Patterns of inheritance!

Although we are SOOOO thankful for Mendel, there are many exceptions to Mendel’s Laws of Heredity…. Genetics is more complicated!

Incomplete dominance: One allele is not completely dominant over another

Incomplete dominance Heterozygous offspring have an appearance in between the phenotype of the parents! Example: Snapdragons (flower) Red (RR) x White (rr)

Incomplete dominance Heterozygous phenotype is between the dominant & recessive phenotype! R Rrr Rr All F 2 generation Are Rr Rr = PINK flowers!!!!!

Incomplete dominance

Quick tip….

Codominance BOTH alleles contribute to the phenotype!!!

Codominance When heterozygous, BOTH alleles act dominant…BOTH alleles are seen! Example: Chickens BB = black bb = white BB = black feathers bb = white feathers

Codominance Heterozygous offspring show both phenotypes!! Example: Chickens BB = black feathers bb = white feathers All F 1 generation are Bb … Bb = black and white speckles! bb B B Bb

Codominance in Chickens P generation

Codominance is SOOO beautiful!

Quick tip…

Review: Mendel Complete Dominance Red (RR) Red (Rr) White (rr) Yellow #12 Incomplete dominance -Long tails (L) -Short tails (S)

Multiple Alleles Genes that have more than two alleles

Color coat in rabbits is determined by a single gene that has at least four different alleles. Different combinations of these alleles result in the four colors you see here.

In some rabbits, there are four alleles for fur color but each rabbit only has two alleles. Depending on which two alleles they have, they will be one of four colors! Red is dominant over Tan, which is dominant over Black, which is dominant over Albino (R) (T) (B) (A) Red > Tan > Black > Albino If a heterozygous black male rabbit mates with a homozygous tan rabbit, what will the babies look like?

Another example of multiple alleles… (Codominance, TOO!) Human blood type A B O Three alleles for one trait!

Human Blood Type Blood type is determined by an antigen found on the surface of the blood cell (protein that can stimulate the production of antibodies) A BO Everybody receives one allele for blood type from each parent! A and B are CODOMINANT! O is recessive! Blood TypePhenotype AABlood Type A ABBlood Type AB AOBlood Type A BBBlood Type B BOBlood Type B OOBlood Type O So…there are FOUR blood types A B AB O

Multiple Allele & Codominance Problem: Homozygous male Type B (BB) X Heterozygous female Type A (AO) ½ = AB ½ = BO SO, what are there actual blood types? BB A O AB BO

If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?

Quick tip…

Polygenic Traits Traits controlled by two or more genes

The wide range of skin color in humans is due to more than four different genes that control this trait!

And eye color!

Quick Tip… Polygenic traits are more complex than our punnett squares!

Sex-Linked traits Genes that are carried on the X or Y chromosomes (the sex chromosomes)! Ex: Colorblindness, Hemophilia and Duchenne Muscular Dystrophy

First, remember how to determine gender… Females have XX chromosomes Males have XY chromosomes

Sex-Linked traits BUT…the X chromosome is BIGGER and holds WAY more genes than the Y -The Y chromosome appears to only contain a few genes total -Currently 100 x-linked genetic disorders have been mapped

Sex-Linked Traits FEMALES: X R X r X R X R MALES: X R Y X r Y

Carriers Since females have two copies of the X chromosome, it is possible to have certain alleles “hidden” by a dominant allele. She is a healthy “CARRIER” However, because males only have one X chromosome, they either have it…or they don’t. They can NOT be carriers!

B: Healthy b: Muscular Disorder FEMALE Bb Healthy Phenotype “Carrier” MALE b Muscular Disorder

Healthy Father, Carrier Mom 2 out of 4 children will have the hemophilia allele. -The female: Carrier -The male : HAS hemophilia

The infected son has children with a healthy woman None of the children would have hemophilia. ALL females: Carriers This is why sex-linked traits often disappear and reappear from generation to generation!

Quick Tip! Sex-linked traits affect males and females differently!!!

Genetics and Environment Traits are determined by a combination of genes and environment!!! A sunflower gene for height or flower size BUT, these are influenced by: sunlight, soil, water Genes provide a plan for development…but how that plan unfolds depends on the environment!

Some more examples…. -Blood Pressure -Intelligence -High yielding tomato plant -Fair skin prone to cancer -Woman baldness

Practice Problems Incomplete dominance: In a particular species of bird, feather color shows incomplete dominance. A cross between a blue bird (BB) & a white bird (bb) produces offspring that are silver (Bb). If two silver birds were to mate, what would the genotypes & phenotypes be of their babies?

Practice Problems Codominance: Cow coloration is commonly an example of codominance. Homozygous cows can be white or brown and heterozygous cows are called roan. Describe the appearance of the baby cows if a white cow crosses with a brown cow:

Practice Problems Multiple Alleles: In one kind of mouse, fur color is a multiple allele trait because there are three alleles. Black (B), Tan (T), and white (W) are all alleles that mice can have but each mouse only has two alleles. Black is dominant over Tan, which is dominant over White. Often written: Black > Tan > White If a homozygous black mouse mates with a heterozygous tan mouse, what will the genotypes & phenotypes be of the offspring?

Practice Problems Sex Linked Trait: The bison herd on Konza Prairie shows a sex linked genetic defect carried on the X chromosomes. Some males have a malformed back leg that interferes with its normal motion. If a healthy male bull mates with a female cow that is a carrier, what are the chances of producing a normal son? Male Genotype: Female Genotype: If he mates with this cow every year, what percentage of their daughters will have normal knees? What percentage of their daughters will be carriers of this disease?