4.3 MEIOSIS

T/F? MEMBERS OF THE SAME SPECIES HAVE THE SAME GENES.

True.

WHAT DOES IT MEAN TO BE A GENETICALLY DIVERSE POPULATION?

When a population has many different alleles for a particular gene.

WHAT IS THE GENE POOL?

• Total information from all of the genes and alleles of the breeding individuals of a population at a particular time.

WHAT DOES GENETIC DIVERSITY CREATE?

WHAT IS IT A RESULT OF?

• It creates variation WITHIN a species.

• It therefore allows natural selection.

• RESULT OF:

  • Mutations.

  • Meiosis.

  • Random fusion of gametes.

WHAT TYPE OF CELL DOES MEIOSIS PRODUCE (HINT HAPLOID OR DIPLOID)?

• In the formation of gametes:

  • Ovum, sperm, ovule, pollen grain.

HOW DOES MEIOSIS RESULT IN HAPLOID CELLS?

1. DNA replication forms chromatids;

2. Two (nuclear) divisions;

3. Separation of homologous chromosomes and cells become haploid.

4. Separation of sister chromatids by centromere breaking.

WHAT IS CHROMOSOME DISJUNCTION?

• Sometimes homologous chromosomes don’t separate and both chromosomes of a pair go into the same cell.

• As a consequence, after fetilisation, zygotes can end up with an extra copy of a particular gene.

HOW DOES MEIOSIS LEAD TO INTRASPECIFIC VARIATION?

• Meiosis provides opportunities of new combinations of alleles to occur in the gametes.

WHY ARE CELLS FROM MEIOSIS GENETICALLY DIFFERENT?

• Independent segregation.

• Crossing Over.

• Different combinations of maternal and paternal chromosomes.

WHAT IS INDEPENDANT SEGRAGTION?

• First division, the pairs of homologous chromosomes pair up at the start.

• When they line up along the equator, their orientation is completely random.

• Subsequent separation of these pairs result in random shuffling of maternal and paternal chromosomes ::: different combinations of in the gametes formed.

• 2ⁿ.

CROSSING OVER AND HOW DOES IT INCREASE GENETIC DIVERSITY?

• Homologous pairs of chromosomes associate.

• Chiasma(ta) form.

• (Equal) lengths of (non-sister) chromatids / alleles are exchanged.

• Producing new combinations of alleles.

HOW CAN GENETIC VARIATION BE FURTHER INCREASED?

• Further increased in sexual reproduction due to random recombination of maternal and paternal gametes during fertilisation,

IF THERE ARE X CHROMOSOMES, HOW MANY CHROMATIDS WILL THERE BE IN THE ZYGOTE?

4X

WHY WILL ALL THE CELLS OF THE BODY HAVE THE MUTATION?

• Mutation in gamete.

• All cells derived from single zygote during mitosis.