Module 5: Genetics & Breeding

Genetic Progress

improvements in traits of interest in new generations

genotype

genetic makeup

phenotype

expression of genotype or the physical characteristics

Genetic makeup includes:

coat type/color, speed, gaits, body composition, growth, reproduction, milk production, disease resistance

What provides the basis for worth when an animal is marketed?

their genetic makeup

Applied Genetics in Animal Breeding

breeding "better," more efficient, more desirable animals

heredity

the transmission of traits from one generation to the next

Do holstein bulls have the dairy gene?

Yes, bulls do have a gene for dairy production however it is not expressed because they do not have a mammary system

Chromosome

rod like structures in the nucleus, come in pairs, composed of DNA strands

What chromosomes determine sex?

x & y

X chromosomes

female sex chromosome in mammals, male in birds

Y chromosomes

male sex chromosome in mammals, female in birds

Gene

segment of DNA that codes for a specific protein

forms of a gene

alleles

alleles

different varieties of the same gene that affect the same trait but each one causes the production of a different protein and leads to differences in the way the trait is expressed

homologous chromosomes

chromosomes that have pairs of genes that are the same size and affect the same trait

homozygous

An organism that has two identical alleles for a trait

heterozygous

An organism that has two different alleles for a trait

inheritance

method by which alleles are passed on through generations

DNA

- deoxyribo nucleic acid

- composed of repeating nucleotide molecules

- containing the genetic information that makes up the chromosomes.

DNA nucleotides

deoxyribose + phosphate + a base

DNA nucleotide examples

Cytosine (C), thymine (T), adenine (A), guanine (G)

Purines

adenine (A), guanine (G)

Pyrimidines

cytosine (c), thymine (t)

DNA nucleotide "base pairs"

C & G, A & T

gene

specific linear sequence of DNA nucleotides that specifies the instructions to synthesize a protein

DNA strand

Double stranded helix that consist of alternating nucleotide sequences of sugar-deoxyribose and phosphate bonds

- connected to each sugar is nitrogen bases composed of both purines & pyrimidines

DNA Replication

the process of making a copy of the DNA molecule so that the new cell contains the same genetic information as the original

Explain the process of DNA Replication

The DNA double helix is "unzipped" between the base pairs to expose each base (done by the DNA polymerase enzyme). Then new nucleotides are added which creates two identical DNA molecules (mRNA) with matching base pairs.

Ribosomes

manufactures a chain of amino acids from the info found in the specific DNA sequence of a gene (amino acids will soon become a polypeptide then a protein)

What is DNA's purpose?

To serve as a template for the synthesis of a protein the genetic message found in DNA must be transported out of the nucleus to the ribosomes

RNA

ribonucleic acid that passes along genetic messages

DNA Transcription

the formation of an RNA strand complementary to the DNA strand by RNA polymerase

DNA Translation

mRNA leaves the nucleus and travels through the cytoplasm to the ribosome that is responsible for interpreting the RNA message into the exact sequence of amino acids and assembling them into a protein

What are enzymes?

A protein

What are somatic cells?

the regular body cells (does not include reproductive cells ie. sperm/egg)

What do somatic cells contain?

the diploid (2n) number of chromosomes

What are germ cells (gametes)?

sex cells, sperm, egg

What do germ cells contain?

the haploid (n) number of cells

swine haploid cell #

19

swine diploid cell #

38

human haploid cell #

23

human diploid cell #

46

cattle & goats haploid cell #

30

cattle & goats diploid cell #

60

horse haploid cell #

32

horse diploid cell #

64

donkey haploid cell #

31

donkey diploid cell #

62

chicken haploid cell #

39

chicken diploid cell #

78

What happens when horses and donkeys breed?

