3.12 and 3.12 - Alleles and Basic Definitions Gamete Chromosome Alleles Dominant allele Flashcards
What is a gamete?
An organism’s reproductive cell (egg in females and sperm in males), which has half the number of chromosomes (23).
What is a chromosome?
A structure found in the nucleus which is made up of a long strand of DNA.
What are alleles?
The different forms of a 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.
What is a recessive allele?
Two copies are needed for it to be expressed and for the corresponding phenotype to be observed.
What does homozygous mean?
When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles).
What does heterozygous mean?
When one of the inherited alleles is dominant and the other is recessive.
What is a genotype?
The combination of alleles an individual has, e.g. Aa.
What is a phenotype?
The physical characteristics that are observed in the individual, e.g. eye colour.
What is a zygote?
The stage of development immediately after fertilisation - a diploid (2n) cell formed from the fusion of two haploid gametes.
What is a gene?
A short section of DNA that codes for a protein, and therefore contributes to a characteristic.
Some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans. However, most characteristics are the result of many different genes interacting.
What are alleles?
Alleles are different forms of the same gene.
How do alleles affect inherited characteristics?
Different alleles lead to differences in inherited characteristics.
What do different alleles code for?
Different alleles code for different forms of the same protein.
What can an allele that codes for a damaged form of a protein cause?
It can cause illness.
What is an example of a condition caused by a different allele?
Huntington’s Disease.
In Huntington’s Disease, an allele of the gene that codes for a particular protein is different, leading to the protein becoming folded incorrectly.
