Inheritance Flashcards
Definition of chromosome.
Made of proteins and DNA containing hereditary information which is physcially passed on to the next generation.
Definition of gene.
A length of DNA which codes for a protein / polypeptide.
Definition of allele.
Different forms of a gene.
Definition of genotype.
The genetic constitution of an organism.
Definition of phenotype.
The observable characteristics of an organism, resulting from its genotype and interaction with the environment.
Definition of homozygous.
The two alleles of a gene are the same.
Definition of heterozygous.
The two alleles of a gene are different.
Definition of dominant.
The allele is always expressed in the phenotype, even if a different allele for the same gene is present.
Definition of recessive.
The allele which is only expressed in the phenotype, in abscence of a dominant allele.
Definition of monohybrid.
Genetic diagram involving the inheritance of a single gene.
Definition of co-dominance.
Both alleles have an effect on the phenotype of the offspring.
Definition of sex linkage.
Any gene carried on either the X or Y chromosome is said to be sex-linked. Males will only have one allele of a sex-linked gene. Females need to be homozygous recessive to have the condition.
Definition of dihybrid.
The inheritance of 2 characterstics controlled by 2 separate genes inherited independetly.
Definition of epistasis.
One gene locus masks or supresses the expression of another gene locus.
Definition of autosomnal.
Genes are linked if they are inherited on the same chromosome.
Definition of null hypothesis.
The null hypothesis states that there is no significant difference between the observed and expected results.
What are the rules for drawing a genetic diagram? (8 points).
- Identify the interaction between alleles.
- Give alleles symbols.
- State parent’s phenotype.
- State parent’s genotype- 2 alleles per genotype.
- Possible gametes from each parent- always draw in circles.
- Punnet square to show the random fertilisation of the gametes.
- Offspring phenotypes linked to the square.
- Phenotypic ratio / percentage.
Describe how to identify the genotype of a parent in a monohybrid inheritance cross (4 points).
- Cross the unknown parent with a homozygous recessive organism.
2.Observe the phenotype of the offspring. - If any of the offspring show the recessive phenotype, the original parent must be heterozygous.
- If all offspring have the dominant allele, parents must be homozgous.
State 8 reasons the expected ratios and actual oberved numbers of offspring will be different.
- Fertilisation of gametes is random.
- Fusion of gametes is random.
- Small population / sample size.
- Selective advantage to alleles.
- Epistasis / linkage.
- Gametes may not be produced in euqal numbers.
- Small sample.
- Offspring ratios are a probability / not fixed / arise by chance.
Definition of pedigree.
Family tree of genetically releated people used to identify simple inheritance patterns.
What is the typical ratio for a dihybrid cross between two parents who are dominant at both gene loci and the alleles show complete heterozygous?
9 : 3 : 3 : 1
What are the three types of epistatic inheritance?
- A dominant allele at one locus masks the expression of alleles at the second locus.
- Homozygous recessive alleles at one locus masks the expression of alleles at the second locus.
- 2 enzymes coded for by 2 genes act sequentially ina metabolic pathway.
What type of allele codes for a functional enzyme?
Dominant.
What type of allele codes for a non-functional enzyme?
Recessive.
Definition of linked.
Only two different gametes are produced as no independent assortment.
Explain autosomnal linkage.
Genes are linked if they are inherited on the same chromosome. This means the alleles are inherited together. The alleles are on the same chromosome so cannot independently assort.
Explain the effects of linkage (5 points).
- Alleles are linked.
- State common gametes produced.
- Crossing over will produce other gametes.
- State other gametes.
- Fewer speciifc individuals will be produced.
What is the chi-squared test?
Used to compare expected and observed data.
What is the student-t test?
Used to compare means from 2 sets of data.
What is the correlation co-efficient test?
Used to compare data from 2 different variables that have been sampled.
What do statistical tests do?
They test the probability of the differnce in the values is due to chance or the difference in the values is statistically different.
Describe how to use the results from a chi-squared test to calculate the probability of the statistical test (4 points).
- Work out the degrees of freedom (df): df = n-1 (where n is the number of different phenotypes of=r phenotypic classes).
- Find the calculated value for the chi-squared test.
- Find the probability value.
- Compare values and draw a conclusion- greater or smaller than 0.05.
If the p-value is greater than 5% or 0.05…
The probability that the difference between the observed and expected value is due to chance more than 5%. The difference between the observed and expected is not significant so is due to chance. Accept the null hypothesis. Always re-state the null hypothesis.
If the p-value is less than 5% or 0.05…
The probability that the differnce between the observed and expected value is due to chance is less than 5%. The differences between the observed and expected values is due to chance is less than 5%. The differnces between the observed and expected values is significant so is not due to chance. Reject the null hypothesis. Give an example of another factor.
Definition of population.
A group of organisms of the same species that lives in a habitat and can interbreed.
Definition of gene pool.
All the alleles of all the genes in a population.
Definition of allele frequency.
Number of times an allele occurs in a gene pool.
Definition of Hardy-Weinberg.
Mathematical model, which predicts that allele frequencies will not change from generation to generation.
What assumptions are made when using Hardy-Weinberg? (5 points).
- Population is very large.
- Mating within the population is random.
- There is no selective advantage for any genotype.
- There is no mutation.
- The population is isolated, so no migration.
What are the 2 equations used to calculate Hardy-Weinberg?
- p + q = 1
- p^2 + 2pq + q^2 = 1
What does p and q represent in the p + q = 1 equation?
p = frequency of dominant allele.
q = frequency of recessive allele.
What does p^2 , q^2 and 2pq represent in the equation p^2 + 2pq + q^2 = 1?
q^2 = sufferers.
2pq = carriers.
p^2 = non-sufferers.
