multiple alleles and polygenic traits
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Multiple Alleles and Polygenic Traits. Multiple Alleles: when more than two different alleles exist for the same trait. (Remember: each individual will only have two alleles for a trait but there are several alleles to choose from.). - PowerPoint PPT PresentationTRANSCRIPT
Multiple Alleles and Polygenic Traits
Multiple Alleles: when more than two different alleles exist for the same trait.
(Remember: each individual will only have two alleles for a trait but there are several alleles to choose from.)
In rabbits, coat color is controlled by multiple alleles. Full color (C), white (c), light-gray or chinchilla (cch) and white with black points or a Himalayan (ch). Full color is dominant to all the other alleles. Chinchilla is dominant to Himalayan and white.
Cross a heterozygous Chinchilla (cchc) with a heterozygous full color with himalayan (Cch).
cchc x Cch
cch c
C
ch
cch c
C Ccch
ch
cch c
C Ccch Cc
ch
cch c
C Ccch Cc
ch cchch
cch c
C Ccch Cc
ch cchch chc
Genotypic Ratios: 1 Ccch: 1Cc : 1 cchch: 1 chcPhenotypic Ratios: 2 full color: 1 Chinchilla: 1 Himalayan
In humans, blood type has multiple alleles. IA and IB are codominant and i (type O blood) is recessive.
Blood Type Type of Antigen Possible Genotypes
Type A
Type B
Type AB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen
Type B
Type AB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B
Type AB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen
Type AB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen IBIB, IBi
Type AB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen IBIB, IBi
Type AB A and B antigens
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen IBIB, IBi
Type AB A and B antigens IAIB
Type O
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen IBIB, IBi
Type AB A and B antigens IAIB
Type O No antigens
Blood Type Type of Antigen Possible Genotypes
Type A A antigen IAIA, IAi
Type B B antigen IBIB, IBi
Type AB A and B antigens IAIB
Type O No antigens ii
Cross a heterozygous type A with a heterozygous type B.
IAi x ___
Cross a heterozygous type A with a heterozygous type B.
IAi x IBi
IA i
IB
i
IA i
IB IAIB
i
IA i
IB IAIB IBi
i
IA i
IB IAIB IBi
i IAi
IA i
IB IAIB IBi
i IAi ii
Genotypic Ratios: 1 IAi : 1 IAIB : 1 IBi : 1 iiPhenotypic Ratios: 1 Type A: 1 Type AB: 1 Type B: 1Type O
Cross a person with type AB blood with another person with type O blood.
IAIB x ___
Cross a person with type AB blood with another person with type O blood.
IAIB x ii
IA IB
i
i
IA IB
i IAi
i
IA IB
i IAi IBi
i
IA IB
i IAi IBi
i IAi
IA IB
i IAi IBi
i IAi IBi
Genotypic Ratios: 2 IAi : 2 IBi
Phenotypic Ratios: 2 Type A: 0 Type AB: 2 Type B: 0 Type O
Polygenic Inheritance: the inheritance pattern is controlled by two or more genes each with two alleles.
In humans, eye color is the result of polygenic inheritance. At the present, three gene pairs controlling human eye color are known. Two of the gene pairs occur on chromosome pair 15 and one occurs on chromosome pair 19. The bey 2 gene, on chromosome 15, has a brown and a blue allele. A second gene, located on chromosome 19 (the gey gene) has a blue and a green allele. A third gene, bey 1, located on chromosome 15, is a central brown eye color gene.
The brown allele is always dominant over the blue allele so even if a person is heterozygous (one brown and one blue allele) for the bey 2 gene on chromosome 15 the brown allele will be expressed. The gey gene also has two alleles, one green and one blue. The green allele is dominant to the blue allele on either chromosome but is recessive to the brown allele on chromosome 15. This means that there is a dominance order among the two gene pairs. If a person has a brown allele on chromosome 15 and all other alleles are blue or green the person will have brown eyes. If there is a green allele on chromosome 19 and the rest of the alleles are blue, eye color will be green. Blue eyes will occur only if all four alleles are for blue eyes.
Polygenic inheritance usually shows up as a range of variation such has height, skin color or hair color.
The results of an average population will result in a bell-shaped curve.
