Bellringer What are organisms that have two identical alleles for a certain trait called? Which one of Mendel’s principles states that during gamete formation, genes for different traits separate without influencing each other’s inheritance?

Learning Targets Explain Mendel’s Law of Independent Assortment and how to complete a dihybrid cross. Be able to complete a statistical analysis from the results of monohybrid and dihybrid crosses. Describe the common variations on inheritance patterns: intermediate inheritance (also known as incomplete dominance), codominance, multiple alleles, polygenic inheritance, and epistasis. Explain how environmental conditions can impact gene expression.

Dominance Relationships

What is genotype and phenotype again? Recap What is genotype and phenotype again? So … If you show the dominant phenotype, what could your genotype be?

If you are unsure if the organism is a pure-bred, you can do a Test Cross  Test Cross: Cross the individual that shows dominant phenotype with a recessive individual If offspring 100% dominant Original was pure (HD) If offspring not 100% dominant Original was heterozygous

Predicting a Test Cross

Looking at just one trait is called a MONOHYBRID Cross Remember, Punnett Squares are usually good only for single-gene traits. A a A a Aa AA aa Looking at just one trait is called a MONOHYBRID Cross 

Looking at TWO traits in one Punnett Square is called a DIHYBRID Cross 

TRY A DIHYBRID CROSS! Show the probabilities of a cross between two people, both heterozygous Full Lips (Ff), Clefted Chin (Cc)! F = Full Lips (dominant), f = Thin Lips (recessive) C = Cleft Chin (dominant), c = Non-clefted Chin The hardest part is segregating the alleles…Remember Mendel’s principle (also known as law) of Independent Assortment! Start with FfCc X FfCc … Go!

 FfCc X FfCc FFCC Ff Cc FC Fc fC fc FC Ff Cc Finish Up! (full lips, cleft chin) FC Ff Cc Finish Up!

9:3:3:1 -This is the classic ratio for a heterozygous dihybrid cross!  Numbers: How many Full Lips/Clefted Chins? _____ How many Thin Lips/Clefted Chins? _____ How many Full Lips/Non-clefted? _____ How many Thin Lips/Non-clefted? _____ So, what’s your HomD:Het:Het:HomR ratio? ___:___:___:___ 9/16 3/16 3/16 1/16 9 3 3 1 9:3:3:1 -This is the classic ratio for a heterozygous dihybrid cross!

Dominance Relationships  Dominance Relationships Complete dominance: one allele shows full dominance over the other (dominant v. recessive) Incomplete dominance (also called intermediate inheritance): neither allele is fully dominant over the other (mixed phenotype)

Dominance Relationships Codominance: Both alleles dominant; one phenotype “wins” (shows) in some cells, the other shows in other cells (either can show in phenotype)

Genes interacting to produce one trait Polygenic inheritance: Traits produced by two or more genes. For example: human skin color, more than one gene interacts to produce a range of color variations. Epistasis: One gene masks over another.

Example of Epistasis 2 genes: (E,e) & (B,b) Pigment: pigment (E) or no pigment (e) pigment concentration: black (B) to brown (b)

Remember…environmental conditions can affect gene expression:  Remember…environmental conditions can affect gene expression: If DNA gets damaged, cells stop listening to correct instructions mutations Causes of mutations: UV radiation chemical exposure radiation exposure cigarette smoke Pollution Diet

Let’s Practice Dominance Relationships Which Is This?  Complete Dominance Incomplete Dominance (also known as intermediate inheritance) Codominance

 Which Is This Complete Dominance Incomplete Dominance (also called intermediate inheritance) Codominance 

Which Is This Complete Dominance Incomplete Dominance (also known as intermediate inheritance) Codominance  (Though darker colors tend to show more strongly than lighter colors)

Which Is This Complete Dominance Incomplete Dominance Codominance 

Practice Problems

Incomplete Dominance In Kansas there is a creature know as a prairie cat. It comes in three colors, blue, red, and purple. This trait is controlled by a single gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one? Cross a Purple Cat and a Red cat. Can they have Blue offspring?

Co-Dominance Longhorns may be white (CWCW), red (CRCR) or roan (CRCW). Roan longhorns have a mixture of both white hairs and red hairs due to a codominant gene. Cross a Roan Bull with a Red Female! What are the genotypes and Phenotypes? Can roan cows produce more roan cows?