Since they are genetically different and have different numbers of chromosomes, the offspring they produce are sterile because they can not produce functional sperm/egg

Sex chromosomes in somatic cells

each somatic cell has 2 sex chromosomes or 1 pair of sex chromosomes

autosomes

Any chromosome that is not a sex chromosome

Sex chromosomes in the gamete

the gamete only has one sex chromosome

karyotype

diagram of a persons chromosomes

homo gametic

sex chromosomes are the same (XX - female in mammals, male in birds)

heterogametic

sex chromosomes that are different (XY - male in mammals, female in birds)

Mitosis

the process of somatic cell division (body cells in tissues responsible for everyday maintenance of the body/growth)

Explain the process of mitosis

1 diploid cell duplicates DNA then undergoes division to create two matching diploid cells

Gametogenesis

the development of the sex cells

meiosis

there are two stages:

stage 1: one diploid cell (2n) is split in half to create two haploid cells (n)

stage 2: each haploid cell is replicated to produce 4 haploids

what is spermatogenesis?

sperm generation

how does spermatogenesis work?

each diploid cell in the seminiferous tubule forms 4 functional haploid cells that become functional, this process is continuous and begins at puberty (never stops)

What happens as sperm cells mature?

As sperm cells mature, they move closer to the lumen (hollow center of tubule), once they are nearly fully mature, they can leave the seminiferous tube and move through the male reproductive tract

what is oogenesis?

egg generation

how does oogenesis work?

each diploid cell in the ovary only forms one functional haploid cell and the other 3 cells do not function, this process begins and is completed during embryonic and fetal development (born with all the eggs she will ever have), at puberty she begins to release eggs via the estrous cycle

what happens to eggs as they mature?

egg cells mature on the ovary and the develop inside of a follicle, the ovaries are covered with follicles/eggs of various developmental stages, primary follicle becomes a secondary follicle, then finally a mature follicle

Structures in the maturing follicle:

theca extrema, theca interna, zona pellicula, cumulus oophorus (which contains the egg)

Fertilization

the union of the haploid sperm and the haploid ovum, creates a new individual with half the genetic info from each parent and the diploid # of cells is restored

Dominant Alleles

express themselves over recessive alleles

Alleles

different versions of a gene

Cell vs. Chromosome vs. DNA vs. Gene

The cell has a nucleus with chromosomes attached to it, the chromosomes are structures made of DNA, segments of DNA are known as genes

telomere

DNA at the tips of chromosomes

centomere

the region of the chromosome that holds the two sister chromatids together during mitosis

incomplete dominance

no dominance exists and neither allele is expressed fully but rather intermediate ground between the two

Example of incomplete dominance

red x white = pink

co-dominance in alleles

when a single gene has more than one dominant allele

Example of co-dominance in alleles

red x white = red & white (roan)

Epistasis

one gene pair influence another, capable of causing a dramatic difference in appearance based on what genes are present and the gene action taking place

- when epistasis exists the gene action could be completely different

What trait is often influenced by epistasis?

coat color

Provide an Example of Epistasis

"Horses either have black hair or they don't, this is controlled by the EGM1 locus however that black hair could be spread all over the body or only on points which is controlled by the E gene at another location.

locus

specific location of a gene on a chromosome

Qualitative trait

Traits having a sharp distinction between phenotypes, and which are usually controlled by only a few genes; e.g., various coat colors and the horned trait in domestic animals

- this trait is something that tends to be descriptive (usually one gene pair)

Quantitative trait

traits that can be measured numerically usually controlled by many gene pairs that all have a small impact on phenotype, we can rarely pinpoint 1 gene to quantitative traits

- usually measured with a tool

- can be influenced by the environment of the animal

What does DNA code for?

the synthesis of proteins

Heritability

measure of the proportion of phenotypic variation that can be passed from parent to offspring, used as an indicator of potential genetic progress in the next generation

What is the range of heritability values?

0-1

like a % or proportion of what you see or of the phenotype

high heritable range

0.4-0.6 (meat quality traits)

moderately heritable

0.2-0.4 (growth traits)

low heritability

0-0.2 (reproductive traits)

What trait leads to a faster genetic progress?

high heritability traits

Breeding Goal

combine genetic potential with superior environmental conditions

Selection Differential

measures how much better the "best" are compared to the rest of the animals

Environmental Influence

gene expression influenced by environmental factor

codon

three-nucleotide sequence on messenger RNA that codes for a single amino acid (3 base pairs in a row)

genetic progress equation

(heritability x selection differential) / generation interval

Heterosis (hybrid vigor)

phenomenon by which crossbred offspring outperform the average of their parents (often seen in traits with high environmental componenet vs genetic)

- is the way for us to work around heritability and breed for quantitative traits

Are most economically important traits influenced by the environment or heritability?

more heavily influenced by the environment (low heritability)

Inverse relationship between...

heritability and heterosis