Complex Inheritance Patterns: Non-Mendelian, Polygenic, and Blood Types

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What are complex patterns of inheritance?

Traits that do not follow simple dominant/recessive patterns and are influenced by multiple genes or other factors.

Why are many traits more complex than Mendelian inheritance suggests?

Because real-life traits are influenced by multiple genes and environmental factors.

What are examples of non-Mendelian inheritance patterns?

Incomplete dominance, codominance, polygenic traits, pleiotropy, epistasis, and multiple alleles.

What is incomplete dominance?

When neither allele is completely dominant and the heterozygous phenotype is a blend of both traits.

What does the heterozygous phenotype look like in incomplete dominance?

A blend or 'mixing' of both traits.

Why is incomplete dominance described as 'mixing paint'?

Because the two traits combine to form an intermediate phenotype.

How is a Punnett square set up for incomplete dominance?

Use two different capital letters (one for each allele).

Why are two capital letters used instead of uppercase/lowercase?

Because neither allele is dominant over the other.

What happens when red (RR) flowers are crossed with white (WW)?

All offspring have genotype RW.

What phenotype results from that cross?

Pink flowers.

What is the phenotype ratio for that cross?

100% pink.

In rabbits, what happens when black (BB) is crossed with white (WW)?

All offspring are gray.

What is the genotype of those offspring?

BW.

What is codominance?

When both alleles are fully expressed in the heterozygous phenotype.

What happens to both alleles in codominance?

Both traits appear fully, side by side.

Give an example of codominance.

Black and white chickens producing offspring with both black and white feathers.

What happens when a black chicken is crossed with a white chicken?

Offspring show both black and white feathers.

How does codominance appear in cattle?

Red and white hairs appear together (roan coat).

What are the genotypes and phenotypes from RR × WW cattle?

Genotypes: RR, RW, WW; Phenotypes: red, roan, white.

What is the phenotype ratio in codominance?

1:2:1.

In fish, what happens when purple (PP) is crossed with yellow (YY)?

Offspring show both purple and yellow traits.

What is a polygenic trait?

A trait controlled by two or more genes working together.

How do polygenic traits work?

Each gene adds a small effect to the overall trait.

Why do polygenic traits show a wide range of phenotypes?

Because many gene combinations are possible.

What type of graph do polygenic traits often form?

A bell-shaped curve.

Why are extreme phenotypes less common?

Because most individuals fall in the middle range.

Give examples of polygenic traits.

Human skin color, hair color, eye color, height.

Are all traits controlled only by genes?

No, the environment also affects how traits appear.

What environmental factors influence traits?

Nutrition, sunlight, temperature, and lifestyle.

How does nutrition affect height?

Better nutrition can increase height.

How does sunlight affect skin color?

It increases melanin, darkening the skin.

Why do Himalayan rabbits have darker fur in certain areas?

Fur grows darker in colder parts of the body.

What is pleiotropy?

When one gene controls many traits.

How can one gene affect multiple traits?

It influences different parts of the body at the same time.

What is an example of pleiotropy?

Marfan syndrome.

What are common effects of Marfan syndrome?

Tall height, long limbs, flexible joints, heart problems, vision issues.

Why can one mutation cause many symptoms?

Because the gene affects multiple body systems.

What is epistasis?

When one gene depends on or masks another gene.

How can one gene affect another?

It can block or change its expression.

What does the switch analogy represent?

Genes controlling whether a trait is on or off.

What happens if one gene is 'off'?

The trait controlled by the other gene is not shown.

How does epistasis affect Labrador coat color?

One gene controls color, another controls pigment deposition.

What happens if pigment is not deposited?

The dog is yellow regardless of other genes.

What are multiple alleles?

When a gene has more than two possible versions in a population.

How many alleles can an individual have?

Only two (one from each parent).

Why do multiple alleles increase variation?

More combinations are possible.

What are the blood type alleles?

A, B, and O.

How is blood type determined?

By a single gene with three alleles: A, B, and O.

Which alleles are codominant?

A and B.

Which allele is recessive?

O.

What genotypes produce each blood type?

A = AA or AO; B = BB or BO; AB = AB; O = OO.

Why does AB show both traits?

Because A and B are both expressed.

What blood types result from AB × AB?

A, B, and AB.

What are the probabilities for AB × AB?

25% A, 50% AB, 25% B.

What blood types result from BO × AO?

A, B, AB, O.

What are the probabilities for BO × AO?

25% each.

What blood types result from AB × OO?

A and B.

Why is type O only expressed with OO?

Because O is recessive.

How is incomplete dominance different from codominance?

Incomplete dominance blends traits; codominance shows both traits fully.

Why do polygenic traits have more variation?

Because multiple genes contribute.

How is pleiotropy different from polygenic inheritance?

Pleiotropy = one gene affects many traits; polygenic = many genes affect one trait.

How does epistasis affect traits?

One gene can mask or alter another gene's effect.

Why are multiple alleles important?

They increase genetic diversity in a population.