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Human Biology
Course Code
Stephen Wright

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LECTURE Feb.1.2011
Do not care about which disease is dominant or recessive
A bit more on ABO
A blood types produce A antigens, expressed on surface of RBC
Would not produce A antibodies otherwise, ill
Type A blood produces B antibodies
With blood transfusion transfusing the red blood cells antibodies are in
serum, not transferred
Type O no antigens produced only receive blood from other Type O and
Sex-linkage and chromosome theory
Dihybrid cross passed on together (yellow, also round) OR independent segregate
Mendel saw independent assortment for the seven traits he examined
Might not always be true
oTraits cosegregate in progeny so probability of passing on one allele
is no longer independent of passing on another allele
Effects with linkage
SSgg x ssGG -> SsGg -> ??
Maybe the sG are linked in parental generation
Can only make two phenotypes the parental ones
oSo only have sG and Sg
oSo genotypes of progeny can only be ssGG and SsGg and SSgg
Three types of progeny
oRound and red is ssgg
Mendel expect 1/16
But with linked expect 0 because it was not a parental gene
oTHIS DOES OCCUR IN NATURE if genes really close together on
same chromosome, assortment no longer independent not all
possible progeny result only parental types result in the gametes
Mendelian inheritance
Boveri and Sutton independently working
Around the time Mendel was being rediscovered
o23 sets of chromosomes in humans
oTwo copies of each -> 46 chromosomes in total
Two copies of parental chromosomes homologous chromosomes
o23 sets of homologous chromosomes
Non homologous chromosomes chromosome 2 and 21
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Centromeres middle or end of chromosomes (metacentric or acrocentric
Sister chromatids identical copies of single homologous chromosome
oAfter replication
Chromosome theory of inheritance
Only gametes passed on to produce fertilized egg
Within gametes, physical basis for inheritance
Sperm and egg unusual cell types only had one copy of every chromosome
oOne n haploid
oVersus somatic cells have two copies
Fertilized egg chromosomes = maternal chromosome + paternal chromosome
Very very like Mendels law of segregation
oCan see under microscope chromosome behaving like how Mendel
said genes should behave
oSuggesting hereditary information encoded on chromosomes
Decision as which homologous chromosome ends up in which gamete happens
oOne copy to one pole, other copy to other pole
oChoices are independent
o-> law of independent segregation
Two copies of chromosome (R and r) meiosis results in four gametes four gamete types
Two chromosomes tracked
Random choice whether mom or dads chromosome ends up in gametes
Independent assortment occurs genes found on different chromosome not
Creates variation
Dihybrid cross ratio to remember 1:1:1:1 one quarter of each possible
combination of chromosomes/gametes
oLaw of independent assortment says one quarter o
o¼ times ¼ times ¼ times ¼
Correlation, but needed proof
Look at sex chromosomes
oUnusual can distinguish homologous chromosomes
oMales have Y degenerate chromosome
Distinct appearance
Males are heterogametic
oTwo distinct looking chromosomes
oHalf of male gametes are X and other half Y
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