Genetics Flashcards
Gene?
A sequence of bases on a DNA molecule that codes for a protein which results in a characteristic.
Alleles?
More than one version of the same gene. There can be many different alleles of a single gene but most plant and animals only carry two alleles of each gene, one from each parent. The order of the bases in each allele is slightly different and are represented using letters.
Locus?
The fixed position on a chromosome where a particular allele is found.
What is meant by diploid organisms?
Humans are diploid organisms, this means we have two copies of each chromosome, one from each parent.
Genotype?
An organisms genetic constitution, the different alleles an organism has. For example, one person may have the genotype BB for eye colour and another Bb for it.
Phenotype?
The expression of the genetic constitution and its interactions with the environment. For example, one person may have brown eyes and another may have blue eyes.
Dominant alleles?
A dominant allele is always expressed in the phenotype, even when there’s only one copy of it. They are shown by a capital letter.
Recessive alleles?
A recessive allele are those with characteristics that only appear in the phenotype if two copies are present. They are shown by a lower case letter.
Co-dominant alleles?
Some alleles are both expressed in the phenotype because neither one is recessive.
Homozygous?
When an organism carries two copies of the same allele at the same locus.
Heterozygous?
When an organism carries two different alleles at the same locus.
Genetic diagrams?
Genetic diagrams can be used to predict the genotypes and phenotypes of the offspring produced if two parents are crossed.
What happens when haploid gametes of two parents fuse together?
The alleles they contain form the genotype of the diploid offspring that is produced.
Monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene.
Monohybrid crosses?
The likelihood of the different alleles of that gene being inherited by the offspring of certain parents.
Phenotypic ratios?
The ratio of different phenotypes in the offspring. Genetic diagrams allow you to predict the phenotypic ratios in F1 and F2 offspring.
Punnet square?
Another way of showing a genetic diagram.
Monohybrid inheritance of codominant alleles?
Occasionally, alleles show co-dominance, both alleles are expressed in the phenotype and neither one is recessive.
What is an example of monohybrid inheritance of codominant alleles?
Sickle cell anaemia.
Multiple allele crosses?
Inheritance is more complicated when there are more than two alleles of the same gene.
Dihybrid crosses?
Dihybrid crosses can be used to show the likelihood of offspring inheriting certain combinations of the two characteristics from particular parents.
Dihybrid inheritance?
The inheritance of two characteristics, which are controlled by different genes. Each of two genes will have different alleles.
Sex-linked characteristics?
When the allele that codes for the characteristic is located on a sex chromosome (X or Y)
Sex-linked genetic disorders?
Colour blindness and haemophilia. The faulty alleles for both of these disorders are carried on the X chromosome and are so called X-linked disorders. Y-linked disorders do exist but are less common.
