Exploring Genotypes and Phenotypes of Longhorn Cattle

Phenotype – describes the physical appearance of a specific genetic trait or characteristic Genotype – the genetic code consisting of a pair of alleles that describes a inheritable characteristic or trait DNA - a double helix chain of nucleic acid in a cell that carries genetic and hereditary information Chromosomes – a strand of DNA that carries genes in linear order Gene- a unit of inheritable information arranged located within chromosomes Allele – one member of a pair of genes that determines genetic characteristics Wild-type Allele – the gene or characteristic that most commonly occurs in the natural environment this allele is identified as wild by a + symbol following it’s letter designation. Heterozygous - a pair of alleles that contain two different alleles one of which is dominant Homozygous – a pair of identical alleles Dominant Trait – a trait that will appear in offspring if one allele is present. This trait will appear in both heterozygous and homozygous gene pairs. Recessive Trait – a trait that will appear only if two copies of the allele are present. This trait only appears in homozygous gene pairs Incomplete dominance – an allele that is not completely recessive to the dominant allele Punnett Square – a square model of the allele genotypes used to predict the outcome of a genetic cross.

Sire ½ Dam ½ Offspring All cells contain DNA which is the “blueprint” that describes how an animal will look or act. DNA the genetic information which determines heredity. Genetics is the Science of ½’s. The genetic information for a specific trait is contained in a pair of genes called alleles. One half of the pair comes from each parent.

Sometimes beef ranchers cross longhorn bulls with their cows because longhorn calves are much smaller than beef calves. Smaller calves mean that less cows and calves die during the birthing process. However many beef ranchers don’t want horns in their herd.

The alleles in a the gene pairs can be the same homozygous or different heterozygous. When they are heterozygous one allele will be dominant and the other recessive. The polled trait is described as HH. The horn allele is described as hh. The polled allele, H, produces no horns, H is completely dominant over the recessive allele, h, that produces horns. Any time the dominant H allele is present the animal will not have horns.

Offspring receives one allele from each parent. The combination of these alleles makes up the genotype which determines the phenotype of each offspring.

Results : 100% of the offspring’s genotype is heterozygous type Hh. 100 % of the offspring’s phenotype is polled, does not have horns.

We know that 100% of the offspring of a homozygous crosses will not have horns. What happens when we cross heterozygous crosses? Will any of the offspring have horns. Fill out the next Punnett Squares to predict the outcome of crossbreeding heterozygous cattle.

What percentages of each genotypes resulted in this cross? What percentage of each phenotypes resulted in this cross? Were the phenotype and genotype results the same? Why or Why not?

Homogeneous crosses result in 100% of the offspring having the same genotype and phenotype. Heterozygous crosses have a variable result. Genotypes: HH - 25% Hh - 50% hh - 25% Phenotypes : Polled - 75% Horns - 25% Genotypes: Hh - 50% hh - 50% Phenotypes : Polled - 50% Horns - 50%

A. Both of this calf’s parents had horns B. This calf’s sire and dam both carry the recessive allele for horns. C. The genotype represented by this calf is hh. D. The genotype represented by this calf is either Hh or HH.

All color in cattle is the result of two pigments black and red. Black can look brown in lower concentrations. Red can appear orange or yellow. White areas are a result of lack of both pigments. Three alleles control the amount of pigments in cattle E D, E+ and e The E D allele produces black pigment. The E+ allele is called the wild-type allele and produces both red and black pigments. Calves are red at birth and turn dark brown or gray as they mature, usually with a light muzzle. The e allele produces red pigment. The wild-type allele is thought to represent the ancestral coloration of the wild Aurochs, from which modern Bos taurus cattle breeds have descended.

BlackDark Brown or GrayRed E D /E D E+/E+ (wild allele) e/e The black allele is dominant over both wild and red alleles. The wild allele is dominant over the red allele. (E D > E+ > e) Three Alleles make the base color genetics more complex list all possible phenotypes under their genotypes. Possible Allele Combinations: E D E D, E+ E+, e e, E D E+, E D e, E+ e

Fill out the Punnett Squares for all possible homozygous color crosses. How do the percentages in genotype results compare with phenotype results in homozygous crosses?

Black Allele X Wild Type Allele Wild Type Allele X Red Allele Black Allele X Red Allele Genotype: 100% E D /E+ Phenotype: 100% Black Genotype: 100 % E+/e Phenotype: 100 % Dark Reddish Brown or Reddish Gray Genotype: 100 % E D /e Phenotype: 100 % Black

Same Genotypes Heterozygous X Heterozygous Two Alleles Homozygous X Heterozygous Now try the following heterozygous crosses: (E D > E+ > e) List all possible phenotypes and genotypes and their percentages for each cross.

a. The cow and calf are both homozygous. b. The calf inherited her color genes from her sire. c. The cow is heterozygous and the calf inherited her recessive gene. d. This cow could not be this calf’s dam.

Three Alleles Homozygous X Heterozygous Different Genotypes Heterozygous X Heterozygous

Seven pairs of alleles control the patterns of color distribution. The pairing or combination of some of these genes creates additional patterns Pigment reducing genes result in lighter variations of the pigment and pattern alleles. All colors and patterns including the roans, spots, brindles, speckled patterns, linebacks, grullas, reds, yellows, oranges, browns, and blacks are a result of pigment concentrations and genetic patterns.

(Phenotypes below are a few examples of each color variations and possible genotypes) Brindle Alleles Br> br ( linear streaks of light and dark color patterned over the base color.) E+/E+, Br/br Roan Alleles R/r+ (base color is mixed with evenly distributed white to give a faded appearance.) E D /E D, R/r+ Dilution Allele D S > d S + E D /E D, D S /D S E+/E+, D S /d S + r/r, D S /D S

Spotted and Lineback Alleles SP>S+>s (The lineback phenotypes will appear to have a complete or broken line of white along their back and belly.) e/e, s/s Color-sided alleles Cs>cs+ (A pattern similar in appearance to line back where color appears on the back and belly.) e/e, Cs/cs e/e, Cs/Cs Dun Allele s D N +> d N Brockling Alleles Bc>bc+ r/r, D N +/d N r/r, s/s, Bc/Bc r/r, s/s, Bc/bc Some allele pairs produce a even wider variety of patterns when combined with other pairs these include: Brockling, Dilution / Dun, and Color Sided / Roan and Spotted Alleles

The combination of color alleles produces an enormous variety of color possibilities. Historical Author J. Frank Dobie wrote, “The colors were more varied than those of the rainbow. … The shadings and combination of colors were so various that no two were alike" - J. Frank Dobie, "The Longhorns" Geneticist study the longhorn for several reasons. Most colors and color patterns found in all cattle breeds occur in the longhorn. Unlike other domestic breeds of cattle longhorns developed through a process of natural selection in the 17 th, 18 th, and 19 th centuries. Longhorn genetics are also studied to establish genetic markers that separate it as a breed.

Dr David M. Hillis, ”The Genetics of Coloration in Texas Longhorns”, Parts I-V, 2004, University of Texas, Dr. David Kirkpatrick, “Color Inheritance in Beef Cattle”, Animal Science, University of Tennesse,