More complicated….11.3 Or Non-Mendelian Genetics More complicated….11.3 Or Non-Mendelian

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Some variations can be observed in all animals including humans. Not all genetic traits strictly follow the laws discovered by Gregor Mendel. Some variations can be observed in all animals including humans. Four types: Incomplete dominance Codominance Polygenic inheritance Sex linked traits and/or Sex Influenced

Codominance Not all alleles are dominant and recessive. Some are equally strong and not masked by the other. Alleles which are equally strong are said to be "codominant". When both alleles are present, they are both expressed in the phenotype. A hybrid is a blend of both alleles, represented by different capitalized letters.

Codominance EX.

Codominance EX.

Red Roan (RW)- red & white hairs intermixed Blue roan (BW) – black and white hairs intermixed sire was black (BB) & dam was white (WW) A nice website on horse color: http://en.wikipedia.org/wiki/Roan_(color)

In cattle brown is dominant over white In cattle brown is dominant over white. These cattle display codominance. Cross a heterozygous “roan” cattle with another heterozygous “roan” cattle. BB bb Bb

Another Example Example: B = black and b = white BB= black bb= white Bb= black and white

Codominance: in humans Blood Type: A & B are equally strong. O is recessive. Type A IAIO Type B IBIO Type AB IAIB Type O IOIO

IA IO IB IA IB IB IO IO IO IO If a heterozygous type A parent mates with a heterozygous type B parentratio 1:1:1:1 The result: 1 type A 1 type B 1 type AB 1 type O Now try another one. Type O x Type A (heterozygous) IA IO IB IA IB IB IO IO IA IO IO IO

Incomplete dominance Incomplete dominance is a situation in which one allele is not completely dominant over another. There is a blending effect.

Incomplete Dominance: In the F1 generation Homozygous R R W R W R W W R W R W Homozygous 100% pink offspring

Incomplete dominance: In the F2 generation Heterozygous R W R R R R W W R W W W Heterozygous What are the genotypic and phenotypic ratios produced?

Heterozygous A 1:2:1 ratio with 25% red, 50% pink & 25% white offspring R W R R R R W W R W W W Heterozygous

Another Example: In rabbits black fur is dominant over white fur. Incomplete dominance is seen. Cross a black fur male with a white fur female Black= White= BB bb 11/12/2018

A complicated case POLYGENIC INHERITANCE- a trait controlled by two or more genes that may be on the same or on different chromosomes. Examples of polygenic inheritance: skin color, height, eye color.

Sex Linked or Influenced traits Sex linked traits are controlled by a gene located only on the X chromosome Females have two X’s: XX Males have only one X: XY Females get sex linked diseases less often than males because statistically it is harder to inherit two “bad/lethal genes” than it is to inherit one.Females must inherit one from her father & one from her mother. (XX) Males only inherit one lethal gene which comes from his mother. (XY)

Red-Green Colorblindness

Practice Problem In humans the gene for colorblindness (a) is recessive to the gene for normal vision (A). Colorblindness is a sex linked trait. Cross a colorblind male with a heterozygous or carrier female. Xa Y x XA Xa

Hemophilia

Muscular Dystrophy

New terms you must know: Carrier: a person who is normal but they carrier the gene for a genetic disease and may pass that gene on to their child.

Practice Problem In humans the gene for hemophilia is recessive (h) to the gene for normal blood type(H). Hemophilia is a sex linked trait. Cross a hemophilic male with a female with normal blood whose father has hemophilia. XhY x XHXh