7.1 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 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 must 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
Where one phenotypic characteristic is controlled by a single gene
What percentage of offspring between homozygous dominant and recessive will express the characteristic determined by allele Gg?
100% ; all potential offspring genotypes are Gg
What percentage of offspring between heterozygous alleles should express the characteristic determined by allele G?
75% ; only one combination results in expression of the recessive allele
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
How many of the offspring between parental genotypes of RrGg and RrGg should have the same phenotype as their parents?
9 (out of 16)
6 will match their parents on one characteristic, but differ on the other
1 will differ on both characteristics
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 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 and may pass on the trait
Describe the four possible phenotypes of these offspring between X^H X^h and X^H Y
Normal female, carrier female, normal male, affected male
What is meant by autosomal linkage?
Where two or more genes are located on the same 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
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?
A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect
What are criteria for the chi-squared test?
- Data placed in discrete categories
- Large sample size
- Only raw count data allowed
- 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. If the number is greater than or equal to the critical value, we conclude there is a significant difference between the observed and 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 this topic?
We can compare expected phenotypic ratios with observed ratios to test our understanding of how different genes and alleles are inherited
