Exam 3- Meiosis Flashcards
What is meiosis?
- a special type of cell division
- sexual reproduction
- halves the chromosome number
Where is meiosis present?
- in germ cells
- gametes
What are germ cells?
cells capable of meiosis
How do the haploid cells become diploid in fertilization?
- gametes fuse in fertilization to form the diploid zygote
- n ( egg) + n ( sperm) = 2n zygote
- become the next diploid generation
what are alleles?
alternate forms of a gene
- homozygous AA or aa
- heterozygous Aa
- Human 2n= 46
What is the main event of Meiosis I?
reduction division
- homologous pairs will first synapse and then separate
What is the main event of Meiosis II?
equatorial division- sister chromatids separate
what happens in prophase I?
- most important
- create genetic versatility
- cross over
- S phase already complete
what does synapsis mean?
homologous chromosomes pair up end to end
- end view shows four chromatids ( 2 chromosomes) = tetrad ( bivalent form)
How does cross-over work?
chromosomes are aligned and connected by the nucleoprotein lattice
- enzymes come in at the chiasmata and graft the maternal genes on the paternal chromosome and vice versa
- the amount of cross-over in prophase is random
What is chiasma?
- chiasma ( sg.)
- chiasmata ( pl.)
points where the chromosomes touch and swap genetic material.
what forms the nucleoprotein lattice?
cohesions: sticky proteins allow homologous chromosomes to adhere to each other
What happens in Prometaphase I and Metaphase I?
- independent assortment
-homologous pairs attached to kinetochore fibers; arranged onto the middle of the metaphase plate - The same stuff from mitosis also occurs simultaneously
What happens in Anaphase I?
Homologous pairs separate
- synapsis breaks up
- centrosome stays
What happens in Telophase I?
Daughter cells each have one internally duplicated chromosome from each homologous pair
- ( n haploid)
What happens in Cytokinesis I?
- two daughter cells
- both with internally duplicate chromosomes of each type = haploid ( n)
What happens in prophase II?
chromosomes condense
what happens in prometaphase?
chromosomes attach to kinetochore fibers
What happens in Metaphase II?
Align on the metaphase plate ( 23 chromosomes)
What happens in anaphase II?
centrosomes dissolve
chromosomes pulled apart
what happens in telophase II and cytokinesis?
- four haploid cells
- all genetically unique
What are the three things that provide genetic variation?
- crossing over between homologous chromosomes
- independent assortment
- Fertilization
How does fertilization contribute to genetic variation?
- when gametes fuse at fertilization
- chromosomes donated by parents are combined
What is the importance of genetic variation?
reproduction may be advantages
- improves the chance of adaptability to the environment
what is a zygote?
the fertilized fusion of sperm and egg
- the one-celled stage of an individual of the next generation
- results in the multicellular embryo that gradually takes on the features determined when zygote was formed
What is gametogenesis?
Production of gametes
What is spermatogenesis?
production of sperm
What is spermiogenesis?
maturation process of the spermatids
What are the secondary spermatocytes?
- meiosis II
- haploid
What are the primary spermatocytes?
- first stage of spermatogenesis
- meiosis 1 at puberty
- diploid
What are the spermatids?
-to go from spermatocytes to spermatids spermiogenesis must occur
What is the structure of sperm?
- the head is full of DNA
- acrosome= coating ( important to fertilizing egg)
- midpiece = full of mitochondria
- flagellum= propeller motion
What is oogenesis?
Production on eggs
- only one of four nuclei gets cytoplasm
What is the primary oocyte?
Diploid
meiosis I
- seen at birth and is stalled in prophase I until puberty
What is a secondary Oocyte?
has one polar body
- haploid
- stuck at meiosis II until it’s fertilized
- this is where periods start to occur
when is meiosis II completed?
Only completed after entry of sperm
- adds a second polar body
