Not-so-Simple Inheritance Patterns

#1 and #2 Remember… Genes are sections of a chromosome that have coded instructions for making proteins. Alleles are different forms of a gene.

#3 Simple Inheritance 2 alleles 2 phenotypes One allele is dominant The other allele is recessive The DOMINANT allele completely masks the recessive allele

Mendel Got Lucky In many ways Gregor Mendel was quite lucky in discovering his 4 genetic laws.  He happened to use pea plants.  Things in nature aren’t always so simple.

Not-so-Simple Inheritance 4 Main Types Codominance Incomplete Dominance Multiple Alleles Polygenic Traits

Red Cow x White Cow  Roan Cow Codominance #4,5,& 6 “Co” means together! Codominance = two alleles are dominant together. This produces a third heterozygous phenotype where BOTH traits are expressed TOGETHER Ex: Human Blood Type A B O AB Red Cow x White Cow  Roan Cow Roan cattle have both red and white hairs mixed in together!

red x white  red & white spotted Codominance red x white  red & white spotted

copyright cmassengale Mendelian Genetics 7/30/2019 #7 Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type 1. type A = IAIA or IAi 2. type B = IBIB or IBi 3. type AB = IAIB 4. type O = ii copyright cmassengale 8 8

copyright cmassengale Mendelian Genetics 7/30/2019 #7 Codominance Problem Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IB IA i IAIB IBi 1/2 = IAIB 1/2 = IBi copyright cmassengale 9 9

Another Codominance Problem Mendelian Genetics 7/30/2019 Another Codominance Problem Example: male Type O (ii) x female type AB (IAIB) i IA IB IAi IBi 1/2 = IAi 1/2 = IBi copyright cmassengale 10 10

copyright cmassengale Mendelian Genetics 7/30/2019 Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (IAIB) copyright cmassengale 11 11

copyright cmassengale Mendelian Genetics 7/30/2019 Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale 12 12

Incomplete Dominance #8,9, & 10 Incomplete Dominance = neither of the two alleles is completely dominant This produces a third heterozygous phenotype where the traits are BLENDED. Amel & Ultra are incompletely dominant to each other. Amel x Ultra  Ultramel

red flower x white flower  PINK flower Incomplete Dominance red flower x white flower  PINK flower

Multiple Alleles #11 & 12 Any of a set of three or more alleles. Only two of alleles can be present in a diploid organism. Examples: Human Blood Type Human skin, hair, and eye colors

Polygenic Traits #13 &14 Result of the interaction of several genes Human skin, hair, and eye color Influenced by more than one gene at different locations on the chromosomes Human Blood Pressure Not just 1 “blood pressure” gene with several alleles Caused by several genes that control other traits such as weight, cholesterol level, kidney function, etc… Human Height The combined size of all of the body parts from head to foot determines the height of an individual. 

Role of Environment #15 Our environment also plays a key role in how traits are expressed. Genes can be turned on/off due to external environmental factors. Examples: Stress Nutrition Chemical exposure Light Temperature

Anyone (universal recipient) Anyone (universal donor) Work on Pages 18-22 in your packet. Follow directions. BLOOD TYPE Genotypes Can DONATE TO: Can RECEIVE FROM: A IA IA or Iai A or AB A or O B IB IB or IBi B or AB B or O AB IA IB Anyone (universal recipient) O ii Anyone (universal donor)