Download KEY: Chapter 9 – Genetics of Animal Breeding.

KEY: Chapter 9 – Genetics of Animal Breeding.
Answer each question using the reading assigned to you. You can access this information by clicking on
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aring
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1. What is a heritability estimate and how is it used to improve livestock through breeding?
A heritability estimate expresses the likelihood of a trait being passed on from parent to offspring.
Traits that are highly heritable will rapidly improve the animal’s characteristics; traits that have low
heritability require several generations of genetic improvement (selecting for that specific trait), for the
selected trait to become strong.
2. Name the parts of the cell (all of them)
Smooth and Rough Endoplasmic Reticulum
Plasma / Cell Membrane
Golgi Apparatus
Vacuole
Ribosomes
Centriole
Lysosome
Nucleolus
Nucleus
Cytoplasm
Mitochondria
3. How many pairs of chromosomes does each of the following animals have:
a. Cattle: 30
b. Swine: 19
c.
Sheep: 27
d. Goats: 30
e. Horses: 32
f.
Chickens: 39
4. Describe (in detail) Mitosis:
Mitosis is defined as the division of body cells in an animal. Mitosis increases the number of body
cells, which causes the animal to grow. During mitosis, chromosome pairs are duplicated in each
daughter cell (becoming exactly like the old cell). The number of times a cell can continue to divide
throughout the life of an animal is limited - Each time a cell divides, a portion of the telomere (which is a
specific DNA repeating sequence) is lost from the end of the chromosome. As an animal ages, the
telomeres become shorter and shorter until eventually the cell stops dividing.
5. Describe (in detail) Meiosis:
Chromosome pairs are divided in such a manner that each gamete (sexual reproductive cell) has
one of each type of chromosome. When the male and female gamets (or haploid cells) unite, the
zygote that results from the union has a diploid number of chromosomes. Haploid cells are
produced through meiosis where chromosome pairs are divided in such a manner that the
resulting cells only have one of each type of chromosome.
6. What is fertilization?
Fertilization occurs when a sperm cell from the male reaches an egg cell from the female. The
two haploid cells unite to form one complete cell called a zygote.
7. Why are genes important in animal breeding?
Genes are located on chromosomes and are composed of DNA. Genes provide the code for the
synthesis of enzymes and other proteins that control the chemical reactions in the body. These chemical
reactions ultimately determine the physical characteristics of the animal. Some traits are controlled by a
single pair of genes; however, most of the traits that are important in animals are controlled by many
pairs of genes.
8. Name and briefly describe the two ways in which genes control inherited traits
Genes control inherited traits through Genotype & Phenotype.
Genotype: The actual genetic makeup of an animal
Phenotype: The appearance of an animal, as determined by its genetic makeup
9. Define Dominant Gene: A dominant gene in a heterozygous pair hides the effect of its allele.
When working genetic problems, the Dominant gene is usually represented by a capital letter
10. Define Recessive Gene: A recessive gene in a heterozygous pair that is hidden. When working
genetic problems, the Recessive gene is usually represented by a small letter.
11. Define Homozygous Gene Pairs: Homozygous gene pair is one that carries two genes for a trait.
12. Define Heterozygous Gene Pairs: Heterozygous gene pair is one that carries two different
genes (called alleles) that affect a trait. The dominant gene masks the recessive gene - both
genes are present in the animal, but only the dominant gene is expressed.
13. Demonstrate the use of the Punnett Square to predict the traits of the offspring when the male
and female carry heterozygous gene pairs of a given trait:
PP, Pp, Pp, pp
14. Define and give an example of Incomplete Dominance
Occurs when alleles at a gene locus are only partially expressed because one allele is not always
dominant over the other. This usually produces a phenotype that is intermediate between the
phenotypes that either of the alleles would express. For example, a Red Cow crossed with a
White Bull usually produces a blonde colored calf.
15. How is sex of the offspring determined in mammals?
a. The father (male) determines the sex of offspring in mammals - because the female has
2 X chromosomes. The male has and X and a Y chromosome. All offspring will have one X
chromosome (from their mother) - those that get an X chromosome from their father will
be female. Those that get a Y chromosome from their father will be male.
16. How is sex of the offspring determined in poultry?
a. The female determines the sex of offspring in poultry. The male carries two sex
chromosomes, while the female only carries one sex chromosome - so the process we see in
mammals is reversed in poultry.
17. Define and give an example of a sex-linked characteristic
Genes that are carried only on the sex chromosome are called sex-linked genes. An example of
sex-linked characteristic is Calico coat color in cats. Only female cats have the calico coat color;
male cats can not have the calico coat color because the gene for the calico coat is only found on
the female chromosome.
18. Define Linkage: Some groups of traits seemed to stay together in the offspring; certain traits
appear in groups in the offspring - the closer genes are located together on a chromosome - the
more likely they are to stay together (or be linked).
19. Define Crossover:
During meiosis, chromosomes line up together, and are very close to each other. Sometimes the
chromosomes cross over one another and split, this forms new chromosomes with different
combinations of genes. The farther apart two genes are on a chromosome, the more likely they
are to end up in a new combination.
20. Define Mutation
Mutation occurs when a new trait is shown that did not exist in either parent. Mutations are
usually caused by external forces such as radiation. Some mutations are beneficial, while others
are harmful. Mutations do not occur frequently. An example of a beneficial mutation is a Polled
Hereford.
Review Questions:
True / False
1. Genetics accounts for all differences in animals FALSE - Environmental Factors play a large role as
well.
2. The female determines the sex of mammals TRUE
Fill in the Blank
1. In poultry, the sex of the offspring is determined by THE FEMALE
2. Genotype refers to the GENETIC MAKEUP OF THE ANIMAL
3. When chromosome pairs are divided in such a manner that each gamete has one of each type of
chromosome, the process is called MEOSIS
4. The diploid number of chromosomes in cattle is 60
5. When cells divide to form specialized tissues and organs, this process in animals is called MITOSIS
6. The DNAmolecule is shaped like a double helix
Short Answer
1. What are the two factors responsible for genetic variation in animals?
PHENOTYPE
GENOTYPE
2. When some traits are expressed as dominant in one sex but recessive in the other sex, what is this
action called?
SEX-LINKED TRAITS
3. Define mutation.
Mutation occurs when a new trait is shown that did not exist in either parent. Mutations are usually
caused by external forces such as radiation. Some mutations are beneficial, while others are harmful.
Mutations do not occur frequently. An example of a beneficial mutation is a Polled Hereford.