Topic 7A: Genetics Flashcards
Definition: Gene
Sequences of bases in a DNA molecule which code for a polypeptide, resulting in a characteristic.
Definition: Allele
A different version of the same gene.
Definition: Loci
A point in a gene where the same allele can be found in a pair of chromosomes.
Definition: Genotype
The actual alleles an organism has.
Definition: Phenotype
The characteristics an organism has
Definition: Dominant allele
The allele which is always expressed in the phenotype.
Definition: Recessive allele
The allele which is only expressed if two copies are present.
Definition: Co-dominant alleles
When both alleles are dominant and therefore both expressed.
Definition: Homozygous
When an organism carries two copies of the same allele.
Definition: Heterozygous
When an organism carries two different alleles for the same gene.
How do you complete a mono-hybrid cross?
1) Write out the parents’ genotype.
2) Show the possible gametes each in a circle.
3) Show all of the possible ways the gametes could combine.
4) Write out the phenotypes produced.
Definition: Sex-linked characteristics
When alleles are located on a sex chromosome.
Why are males more likely to show recessive characteristics than females?
1) If the characteristic is sex-linked, the allele may be found on the X chromosome.
2) Therefore, the male may only have one allele as they only have one X chromosome.
3) Because of this, even if this allele is recessive, it will be expressed.
Definition: Autosome
Any chromosome which is not a sex chromosome.
What are the effects of linkage of autosomal genes?
1) Unless crossing over splits up genes on the same autosome they are said to be linked - because they aren’t separated during independent segregation in meiosis I.
2) Therefore you won’t get the expected phenotypic ratio in the offspring.
Definition: Epistasis
- When the allele of one gene masks the expression of alleles of another gene.
- e.g. if you were bald, you cannot have a widow’s peak regardless of whether or not you have the allele for it.
What is the effect of epistatic genes?
You won’t get the expected phenotypic ratio.
Why is the chi-squared test used?
To see if results support a theory (null hypothesis).
How do you calculate the degrees of freedom?
The number of categories minus one.
How would you write a chi-squared test conclusion?
1) χ² is larger than ‘0.05’.
2) Therefore, there is significant difference between the observed and expected value.
3) This means the null hypothesis should be rejected.
4) Write a conclusion supporting or disregarding hypothesis.
