Animal Breeding & Genetics – Exam Review

These flashcards cover fundamental definitions, processes, numerical facts, and selection principles from the Animal Breeding & Genetics lecture, providing a comprehensive question-and-answer review for exam preparation.

What equation explains an animal’s phenotype?

Phenotype = Genotype + Environment (+ G × E interactions).

Who is considered the father of modern genetics?

Gregor Mendel.

In what year did Mendel present his pea-plant research?

1865.

What cellular structure contains genes?

Chromosomes located in the nucleus.

Define gene.

A unit of inheritance; a specific segment of DNA found on a chromosome.

Define mitosis.

Somatic-cell division that produces two diploid daughter cells genetically identical to the parent.

Define meiosis.

Specialized division in gametes that halves the chromosome number, producing haploid sperm or ova.

What is the diploid number?

The species-specific total of chromosome pairs in somatic cells.

Diploid chromosome number of cattle?

60 total chromosomes (30 pairs).

Diploid chromosome number of swine?

38 total chromosomes (19 pairs).

What structure shortens with each cell division and is linked to aging?

Telomere.

Name the male and female gametes.

Sperm (male) and egg/ovum (female).

What is a zygote?

The diploid cell produced when a sperm fertilizes an egg.

Define dominance in genetics.

A gene whose effect masks the expression of its allele in heterozygous condition.

Define recessive gene.

An allele whose expression is masked by a dominant allele in heterozygotes; expressed only when homozygous.

What is codominance (lack of dominance)?

Both alleles in a heterozygote are fully expressed (e.g., roan coat in Shorthorn cattle).

Define allele.

Alternate form of a gene occupying the same locus on homologous chromosomes.

Define locus.

The specific physical location of a gene on a chromosome.

Which chromosome contains the SRY gene?

The Y chromosome.

Function of the SRY gene?

Initiates testis development, determining male sex in mammals.

What determines sex in mammals?

The male’s sperm (XY); presence of Y produces male offspring.

What determines sex in birds?

The female (ZW); eggs contribute either Z or W.

Define replication.

Duplication of DNA, catalyzed by DNA polymerase.

Define transcription.

Synthesis of RNA from a DNA template, catalyzed by RNA polymerase.

Define translation.

Decoding mRNA at ribosomes to assemble amino-acid chains (proteins).

Start codon and its amino acid?

AUG; codes for methionine.

Three mRNA stop codons?

UAA, UAG, UGA.

Additive gene effect characteristics?

Many genes, small individual effects, cumulative, little dominance, quantitative traits.

List three economically important additive traits.

Carcass traits, weight gain, milk production.

Non-additive gene effects are associated with what phenomenon?

Hybrid vigor (heterosis).

Traits from non-additive effects tend to be qualitative or quantitative?

Qualitative (easily observed categories).

Define heritability (h²).

Proportion of total phenotypic variation explained by additive genetic variance.

Which selection method indexes traits by economic merit and correlations?

Selection Index.

Weakness of tandem selection?

Focuses on one trait at a time; ignores others, least effective overall.

Independent culling level principle?

Animals must meet minimum thresholds for each trait; failure on any trait leads to culling.

Equation for expected genetic progress per generation?

Progress = Selection Differential × h².

What is selection differential?

Average superiority of selected parents over the herd average.

Give an example of a dominant trait in cattle.

Black coat colour is dominant over red.

Give an example of a dominant trait in chickens.

Rose comb is dominant to single comb.

Define homozygous.

Having identical alleles at a gene locus (e.g., PP or pp).

Define heterozygous.

Having two different alleles at a locus (e.g., Pp).

What tool predicts offspring genotypes?

Punnett Square.

What is incomplete dominance?

Heterozygote phenotype is intermediate between homozygous forms.

Sex-limited gene example in poultry.

Plumage pattern expressed only in males, influenced by androgens.

Sex-influenced trait example in sheep.

Horns dominant in males, recessive in females.

Define linkage.

Genes close together on a chromosome tend to be inherited together.

Purpose of crossover during meiosis.

Exchange of chromosome segments, creating new gene combinations and genetic variation.

Define mutation.

A heritable change in DNA sequence; may be beneficial, harmful, or neutral.

Example livestock breed believed to originate from mutation.

Polled Hereford cattle (hornless).

Four rules for maximum genetic improvement?

(1) Maximize genetic variation, (2) emphasize highly heritable traits, (3) measure traits accurately, (4) use selected animals effectively.

Why can uniform herds limit genetic progress?

Reduced genetic variation restricts selection response.

Give typical heritability level for carcass traits.

High (>40%).

Generation interval effect on progress?

Longer generation intervals slow genetic improvement.

Which species reaches sexual maturity fastest, aiding rapid genetic progress?

Poultry (generations completed in ~7–8 months).

Define gamete.

A haploid reproductive cell (sperm or ovum).

Define protoplasm.

Living substance of a cell, including cytoplasm and nucleus.

Name cell organelles found in cytoplasm (list any two).

Mitochondria, ribosomes, lysosomes, Golgi apparatus (any two).

What is a telomere’s role?

Protects chromosome ends; shortening limits cell divisions, contributing to aging.

Difference between diploid and haploid numbers.

Diploid = full chromosome pairs in somatic cells; Haploid = half that number in gametes.

How many autosomes does a human somatic cell have?

44 autosomes (22 pairs) plus 2 sex chromosomes = 46 total.

Which livestock species has 32 chromosome pairs?

Horse (64 chromosomes).

What is hybrid vigor (heterosis)?

Offspring outperforms the average of its parents for a trait due to non-additive gene effects.

Define Expected Progeny Difference (EPD).

Forecast of an animal’s genetic transmitting ability for a trait compared with breed average.

Why are extensive records critical for selection index method?

Accurate economic weighting and genetic correlations depend on reliable performance data.

What process reunites haploid gametes to restore diploid chromosome number?

Fertilization.

Explain sex-linked inheritance in chickens using barred plumage.

Barred allele on Z chromosome is dominant; crossing barred female (ZW) with black male (ZZ) yields sex-specific barred patterns.

Why might predicted mating ratios deviate from expectations?

Linkage & crossover can reshuffle genes, altering expected combinations.

Why are mutations not the primary tool for livestock improvement?

They occur rarely and unpredictably; selective breeding of existing variation is more reliable.

Three factors affecting genetic progress aside from heritability.

Genetic variation present, accuracy of measurements, and extent of use (prolificness & generation interval).

Example formula to adjust herd milk average after replacing 10 % with better cows.

New Avg = (Old Avg × 0.90) + (Improved Avg × 0.10).

Why is accurate trait measurement vital?

Incorrect data lowers selection accuracy, slowing or misdirecting genetic progress.