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Blood Type and Sex Linked Inheritance. Multiple Alleles. Multiple alleles for a particular gene means that more than two alleles exist in the population. This does not mean that the gene in a particular individual possesses more than two alleles. - PowerPoint PPT Presentation
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Blood Type and Sex Linked Inheritance
Multiple AllelesMultiple alleles for a particular gene means that
more than two alleles exist in the population.This does not mean that the gene in a particular
individual possesses more than two alleles. An individual can only have a maximum of
two of alleles, one maternal and one paternal, no matter how many alleles exist in the population.
Example: a population of dogs can have 5 alleles for coat color at one gene.
The Classic Example of Codominance and Multiple Alleles
in Humans is BLOOD TYPE
Gene that controls ABO blood type codes for an enzyme that makes an antigen on blood cells.Two alleles (IA and IB) are called “A” and “B” which are codominant. A and B can both be expressed on the same cell. Third allele (i) is called “O”) and it is recessive to both A and B
Possible Genotypes for Blood Types
If the Phenotype: A
Genotype(s): AA, Ao
If the Phenotype: B
Genotype(s): BB,Bo
If the Phenotype: AB
Genotype(s): AB
If the Phenotype: O
Genotype(s): oo
Possible combinations of alleles
A Real Problem:Mom is Type B, Dad is Type O … Baby is
Type AB. Is this possible?• Cross: ____ X ____Bo
MOMoo Remember,
when in doubt, heterozygous is more likely
B o
o
o
Bo
Bo
oo
oo SORRY! NOT
POSSIBLE
!
Check your understanding
Could an AB father have a type O child?Why?
Are the father’s alleles
codominant or recessive?
O is homozygous recessive. A or B would hide the o
allele.
Sex Chromosomes:the 23rd pair in humans
All others (1-22)
are called
autosomes
Boy Girl
The Sex Chromosomes
The “X” ChromosomeHas essential genesCan’t live without it!Females have a 23rd pair = XX (one usually deactivated)
The “Y” ChromosomeHas few genesMale 23rd pair = XY
What’s the probability of having a boy or girl?
XX
XY
XX
XY
X X
Y
X
50%
50%
Some X-Linked Traits:Hemophilia (missing clotting enzymes)
Bleeding disorders in which it takes a long time for the blood to clot.
ColorblindnessDefect in color vision
“Male-pattern” baldnessMost are recessive.
A man with normal vision marries a colorblind woman. What is the probability
that they will have a colorblind SON?
• Cross: ____ X ____XcXcMOM
XY Remember, Mom only shows if she is homozygous!
Xc Xc
X
Y
XcX
XcY
XcX
XcY
Focus only on SONS(not daughters)!
100%
(2/2) SONS
A hemophiliac man marries a healthy woman. What is the probability that they will have any
hemophiliac children?
All sons healthy
All daughters carriers
0%
ColorblindnessRed-green colorblindness-
Red and green appear to be the same. X-linked
Red-green affects:1 in 10 males in the US 1 in 100 females in the US
Remember: Males have just one X chromosome. All X-linked alleles are expressed in males.Other forms:
Total Colorblindness
Blue-Yellow colorblindness
Blue-yellow appears to be the same. It is autosomal Chromosom
es 1 to 22
What do you see?
No.Va.CRIME SCENE INVESTIGATON
http://www.ansci.cornell.edu/usdagen/mult_alleles.html
Medline Plus, 2014, US National Library of Medicine, National Institutes of Health http://www.nlm.nih.gov/medlineplus/ency/article/002051.htmVirtual Fruit Fly Lab, 2014, http://www.mhhe.com/biosci/genbio/virtual_labs/BL_15/BL_15.html