Download - Multiple Alleles
Multiple Alleles
• Multiple alleles - for some traits there are more than two alleles in the species
• Single individual cannot have more then two alleles for each trait (1 on each homologous chromosome)
• Multiple alleles explains why there are four different blood types
(A, B, AB, and O)
Multiple Alleles
• Three alleles code for blood type (A, B, O)• O is the recessive allele• A & B are both dominant over O, but neither
one is dominant over the other.
• Which genetic relationship does this sound like?
Multiple Alleles
• Use capital letter “I” to show a dominant allele
• Use a lower case letter “i” to show the recessive allele
• Superscript letters stand for each dominant allele
• Six possible genotypes!
Blood Antigens
•On the surface of red blood cells are chemical structures (proteins) called antigens• Blood plasma contains antibodies- proteins that bind to/attack specific antigens
Blood TypingBlood also contains antibodies – proteins that recognize and bind to certain, specific antigens
Blood Type Antigens on RBC Antibodies Can Receive
A A anti-B A, O
B B anti-A B, O
AB AB none A, B, AB, O
O none both A & B O
(Rh + blood) contains Rh antigen
(Rh – blood) no Rh antigen
Why is it bad if you receive the wrong blood type?
• If blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots
• Universal donor- (type O blood) no antigens (RBC) to be attacked
• Universal recipient- (type AB) no antibodies to attack received blood
Blood Typing Human serum containing specific antibodies can be purchased
Separately mix a drop of unknown blood sample with drop of each anti-serum
Reaction between blood and anti-serum
No reaction between blood and anti-serum
Blood Typing Example
A sample of unknown blood is mixed with three anti-sera samples:Tube 1 (Anti-A): No reaction
Tube 2 (Anti B): No reaction
Tube 3 (Anti Rh): Cloudy reaction
In terms of the A-B-O and Rh systems, what type blood is the sample?
Sex Chromosomes & Sex Determination
• 1905 Wilson studied insects• In male, 1 homologous pair or chromosomes did not match• In female, all homologous chromosomes matched• Called the female sex chromosome the X chromosome & the
unmatched male chromosome the Y (determine sex• All the other body chromosomes are called autosomes
• Male Gametes (X & Y) Female (X & X)
Sex-linked Traits
• Sex-linked traits- a trait that is controlled by a gene found on the sex chromosome.
• Chance of showing trait is affected by the sex of the individual
• Most determined by genes found on the X chromosome
Sex-linked Genes
• Morgan studied Drosophila melanogaster (fruitflies)• Surprised to see a white-eyed fly (it was male)• Mated white-eyed male with normal red-eyed female
resulting in an F1 generation: all red eyes• Conclusion: red eyes is _________ over white• Mated members of F1 generation: Results: ¾ red eyes, ¼ white eyes• BUT all white eyes were male!!• Concluded that this trait is carried on a sex chromosome!
(sex-linked)• Gene for red & white eye carried on the X chromosome… no
corresponding allele on the Y chromosome
Sex-Linked Genes
• Therefore, males get eye color from 1 gene…on the X chromosome from mom
• For a female to have white eyes, must get two white alleles• Determine genotypes of crossing two individuals from the F1
fruitfly generation: Crossed male & heterozygous female with red eyes… Resulted in 3 red eye: 1 white eye (male=white)
= red allele on X chromosome = white allele on X chromosome Y = male sex chromosome with no allele for eye color
Genotypes if F1 fruitfly generation
Human Sex-linked Traits
• Color-blindness• Hemophilia• Duschenne muscular
dystrophy
Testcross
Testcross- the crossingof an individual of unknown genotype with an individual with ahomozygous recessiveindividual to determine the unknown genotype.
Can determine thegenotype of any individualWhose phenotype expresses the dominant trait.