Inheritance

Question 1

What is meant by the term genotype and phenotype?

Answer 1

Genotype: combination of alleles for a particular gene a organisms carries on its chromosomes.

Phenotype: Physical expression of the genotype as an observable characteristic (discontinuous/continuous variations)

Question 2

What are multiple alleles?

Answer 2

More than 2 alleles at the same locus.

Question 3

What are dominant, recessive and codominant alleles?

Answer 3

Dominant: only one allele required for subsequent phenotype.

Recessive: only expressed if no dominant is present, must have two recessive alleles to express this phenotype.

Codominant:
2 different dominant alleles are inherited and both expressed in the phenotype.

Question 4

What is monohybrid inheritance?

Answer 4

Inheritance of 1 gene determines a single characteristic.

Question 4

Explain dihybrid inheritance:

Answer 4

Dealing with 2 characteristics, phenotype inherited from 2 different genes.

Question 5

How is sex determined genetically?

Answer 5

23rd chromosome.
XX Female
XY Male

Question 6

. How are pedigree diagrams useful?

Answer 6

Provides phenotypes

Patterns of inheritance of a specific trait through
generations of a family.

Can provide info on D/R alleles

Question 7

What is sex linkage?

Answer 7

A gene carried on one of the sex chromosomes, usually X

Question 8

How does co-dominance affect the inheritance of characteristics?

Answer 8

Homozygous will produce the subsequent phenotype.

Heterozygous will produce a unique phenotype expressing both alleles.

Question 9

What is autosomal linkage and how does it affect the combination of alleles in gametes?

Answer 9

2 genes (alleles that code for different genes) are carried on the same chromosome are inherited together.

Reduces the probability of crossing over due to the genes close proximity to one another.

Parental phenotypes are inherited, recombinant configurations of alleles are much rarer as crossing over must occur.

Question 10

How does multiple alleles affect inheritance?

Answer 10

Several alleles within a population for a gene coding for hair colour.

Q will state dominance hierarchy.

Question 11

How are blood groups inherited in humans?

Answer 11

On gene I an antigen producer
O is an absence of antigen A or B.

A and B are co dominant
O is recessive

Question 12

What are the effects of epistasis?

Answer 12

Dominant: 12:3:1
Recessive: 9:3:4
Complementary: 9:7

Question 12

What is the chi-squared test and how would you use it in genetics?

Answer 12

Sum of (observed-expected)^2/expected

Null hypothesis: there is no sig diff between O and E results.

If chi squared is bigger than crit value then reject null

Less than 5% probability the difference is due to chance so is significant.

Question 13

What is meant by epistasis?

Answer 13

Interactions between genes at different loci, masking the expression of one gene when another is expressed.

Dominant: one dominant genotype required to mask expression of another.

Recessive: one recessive required.

Complementary: both dominant required to achieve final product.

Question 14

Explain why results of genetic crosses often differ from predicted results:

Answer 14

Small sample size
random fertilisation
sex linkage
epistasis
lethal genotypes.

Question 15

Define the Hardy-Weinberg principle.

Answer 15

A calculation of allele frequency.

Predicts allele frequencies will not change over many generations because a populations alleles/genotype frequencies are stable.

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

Question 15

What is meant by the terms Population and allelic frequency?

Answer 15

Population: group of organisms of the same species occupying a particular space at a particular time that can interbreed.

Allelic frequency: Proportion of a certain allele in a gene pool expressed as a decimal/%.

Question 16

What are the assumptions of the Hardy-Weinberg principle?

Answer 16

No mutation
Isolated population - no migration.
Large population
No selection
Mating is random