Meiosis Flashcards
Gene
Units of heredity, made up of segments of DNA
Allele
Different versions of genes
Locus
Specific location of gene
Gametic Cell (Gametes)
Genes are passes to the next generation through gametes (sperm and egg)
Haploid
Produced by meiosis
Diploid Zygote
Fertilized egg, has one set of chromosomes from each parent (2 sets in total)
Somatic Cells
Produced by zygote by mitosis and develops into an adult organism
All other cells in body excluding sperm and egg
Diploid
Which parts of the human sexual life cycle is haploid and diploid
Diploid - ovary and testis to meiosis, after fertilization (mitosis and development)
Haploid - meiosis to egg and sperm to fertilization
Homologous chromosomes (homologs)
The 2 chromosomes in each pair
Can exist un-replicated or replicated
Same size, have genes which are arranged in same order
Karyotype
An ordered display of chromosomes of an individual cell
What is the purpose of adding colchicine during karyotype preparation
Arrests the cell at the metaphase during cell division, so its easier to locate chromosomes and extract them out for the karyotype
At metaphase the chromosomes are the most condensed (lined up in the middle)
How many chromosomes are found in human haploid cells (gametes) and human diploid cells (somatic cells)
How many autosomes and sex chromosomes in the number of chromosomes?
Human diploid cell (somatic cell) - 46, 2 sets of 23
22 pairs are autosome (don’t determine sex)
23rd pair is sex chromosomes
Human haploid cell (gametes) - 23, 22 autosomes, 1 sex
Reductional division (meiosis l) versus Equational division (meiosis ll)
Reductional division - diploid parent cell results in 2 haploid daughter cells
Equational division - 4 haploid daughter cells with unreplicated chromosomes
What steps are associated with meiosis l and meiosis ll
Meiosis l - prophase 1, metaphase 1, anaphase 1, telophase 1 and cytokinesis
Meiosis ll- prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis
Synapsis
Homologous replicated chromosomes loosely pair up, aligned gene by gene
Bivalent
Pair of homologs
Each bivalent has one or more chiasmata
Crossing over
Non-sister chromatids exchange DNA segments to produce chromosomes with a combination of maternal and paternal alleles
Chiasmata in Prophase l
Chiasmata - regions where crossing over occurs
Centrosome
Organelle that serves as microtubule organizing center
Replication lead to 2 centrosomes that migrate opposite ends of cell
Asters
A radial array of short microtubules that extend from each centrosome, help to anchor centrosome
Spindle microtubules (kinetochore and non-kinetochore (or polar) microtubules)
Kinetochore - capture chromosomes by binding to kinetochore proteins
Non-kinetochore - (polar microtubules) do not capture chromosomes
In addition to mutations, list 3 other mechanisms that contribute to genetic variation in humans
Independent assortment of chromosomes -homologous pairs of replicated chromosomes (bivalents) orient randomly at metaphase 1
Crossing over - produces recombinant chromosomes, which combine genes inherited from each parent, begins at prophase 1, combines DNA from 2 parents into a single chromosome
Random fertilization - Any sperm can fuse with any ovum(unfertilized egg)
Chromosomal Disorders
examples?
Down syndrome - due to 3 copies of chromosome 21
Klinefelter syndrome - an XXY male (individual has male sex organs but are sterile)
Turner syndrome - an XO female (do not mature sexually during puberty, sterile) missing a chromosome
Stages of Meiosis l
What occurs in each stage
Prophase 1 - replicated chromosomes condense and spindle microtubules begin to form centrosomes (diploid)
Metaphase 1 - paired homologs line up at metaphase plate at random (diploid)
Anaphase 1 - paired homologs sperate (diploid), chromosomes move guided by spindle microtubules
Telophase 1- homologs finish migrating to the poles of the cell (diploid)
Cytokinesis - forming 2 haploid daughter cells
Stages of Meiosis ll
What occurs in each stage
Prophase 2 - spindle microtubules form, replicated chromosomes (composed of 2 sister chromatids) move toward metaphase plate (no synapsis, chiasmata, crossing over)
Metaphase 2 - replicated chromosomes arranged at metaphase plate (due to cross over in meiosis 1, 2 sister chromatids no loner genetically identical
Anaphase 2 - sister chromatids separate, move as individual chromosomes to opposite poles of cell (un-replicated chromosomes)
Telophase 2 - chromosomes (un-replicated) arrive at opposite poles, nuclei form, chromosomes begin decondensing
Cytokinesis - 4 daughter cells, each have haploid set of un-replicated chromosomes, cell is genetically distinct
