Animal Science Genetics Competency 18.01: Describe the cell and processes involved in cell division including how genes affect the transmission of characteristics Competency 18.02: Discuss heritability estimates for beef and swine

Genetics is the science of heredity and variation It is the science that deals with the differences and similarities among related individuals

A genotype is the inheritable information that is carried by an animal In agricultural systems manipulation of genetic makeup has been done to improve productivity and increase efficiency

Gregor Mendel Considered the father of genetics Did an experiment with pea plants where he discovered there were crosses between tall and short plants helping him discover heritability through dominant and recessive traits.

Different Principles of Genetics Principle of Dominance Deals with heterozygote, one allele may conceal the presence of another one Principle of Segregation Deals with a heterozygote, two different alleles segregate from each other during the formation of gametes There are four main concepts related to this principle. They are as follows: A gene can exist in more than one form. Organisms inherit two alleles for each trait. When gametes are produced (by meiosis), allele pairs separate leaving each cell with a single allele for each trait. When the two alleles of a pair are different, one is dominant and the other is recessive. Principle of Independent Assortment Deals with alleles of different genes segregating independently of each other For example, a plant that had green pod color and yellow seed color was cross-pollinated with a plant that had yellow pod color and green seeds. In this cross, the traits for green pod color (GG) and yellow seed color (YY) are dominant. Yellow pod color (gg) and green seed color (yy) are recessive. The resulting offspring (Figure A) or F1 generation were all heterozygous for green pod color and yellow seeds (GgYy).

Cells have multiple parts Genetic material of cells can be found in the nucleus

Genotype vs. Phenotype Phenotype Genotype The observable properties of an animal Genotype The inheritable information carried by an animal Different environmental conditions or influences from their surroundings can cause animals with the same genotype to appear differently

Cells The body is made up of millions of cells that can be only seen by a microscope The most important part of any cell is the nucleus Chromosomes are found in the nucleus, they are dark-staining, rod-like or rounded bodies in the nucleus that occur in pairs Chromosomes are made up of tightly coiled strands of DNA

Genes A gene is made up of a specific functional sequence of nucleotides The collection of genes that an organism has is called its genome Chromosomes in the body occur in pairs, these are called homologous pairs

In order for animals to grow, cells must divide and increase in number Gametes are reproductive cells that do not have paired chromosomes are referred to as haploid Paired would be referred to as diploid In order for animals to grow, cells must divide and increase in number

Cell Division The type of cell division in which the genetic material of the parent cell is duplicated and then divides into two separate cells is called mitosis The process of cell division that occurs in reproductive cells is meiosis and that ensures that the gametes only receive ½ the number of chromosomes

Gametes from one individual join with another gamete of the opposite sex during fertilization All animals originate from the female’s ovum or egg which is fertilized by the male spermatozoa and becomes a zygote The zygote will have a full set of chromosomes with ½ from the male and ½ from the female

The first generation is known as the parent or P The offspring are referred to as the F1 generation Their offspring are referred to as the F2 generation And so on…

A capital letter is used to denote a dominant form of a gene A lowercase letter represents a recessive form of a gene Example: D – drooped dominant ears in pigs, while d – erect recessive ears in pigs

When both genes in a pair take on the same form they are called: homozygous Example: DD or dd If they are both dominant this is called homozygous dominant and if they are both recessive this is called homozygous recessive

A gene pair that has one dominant and one recessive is called: Heterozygous dominant for that trait Example Dd – D=drooped ears so this animal will have drooped ears since D is dominant over d (erect ears)

Punnett Square A Punnett Square can be used to determine the possible outcomes for breeding livestock Example I have a sow that is homozygous recessive for drooped ears and one that is heterozygous dominant dd x Dd

So we know what dominance is … What is codominance? This occurs when one trait doesn’t completely dominate another trait Example: The color Roan in horses is an example of codominance… If a mare that is homozygous dominant white (WW) mates with a homozygous dominant red stallion (RR) you will get RW as your cross So what really happens is the horse has both red AND white hairs, not pinkish color like many people think

What is epistasis? One or more gene can control a single trait An allele of one of them may have an overriding effect on the phenotype Example: Comb shape in chickens Chickens can have four different combs: walnut, rose, pea, single

Mutations Are responsible for variations in color, size, shape, behavior, and other traits Mutations can occur the following ways Nondisjunction – change in chromosome number Translocation/deletion – chromosome breakage Inversion - rearrangement of genes on a chromosome

What are sex-linked traits? Traits that are carried on the X or Y chromosomes (which are involved in determining the sex of the animal) XX – female XY – male Sex-linked traits are often recessive and are covered up in the female mammal by dominant genes

Improvements in Breeding? Improvements in breeds of animals can be done: naturally or artificially Natural occurs in the wild or without plan of humans Artificial is planned and controlled by humans

Selection is done to improve breeding stock The goal of selection is to increase the frequency of animals with optimal levels of performance Culling aims to reduce frequency of individuals with poor performance (culling is the process of weeding out poor individuals)

Two breeding methods Single trait selection Multiple Trait selection Aim at improving one trait in a breeding program Multiple Trait selection Simultaneously improve multiple traits in a program

Types of Modern Genetics and Artificial Genetics Gene Transfer Transferring a gene from one individual to another Embryonic Cloning Chemical or surgical splitting of developing embryos shortly after fertilization and developing two identical offspring Nuclear Transfer Microsurgical collection of cells from the outer layer of a developing embryo and transferring them into an unfertilized ovum that has had its own nucleus removed Nuclear Fusion Involves the union of nuclei from two gametes