Inheritance 4.3 Flashcards
What are the 3 assumptions Mendel made whilst carrying out his experiment?
1: Fertilization is random
2: Equal opportunity of survival among the offspring
3: Large numbers of offspring are produced
What is Mendels first law?
The law of segregation.
What is monohybrid inheritance?
Inheritance of a single pair of contrasting characteristics.
What is the phenotypic ratio produced in monohybrid inheritance?
2 heterozygous individuals will produce offspring with a phenotypic ratio of 3 dominant to 1 recessive. (3:1).
What is mendels second law?
The law of independent assortment.
What is the dihybrid phenotypic ratio?
9:3:3:1
What is used to test cross in dihybrid inheritance?
Organism is test crossed with one that is recessive for both characteristics - ie homozygous for the recessive alleles for both characteristics.
What is a mutation?
Random change in the amount, arrangement or structure of the DNA of an organism.
What are point mutations?
Mistake in the copying of one gene. Example - sickle-cell anaemia.
In what form can gene mutations take place
Duplication, insertion, deletion, inversion or substitution of bases.
What is sickle-cell anaemia?
A gene mutation in the gene producing haemoglobin results in a defect.
What are chromosome mutations?
Chromosomes damaged and break. Example - Down Syndrome.
What are oncogenes?
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.
What is the importance of mutations?
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
When can a recessive mutant allele be expressed in the phenotype?
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.
What is epigenetics?
Epigenetic events regulate the activities of genes without changing the DNA sequence.
Explain epigenetics.
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.
Describe the addition of methyl groups to bases.
The addition of methyl groups to bases prevents those bases being recognised and reduces the ability of that gene to be expressed.
What happens with the histone proteins in epigenetics?
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.
