Inheritance and selection Flashcards
What is a Gene?
A sequence of bases on a DNA molecule that codes for a protein(polypeptide), which results in a characteristic e.g. the gene for eye colour.
What is an Allele?
An alternative version of a gene.
What is a genotype?
The genetic constitution of an organism - the alleles an organism has e.g. BB or Bb or bb for eye colour.
What is a phenotype?
The expression of the genetic constitution and its interaction with the environment (an organisms characteristics e.g. brown eyes)
What is a dominant allele?
An allele whose characteristics appears in the phenotype even when there is only 1 copy. Dominant alleles are shown by a capital letter.
What is a recessive allele?
An allele whose characteristics only appears in the phenotype if two copies are present. Recessive alleles are shown by a lower case letter.
What are codominant alleles?
Alleles that are both expressed in the phenotype - neither one is recessive, e.g. the alleles for haemoglobin.
What is a locus?
The locus is the fixed position of a gene on a chromosome.
homozygote
An organism that carries two copies of the same allele e.g. BB or bb
Heterozygote?
An organism that carries two different alleles. e.g. Bb.
What is monohybrid inheritance?
The inheritance of a single characteristic/gene controlled by different alleles.
You can figure out the frequency of one allele if you know the frequency of the other.
What equation is it? p + q = 1.
what does the P represent?
the frequency of the DOMINANT allele.
What does Q represent?
the frequency of the recessive allele.
You can figure out the frequency of one genotype if you know the frequencies of the others. What equation is it?
p2 + 2pq + q2 = 1
what does p2 represent
What does q2 represent?
What does 2pq represent?
the frequency of the HOMOZYGOUS DOMINANT GENOTYPE.
the frequency of the HOMOZYGOUS RECESSIVE genotype.
the frequency of the heterozygous genotype.
describe the process of natural selection.
- Sometimes, frequency of an allele within a population changes.
- Differential reproductive success, beneficial allele more likely to be passed on.
- So a greater proportion of the next generation inherit the beneficial allele.
- The next generation are then more likely to survive reproduce and pass on their genes.
- So the frequency of the beneficial allele increases from generation to generation.
- THIS is natural selection.
stabilising selection.
Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
This occurs when the environment is not changing and it reduces the range of possible phenotypes.
directional selection.
Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This could be in response to an environmental change.
what does the hardy Weinburg expression assume
large population-no genetic drift
no migration
no gene flow bet pop
no mutations
random mating 🐘🐘
natural selection is not operating on pop-all alleles equally likely to b passed to nxt gen🐒
How does Genotype control Phenotype
A gene is also a length of DNA that codes for a protein.
It is the proteins that actually control phenotype in their many roles as enzymes, pumps, transporters, motors, hormones, or structural elements
Why the actual numbers were different than those predicted in the genetic diagram
- Offspring ratios are a probability/not fixed/arise by chance/
- gametes may not be produced in equal numbers/
- fertilisation/fusion of gametes is random/
- small sample;
