Variations of Genetics There are other patterns of inheritance that are variations of Mendelian Genetics: Incomplete Dominance Codominance Sex-linked Polygenic Inheritance Pleiotropic Inheritance

Incomplete Dominance Incomplete dominance is when the phenotype of a heterozygous individual is an intermediate between the two homozygous forms. Results in a blended phenotype Unlike Mendelian genetics, you use a different letter for each allele (Ex. R for red and W for white)

Incomplete Dominance Certain breeds of cattle show incomplete dominance in coat color. When pure breeding red cows are bred with pure breeding white cows, the offspring are roan (a pinkish coat color). What are the genotypes & phenotypes of the possible offspring when a roan cow is mated with a roan bull.

Incomplete Dominance R W

Incomplete Dominance R W RR RW WW

Incomplete Dominance In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. What is he probability of having red offspring when a homozygous red flower is crossed with a pink flower.

Incomplete Dominance R W

Incomplete Dominance R RR W RW

Codominance Codominance is when the phenotype of both alleles are expressed at the same time. Blood type is a good example of this type of inheritance since when you have an A allele and a B allele, you have an AB blood type. When doing blood type problems, O is recessive! Alleles are written IA, IB, and i

Codominance In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette. What is the probability of having a erminette chicken when crossing two heterozygous individuals

Codominance B W

Codominance B W BB BW WW

Codominance A man with type AB blood marries a woman with type B blood. Her mother has type O blood. What blood type could their children have?

Codominance IA IB i

Codominance IA IB IAIB IBIB i IAi IBi

Sex Linked This occurs when genes are located on the sex chromosomes (X or Y chromosome). Usually passed down on the X chromosome since the Y chromosome has very little genetic information. Many of these traits are X-linked recessive disorders where the recessive allele codes for the mutated phenotype. Affects more males than females since they only have one X chromosome.

Sex Linked AVOIDING COMMON MISTAKES: The alleles are written like sex linked: XH or Xh The Y chromosome NEVER gets an allele assigned to it. If asked to find the chance of a male child that has the disease you ignore any offspring that are not male. Women can be a carrier for X-linked recessive disorders, which means they are heterozygous and can pass the disorder to their offspring.

Sex-linked Hemophilia, a disorder that affects blood clotting, is an X-linked recessive disorder where the recessive allele codes for the disorder. What is the probability that the male offspring would have hemophilia if a female carrier is crossed with a male who does not have hemophilia?

Sex Linked XH Xh Y

Sex Linked XH Xh XHXH XHXh Y XHY XhY

Sex-Linked Red-green color blindness is caused by a sex-linked recessive allele.  A color-blind man marries a woman with normal vision and is homozygous. What is the probability that their daughter will be colorblind? What is the probability that their son will be colorblind?

Sex Linked XB Xb Y

Sex Linked XB Xb XBXb Y XBY

Video Incomplete dominance, codominance, and sex linked traits (Resources Page) https://www.youtube.com/watch?v=fQvER3MyI2c

Polygenic vs Pleiotropic Polygenic is when many genes code for one phenotypic character. One major example is skin color. Pleiotropic is when one gene has many effects. The gene for Sickle Cell Disease is an example of this because the change in cell shape affects many things.

Linked Genes Some genes will get passed down together because they are located close to one another on the same chromosome. The closer they are to each other on a chromosome, the less likely they are to get split up during crossing over, and the more likely they are to be passed down together.

Mapping Gene Loci A genetic map is an ordered list of the genetic loci along a particular chromosome. A linkage map is a genetic map based on recombination frequencies The higher the recombination frequency, the further apart the loci are. Distance is expressed in map units, where one map unit represents 1% recombination frequency. The maximum percentage is 50% before they are said to be on different chromosomes.

Parental and Recombinant Types Parental Types are offspring that share a phenotype with any of the parents Ex. Parent and offspring both have blue eyes and brown hair. Recombinant types, or recombinants, is when the offspring have a different combinations of phenotypic traits. Having Red hair and green eyes when the parents have brown hair/green eyes and Red hair/blue eyes If 50% of the offspring are recombinants, the recombination frequency is said to be 50%

Calculating Recombination Frequency

Calculating Recombination Frequency A wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are wildtype, 721; black-purple, 751; gray-purple, 49; black-red, 45. What is the recombination frequency between these genes for body color and eye color? Are these genes on the same chromosome?

Calculating Recombination Frequency A pea plant with Yellow peas and purple flowers is crossed with a plant with green peas and white flowers. The following offspring are observed: Yellow/purple, 50; Green/purple, 200; Green/white, 15; Yellow/white, 150. What is the recombination frequency? Are these genes on the same chromosome?

Pedigrees A family tree that displays genetic information for parents and offspring for generations is called a pedigree. Used to track traits or disorders Squares represent males Circles represent females Shaded shapes show individuals affected by the disorder or that have the trait. Sometimes carriers are half shaded.

Pedigree Practice In humans, albinism is a recessive trait. The disorder causes a lack of pigment in the skin and hair, making an albino appear very pale with white hair and pale blue eyes. This disorder also occurs in animals, a common albino found in a laboratory is the white rat. The pedigrees below trace the inheritance of the allele that causes albinism. Label the genotypes of the individuals in the pedigree