Patterns of Inheritance
Complete DominanceIncomplete Dominance
CodominanceSex-Linked Inheritance
Complete Dominance
• You know this!• Dominant – completely masks recessive• Dominant – represented by Capital letter.• Recessive – represented by lower case.• Genotypes: BB – homozygous dominant• Bb- heterozygous (dom.)• bb – homozygous recessive• bb only way recessive trait can be expressed!
BB Bb bbBrown Brown Blue
Practice!!!
• Draw a Punnett Square to show the cross between a male cat heterozygous for having a tail with a female cat homozygous recessive for no tail.
• Provide the genotypic and phenotypic results.
Check your answer! Tt x tt
Tt Tt
tt tt
Keep Checking!
• Genotypic Ratio:
• TT – 0/4 , Tt – 2/4 , tt – 2/4
• Phenotypic Ratio:
• Tail – 2/4
• No tail – 2/4
Incomplete Dominance
• NEITHER allele completely masks the other.
• Still use Capital and lower case letters.• Example: Carnations can be red, pink, or
white. Use the letter C for color.• CC – red, Cc – pink, cc – white• Homozygous gives either extreme,
heterozgyous give a “new” blend of the two.
CC Cc cc
Practice Incomplete Dominance!
• A breed of dog has hair texture that is determined by incompletely dominant traits. The hair texture can be Straight (TT), Wavy (Tt), or Curly (tt).
• Cross to wavy haired dogs and provide genotypic and phenotypic results.
Check your answers!
TT Tt
Tt tt
Genotypes and phenotypes
• Genotypes: Phenotypes:
• ¼ TT Straight Hair
• 2/4 Tt Wavy Hair
• ¼ tt Curly Hair
Codominance
• Both Alleles are EQUALLY dominant.
• Still use Capital and lower case letters.
• Example: A breed of horse has hair color that is controlled by codominant alleles.
• The hair can be Red, White or an equal combination of both red and white hairs together.
• HH – Red, Hh – both, hh – white.
Roan Horse
Another Example: Blood Type
• This can be confusing, pay attention!!!
• Possible Blood types:
• Type A – Codominant with type B.
• Type B - Codomiant with Type A giving
• Type AB
• Type O – Completely Recessive
Phenotypes Genotypes
• Type A Blood AA or AO
• Type B Blood BB or BO
• Type AB Blood AB
• Type O Blood OO
• RH Factor can be Positive or Negative but is a case of complete dominance.
You be the detective!
• Is it possible for a couple, both with type A blood, to have a child with type O blood?
Create a Punnett Square to support your answer.
• Is it possible for a couple, father type AB blood and mother type O blood, to have a child with type AB blood? Support your answer.
Sex-Linked Inheritance
• Some genes that have nothing to do with sex determination are on the X and Y chromosomes.
• The genes (alleles) are described as “sex linked”.
• Notation uses the X and Y to represent the chromosomes along with an additional letter to represent the allele on each chromosome.
Examples of Sex-linked Inheritance.
• Color blindness – genes on the X chromosome. (can’t see red and green)
• Hemophilia – genes on the X chromosome. (blood clotting disorder)
• Muscular Dystrophy – genes on the X chromosome. (muscles degenerate)
• Would disorders be more common in girls or boys? Why?
Practice:
• Create a Punnett Square to show the cross between a mother who is a carrier for color blindness and a father who is color blind.
• What are the genotypic and phenotypic results?