7A - Genetics Flashcards
What is a gene?
- sequence of bases on a DNA molecule that codes for a protein which results in a characteristic
What are alleles?
- different versions of the same gene
What is a genotype?
- genetic makeup of an organism
What is a phenotype?
- expression of the genotype and it’s interaction with the environment
What is meant by a dominant allele?
- an allele whose characteristic appears in the phenotype even when there’s only one copy
What is meant by a recessive allele?
- an allele whose characteristic only appears in the phenotype if two copies are present
What are co-dominant alleles?
- alleles that are both expressed in the phenotype
What is meant by a locus?
- fixed position of a gene on a chromosome
What is a homozygote?
- an organism that carries two copies of the same allele
What is a heterozygote?
- an organism that carries two different alleles
What is a carrier?
- a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring
What is meant by a diploid?
- 2 sets of chromosomes
What is a gamete?
- sex cells containing only one allele for each gene
What is the function of genetic diagrams (Punnett squares)?
- used to predict the genotypes and phenotypes of the offspring produced if two parents are crossed
What is monohybrid inheritance?
- inheritance of a characteristic controlled by a single gene
What is meant by multiple alleles?
- when there are more than two alleles for the same gene e.g. blood group
What is dihybrid inheritance?
- inheritance of two characteristics which are controlled by different genes at the same time
What are the 3 reasons for not getting the predicted phenotypic ratio?
- sex linkage
- autosomal linkage
- epistasis
What is sex linkage?
- when an allele coding for a characteristic is located on a sex chromosome
Why are most genes carried on the X chromosome?
- Y chromosome is smaller than the X chromosome and therefore carries fewer genes
Why are males more likely to inherit sex-linked recessive traits?
- As males have only one X chromosome, they often only have one allele for sex-linked genes
- because they have only one copy, they express the characteristic of this allele even if it’s recessive
Why are males more likely to inherit colour-blindness or haemophilia?
- faulty alleles for both of these disorders are carried on the X chromosome
- males only need one copy if the recessive allele they are more likely than females to have this disorder
What is autosomal linkage?
- genes present on the same, non-sex chromosome
What is the result of autosomal linkage?
- since the genes are linked, they’ll stay together during the independent segregation of meiosis I
- alleles will be passed onto offspring together unless there is crossing over
What is crossing over?
- process in which homologous chromosomes exchange portions of their chromatids during meiosis
What is the relationship between genes on a autosome?
- the closer together two genes are on the autosome, the more closely linked they are as crossing over is less likely to split them up
What is epistasis?
- a type of gene interaction in which the allele of one gene masks the expression of the alleles of other genes
What is Chi-squared test?
- A statistical test used to see if the results of an experiment support a theory
What is a null hypothesis?
- that there’s no significant difference between the observed and expected results (negligible difference is due to chance)
What is the function of Chi-squared test?
- to compare the goodness of fit of the observed and expected results
- so the outcome either supports or rejects the null hypothesis
What is the formula for Chi-squared test?
- x^2 = sum of (observed-expected)^2 / expected
What is a critical value?
- a value that corresponds to a 5% level of probability that the difference between the observed an expected results due to chance
What does it mean when calculated value is larger than the critical value?
- there is a significant difference between the observed and expected results
- null hypothesis can be rejected
What is the degrees of freedom?
- no. of categories - 1
