7.1 - Inheritance Flashcards
Define ‘genotype’.
The genetic constitution of an organism.
The alleles an organism has e.g. BB, Bb or bb
Define ‘phenotype’.
The expression of an organism’s genetic constitution, combined with its interaction with the environment - the organism’s characteristics.
What is an allele?
Different forms of a particular gene, found at the same locus on a chromosome. A single gene could have many alleles.
How many alleles per gene do diploid organisms carry?
2
What is meant by a ‘dominant’ allele?
An allele where only 1 copy needs to be present for the allele to be expressed.
What is meant by a ‘recessive’ allele?
An allele where 2 copies need to be present for the characteristic to be expressed.
What is meant by ‘co-dominant’ alleles?
Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together.
What is meant by ‘homozygous’?
An organism that carries 2 copies of the same allele.
What is meant by ‘heterozygous’?
An organism that carries 2 different alleles.
Define ’monohybrid’ inheritance’.
Where one 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-linkage allele?
Most sex-linked alleles are located on the X chromosome. Therefore, males only get one copy of the allele, so will express the characteristic even if it’s recessive. Since females get 2 X 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 the sex-linked alleles, she is a carrier and may pass the trait on.
What is meant by ‘autosomal linkage’?
Where 2+ 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.
