Unit 3 lecture 1 part 2 10/12/22 Flashcards
Prophase I typically occupies more than __________ of the time required for meiosis
90%
In 1.__________, homologous chromosomes loosely pair up, aligned gene by gene forming structures called 2.__________
1.Synapsis
2.Tertrads
In __________, nonsister chromatids exchange DNA segments
crossing over
Each homologous pair has one or more X-shaped regions called __________
Chiasmata
__________ exist at points where crossing over has occurred. AND THIS STEP IS RESPONSIBLE FOR GENETIC VARIATION IN THE NEXT GENERATION
Chiasmata
In __________, tetrads line up at the metaphase plate, with one chromosome facing each pole and Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad
Metaphase 1
In __________, pairs of homologous chromosomes separate from tetrads
anaphase 1
In the beginning of 1.__________, each half of the cell has a 2.__________ of chromosomes; each chromosome still consists of two sister chromatids
1.telophase 1
2.haploid cell
In __________, a spindle apparatus forms
Prophase 2
In __________, the sister chromatids are arranged at the metaphase plate
Metaphase 2
In metaphase 2 because of crossing over in meiosis I, the two sister chromatids of each chromosome are ____________________
no longer genetically identical
In __________, the sister chromatids separate
Anaphase 2
In __________, the chromosomes arrive at opposite poles
Telophase 2
Three events are unique to meiosis, and all three occur in __________
Meiosis 1
1.__________ and 2.__________ in 3.__________ : Homologous chromosomes physically connect and exchange genetic information
1.Synapsis
2.Crossing over
3.prophase 1
__________ at the metaphase plate: Homologous pairs of chromosomes are positioned there in metaphase I
homologous pairs
Separation of homologs during __________
anaphase 1
Protein complexes called __________ are responsible for this cohesion
cohesins
In mitosis, 1.__________ are cleaved at the end of 2.__________
- Cohesins
- Metaphase
In meiosis, __________ are cleaved along the chromosome arms in __________(separation of homologs) and at the centromeres in __________
chesins
anaphase 1
anaphase 2
Meiosis I is called the __________ because it halves the number of chromosome sets per cell from diploid (2n) to haploid (n)
reductional division
Meiosis II is called the __________ because the haploid cells divide to produce haploid daughter cells
equational division
__________(changes in an organism’s DNA) are the original source of genetic diversity
Mutations
Mutations create different versions of genes called __________
alleles
Reshuffling of alleles during sexual reproduction produces __________
genetic variation
Three mechanisms contribute to genetic variation
1.independent assortment of chromosomes
2.Crossing over
3.random fertilization
In __________, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs
independent assortment
Crossing over produces __________, which combine DNA inherited from each parent
recombinant chromosomes
Crossing over begins very early in __________, as homologous chromosomes pair up gene by gene
prophase 1
In __________, homologous portions of two nonsister chromatids trade places
Crossing over
__________ adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)
Random fertilization
__________ results in the accumulation of genetic variations favored by the environment
Natural selection
Asexual reproduction is __________ expensive than sexual reproduction
less
Overall, genetic variation is evolutionarily __________
