Inheritance Flashcards
What is the definition of gene?
A sequence of bases on a DNA molecule that codes for a protein which results in a characteristic e.g a gene for eye colour
What is the definition of allele?
A different version of a gene.
What is the definition of a genotype?
The alleles an organism has/ the genetic make up e.g BB, Bb or bb for eye colour
What is the definition of phenotype?
The physical expression of the genes, which may also be influenced by the environment e,g brown eyes
What is the definition of dominant?
An allele whose characteristic appears in the phenotype even when there’s only one copy. They are shown by a capital letter
What is the definition of recessive?
An allele whose characteristic only appears in the phenotype if two copies are present. Shown by a lower case letter
What is the definition of codominant?
Alleles that are both expressed in their phenotype, neither one is recessive
What is the definition of locus?
The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair
What is the definition of homozygote?
An organism that carries two copies of the same allele e.g BB or bb
What is the definition of a heterozygote?
An organism that carries 2 different alleles e.g Bb
What is the definition of a carrier?
A person carrying an allele which is not expressed in their phenotype but that can be passed on to offspring
What is the difference between body cells and gametes in terms of alleles?
-Body cells have 2 alleles for each gene, but gametes contain only 1 allele for each gene
-when gametes from two parents fuse together, the alleles they contain form the genotype of the offspring produced
What are genetic diagrams used for?
To predict the genotypes and phenotypes of the offspring produced if two parents are crossed
What is monogenetic inheritance and what does it show?
-the inheritance of a characteristic controlled by a single gene
-they show the likelihood of the different alleles of that gene being inherited by offspring of particular parents
-the cross can be shown through a punnet square:
Explain how codominant alleles work using the example of sickle cell anaemia
1) people who are homozygous for normal haemoglobin don’t have the disease
2) people who are homozygous for sickle haemoglobin have sickle cell anaemia-all their blood cells are sickle shaped
3) people who are heterozygous have an inbetween phenotype, called sickle cell trait. They have some normal haemoglobin and some sickle haemoglobin. The two alleles are codominant because they’re both expressed in the phenotype
4) if you cross 2 parents with sickle trait haemoglobin (heterozygous) you end up with a 1:2:1 ratio with 1bunaffected, 2 sickle trait, and 1 sickle cell
What is dihybrid inheritance and what is it used for?
-inheritance of 2 characteristics which are controlled by different genes
-it is used for looking at how 2 different genes are inherited at the same time
