BIOL 2500 - Topic 7 (part 3)

Autotetraploids

They arise from the doubling of a 2N component to a 4N, occurring either spontaneously or by chemical disruption (such as colchicine, which induces autotetraploidy)

Autotetraploids during meiosis

Unlike triploids, they can undergo regular meiosis where the chromosomes can pair up since we have an even number of chromosomes, resulting in an even reduction division

Paring possibilities of autotetraploids

1.) Two bivalents

2.) One quadrivalent

3.) A univalent + a trivalent (but this is rare)

Example of triploids

Bananas, which are sterile and can only reproduce via induced asexual reproduction

Food crops that are polyploid plants

1.) Bananas

2.) Strawberries

3.) Wheat

Consequences of polyploid plants

1.) Fruit and flower size increase

2.) But have reduced fertility (i.e. results in seedless fruits)

3.) Also observe an increase in heterozygotes relative to diploids due to hybrid vigor

Hybrid vigor

It is when hybrids are more fit and grow faster/bigger than true-breeding plants, which is why we see an increase in heterozygotes relative to diploids

Allopolyploids

It is caused by the hybridization of two 2 or more species coming together to form a new species

Allopolyploids are created by…

Amphidiploids

Amphidiploids

*ASK J*

Can hybrids cross with any of the species from which it arose from?

No, because it would have chromosomes that the other species does not

Aneuploidy

A change in the number of one of the chromosomes, caused by nondisjunction (failure to separate)

Examples of aneuploidy

1.) Monosomic

2.) Trisomic

3.) Nullisomic

Monosomic

2n - 1 (missing one chromosome)

Trisomic

2n + 1 (have an extra chromosome)

Nullisomic

Missing the homologous chromosomes entirely (BBCC, instead of AABBCC)

Nondisjunction

When homologous chromosomes and sister chromatids fail to separate properly

Effect of nondisjunction

1.) It affects the number of chromosomes within the cells, such that some gametes have more copies while the others have less copies

2.) This then alters the phenotype, which can affect development and/or fertility

Nondisjunction in somatic cells vs. germline cells

It can occur in both, but it can only be inherited when it occurs in germline cells

Nondisjunction in germline cells causes…

Aneuploidy