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?