More Complicated Patterns of Inheritance Biology 1-3c More Complicated Patterns of Inheritance

Rules of Inheritance Any guesses on what these terms mean? Some traits follow the simple rules of Mendelian inheritance of dominant and recessive genes Complex traits follow different patterns of inheritance that may involve multiple genes and other factors. For example: Incomplete dominance Codominance Multiple alleles Gene interaction Sex-linked inheritance Any guesses on what these terms mean?

Complete Dominance Complete Dominance results in a phenotype that is a representation of the dominant trait in a heterozygous allele pair. Red flower x blue flower  Red flower

Complete Dominance This is classic Mendelian inheritance. More complex patterns exist!

Incomplete Dominance Incomplete Dominance results in a phenotype that is a blend of a heterozygous allele pair. Red flower x blue flower  purple flower

Incomplete Dominance If black and yellow coat colour exhibit incomplete dominance in dogs and a litter of puppies is born with the following genotypes, what colour will they be? BB = YY = BY =

Codominance Codominance results in a phenotype that shows both traits of an allele pair. Red flower x blue flower  Red & blue spotted flower

Codominance If black and white coat colour exhibit codominance in dogs and a litter of puppies is born with the following genotypes, what colour will they be? BB = WW = BW =

Are the offspring exhibiting incomplete dominance or co-dominance?

Assignment: Incomplete & Co-Dominance Worksheet In partners, please complete the “Create-a-Being” Assignment. (you will share a parent information card but you will both fill out your own booklet)

Multiple Alleles Traits controlled by multiple alleles have more than 2 variations. Ex. Human blood type has 3 different allele variants, A, B and O A and B are Codominant to each other and both are Dominant over O Genotypes Phenotypes AA, AO A blood type AB AB blood type BB, BO B blood type OO O blood type

Multiple Alleles – Human Blood Type If parents have A (AO) and B (BB) blood types, what are the possible genotypes and phenotypes of their children?

Multiple Alleles – Human Blood Type A mother with blood type A (AO) gives birth to a baby with blood type B (BO). The “father” is blood type AB. Could the child be his? Is this test 100% conclusive?

Sex-Linked Traits Henry the VIII was a British Monarch who was desperate for an heir He had 6 wives, blaming them for his lack of sons. He did finally have one son

Question: Who is responsible for a babies gender? The mom? The dad? Random chance?

Sex Determination in Humans Of the 23 pairs of chromosomes in your cells, there is one pair that may not be identical.

Sex Determination in Humans If you are born female, you will have 2 X chromatids If you are born male, you will have 1X and 1Y chromatid What will your offspring be?

Sex Determination in Humans So who is responsible for the gender of their offspring?

Sex Determination in Humans Along with determining gender, the sex chromosomes also contain other genes that control certain traits Because the size of the X and Y chromatids are so different, the X chromatid contains some genes that the Y chromatid does not. An example is the gene that controls an individual’s ability to distinguish between red and green.

Colour-Blindness If a person cannot distinguish between red and green they are said to be colour-blind The gene that controls this trait is only found on the X chromatid. The dominant version of the gene results in normal vision The recessive version of the gene results in colour blindness

Colour-Blindness What would the phenotype for the following genotypes be? Gender Genotype Phenotype Female XNXN XNXn XnXn Male XNY XnY

Colour-Blindness So for a female to be colour blind, she must have inherited 2 recessive copies of the gene For a male to be colour blind he only needs to inherit one recessive copy of the gene. Characteristics such as colour-blindness, that are controlled by genes found on the sex chromosomes, are called sex-linked traits.

Sex-Linked Traits All the sex-linked genes that have been studied so far are found on the X-chromatid. As a result, sex-linked traits are more commonly exhibited by males than females One copy of a recessive gene will be masked by a dominant copy in females One copy of a recessive gene will be expressed in males