Inheritance

Question 1

Definition of chromosome.

Answer 1

Made of proteins and DNA containing hereditary information which is physcially passed on to the next generation.

Question 2

Definition of gene.

Answer 2

A length of DNA which codes for a protein / polypeptide.

Question 3

Definition of allele.

Answer 3

Different forms of a gene.

Question 4

Definition of genotype.

Answer 4

The genetic constitution of an organism.

Question 5

Definition of phenotype.

Answer 5

The observable characteristics of an organism, resulting from its genotype and interaction with the environment.

Question 6

Definition of homozygous.

Answer 6

The two alleles of a gene are the same.

Question 7

Definition of heterozygous.

Answer 7

The two alleles of a gene are different.

Question 8

Definition of dominant.

Answer 8

The allele is always expressed in the phenotype, even if a different allele for the same gene is present.

Question 9

Definition of recessive.

Answer 9

The allele which is only expressed in the phenotype, in abscence of a dominant allele.

Question 10

Definition of monohybrid.

Answer 10

Genetic diagram involving the inheritance of a single gene.

Question 11

Definition of co-dominance.

Answer 11

Both alleles have an effect on the phenotype of the offspring.

Question 12

Definition of sex linkage.

Answer 12

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.

Question 13

Definition of dihybrid.

Answer 13

The inheritance of 2 characterstics controlled by 2 separate genes inherited independetly.

Question 14

Definition of epistasis.

Answer 14

One gene locus masks or supresses the expression of another gene locus.

Question 15

Definition of autosomnal.

Answer 15

Genes are linked if they are inherited on the same chromosome.

Question 16

Definition of null hypothesis.

Answer 16

The null hypothesis states that there is no significant difference between the observed and expected results.

Question 17

What are the rules for drawing a genetic diagram? (8 points).

Answer 17

1. Identify the interaction between alleles.
2. Give alleles symbols.
3. State parent’s phenotype.
4. State parent’s genotype- 2 alleles per genotype.
5. Possible gametes from each parent- always draw in circles.
6. Punnet square to show the random fertilisation of the gametes.
7. Offspring phenotypes linked to the square.
8. Phenotypic ratio / percentage.

Question 18

Describe how to identify the genotype of a parent in a monohybrid inheritance cross (4 points).

Answer 18

1. Cross the unknown parent with a homozygous recessive organism.
   2.Observe the phenotype of the offspring.
2. If any of the offspring show the recessive phenotype, the original parent must be heterozygous.
3. If all offspring have the dominant allele, parents must be homozgous.

Question 19

State 8 reasons the expected ratios and actual oberved numbers of offspring will be different.

Answer 19

1. Fertilisation of gametes is random.
2. Fusion of gametes is random.
3. Small population / sample size.
4. Selective advantage to alleles.
5. Epistasis / linkage.
6. Gametes may not be produced in euqal numbers.
7. Small sample.
8. Offspring ratios are a probability / not fixed / arise by chance.

Question 20

Definition of pedigree.

Answer 20

Family tree of genetically releated people used to identify simple inheritance patterns.

Question 21

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?

Answer 21

9 : 3 : 3 : 1

Question 22

What are the three types of epistatic inheritance?

Answer 22

1. A dominant allele at one locus masks the expression of alleles at the second locus.
2. Homozygous recessive alleles at one locus masks the expression of alleles at the second locus.
3. 2 enzymes coded for by 2 genes act sequentially ina metabolic pathway.

Question 23

What type of allele codes for a functional enzyme?

Answer 23

Dominant.

Question 24

What type of allele codes for a non-functional enzyme?

Answer 24

Recessive.

Question 25

Definition of linked.

Answer 25

Only two different gametes are produced as no independent assortment.

Question 26

Explain autosomnal linkage.

Answer 26

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.

Question 27

Explain the effects of linkage (5 points).

Answer 27

1. Alleles are linked.
2. State common gametes produced.
3. Crossing over will produce other gametes.
4. State other gametes.
5. Fewer speciifc individuals will be produced.

Question 28

What is the chi-squared test?

Answer 28

Used to compare expected and observed data.

Question 29

What is the student-t test?

Answer 29

Used to compare means from 2 sets of data.

Question 30

What is the correlation co-efficient test?

Answer 30

Used to compare data from 2 different variables that have been sampled.

Question 31

What do statistical tests do?

Answer 31

They test the probability of the differnce in the values is due to chance or the difference in the values is statistically different.

Question 32

Describe how to use the results from a chi-squared test to calculate the probability of the statistical test (4 points).

Answer 32

1. Work out the degrees of freedom (df): df = n-1 (where n is the number of different phenotypes of=r phenotypic classes).
2. Find the calculated value for the chi-squared test.
3. Find the probability value.
4. Compare values and draw a conclusion- greater or smaller than 0.05.

Question 33

If the p-value is greater than 5% or 0.05…

Answer 33

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.

Question 34

If the p-value is less than 5% or 0.05…

Answer 34

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.

Question 35

Definition of population.

Answer 35

A group of organisms of the same species that lives in a habitat and can interbreed.

Question 36

Definition of gene pool.

Answer 36

All the alleles of all the genes in a population.

Question 37

Definition of allele frequency.

Answer 37

Number of times an allele occurs in a gene pool.

Question 38

Definition of Hardy-Weinberg.

Answer 38

Mathematical model, which predicts that allele frequencies will not change from generation to generation.

Question 39

What assumptions are made when using Hardy-Weinberg? (5 points).

Answer 39

1. Population is very large.
2. Mating within the population is random.
3. There is no selective advantage for any genotype.
4. There is no mutation.
5. The population is isolated, so no migration.

Question 40

What are the 2 equations used to calculate Hardy-Weinberg?

Answer 40

1. p + q = 1
2. p^2 + 2pq + q^2 = 1

Question 41

What does p and q represent in the p + q = 1 equation?

Answer 41

p = frequency of dominant allele.
q = frequency of recessive allele.

Question 42

What does p^2 , q^2 and 2pq represent in the equation p^2 + 2pq + q^2 = 1?

Answer 42

q^2 = sufferers.
2pq = carriers.
p^2 = non-sufferers.