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Continuing GeneticsDOMINANCE
Unit 5: Mendelian Genetics
Independent Assortment• genes that are
inherited separately do not influence the inheritance of others
• Alleles segregate independently during meiosis
• some go to one gamete and some to another
Types of Dominance
Incomplete Dominance:• Offspring genotype is
heterozygous (hybrid)• Phenotype is between
two parents• In offspring, Dominant
gene cannot fully inhibit the recessive
• Ex: white flower x red flower = pink flowers
Codominance:
• Offspring shows phenotype of neither parent
• Both alleles are dominant
• Ex: black cow x white cow = checkered/spotted cow
Bay horse x white horse = roan horse
• Multiple alleles: more than two alleles control a trait
• Ex: height, hair color, eye color and blood type
Blood type inheritance• Blood type is determined by the presence or
absence of proteins on surface of red blood cells• Blood types: A, B, AB and O
Phenotype (BLOOD TYPE)
GENOTYPE
ANTIGEN on red
blood cell
SAFE TRANSFUSIONS
TO FROM
A AA or AO A A, AB A, O
B BB or BO B B, AB B, O
AB Only AB A & B AB A, B, AB, O
O Only OO None A, B, AB, O O
Sex-linked alleles
• controlled by genes located on sex chromosomes
• Usually carried on X chromosome
• Since females are XX, they are usually carriers of the trait
• Since males are XY, they have a higher tendency for inheritance of trait
Sex-linked • If trait is X-linked: males pass it to all of their daughters, none to sons
• If trait is X-linked: mothers have 50/50 chance of passing it to all of their children
• Ex: colorblindness, hemophilia
• Work the following Punnett Square:
• Male: has Hemophilia (XhY)
• Female: Carrier (XHXh)