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?
2
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 codominant alleles?
Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristic 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
Punnett square to show a monohybrid cross with parental genotypes of GG and gg
What percentage of the offspring of the monohybrid cross with parental genotypes of GG and gg will express the characteristic determined by the allele G?
100% - all potential offspring genotypes are Gg, meaning none of them will express the recessive allele
Punnett square to show a monohybrid cross with parental genotypes of Gg and Gg
What percentage of the offspring of the monohybrid cross with parental genotypes of Gg and Gg should express the characteristic determined by allele G?
75% - only one of the combinations results in expression of the recessive allele
Example of genetic diagram
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
Punnett square to show a dihybrid cross with parental genotypes of RrGg and RrGg
How many of the offspring with a dihybrid cross with 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
Which parents do males inherit sex-linked characteristics from?
- Their mother, since their 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
Punnett square to show a sex-linked cross with parental genotypes of X^H X^h and X^H Y
Describe the four possible phenotypes of the offspring with parental genotypes of 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 (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
Punnet square to show multiple alleles cross with parental genotypes of I^A I^O and I^B I^O
If I^A and I^B are codominant and I^O is recessive, which alleles could the offspring express?
AB, A, B, O
What is meant by epistasis?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene
Define two types of epistasis
- Recessive epistasis: where two homozygous recessive alleles mask expression of another allele
- Dominant epistasis: where one dominant alleles masks expression of multiple other alleles
Punnett square to show an epistasis cross with parental genotypes of AABB and aabb
Genotypes BB or Bb allow expression of gene A with genotype bb masks gene A. With this in mind, what % of the offspring will have gene A masked?
25%
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
Criteria for chi-squared test
- Data placed in discrete categories (nominal)
- Large sample size
- Only raw data count allowed i.e. not percentages
