INHERITANCE Flashcards
Genotype
Genetic constitution of an organism/combination of alleles the individual posses
Phenotype
Expression of the genotype and its interaction with the environment
Gene
A length of DNA that codes for a particular protein
Gene Pool
All the alleles in a population
Chromosome
One long DNA molecules which contains genes
Locus
The position of a gene on a chromosome
Allele
Alternative version of a gene, (there may be multiple alleles of a single gene)
Dominant Allele
The allele always expressed in the phenotype
Recessive Allele
The allele that is only expressed in the phenotype in the absence of the dominant allele
Co-dominance
When both alleles are being expressed in the phenotype
when alleles are co-dominant, so if they are present they are both expressed in the phenotype, takes place usually when a gene has more than 2 alleles
Monohybrid Inheritance
Inheritance of a single gene with two alleles
Why Monohybrid Cross ratios may not take place in reality
fusion of gametes is random
Mating is related to chance
Differential mortality
Sex Linkage
concerns genes found on the sex chromosomes, X and Y, (X gene will contain the disease)
Males have only one X chromosome (XY) therefore can never be carriers. Females have two X chromosomes (XX) therefore can be carriers. The gametes will be each chromosome, i.e. men have genotype XY, separating them gives you two gametes, X and Y.
Sex Linked diseases that kill children will become extinct as children who are affected will not be able to pass on the disease.
VERY rarely there may be a gene that is existent on the Y chromosome, however this would mean that all males would be affected and no females.
Males are more likely to have a sex-linked disease that is recessive
Males have only one alleles, therefore it could be the recessive one
Females need two recessive alleles to have the disease
How to prove that a certain condition is on the recessive allele
Affected child produced from unaffected parents
Therefore parents are heterozygous
How to prove that a certain condition is on the dominant allele
Affected parents produce unaffected child
Therefore parent are heterozygous (and still affected, therefore allele causing condition is dominant)
How to prove a condition is not sex-linked
The condition is on the dominant allele Affected male (XRY) and unaffected female (XrXr) are producing an affected male (XRY) which is not possible
How to prove a condition in on the x-chromosome:
Affected male children from unaffected father
Serious diseases caused by dominant alleles are uncommon compared with serious diseases caused by recessive alleles
If it is on the dominant allele, then all individuals with allele of the disease develop the disease, i.e. they become aware of the disease and therefore decided not to have children
If the serious disease is on recessive allele, it may not affect individual, therefore individual will not be aware of the disease and may have children
Some diseases are fatal, yet they are passed on, this may be due to the fact that the disease takes effect in old age, by which time offspring have already been produced.
If a recessive allele is causing a hindrance to a species’ ability to compete, then the frequency of the recessive allele will decrease over time, because:
Due to directional selection
The dominant allele has an advantage over the recessive allele, therefore more likely to survive.
Dominant Allele frequency + Recessive Allele frequency = 1; p + q = 1 (this is as long as the two alleles are for the same gene)
Homozygous Recessive frequency + Heterozygous frequency + Homozygous Dominant frequency = 1; p2 + 2pq + q2 = 1
Hardy-Weinberg principle
The frequency of alleles will remain constant from one generation to the next providing no mutation, geographical isolation, selection, migration etc. takes place. (The Hardy-Weinberg Principle is actually more of a PREDICTION than a principle)
We cannot do an investigation on the frequency of certain alleles in a group of organisms if one of the organisms is deaf, blind, etc. This is because this organism will not survive and therefore will not pass on allele
Assumptions made when using the Hardy-Weinberg equation
No selection Random mating Large gene pool No migration No mutation Equally fertile genotypes Generations do not overlap
When studying genetic crosses, you use an animal which
Gives large number of offspring; low sampling error
Short life cycle; results obtained quickly
Male and female easily distinguished for mating
Small size; easy to handle and less space required
How there is genetic variation in a sexually reproducing animal
Independent alignment of chromosomes which gives a new arrangement of alleles
Random fertilisation which gives a chance combinations of gametes
Mutations create new alleles
