Topic 3 - Alleles And Basic Definitons Flashcards
What is a gamete?
An organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23).
Define chromosome.
A structure found in the nucleus which is made up of a long strand of DNA.
What is a gene?
A short section of DNA that codes for a protein, and therefore contributes to a characteristic.
What are alleles?
The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent.
What is a dominant allele?
Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed.
For example (B) - brown eyes
True or False: Some characteristics are controlled by a single gene.
True
Fill in the blank: Most characteristics are the result of many different _______ interacting.
genes
What is a recessive allele?
An allele that requires two copies to be expressed in the phenotype
Recessive alleles are masked by dominant alleles.
For example (b) blue eyes
Define homozygous.
When both inherited alleles are the same (i.e. two dominant or two recessive alleles)
Homozygous dominant: BB -
Homozygous recessive : bb
Define heterozygous.
When one of the inherited alleles is dominant and the other is recessive
Example: Bb
What is meant by genotype?
The combination of alleles an individual has, e.g. Aa
Genotype contains:
Homozygous dominant
Heterozygous
Homozygous recessive
Genotype determines the potential for phenotypic expression.
Define phenotype.
The physical characteristics that are observed in the individual, e.g. eye colour
Phenotype is influenced by genotype and environmental factors.
In the heterogeneous alleles it will always pick out the dominant allele (Bb) - (B)
What is a zygote?
A diploid (2n) cell formed from the fusion of two haploid gametes
The zygote is the initial stage of development after fertilization.
How many copies of a recessive allele are needed for the corresponding phenotype to be observed?
Two copies
Both alleles must be recessive for the trait to be expressed.
What are alleles?
Different forms of the same gene
