Chapter 10 Meiosis Flashcards
Heredity
Transmission of traits from one generation to the next
Variation
Differences by the differences in appearance that offspring show from parents and siblings
Genetics
Scientific study of heredity and variation
Units of heredity made of segments of DNA
Genes
Gametes
Reproductive cells
Most DNA is packaged in
Chromosomes
Somatic cells
The cells of the body except for gametes
Humans have 46 chromosomes in their somatic cells
Each gene has a specific position or_____, on a certain chromosome
Locus
In________, a single individual passes genes to its offspring without the fusion of gametes
Asexual
A_______is a group of genetically identical individuals from the same parent
Clone
In _________reproduction, two parents give rise to unique offspring that have unique combinations of genes inherited from the two parents
Sexual
A__________ is the generation to generation sequence of stages in the reproductive history of an organism
Life cycle
Human somatic cells have _______pairs of chromosomes
23
A________is an ordered display of the pairs of chromosomes from a cell
Karyotype
The two chromosomes in each pair are called
Homologous chromosomes or homologs
Chromosomes in a homologous pair are the same _______ and Carey genes controlling the same _______characters
Length, inherited
Sex chromosomes are called
X and Y
The remaining 22 pairs of chromosomes are called
Autosomes
Each pair of homologous chromosomes include one chromosome from each
Parent
A _______ (2n) has two sets of chromosomes
Diploid cell
Human diploid number is
46
2n=46
A gamete contains a single set of chromosomes and is
Haploid(n)
Human haploid number is
23
Each set contains 22 autosomes and a single sex chromosome
In an egg the sex chromosome is
X
In a sperm cell the sex chromosome is
Either X or Y
The union of gametes
Fertilization
The fertilized egg is called a
Zygote
The _______produces somatic cells by mitosis and develops into an adult
Zygote
_________are the only type of human cells produced by meiosis
Gametes
Meiosis results in ______set of chromosomes in each gamete
One
Gametes undergo no further __________ before fertilization
Cell division
Gametes fuse to form a
Diploid zygote
Plants and some algae exhibit an alternation of
Generations
The life cycle includes both diploid and haploid organisms
The diploid organism is called a sporophyte makes haploid spores by meiosis
Meiosis takes place in two sets of cell divisions
Meiosis I and meiosis II
Meiosis results in
Four daughter cells
Each daughter cell in meiosis has ________ as many chromosomes as the parent cell
Half
The diploid organism (plants and some algae) called a _________ makes haploid spores by mitosis
Sporophyte
Each spore grows by mitosis into a haploid organism called a
Gametophyte
In most fungi and some protist, the only diploid stage is the single called
Zygote-there is no multicellular diploid stage
Only _______cells can undergo meiosis
Diploid
Interphase I
Meiosis is preceded by an interphase in which each of the chromosomes replicates.
The result is sister chromatids that remain attached at their centromere
Prophase I
Chromosomes begin to condense
Homologous chromosomes pair up (synapsis) aligned gene by gene
At numerous places chromatids of homologous pairs are crisscrossed in regions called chiasmata
Centrosomes begin to move away
Nuclear envelope and nucleoli disperse
Metaphase I
Homologous chromosome pairs are arranged along metaphase plate
Kinetochore microtubules from one pole of the cell are attached to one chromosome of each pair
Anaphase I
Pairs of homologous chromosomes separate
Sister chromatids remain attached at the centromere and move as one unit toward the pole
Telephase I and Cytokinesis
Each half of the cell has a haploid set of chromosomes
Each chromosome still consists of two sister chromatids
Cytokinesis usually occurs simultaneously forming two haploid daughter cells
In animal cells, a cleavage furrow forms and in plant cells
A cell plate forms
No chromosome replication occurs between Meiosis I and Meiosis II because
The chromosomes are already replicated
Meiosis II phases
Pro II
Meta II
Ana II
Telo II
Prophase II
Spindle apparatus forms and the chromosomes move toward metaphase plate
Metaphase II
Sister chromatids are arranges at metaphase plate
Because of crossing over in Meiosis I, the two sister chromatids are no longer genetically identical
The kinetochores of each sister chromatids are pointing towards opposite poles
Anaphase II
The centromeres of the sister chromatids finally separate and the sister chromatids of each pair, now chromosomes, move towards opposite poles of the cell
Telephase II and Cytokinesis
Nuclei form and chromosomes begin decondensing
There are four daughter cells each with a haploid set of unreplicated chromosomes
Each daughter cell is genetically distinct from the others and from the parent cell
A zipper like structure forms during prophase I when homologous pairs align
Synaptonemal complex
Three events unique to Meiosis
Synapsis and crossing over in prophase I
Alignment of homologous pairs at the metaphase plate in Metaphase I
Separation of homologs in anaphase I
In meiosis sister chromatids stay together due to sister chromatid cohesion. In mitosis cohesins are cleaves during
Metaphase
In meiosis, cohesins are cleaved along the chromosome arms in ________, and at the centromeres in __________
Anaphase I, anaphase II
_________are the original source of genetic diversity
Mutations
Mutations create different versions of genes called
Alleles
Three mechanisms contribute to genetic variation
Independent assortment of chromosomes
Crossing over
Random fertilization
The number of combinations possible when chromosomes assort independently into gametes is
2^n where n is the haploid number
For humans there are more than 8 million combinations of chromosomes
Recombinant Chromosomes
Combine DNA from each parent and occurs during crossing over
In Humans, one to three crossover events per chromosome pair
What is the diploid stage of a plant that follows fertilization called?
Sporophyte
