Inheritance Flashcards
Define genotype.
The genetic constitution of an organism.
Define phenotype.
The expression of an organism’s genetic constitution, combined with its interaction with the environment.
What is an allele?
Different forms of a particular gene, found at the same locus (position) on a chromosome.
How many alleles per gene do diploid organisms carry?
2
What is meant by a dominant allele?
An allele whose characteristic will always
appear in the phenotype, whether 1 or 2 are present.
What is meant by a recessive allele?
An allele whose characteristic only appears in the phenotype if no dominant allele is present, meaning 2 must be present.
What is meant by codominant alleles?
2 dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the
characteristics appearing together.
What does homozygous mean?
both alleles are dominant,
or both alleles are recessive.
What does heterozygous mean?
1 allele is dominant, the other is recessive.
Define monohybrid inheritance.
Where 1 phenotypic characteristic is controlled by a single gene.
Define dihybrid inheritance.
Where 2 phenotypic characteristics are determined by 2 different genes present on 2 different chromosomes at the same time.
What is meant by sex-linkage?
Where an allele is located on one of the sex chromosomes, meaning its
expression depends on the sex of the individual.
Why are males more likely to express a recessive sex-linked allele?
Most sex-linked alleles are located on the X chromosome.
Therefore males only get 1 copy of the allele, so will express this characteristic even if it’s recessive.
Since females get 2 alleles, this is less likely.
Which parent do males inherit sex-linked characteristics from?
Their mother, since the Y chromosome can only come from their father. Therefore if the mother is heterozygous for sex-linked
alleles, she is a carrier and may pass on the trait on.
What is meant by autosomal linkage?
Where 2 or more genes are located on the same (non-sex) chromosome.
In this case, only 1 homologous pair is needed for all 4 alleles to be present.
For genes that aren’t linked, 2 homologous pairs are needed.
