Genetics And Breeding

Question 1

What is an allele?

Answer 1

A pair of genes which are located at the same place on homologous chromosomes. (the matched pair). Often applied to the traits associated with the genes.

Question 2

What does phenotype mean?

Answer 2

The physical appearance of the animal because of its genetic make up.

Question 3

What does genotype mean?

Answer 3

Genetic constitution (make up) of an individual.

Question 4

What does gene mean?

Answer 4

A specific region of a chromosome which is capable of determining the development of a specific trait that is composed partially or wholly of dna.

Question 5

What does dominant mean?

Answer 5

Refers to genes which hide or mask the presence of other genes.

Question 6

What does recessive mean?

Answer 6

Gene whose phenotypic expression is masked when in the presence of a dominant allele.

Question 7

Homozygous…

Answer 7

An animal that carries a gene with 2 identical alleles.

Question 8

Heterozygous

Answer 8

An animal that carries a gene with 2 different alleles.

Question 9

Characteristics of genes.

Answer 9

Traits are controlled by genes

Genes have different forms which are known as alleles.

Question 10

In diploid organisms…

Answer 10

Like man and the higher animals, there are 2 alleles. One on each chromosome of the homologous pair.

Question 11

Recessive genes..

Answer 11

For a recessive trait to appear (phenotypically) the animal must be homozygous (have 2 of the same gene-one on each homologous chromosome) for that characteristic to appear.

Question 12

Incomplete dominance..

Answer 12

Sometimes traits do not have one clear dominant gene or one clear recessive gene.
In incomplete dominance, traits appewr to blend together
When crossing a red snap dragon with a white snap dragon the offspring is pink if incomplete dominance occurs.
The heterozygous genotype in imcomplomete dominance appears different than either the homozygous alternatives.

Question 13

What are chromatin?

Answer 13

Thread like strands inside the nucleus which organise themselves into chromosomes when approaches division by mitosis or meiosis.

Question 14

What is a karyotype?

Answer 14

Karotyping is a labrotory technique where chromosomes of a given cell are arranged in pairs and photographed. Some make perfect x’s. And some don’t. This is governed by the position of their centromeres. If the centro mere is central it is called a metacentric chromosome. If found intermediately it is called submetacentric and if found at one end it is called acrocentric.

Question 15

Diploid or somatic body cells contains..

Answer 15

Pairs of chromosomes, this pair is called a homologous pair.

Question 16

Haploid cells, the gametes( sperm and ova) …

Answer 16

Have half the number of chromosomes as the diploid celle (one chromosome from each pair)

Question 17

Genes are arranged..

Answer 17

In a specific order and ever gene is always in the same place, locus on the chromosome in any given species.

Question 18

The gene for example eye colour..

Answer 18

Is always on the same homologous chromosome pair and indeed on the same loci of those chromosomes. This ensures that individuals from the same species can successfully mate with eachother.

Question 19

Any given gene on a particular locus on a chromosome is..

Answer 19

Paired with another gene on exactly the same locus on the opposite chromosomes.

Question 20

Alleles..

Answer 20

Can be either identical or non identical. Identical alleles are called homozygous alleles. Non identical alleles are called heterozygous alleles.

Question 21

In the diploid cell..

Answer 21

There are varying numbers of homologous pairs of chromosomes. During meiosis only one of the chromosome pair ends up in a haploid cell (the gamete) - the haploid cell only inherits one of the alleles.

Question 22

The haploid cell (be it a spermatozoa or an ovum) becomes..

Answer 22

A zygote upon fertilisation.

Question 23

The zygote is..

Answer 23

A diploid cell made up of half of the chromosomes and therefore the genes of one parent and half of the other parents.

One allele comes from each parent.

Question 24

Whether or not the inherited alleles phenotype, the genes phenotype will be expressed is determined by..

Answer 24

If it is dominant, recessive or x-linked(on the female chromosome)

Question 25

Coat colour in mammals is brought about by the presence of..

Answer 25

Pigment granules called melanins. 2 varieties of melanin are converted into the amino acid tyrosine. One is called eumelanin and gives rise to dark coat colour. And the other is phaemelanin which produces light colour.

Question 26

A labrador with a black coat phenotype..

Answer 26

May be genetically either homozygous BB or heterozygous Bb .
Two alleles of the same gene are responsible for the black and chocolate colours. Black is dominant and is represented by uppercase B. And chocolate is recessive and is represented by lower case b.

Question 27

The yellow coat colour in a labrador is..

Answer 27

Brought about by a second gene whose function is to mask the dark colour by producing phaemelanin instead of eumelanin. Eumelanin is produced by the dominant allele E and phaemelanin by the recessive allele e.