Modern Genetics

Multiple Alleles

• More than two alleles can be inherited– Example: Blood Types– Alleles= IA, IB, i

Blood Type (Phenotype)

Type of Antigen

Possible Genotypes

A A IAIA, IAi

B B IBIB, IBi

AB AB IAIB

O None ii

Multiple Alleles: Cont’d

Blood Type Antigens on RBC Antibodies present

A

Anti-B

B

Anti-A

AB

None

O

Anti-B & Anti A

• Agglutination– Blood coagulates or

clumps together– Antibodies recognize

antigen on surface of blood and attack it

• i.e. B antibodies recognize B antigens

Phenomenon occurs because of genotypes!

Multiple Alleles: Punnett Squares

• Heterozygous A x Heterozygous B

• Genotypes: IAi x IBi

• Type O x AB• Genotypes: ii x IAIB

Chromosomes & Sex Determination

• 23 pairs of chromosomes found in nuclei of a human cell or 46 total chromosomes

• Pairs 1-22: Somatic• Pair #23: Sex-

determining chromosome Karyotype

1. Extract chromosomes from nucleus of a cell

2. Pair up matching chromosomes3. Arrange chromosomes by size

Sex Determination• Female: XX• Male: XY• Baby’s sex

determined by male– Mom X– Dad X or Y

X chromosome

Y chromosome

Sex-Linked Traits

• The X chromosome carries the trait, not the Y

Male Female

Normal

Carrier

Diseased Person

Sex-Linked Traits Examples

• Sex-linked diseases: Color blindness, hemophilia

• Example: Carrier Female & Normal Male

Incomplete Dominance

• Contrasting alleles• 1 allele is partially dominant• Intermediate traits are expressed• Example: Cross Red Flower & White Flower

F1 Generation F2 Generation

Codominance

• Heterozygous with both alleles expressed

• Homozygous red cow mates with homozygous white bull

CRCR x CWCW

CRCW (roan)

Polygenic Traits

• Traits controlled by 2 or more genes– Additive effect

• Example: Height Combination of all body parts put together; determined by many genes on different areas of chromosomes

Environmental Factors

• The environment an organism lives in can change its phenotype

Examples: Snowshoe hare Example: Hydrangea

pH and presence of

iron affect color