Post on 31-Dec-2015
Modes of InheritanceModes of Inheritance
Autosomal InheritanceAutosomal Inheritance– Dominant vs. RecessiveDominant vs. Recessive
X-linked InheritanceX-linked Inheritance– Genes only on X chromosomeGenes only on X chromosome– Dominant vs. RecessiveDominant vs. Recessive
Codominance or Incomplete Codominance or Incomplete DominanceDominance
Cytoplasmic or Maternal InheritanceCytoplasmic or Maternal Inheritance
Sex DeterminationSex DeterminationPairs of chromosomes matchPairs of chromosomes matchSex chromosomes don’t Sex chromosomes don’t always matchalways match– X and YX and Y– Females: X and X chromosomeFemales: X and X chromosome– Males: X and Y chromosomeMales: X and Y chromosome
Cannot live without X Cannot live without X chromosomechromosome– Y chromosome determines Y chromosome determines
malesmales
Females are XXFemales are XX
Possible gametes: all eggs will have Possible gametes: all eggs will have one X chromosomeone X chromosome
X X
X X
X
X
Males are XYMales are XYHalf of male Half of male gametes will have gametes will have one X one X chromosomechromosome
Half of male Half of male gametes will have gametes will have one Y one Y chromosomechromosome
X Y
X
X
Y
Y
Punnett squares predict sex of Punnett squares predict sex of offspringoffspring
Genotype: 1XX:1XY phenotype: 1 female:1 male
X-linked traitsX-linked traitsX is a sex chromosomeX is a sex chromosomeIt also has hundreds of It also has hundreds of genes genes – Very few have to do with Very few have to do with
gendergender
Y does not have many of Y does not have many of these genesthese genes– Very small chromosomeVery small chromosome– ““sex determining” genesex determining” gene– ““male fertility” genesmale fertility” genes
http://www.uni.uiuc.edu/~dstone/XY.jpg
History of X-linked genesHistory of X-linked genesThomas Hunt Thomas Hunt Morgan @Columbia Morgan @Columbia University in 1910University in 1910– Two students: Two students:
Alfred Strutevant & Alfred Strutevant & Calvin BridgesCalvin Bridges
Found white eye Found white eye male fly(mutant)male fly(mutant)
Normal(red eyes)Normal(red eyes)
They noted something weird…They noted something weird…Mated white eyed Mated white eyed male w/ red eyed male w/ red eyed female(normal)female(normal)
F1 all had red eyesF1 all had red eyes
F2 had 3:1 ratioF2 had 3:1 ratio
Only males had Only males had white eyeswhite eyes
Why?Why?
http://www.nature.com/genomics/images/drosophila_200.jpg
x
Male Female
Male
More researchMore research
Morgan did find a white eyed femaleMorgan did find a white eyed female
Cross with red-eyed femaleCross with red-eyed female
All the male offspring had white All the male offspring had white eyes!!!eyes!!!
What was going on?What was going on?
ExplanationExplanationGene for eye color is found Gene for eye color is found on X chromosomeon X chromosome– Eye color gene is on Eye color gene is on
different chromosomes in different chromosomes in humanshumans
Gene not found on Y Gene not found on Y chromosomechromosome– So males only have allele of So males only have allele of
that genethat gene
These genes called These genes called X-X-linked traits or X-linked linked traits or X-linked genesgenes
Color Blindness: X-linked Color Blindness: X-linked InheritanceInheritance
B: dominant normalB: dominant normal
b:recessive color blind b:recessive color blind alleleallele
Father only has one Father only has one
X chromosome to X chromosome to contributecontribute
Mom gives all normal Mom gives all normal genesgenes
All offspring are All offspring are normalnormal
But all females are But all females are now now carrierscarriers– Seem normal, but carry Seem normal, but carry
disease alleledisease allele– Carry the hidden color Carry the hidden color
blind geneblind gene– Create a punnett with a Create a punnett with a
carrier as a mothercarrier as a mother
X-linked DiseasesX-linked DiseasesCertain genes linked to diseasesCertain genes linked to diseases““+” means wildtype+” means wildtype– Stands for normal geneStands for normal gene– Found in “wild” populationsFound in “wild” populations““M or m” stands for mutation that causes M or m” stands for mutation that causes diseasedisease– M= means mutations is dominant over M= means mutations is dominant over
wildtypewildtype– M= means mutations is recessive to wildtypeM= means mutations is recessive to wildtype
M > + > mM > + > m
Examples of X-linked diseasesExamples of X-linked diseasesDominant X-linked disease (XDominant X-linked disease (XMM))– Rett’s syndromeRett’s syndrome– Vitamind D resistanceVitamind D resistance
Recessive X-linked disease (XRecessive X-linked disease (Xmm))– Infantile spasm syndromeInfantile spasm syndrome– Duchenne Muscular DystrophyDuchenne Muscular Dystrophy– Hemophilia A and hemophila BHemophilia A and hemophila B– Two types of autistic disordersTwo types of autistic disorders– Color blindnessColor blindness
Color BlindnessColor BlindnessLack to see certain colors wellLack to see certain colors wellHard to distinguish them from other colorsHard to distinguish them from other colorsRed/Green Color Deficiency: most commonRed/Green Color Deficiency: most common– 99% of color deficiencies99% of color deficiencies
Blue/Yellow Deficiency: very rareBlue/Yellow Deficiency: very rare– Very rare and way to testVery rare and way to test
Seeing only gray is extremely rareSeeing only gray is extremely rare
In 8-12% of European malesIn 8-12% of European males0.5% of females0.5% of females
2 types of cells in eye2 types of cells in eye
Rod cellsRod cells– Supersensitive in dim lightSupersensitive in dim light– Lets you see at nightLets you see at night– Doesn’t see in colorDoesn’t see in color
ConesCones– Sees in bright lightSees in bright light– Distinguishes colorDistinguishes color
One absorbs red, green, and blueOne absorbs red, green, and blue
Color BlindnessColor Blindness
Red and green cones impaired or Red and green cones impaired or don’t work at alldon’t work at all
Can’t see red or green or see it Can’t see red or green or see it differently than normaldifferently than normal
Ready to see colors?Ready to see colors?