Meiosis Flashcards
What is meiosis?
a form of nuclear division occuring in germ cells
What is the product of meiosis?
Haploid cells that carry only one copy of each chromosome
What happens to haploid gametes at fertilisation?
fuse to form a diploid zygote (embryo)
What are the stages of mitosis and what occurs at each stage?
What are the stages of meiosis?
What are the 5 stages of prophase 1
Describe the process of spermatogenesis
Describe the process of oogenesis
How does spermatogenesis differ from oogenesis?
The second meiotic division in oogenesis results in a single haploid ovum and a polar body (package of chromosomes that is not used any further)
What is an allele?
alternative version of the same gene
What are the sources of genetic variation?
What is independent assortment of chromosomes?
Random orientation of homologous chromosomes at metaphase of meiosis I
What is X chromosome inactivation?
During embryonic development one of the X chromosomes inherited by a female is inactivated so there is only 1 copy of X-linked genes
What is non-disjunction?
Chromosomes remain linked together in meiosis I or II - leads to an abnormal number of chromosomes in germ cells
What is aneuploidy?
The fertilization of gametes in which non-disjunction has occured - leading to abnormal numbers of a particular chromosome
What is a monosomic zygote?
only has one copy of a particular chromosome
What is a trisomic zygote?
has 3 copies of a particular chromosome
What is polyploidy?
a condition in which an organism has more than 2 complete sets of chromosomes:
- triploidy (3n)
- tetraploidy (4n)
What are the different types of chromosomal abnormality that can occur?
deletion
duplication
inversion
translocation (moves a segment from one chromosome to another)
What does non-disjunction aneuploidy cause?
infertility
Describe meiosis I
Prophase I:
- nucleolus shrinks
- centrioles migrate to poles
- spindle forms
- chromosomes condense
- chiasmata form (crossing of genetic material)
Metaphase I:
- nuclear envelope disappears
- homologous chromosomes move to equator
- centromeres of each bivalent chromosomes orientate to opposite poles
Anaphase I:
- homologous chromosomes separate to opposite poles
- one chromosome with 2 chromatids at each pole
Telophase I:
- cytoplasmic division
- spindle breaks down
- nuclear envelope and nucleoli form
Describe meiosis II
