Inheritance Flashcards
Genotype definition
The genetic constitution of an organism
Phenotype definition
The expression of the genetic constitution and its appearance due to the environment
Gene definition
DNA base sequence which codes for either the amino acid sequence of a polypeptide of functional RNA
Allele definition
Different version of a gene
Homologous chromosomes definition
Have the same genes
Recessive definition
Only expressed in the phenotype when homozygous
Dominant definition
Always expressed in the phenotype
Locus definition
Fixed position of a gene on a chromosome
Homozygous definition
Allele on each homologous chromosome is the same
Heterozygous definition
Allele on each homologous chromosome is different
Monohybrid inheritance definition
The inheritance of a single gene which determines a single characteristic
Why is the observed phenotypic ratio sometimes different to the expected?
Random fertilisation OF GAMETES, small sample size
Codominance definition
Both alleles are expressed in the phenotype (e.g. C^R and C^W)
Multiple alleles definition
More than 2 alleles which follow a dominance hierarchy e.g. blood type (I^A, I^B and I^O)
Sex-linked gene definition
Sex-linked gene is carried on the X chromosome
Why are males more likely to express the recessive phenotype than females for sex-linked genes?
Males only have 1 X chromosome so only need 1 recessive allele for it to appear in their phenotype, whereas females need 2 recessive alleles
Dihybrid cross definition
2 different genes on different chromosomes (e.g. RrGg)
Autosomal linkage definition
2 genes carried on the SAME chromosome (dominant genes could be the ones which are linked e.g. Gg and Nn gametes = GN and gn)
Epistasis definition
Allele of one gene affects or masks the expression of another gene (e.g. Gene A dominant for red pigment –> Gene B dominant for purple pigment so aabb would be white, Aabb would be red, AaBb would be purple)
What does p^2 mean in the Hardy Weinberg equation?
Homozygous DOMINANT
What does q^2 mean in the Hardy Weinberg equation?
Homozygous RECESSIVE
What does 2pq mean in the Hardy Weinberg equation?
Heterozygous
What do p and q mean in the Hardy Weinberg equation?
p = dominant ALLELE frequency
q = recessive ALLELE frequency
When given p, how would you work out q?
1 - p = q
If a question gives you p^2 and asks you to calculate heterozygous frequency, what should you do?
Find q^2 FIRST (1 - p^2)
1 - q = p
Heterozygous = 2pq
What are the 4 assumptions made by Hardy-Weinberg?
- Mating is random
- No immigration
- No mutations
- No selection
