentages of each type Knowing the gene distance allows us to predict the expected percentages of each type of gamete. of gamete.
How Do We Study How Do We Study
Gene Linkage?Gene Linkage?
ParentalParental Recombinant Recombinant
XXr Br B
R bR b
r Br B
R bR b
39%39%
39%39%78%78%
R BR B
r br b 11%11%
11%11%22%22%
Alleles are inAlleles are inTrans ConfigurationTrans Configuration
Gene Linkage SummaryGene Linkage SummaryA.A. Linked genes tend to be inherited together in Linked genes tend to be inherited together in
their original, parental arrangement.their original, parental arrangement.
B. Alleles of linked genes can be separated by B. Alleles of linked genes can be separated by crossing over (recombination) during meiosis.crossing over (recombination) during meiosis.
C.C. Distance between genes is calculated as 1% Distance between genes is calculated as 1% recombination = 1 map unit.recombination = 1 map unit.
D.D. Gene distances can be calculated for genes that Gene distances can be calculated for genes that are less than 50 map units apart. At 50 map units are less than 50 map units apart. At 50 map units and beyond, we cannot distinguish between and beyond, we cannot distinguish between genes far apart on the same chromosome and genes far apart on the same chromosome and genes on separate chromosomes.genes on separate chromosomes.
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