B17 Inherited Change 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 (position) on a chromosome.
A single gene has 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 1 or 2 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 2 must be present
Why’s meant by codominant alleles
2 dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together
What’s is meant by homozygous
Both alleles are dominant or both alleles are recessive
What’s meant by heterozygous
One allele is dominant, the other is recessive
Define monohybrid inheritance
Where 1 phenotypic characteristic is controlled by a single gene
What % of offspring of monohybrid cross of GG and gg will express the characteristic expressed by allele G
100%
All potential offspring genotypes are Gg meaning none of them will express the recessive allele.
What % of the offspring of the monohybrid cross of parental genotypes Gg and Gg should express the characteristic determined by allele G
75%
Only 1 of the combinations results in expression of the recessive allele
Define dihybrid inheritance
Where 2 phenotypic characteristics are determined by 2 different genes present on 2 different chromosomes at the same time
How many of the offspring of the dihybrid cross of the parental genotypes 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 meant by sex-linkage
Where an allele is located on 1 of the sex chromosomes, meaning its expression depends in 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 1 copy of the allele, so will express this characteristic even if it’s recessive.
Since females get 2 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’s a carrier and may pass the trait on.
Describe the 4 possible phenotypes of the offspring of the sex-linked cross of parental genotypes X^H X^h and X^h Y
Normal female
Carrier female
Normal male
Affected male
What’s meant by autosomal linkage
Where 2 or more genes are located on the same (non-sex) chromosome.
In this case, only 1 homologous pair is needed for all 4 alleles to be present.
For genes that aren’t linked, 2 homologous pairs are needed.
If I^A and I^B are codominant and I^O is recessive, which alleles could the offspring express
AB
A
B
O
What meant by epistasis
Where 2 non-linked genes interact, with 1 gene either masking or suppressing the other gene
Define 2 types of epistasis
Recessive epistasis = where 2 homozygous recessive alleles mask expression of another allele.
Dominant epistasis = where 1 dominant allele masks expression of multiple other alleles
Genotypes BB or Bb allow expression of gene A, while genotype bb masks gene A. With this is mind, what % of the offspring will have gene A masked?
25%
What’s the chi-squared test?
A statistical test to find out whether the difference observed and expected data is due to chance or a real effect
What are the criteria for the chi-squared test?
Data place in discrete categories
Large sample size
Only raw date allowed i.e. not %
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 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
