7.1 - Inheritance Flashcards
Define genotype
The genetic constitution of an organism
Define phenotype
The expression of an organisms genetic constitution, combined with its interaction with the environment
What is an allele
Different forms of a 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 characteristics only appear 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 characteristics is controlled by a single gene
Draw a Punnett square to show a monohybrid cross with parental genotypes of GG and 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
What % of these offspring should express the characteristics determined by allele G
75%; only one of the combinations results in expression of the recessive allele
Draw an example of a genetic diagram
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
Draw a Punnett square to show a dihybrid cross with parental genotypes of RrGg and RrGg
How many of these offspring 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 it’s 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
Draw a Punnett square to show a sex-linked cross with parental genotypes of XHXh and XHY
Describe the four possible phenotypes of these offspring
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
Draw a Punnett square to show a multiple alleles cross with parental genotypes of IAIO and IBIO
If IA and IB are codominant and IO 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 the two types of epistatsis
Recessive epistasis = where two homozygous recessive alleles mask expression of another allele
Dominant epistasis= where one dominant allele masks expression of multiple other alleles
Draw a Punnett square to show a epistasis cross with parental genotypes of AABB and aabb
Genotypes BB or Bb allow expression of gene A, while genotype bb masks gene A. With this in mind, what % of the offspring will have gene A masked
25%
What is the chi-square test?
A statistical test to find out whether the difference between observed and expected data is due to chance or real effect
What are the 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 square 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 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
