canine/feline test 1 review Flashcards

Question

HYBRIDS

Answer 1

 An individual that is the offspring of a cross between two purebred animals, but whose parents belong to different breeds or species, is called a hybrid.  The advantage is that the hybrid offspring appear to be healthier and more disease resistant than either of the parent lines. The hybrid exhibits the best characteristics of each allele. This phenomenon is called hybrid vigour or heterosis.  Depending on breed, purebred dogs are often subject to many diseases.  Fortunately, most of these disease-causing genes are recessive; therefore, if one breed is mated to a different breed that carries the dominant, normal gene, the offspring are unlikely to exhibit any of these diseases. They have hybrid vigour.  This is assuming both parent dogs do not share the same defective genes.  It is possible that the phenomenon of hybrid vigour explains why mutts tend to have a lower incidence of genetic diseases than purebred dogs, no matter the breed.

Answer 2

 The inheritance of each characteristic is a separate event (characteristics are not inherited together).  In animal terms, this could be illustrated by the mating of two dogs: * Dog 1 has a genetic defect for blindness and a black coat colour * Dog 2 has normal vision and a white coat colour * Offspring will inherit their parent’s genes for coat colour and the genes for vision; however, the two are inherited separately o Inheriting normal vision does not mean the dog will inherit a white coat colour o This makes sense since these genes may be on different chromosomes  The only exception to this type of inheritance occurs when the genes for two characteristics are found on the same chromosome. If this happens, they will be passed on together, and are said to be linked.

Answer 3

 The Punnett square is useful in determining the possible outcomes of a cross involving more than one characteristic (A and B on separate genes). Although phenotypes can be known visually, unless test crosses are performed dominant genotypes based on pedigree analysis are merely well-educated guesses.

Answer 4

incomplete dominance, co-dominance and complete dominance. Incomplete dominance occurs when there is a relationship between the two versions of a gene, and neither is dominant over the other so they mutate to form a third phenotype.Jun 16, 2022  For many characteristics, an animal that is heterozygous (Bb) does not appear identical to the homozygote (BB); rather, it appears as mainly B with a bit of b.  Therefore, a dog that was Bb might appear mainly black with a few white hairs. This type of gene interaction is called incomplete dominance. The dominant trait does not completely mask the recessive trait.  For any set of alleles (B, b, etc), only one form of dominance will be seen: • Complete dominance • Incomplete dominance • Co-dominance

Answer 5

what happens at one gene can mask what's happening at another gene. Because of epistasis, it's rare to see those masked genes actually expressed in a dog's coat color. Epistasis occurs when the expression of one gene is affected by the expression of one or more independently inherited genes. One example is how white coat colour is regulated: white fur in cats is epistatic over all other coat colours.

Answer 6

Every dog has two sex chromosomes, females have two X chromosomes and males have an X chromosome and a Y chromosome. Since the distribution of the X and Y chromosome varies with the sex of the individual (they are either XX or XY), inheritance of the genes found on the X and Y chromosomes will also vary with the sex of the individual.  All females have two X chromosomes and characteristics that are determined by genes on the X chromosomes are called sex-linked characteristics.

Answer 7

Sex-limited traits are those characteristics expressed only by one sex, such as milk production, egg production, and semen production.  These characteristics, like all inherited characteristics, are controlled by genes. Governing hormones such as estrogen and testosterone o If estrogen is present, female characteristics will develop (mammary development, milk production) o If testosterone is present, male characteristics will develop (beard growth in humans)控制激素，如雌激素和睾酮

Answer 8

 It is evident that some genes inherited on either the sex chromosomes or the autosomes may be defective and result in disease.  In many cases, the defective gene; a heterozygous individual (Mm) will be a carrier but will not show signs of disease.  In some cases, the defective genes are detrimental to the normal function of the individual that the homozygous form (mm) is not compatible with life. These genes are called lethal genes.  When a recessive lethal gene is present in both parents, probability suggests that 25% of offspring will die before or soon after birth. In fact, the gene is considered lethal if the individual dies before reaching reproductive maturity.

Answer 9

he idea of selective breeding is simple: the animal’s owner (farmer or breeder) wishes to achieve the best quality offspring from each mating and selects the animal’s mate on that basis.  The selection of an animal’s mate based on the genotype of each animal is called artificial selection.  This differs from natural selection in which an animal chooses its own mate, presumably at random

Answer 10

 Traits can be described by their level of heritability: * Collie eye syndrome is highly subject to genetic selection; it has high heritability * Hip dysplasia is somewhat subject to genetic selection; it has medium heritability  Traits that have high heritability tend to have the following characteristics: * Controlled by only one or two genes * Sharp distinction between phenotypes (animal is either normal or abnormal) * Qualitative (black versus white) * Defects or diseases are obvious * Little environmental influence on phenotype; all animals with the gene show the same characteristics, regardless of environment * Example of a trait with high heritability would include: o Hip dysplasia in dogs  Traits that have low heritability tend to have the following characteristics: * Controlled by many genes * No sharp distinction between phenotypes (degree of trait expressed may vary greatly) * Quantitative (measured in terms of numbers) * Some environmental influence on phenotype; genes alone do not determine appearance * Example of a trait with low heritability include: o Growth rate in dogs

Answer 11

. Most characteristics (height, personality, etc) are controlled by more than one gene. * Any one gene may have five or ten different alleles. * Examples given thus far illustrate the simplest inheritance; one gene controls one characteristic. This pattern holds true for some diseases and genetic disorders (hemophilia in humans) but is too simplistic to explain most inherited traits.

Answer 12

 A mutation is a change in DNA structure which may be present in a single cell or in every cell of the body.  Some mutations are very large and may involve many genes: * A piece of chromosome may break off and be lost from the cell o All proteins coded by the lost genes cannot be manufactured by the cell or its progeny  Mutations usually arise because the DNA has been altered by an accidental exposure to a mutagen; any material or energy form that can cause a mutation can act as a mutagen. Examples of mutagens include:

Answer 13

 Large, state-of-the-art DNA diagnostic laboratories are designed and equipped for development and implementation of diagnostic tests based on the analysis of nucleic acid, the genetic blueprint for all living organisms.

Answer 14

Buccal Swab Sample Collection: The collection of epithelial cells from the lining of the cheek using a swab technique should not be used on dogs under 6 weeks of age.  Blood Sample Collection: Cause a small amount of bleeding by trimming the dog’s nail short or by pricking the paw pad with a sterile needle. Collect the blood by tapping the indicated corners of the blood card the bleeding area. Fill the indicated corners as wholly as possible. Allow the blood sample to dry completely for at least 30 min (depending on saturation level) before placing in plastic bag for transport to the lab. Dewclaw or Docked Tail Sample Collection: After removal place the dewclaw or tail in a paper envelope (avoid plastic, as the sample could grow bacteria or decay in plastic). You must allow the sample to dry completely prior to sealing the paper envelope.

Answer 15

 The comparison between parents is done by a cross-match of DNA. Each offspring receives two copies, called alleles, one from each parent in a random process. The offspring’s genetic phenotype depends on the combination of dominance and/or recessive traits that it receives.  The probability of recessive gene inheritance escalates as the number of combinations of traits increases (ie, coat colour combined with texture and length). For this reason, scientists do not use the actual genes to generate DNA profiles, but rather use DNA sequences called markers.  A marker is a gene or DNA sequence with a known location on a chromosome used to identify an individual or species. These markers are inherited in the same manner as genes.