M2 Lecture 17-18 Flashcards
8.3 Genetic Recombination Occurs in Eukaryotes during Meiosis
Sexual reproduction depends on what?
What is meiosis?
Fertilization results in what?
Meiosis and fertilization results in what? What is the advantage?
What is the Foundation of sexual reproduction?
= Depends on meiosis
= o Specialized process of cell division recombining DNA sequences produces cells with half number of chromosomes of each parent
= - @ Fertilization = nuclei of egg + sperm fuse, produces zygote
= - Meiosis + fertilization = mix genetic info = genetic variability
= mix of genetic info (halving chromosomes) and restoration of chromosomes via fertilization
8.3 a Meiosis occurs at different times in different organismal life cycles
The life cycle of eukaryotes alternates between what?
Describe the animal life cycle?
which cycle dominates the animal life cycle?
= haploid and diploid
= o Diploid phase dominates life cycle: multicellular
o Haploid phase is reduced
o Meiosis followed directly by gamete formation
o Male animals:
Four nuclei produced by meiosis = enclosed by separate cell by cytoplasmic division + forms functional sperm cell
o Female animals:
One of four nuclei = functional egg cell nucleus (loaded with cytoplasm)
o Animals are haploid only as sperm or egg, no mitotic divisions occur during haploid phase of life cycle
= diploid
- 3 b Meiosis Changes Both Chromosome # and DNA sequence
- Mitotic cell division means what?
- What are somatic cells? What do they typically become?
- Meiosis division means what?
What are the 2 kinds of meiosis division?
Do the products of meiosis contribute to body of host?
What do we call the 2 representatives of chromosomes in diploid cell ? What constitues this term?
= sameness
o Aka chromosomes are replicated + organized = same # of chromosomes, same DNA sequence
= any cell of a living organism other than the reproductive cells. o Somatic cells become multicellular organisms
= Difference
o 2 kinds:
1: halved chromosome number
2: new combos of alleles arising from recombined DNA sequences
= no
= homologous pair
= Same genes, same order in DNA of chromosomes
• One chromosome of pair: paternal chromosome
o Derived from male parent
• Other chromosome: maternal
o Derived from female parent
• Homologous chromosomes: carry same genes arranged in same order, but have diff. version of genes alleles present
- RECAP: the C’s
- Chromatin:
- Centromere:
- Chromosome:
= stuff chromosomes are made from (nucleic acid and proteins)
= structure that helps a chromosomes sto get oriented during cell division and holds sister chromatids together
= made up of nucleic acids and proteins, made up of genetic info in form of genes,
- joined sister chromatids part of one chromosome
o Determining diploid/haploid: count # of centromeres
o Chromosomes passed on = mixture of maternal and paternal DNA sequences
- 3c Meiosis Produces four genetically different daughter cells
- What are meiocytes?
Descirbe their movement throughout the cell cycle?
What is meiosis 1?
Meiosis 2?
True or false, ploidy is influenced by # of chromosomes, not its replication.
Describe prophase 1?
What is Genetic recombination?
Descirbe prometaphase 1?
Descirbe metaphase 1 and anaphase 1?
Describe Telophase 1 and Interkinesis?
Descirbe Prophase 1, prometaphase 2, metaphase 2
Describe Anaphase 2 and Telophase 2
= : cells destined to divide
= o Move through last turn of cell cycle (replicate DNA + make more chromosomal proteins in S phase)
Resulting G2 cells carry replicated chromosomes (composed of 2 sister chromatids each) – premeiotic interphase
Cells enter meiotic divisions:
= • Meiosis 1
o Homologous chromosomes find partners and pair lengthwise (synapsis)
Recombination occurs, chromosomal segments are exchanged
End of first division: members of homologous pairs = moved into daughter cells
• Daughter cells = contains replicated chromosomes (# of chromosomes = ½ of og meiocyte)
= • Meiosis 2
o Sister chromatids = separated into diff. cells (reducing amnt. DNA in each product of meiosis)
4 cells (haploid # of chromosomes) = result of 1 and 2 meiotic division
= true
= - Prophase 1:
o Replicated chromosomes (result of S phase), having 2 sister chromatids = fold + condense in nucleus
o The 2 chromosomes of homologous pairs = line up/stack
Chromatids then exchange segments (GENETIC RECOMBO.)
End of prophase 1: spindle forms in cytoplasm
= process where mixture of alleles takes place – contributes to genetic variability in sexual reproduction
= - Prometaphase 1:
o Nuclear envelope breaks down, spindle enters former nuclear area
o 2 chromosomes of each pair attach to kinetochore microtubules (anchored to opposite spindle poles)
= - Metaphase 1 and Anaphase 1:
o Movements of spindle microtubules (metaphase)= aligned on metaphase plate b/w spindle poles
o 2 chromosomes of homologous pairs climb in anaphase
Movement = haploid set of chromosomes @ each spindle
Chromosomes are still double structures (2 sister chromatids joined ay centromeres)
= Telophase 1 and Interkinesis
o Brief stage = no change to chromosome
o Cell division (cytokinesis) = creates haploid cells
o Interkinesis = spindle of meiotic division = disassembles and microtubules reassemble into new spindles for 2nd division
= o Prophase of meiosis 2= condensation of chromosomes
o Prometaphase 2 = break down of nuclear envelope, spindle enters former nuclear area, spindle microtubules @ each pole attaches 2 kinetochores of chromosomes
o Metaphase 2: chromosome on spindle = now at rest @ metaphase plate
= Anaphase 2 and Telophase 2
o Anaphase 2 begins with separation of sister chromatids of each chromosome – movement to opposite poles
o Separated chromatids, now chromosomes, @ opposite poles
o Telophase 2: chromatids decondense to interphase state, spindles disassemble, new nuclear envelopes form
Results in 4 haploid cells
- Overall goal of meiotic division = genetic variability + reduction in chromosome #
8.3c Meiosis Produces four genetically different daughter cells
Describe 4 key differences between meiosis and mitosis?
DIFF: CHROMOSOMES DON’T PAIR UP IN MITOSIS
DIFFERENT FROM SPINDLE ATTACHMENT IN MITOSIS
NO DNA REPLICATION IN FIRST AND SECOND DIVISION
- SEPARATION OF CHROMATIDS IN MEIOSIS 2 PRODUCES REPRODUCTIVE CELLS (NO IMMEDIATELY PRECEDING DNA REPLICATION PHASE)
o RESULTING DAUGHTER CELLS = NOT IDENTICAL
- 3 d Several mechanisms contribute to genetic diversity
- What does meiotic division result in? (from an advantageous point of view)
What are the 4 sources of genetic variability?
= genetic variability for evolution and reparation of chromosomes to offspring
= 1. Genetic recombo. Between homologous chromosomes
- Differing combination of maternal + paternal chromosomes segregated to poles in anaphase 1
- Diff. combos of recombinant chromatids segregated to poles in anaphase 2
- Specific sets of male + female gametes uniting in fertilization
- 3 d Several mechanisms contribute to genetic diversity
- In Genetic recombination what does crossing over produce?
Decsirbe the crossing over process?
Where does random segregation occur in the cell cycle?
= o Crossing over produces recombinant chromosomes (combine genes)
= Begins very early, stacking site = synaptonemal complexes
Two non-sister chromatids trade places (location of crossovers= chiasmata)
= - Random segregation:
o Prophase 1: random segregation of maternal/paternal chromosomes in prophase 1
o Segregation of recombinant vs parental chromatids in metaphase 2
o Random fertilization among gamete variants (which egg or sperm is available)
Means identical gametes in fertilization = impossible (except twins)
