inheritence 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 an particular gene, found at the same locus (position) on a chromosome. A single gene could have many alleles.
How many alleles per gene do diploid organisms carry?
Two.
What is meant by a dominant allele?
An allele whose characteristic will always appear in the phenotype, whether one or two 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 two most be present.
What is meant by codominant 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 and heterozygous?
Homozygous = both alleles are dominant, or both alleles are recessive.
Heterozygous = one allele is dominant, the other is recessive.
Define monohybrid inheritance.
When one phenotypic characteristic is controlled by a single gene.
Draw a punnet square to show a monohybrid cross with parental genotypes of GG and gg.
G G
g Gg Gg
g Gg Gg
What % of these offspring will express the characteristic determined by allele G?
100%; all potential offspring genotypes are Gg meaning none of them will express the recessive allele.
Draw a Punnett square to show a monohybrid cross with parental genotypes of Gg and Gg.
G g
G GG Gg
g Gg gg
What % of these offspring should express the characteristic determined by allele G?
75%; only one of the combinations result in expression of the recessive allele.
Define dihybrid inheritence.
Where two phenotypic characteristics are determined 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.
Wy 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 one copy of the allele, so will express this characteristic even if its 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 and may pass on the trait.
What is meant by autosomal linkage?
Where two or more genes are located on the same (non-sex) chromosome. In this case, only one homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed.
Where 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 asks expression of multiple other alleles.
What is the chi-squared test?
A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect.
What are the criteria for the chi-squared test?
Data placed in discrete categories.
Large sample size.
Only raw count data allowed i.e. not percentages.
No data values equal zero.
How is a chi-squared test performed?
The formula results in a number, which is then compared to a critical value (for the corresponding degrees of freedom). If the number is greater than or equal to the critical value, we conclude there is a significant difference between the observed and the expected data and that the results did not occur due to chance.
How can we use a chi-squared test in relation to the content of inheritance?
We can compare expected phenotypic ratios with observed ratios to test our understanding of how different genes and alleles are inherited.
