Meiosis Flashcards
In Asexual Reproduction
A single individual passes all of its genes to its offspring without the fusion of gametes
A clone is..
a group of genetically identical individuals from the same parent
In sexual reproduction, two parents ..
give rise to offspring that have unique combinations of genes inherited from the two parents
How many pairs are in Human Somatic Cells?
They have 22/23 pairs (plus XX or XY) of Chromosomes
What is a karyotype?
An ordered display of the p airs of chromosomes from a cell
Two chromosomes in each pair are called
Homologous Chromosomes, or Homologs
Chromosomes in a homologous pair are..
the same length and shape and carry genes controlling the same inherited characters
Each pair of homologous chromosomes include one chromosome from each _____
parent
The 46 chromosomes in a human somatic cell are two sets of ____
23: one from the mother and one from the father
A diploid cell has how many sets of chromosomes?
Two sets
For humans, the diploid number is
46 (2n = 46)
For humans, the haploid number is
(n) = 23
The sex chromosomes that determine the sex of the individual are called..
X and Y
Human females have a homologous pair of
X Chromosomes (XX)
Human males have _______ chromosomes
one X and one Y
Sex in human is determined by the presence of
the Y chromosome
The remaining 22 pairs of chromosomes are called..
Autosomes
A gamete (sperm or egg) contains a single set of ____ and is ____
Chromosomes, and is haploid (n)
For humans, the haploid number is
23 (n = 23)
Each set of 23 in Haploid consist of
22 Autosomes and a single sex chromosome
In an unfertilized egg (ovum), the sex chromosome is
X
In a sperm cell, the sex chromosome may be either
X or Y
What is Fertilization?
The union of gametes (the sperm and the egg)
The fertilized egg is called a …
Zygote, and has one set of chromosomes from each parent
The zygote produces somatic cells by.
Mitosis and develops into an adult
Meiosis reduces the number of chromosome sets from ..
diploid to haploid
Like Mitosis, Meiosis is preceded by
the replication of chromosomes
Meiosis takes place in two consecutive cell divisions called
Meiosis I and Meiosis II
The two cell divisions in Meiosis result in
Four daughter cells, rather than the two daughter cells in Mitosis
Each daughter cell in Meiosis has only
half as many chromosomes as the parent cell
Chromosomes duplicate during
Interphase
The resulting sister chromatids are closely associated
along their lengths
Sister chromatids that are closely associated along their lengths are called
Sister Chromatic Cohesion
Chromatids are sorted into
four haploid daughter cells
Division in Meiosis I occurs in four phases
Prophase I
Metaphase I
Anaphase I
Telophase I and Cytokinesis
Division in Meiosis II also ocurs in four phases
Prophase II
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Prophase I info
Each chromosome pairs with its homolog and crossing over occurs
(Prophase I) What are Chiasmata?
They are X-Shaped regions and are sites of crossing over –> Genetic Variability
Prophase I; Gametes are not
like each other and not like their parents
Prophase I; After interphase, the sister chromatids are held together by proteins called
Cohesins – Sister Chromatid Cohesion
Prophase I; Non-sister chromatids broken at
precisely corresponding positions
Prophase I; what is the Synaptonemal Complex
It is zipper-like structure that holds the homologs together tightly
Prophase I; DNA breaks are repaired, joining…
DNA from one non-sister chromatid to the corresponding segment of another
Mitosis vs Meiosis: Mitosis
Conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
Mitosis vs Meiosis: Meiosis
Reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
Mitosis Property
Occurs in both Diploid and Haploid Cells
Meiosis Property
Can occur only in diploid cells
Mitosis DNA replication
Occurs during interphase before mitosis begins
Meiosis DNA replication
Occurs during interphase before Meiosis I begins
Mitosis Number of Divisions
One, including Prophase, Prometaphase, Metaphase, Anaphase, and Telophase
Meiosis Number of Divisions
Two, each including Prophase, Metaphase, Anaphase, and Telophase
Mitosis Synapsis of Homologous Chromosomes
Does Not Occur
Meiosis Synapsis of Homologous Chromosomes
Occurs during Prophase I along with crossing over between nonsister chromatids; resulting Chiasmata hold pairs together due to sister chromatid cohesion
Mitosis Number of daughter cells and genetic composition
Two, each genetically identical to the parent cell, with the same number of chromosomes
Meiosis number of daughter cells and genetic composition
Four, each haploid (n); Genetically different from the parent cell and from each other
Mitosis Role in the animal or plant body
Enables multicellular animal or plant (gametophyte or sporophyte) to arise from a single cell; produces cells fpr growth, repair, and in some species, a sexual reproduction produces gametes in the gametophyte plant
Meiosis Role in the animal or plant body
Produces gametes (in animals) or spores (in the sporophyte plant); Reduces number of chromosomes sets by half and introduces genetic variability among the gametes or spores
Mutations
Changes in an organism’s DNA are the original source of genetic diversity
Alleles
Mutations create different versions of genes, these are called alles
Genetic Variation
The reshuffling of alleles during sexual reproduction
Mechanisms contribute to genetic variation
Independent assortment of chromosomes
Crossing Over
Random Fertilization
Mutation
Independent Assortment , each pair of chromosomes
sorts maternal and paternal homologs into daughter cells independently of the other pairs
The number of combinations possible when chromosomes assort independently into gametes is
2^n, where n is the haploid number
For humans (n=23), there are more than
8 mllion (2^23) possible combinations of chromosomes
Crossing over produces
Recombinant Chromosomes, which combine DNA inherited from each parent
Crossing over contributes to
Genetic Variation, by combining DNA from two parents into a single chromosome
In humans an average number of crossover events per chromosome is
1-3 Crossovers
Random fertilization adds to genetic variation because
Any sperm can fuse with any ovum (unfertilized egg)
The fusion of two gametes produces
a zygote with any of about 70 trillion diploid combinations
Natural selection results in
The accumlation of genetic varations favored by the environment
Meiosis –> Nondisjunction
The members of a chromosome pair fail to separate at Anaphase
Producing gametes with an incorrect number of chromosomes
Can occur in Meiosis I or II
Down Syndrome
Occurs because there is an extra chromosome in number 21; Trisomy 21
Edwards Syndrome
Occurs in Trisomy 18, due in part because of an extra chromosome. Result sin the back part of skull being prominent, along with clenched hands, and a shield chest.
Patau’s Syndrome
Extra Chromosome in Trisomy 13. Results in cleft lip or palate, clenched hands, undescended or abnormal testes. Messed up face yo
Klinefelter’ Syndrome
Result of a XXY male. Male features poor beard growth, breast development, front baldness absent, and female type pubic hair pattern.
Triple X Female
XXX Female. Short Stature, Low Hairline. No Menstruation, Redimenary Ovaries
XO or Monosomy Turner’s Syndrome
No Chromosomes, DNA or Genitalia, but Androgen levels. “She” has a Y chromosome, external female genitalia
Cell Death _ Necrosis
Low Oxygen, Toxins, ATP Depletion
Random Fragmentation
Ingeseted by Phagocytes
Inflammation
Cell Death - Apoptosis
Programmed Cell Death
Chromatin condensation, membrane blebbing, single cell death
Ingested by neighboring cells
Vitamin D dependent
