Unit 2.3b Flashcards
What does diploid mean?
Cell in possession of two sets of chromosomes (2n=46haploid)
What does haploid mean?
Cell in possession of a single set of chromosomes (n=23haploid)
What does meiosis produce?
Genetic variable haploid cells that develop into gametes.
Are cells genetically identical?
No, they are not, which increases variation
What diploid cells are capable of carrying out meiosis?
Gametocytes
Where are gametocytes found and what are they?
They are found in sex organs, in animals they’re in the ovaries and testes and in plants they are in the anther and ovaries I
What are homologous chromosomes?
Pair of chromosomes of the same size, same centromere position, and with the same genes at the same loci
What name is given to genes on the same chromosome ?
Linked genes
What is the same on a homologous chromosome and what is different?
Genes are the same
Alleles of genes may be different
Are homologous chromosomes inherited from the same parent?
No, one is maternal and one is paternal
What must chromosomes do before meiosis can take place? (Stage 1.1)
Each chromosome must replicate to make two identical chromatids held together at the centromere
What happens in stage two of the first part of meiosis? (1.2)
Chromosomes condense and homologous chromosomes pair up
What happens in stage three of the first part of meiosis? (1.3).
Chiasmata form at points of contact between non-sister chromatids of a homologous pair and sections of DNA are exchanged
This random crossing over separates linked genes, and means new combinations of alleles can be produced
What happens in stage four of the first part of meiosis? (1.4).
Spindle fibre is attached to homologous pairs of chromosomes, lining them up at the equator of the spindle
The orientation of pairs is random, this is called independent assortment.
How can the number of different combinations of maternal and paternal chromosomes be calculated?
Using the formula 2n^
n = haploid number
What happens in stage five of the first part of meiosis? (1.5)
The chromosomes in each homologous pair are split and move toward opposite poles
The sister chromatids remain attached
What happens in stage six of the first part of meiosis? (1.6)
Cytokinesis occurs ie. the cytoplasm divides
Two daughter cells are formed
What is produced in the second stage of meiosis?
Four haploid cells.
What happens in stage one of the second part of meiosis? (2.1).
The nuclear membrane in each haploid daughter cell disintegrates
What happens in stage two of the second part of meiosis? (2.2)
Chromosomes lineup singly on the equator
What happens in stage three of the second part of meiosis? (2.3)
Sister chromatids separate and are randomly distributed to the daughter cells
What happens in stage four the second part of meiosis? (2.4)
Cytokinesis takes place ie. the cytoplasm divide
Four genetically different haploid gametes produced
