B18: Continuity and Variation Flashcards
What does DNA mean?
Deoxyribonucleic acid
What is DNA?
The nucleic acid that contains all genetic information
What is a gene?
- A section on a chromosome that is responsible for a particular feature.
- It is the basic unit of inheritance
what is a chromosome?
threads of DNA in the nucleus that are surrounded by proteins(histones), and that carry genes.
What is an allele?
alternate form of a gene that occupies the same position on a particular chromosome and controls the same character
What is a genotype?
The combination of of alleles present in genome of organism.
What is a phenotype?
the observable characterisitc of an organism, ie physical appearance
examples of phenotypes
colour of eyes
colour of hair
colour of lowers
height
What is a dominant allele?
An allele that, if present, will always produce the same phenotype, even if its paired allele is different
What is a recessive allele?
Allele that can only produce a phenotype if its paired allele is identical
What is a dominant trait?
It is a trait that is seen in an individual with with one or two dominant alleles
What is a recessive trait?
A trait that is results only when two recessive alleles are present, or when no dominant allele is present in a particular position on a chromosome
What is codominance?
Give an example
A characteristic where both alleles are expressed in a phenotype of a heterozygote, that is , no allele dominates over the other
an example of codominance is sickle cell or the ABO blood groups
what is an autosome?
A chromosome that is not a sex chromosome
What is a locus?
The specific location of a gene on a chromosome.
if R is the allele for red flowers and W is the allele for white flowers and both alleles pair during fertilization, what will the be colour of the offspring if these genes are codominant and why?
offspring will be pink because both the red and white alleles of the gene with be expressed
What is a homozygote?
An organism that carries 2 copies of the same allele for a particular trait in a genome.
What is a heterozygote?
An organism that carries 2 different alleles for a particular trait
homozygous means:
alleles of a gene are identical
heterozygous means:
the alleles of a gene are different
when are recessive alleles expressed?
only when they are homozygous
when are dominant alleles expressed?
Dominant alleles are always expressed. It does not matter if they are homozygous or heterozygous
What is a carrier?
A person carrying an allele that is not expressed (recessive allele in heterozygotes) but is capable of passing on allele to offspring.
What is linkage?
When 2 or more genes are located on the same chromosome and are always inherited together, unless crossing over occurs in meiosis.



