Meiosis Flashcards
heredity
transmission of traits from one generation to the next
genetics
the study of heredity and the variation of inherited characteristics
genes
a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA
haploid
a cell with only one set of chormosomes
homologous chromosomes
pair of chromosomes with same length, centromere position, and staining pattern that possess genes for the same characteristics at corresponding loci
karyotype
ordered display of chromosome pairs of a cell arranged by size and shape
-allows identification for chromosomal mutations and gender
diploid cells
cells with two sets of chromosomes (2n); one from each parent
autosomes
not a sex chromosome
sex chromosome
chromosome that determines the sex of an individual
locus
a specific place along the length of a chromosome where a given gene is located
gamete
a haploid cell, such as an egg or sperm. gametes unite during sexual reproduction to produce a diploid zygote
variation
differences between members of the same species
asexual reproduction
Asexual
– Single individual passes genes on to offspring
– Creates identical daughter cells (clones)
– Done by binary fission & mitosis
sexual reproduction
– Two parents produce
offspring that has a unique combination of parents’ traits
– Gives genetic variation
– Done by meiosis plus fertilization
Human Life Cycle
• Begins with the fusion of a sperm & egg (fertilization) which results in a zygote
• Zygote develops into a developed person via mitosis to increase somatic
cells & eventually reaches sexual maturity
• Gametes are then produced in the gonads by meiosis until fertilization occurs again
plant and some algae life cycle
alternation of generations
-multicellular diploid sporophyte undergoes meiosis to produce haploid spores. spores divide mitotically, forming multicellular haploid gametophytes. Through mitosis, gametophytes form gametes, in which fertilization results in diploid zygote that will develop into next sporophyte generation.
fungi and protists life cycle
diploid zygote undergoes meiosis, forming haploid cells that develop into unicellular descendants or haploid multicellular adult organisms. the haploid organism carries out further mitosis, producing cells that will develop into gametes.
Meiosis
- crossing over in prophase results in genetic diversity
- two divisions
- 2n→n
- results in four genetically distinct daughter cells (gametes) that can sexually reproduce
Prophase I
homologous pairs line up and cross over at chiasmata
-centrosome movement to opposite poles, spindle microtubule formation, nuclear envelope breakdown, nuclei dispersal
Metaphase I
pairs of homologous chromosomes (tetrads) are arranged on metaphase plate and connected to kinetochore microtubules
Anaphase I
spindle apparatus separates pairs of homologous chromosomes as they move toward opposite poles
Telophase I
each half of cell has complete haploid set of chromosomes (sister chromatids remain intact)
Meiosis II
-depending on the cell tpe, the nuclear envelope will reform and DNA will relax in between meiosis I and meiosis II
sister chromatids are separated, resulting in four haploid daughter cells that are all different
genetic variation
evolutionary
principles & the continuation of populations around the world
-ensures that populations can withstand environmental changes
independent assortment
Homologous pairs line up at the metaphase plate during Metaphase I and metaphase II independent of each other
– Result is a 50% chance that a gamete will end up with maternal or paternal chromosome from the homologous pair
– Each daughter cell from meiosis I represents one option of the possible 8 million combinations of parental chromosomes
crossing over
• Occurs during prophase I when homologous pair line up
• Nonsister chromatids are broken at the same place and swap equal amount of DNA to form recombinant
chromosomes
– This creates new combinations of maternal & paternal genes
• Humans average 1 to 3 crossovers per homologous pair
-can only occur with the two inside, non-sister chromatids of tetrads
random fertilization
• When sexual reproduction occurs one gamete for each parent will fuse to form a zygote
– This represents one possible outcome from 64 trillion possible gene combinations (this doesn’t even include the changes that result from cross over)!
– Hence, siblings can be very different from each other
-each gamete is equally likely to be fertilized
pros and cons of sexual reproduction
pros: more genetic variety so population can survive in changing environment
cons: slower process of reproduction, requires male and female gametes
pros and cons of asexual reproduction
pros: fast rate of reproduction and pop. growth, large pop., does not require partners
cons: no genetic variety so pop. is susceptible to extinction
