Chapter 9.2: Meiosis and Genetic Variation

What are the Stages of Meiosis

Prophase 1, Metaphase 1, Anaphase 1, Telophase 1, Prophase 2, Metaphase 2, Anaphase 2, Telophase 2

How many daughter cells does meiosis produce

four

Why is it important that gametes are haploid

When the two gametes fuse they will collectively have a diploid number of chromosomes. If each gamete had a diploid number of chromosomes before fusing, they would collectively have too many chromosomes

What is a Gene

A length of DNA that codes for a polypeptide

What is a Locus

The position of a gene on a chromosome or DNA molecule

What is an Allele

One of the different forms of a particular gene

What are homologous chromosomes

A pair of chromosomes, one is maternal and one is paternal. They have the same gene loci

What is the definition of Haploid

A cell that only contains a single copy of each chromosome

What is a diploid

a cell in which the nucleus contains two sets of chromosomes

What is crossing over

A process where a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome

What is the importance of Crossing over

It increases genetic variation as during crossing over, alleles are exchanged

When does Crossing over occur

Prophase 1

How does meiosis bring about this genetic variation

• Independent segregation of homologous chromosomes

• New combination of maternal and paternal alleles by crossing over

What is independent segrgation of homologous chromosomes

when each chromosome lines up alongside its homologous chromosome. One of each pair will pass into each daughter cell. Since the pairs are line up at random the chromosomes of maternal and paternal origin that go into the daughter cell at meiosis 1 is a matter of chance.

What are the steps for crossing over

• The chromatids of each pair become twisted around one another

• during this twisting, tensions are created and portions of the chromatids break off

• These broken portions might then rejoin with the chromatids of its homologous partner

• usually it is the equivalent portions of homologous chromosomes that are exchanged

• in this way, new genetic combinations of maternal and paternal alleles are produced

Crossing over happens between what

non-sister chromosomes

What is the calculation for possible chromosome combinations following meiosis?

(2n)²

n=?

n= the number of pairs of homologous chromosomes

What is discontinuous Variation

Variation in which organisms fall into distinct categories

What is a gamete

Reproductive (Sex) Cells that fuse with another gamete during fertilisation

What is Genetic variation

Differences in DNA base sequence between two or more organisms with the possibility of resulting in different alleles

What is interspecific variation

Differences between organisms between organisms of different species

What is intraspecific variation

differences between organisms of the same species

What is meiosis

The type of nuclear division in which the number of chromosomes is halved

What is random fertilisation

Any one male gamete could fuse with any one female gamete

what is standard deviation

A measure of the spread of values around the mean average