Mendelian Genetics Flashcards
Define ‘locus’
Position of gene on chromosome. Alleles, alt. forms of a gene, occupy the same locus. Different genes occupy different loci
Define allele
Alternative forms of a gene
What is a dominant allele and why is the dominant?
- Allele showing its phenotype whether it’s homozygous or heterozygous.
- In heterozygotes, gene pdt of the dominant allele masks the effect of the gene pdt expressed by the other (recessive) allele.
- Dominant allele usually codes for functional protein (give e.g. if qsn has context); recessive alleles codes for non-functional protein ⇒ only 1 copy of dominant allele needed
What is a recessive allele?
Allele showing its phenotype only in presence of another identical recessive allele (homozygous recessive). In heterozygotes, effect of gene pdt expressed by recessive allele is masked by effect of gene pdt expressed by dominant allele
What is meant by codominant?
2 different dominant alleles both equally expressed and influence the phenotype
What is meant by incomplete dominance?
Phenotype of heterozygotes is intermediate between phenotypes of indiv homozygous for both alleles
What is meant by homozygous and heterozygous.
Diploid condition. Identical/differentalleles at locus on a pair of homologous chromosome
Explain how genotype influences phenotype
Genotype is the genetic makeup of an organism.
Expression of genetic info: Nt seq of alleles making up genotype is transcribed and translated, hence determining the 3D conf of protein, which determines the observable trait aka. phenotype.
What is phenotype?
Characteristic/trait of organism arising from interaction of genotype and environment
Explain how environment affects phenotype (+state examples)
- Env switch certain genes on/off (affect expression): temp affecting coat colour inf Siamese cats, UV light affecting skin colour, food affecting whether eggs develop into worker or queen bees
- Env effect greater on polygenes: height, skin colour
- Env may induce mutation, affecting phenotype: Excess UV light–> chromosomal damage and skin cancer
Explain how env results in characteristic coat pattern in Siamese cats
Fur is (by default) black when the enzyme is functional, but high temp inhibits/denature enzyme→ no pigment formed/white in warmer body while black pigment forms in cooler extremities
Explain how env determines whether fertilised eggs develop into queen bees or worker bees
- Diet of larvae.
- Larvae fed royal jelly develop into queen bee, as chemicals in royal jelly trigger expression of genes involved in the development of ovaries and reproductive organs.
- Larvae fed nectar & pollen develop into worker bees
State the meaning of the term linkage
2 or more genes located on the same chromosome + physically close enough so that alleles of the 2 genes inherited tgt and don’t assort independently in meiosis (no 9:3:3:1).
Why are pea plants/drosophila (fruit flies) used in experiments?
- Many distinct observable characteristics w contrasting forms (e.g. round/wrinkled seeds)
- Easy to cultivate: ease in manipulating pollination – can do cross or self-pollination
- Produces many offspring in one cross→ large sample size
- Short life cycle/grow fast: no need wait long to study diff traits of plant appearing in many generations→ produces abundantly, large sample size
What is a test cross? What is its purpose?
Cross w an indiv expressing homozygous recessive trait→ reveal the genotype of an organism that exhibits dominant trait
- If all offspring shows dominant trait→ parent is homozygous dominant
- If offspring ratio is 1:1→ parent is heterozygous
What is mendel’s law of segregation?
2 alleles for each trait separate during gamete formation→ ensure parent w 2 copies of each gene can pass on either allele
