Inheritance Flashcards
Topic 7 revision
What is meant by codominant alleles?
Two dominant alleles that both contribute to the phenoytpe, either by showing a blend of both characteristics, or tge characteristics appearing together
Define monohybrid inheritance
Where one phenotype characteristic is controlled by a single gene
Define dihybrid inheritance
Where two phenotypic characteristics by two different genes present on two 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 chromosomes. Therefore males only get one copy of the allele, so will express this characteristic even if it’s recessive. Since females get two 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 & may pass on the trait.
Define Genotype
genetic constitution of an organism
Define Phenotype
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 locus (position) on a chromosome. A single gene could have many alleles.
What is meant by a dominant allele?
An allele whose characteristics will always appear in the phenotype (is expressed), whether one or two are present.
What is meant by a recessive allele?
An allele whose characteristics only appears in the phenotype if no dominant allele is present, meaning two must be present.
What is meant by homozygous and heterozygous?
Homozygous: both alleles are dominant, or both alleles are recessive
Heterozygous: one allele is dominant, the other is recessive
What is meant by autosomal linkage?
Where two or more genes are located on the same (non-sex) chromosomes. in this case, only homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed
What is meant by epistasis?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene
Define the two types of epistasis
Recessive epistasis: where two homozygous recessive alleles mask expression of another allele
Dominant epistasis: where one dominant allele masks expression of multiple other alleles
What is the chi-squared test?
Statistical test to find out whether the difference between observed and expected data is due to chance or a real effect
How can we use a chi-squared test in relation to the content of this topic?
We can compare expected phenotypic ratio with observed ratios to test our understanding of how different genes and alleles are inherited
