multiple alleles

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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)

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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. - PowerPoint PPT Presentation

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Page 1: 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)

Page 2: Multiple Alleles

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?

Page 3: Multiple Alleles

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!

Page 4: Multiple Alleles

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

Page 5: Multiple Alleles

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

Page 6: Multiple Alleles

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

Page 7: Multiple Alleles

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

Page 8: Multiple Alleles

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?

Page 9: Multiple Alleles

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)

Page 10: Multiple Alleles

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

Page 11: Multiple Alleles

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

Page 12: Multiple Alleles

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

Page 13: Multiple Alleles

Genotypes if F1 fruitfly generation

Page 14: Multiple Alleles

Human Sex-linked Traits

• Color-blindness• Hemophilia• Duschenne muscular

dystrophy

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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.