Inheritance 4.3

Question 1

What are the 3 assumptions Mendel made whilst carrying out his experiment?

Answer 1

1: Fertilization is random
2: Equal opportunity of survival among the offspring
3: Large numbers of offspring are produced

Question 2

What is Mendels first law?

Answer 2

The law of segregation.

Question 3

What is monohybrid inheritance?

Answer 3

Inheritance of a single pair of contrasting characteristics.

Question 4

What is the phenotypic ratio produced in monohybrid inheritance?

Answer 4

2 heterozygous individuals will produce offspring with a phenotypic ratio of 3 dominant to 1 recessive. (3:1).

Question 5

What is mendels second law?

Answer 5

The law of independent assortment.

Question 6

What is the dihybrid phenotypic ratio?

Answer 6

9:3:3:1

Question 7

What is used to test cross in dihybrid inheritance?

Answer 7

Organism is test crossed with one that is recessive for both characteristics - ie homozygous for the recessive alleles for both characteristics.

Question 8

What is a mutation?

Answer 8

Random change in the amount, arrangement or structure of the DNA of an organism.

Question 9

What are point mutations?

Answer 9

Mistake in the copying of one gene. Example - sickle-cell anaemia.

Question 10

In what form can gene mutations take place

Answer 10

Duplication, insertion, deletion, inversion or substitution of bases.

Question 11

What is sickle-cell anaemia?

Answer 11

A gene mutation in the gene producing haemoglobin results in a defect.

Question 12

What are chromosome mutations?

Answer 12

Chromosomes damaged and break. Example - Down Syndrome.

Question 13

What are oncogenes?

Answer 13

A mutation which causes cancer is called a carcinogen. Some genes called proto-oncogenes can mutate to become oncogenes causing uncontrolled cell division to form a cancer.

Question 14

What is the importance of mutations?

Answer 14

1: Mutations are important because they increase genetic variation in a population
2: There are potential advantages from mutations that are beneficial.
3: Most mutations are recessive to the normal allele

Question 15

When can a recessive mutant allele be expressed in the phenotype?

Answer 15

It can only be expressed if there are two copies of the allele in the genotype - it must await replication in the gene pool before chance brings two recessive alleles together, resulting in their expression.

Question 16

What is epigenetics?

Answer 16

Epigenetic events regulate the activities of genes without changing the DNA sequence.

Question 17

Explain epigenetics.

Answer 17

DNA can be modified post-replication. This does not change the DNA base sequence but changes the ability of a gene to be transcribed during protein synthesis.

Question 18

Describe the addition of methyl groups to bases.

Answer 18

The addition of methyl groups to bases prevents those bases being recognised and reduces the ability of that gene to be expressed.

Question 19

What happens with the histone proteins in epigenetics?

Answer 19

The histone proteins used to organise DNA in a chromosome can also be modified - if the histone coils more tightly this can prevent gene expression or if it coils more loosely can increase gene expression.