Ch.10 meiosis Flashcards
Heredity
The transmission of traits from one generation to the next
Varations
Variation is demonstrated by the differences in appearance that offspring show from parents and siblings
Genetics
Is the scientific study of heredity and variation
Genes
Genes are the units of heredity and are made up of segments of DNA
In a literal sense, children do not inherit particular physical traits from their parents
Children inherit Genes from parents
Gamates
Genes are passed to the next generation via reproductive cells called gametes (sperm and egg/ova)
Asexual reproduction
A single individuall passes genes to its offspring without the fusion of gametes
Clone
is a group of gentically identical individuals from the same parent
sexual reproduction
two parents give rise to offspring that have unique combinations of genes from the two parents
Life cycle
the generation-to-generation sequence of stages in the reproductive history of
an organism
How many pairs of chromosomes do human somatic cells have?
23 pairs
total of 46 chomosomes diploid
karyotype
is an ordered display of the pairs of chromosomes from the cell
Homologous chromosomes (homologs)
The two chromosomes in each pair are called homologous chromosomes, or homologs
homologous pair
Chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited characters
Sex chromosomes, what kind do males have and what kind do females have
What are autosomes
The sex chromosomes, which determine the sex of the individual, are called X and Y
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome
The remaining 22 pairs of chromosomes are called autosomes
Diploid cell
Each pair of homologous chromosomes includes 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 (2n) has two sets of chromosomes
For humans, the diploid number is 46 (2n = 46)
Haploid (n)
A gamete (sperm or egg) contains a single set of chromosomes and is haploid (n)
For humans, the haploid number is 23 (n = 23)
Each set of 23 consists 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
Fertilization and Zygote
fertilization is the union of gametes (the sperm and egg)
The fertilized egg is called Zygote and has one set of chromosomes from each parent
The Zygote produces somatic cells by mitosis and develops into an adult
When are haploid gametes produced?
what process produces this?
At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are the only types of human cells produced by meiosis rather than mitosis
Meiosis results in one set of chromosomes in each gamete
Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
Alternation of generations
Plants and some algae exhibit an alternation of generations
This life cycle includes both a diploid and haploid multicellular stage
The diploid organism, called the sporophyte, makes haploid spores by meiosis
fungi and reproduction
In most fungi and some protists, the only diploid stage is the single-celled zygote; there is no multicellular diploid stage
The zygote produces haploid cells by meiosis
Each haploid cell grows by mitosis into a haploid multicellular organism
The haploid adult produces gametes by mitosis
meiosis I and meiosis II
Like mitosis, meiosis is preceded by the duplication
of chromosomes
Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II
he two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis
Each daughter cell has only half as many chromosomes as the parent cell
Meiosis and stages of division
Meiosis halves the total number of chromosomes very specifically
It reduces the number of sets from two to one, with each daughter cell receiving one set of chromosomes
In the first meiotic division, homologous pairs of chromosomes pair and separate
In the second meiotic division, sister chromatids of each chromosome separate
Four new haploid cells are produced as a result
Meiosis prophase I
Chromosomes condense progresively throught prophase I
Homologous chromosomes pairs up, aligned gene by gene
Cross over
non sister chromatides exchange DNA segments
Each homologous pair has one or more X-shaped regions called chiasmata
Chiasmata exist at points where crossing over has occurred.
Metaphase I
In metaphase I, homologous pairs line up at the metaphase plate, with one chromosome facing each pole
Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad
Microtubules from the other pole are attached to the kinetochore of the other chromosome
Anaphase I
Anaphase I
In anaphase I, pairs of homologous chromosomes separate
One chromosome moves toward each pole, guided by the spindle apparatus
Sister chromatids remain attached at the centromere and move as one unit toward the pole
Telophase I and Cytokinesis
Telophase I and Cytokinesis
In the beginning of telophase I, 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
Four Phases of meiosis II
Division in meiosis II also occurs in four phases
Prophase II
Metaphase II
Anaphase II
Telophase II and cytokinesis
Meiosis II is very similar to mitosis
Prohphase II
Prophase II
§In prophase II, a spindle apparatus forms
§In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plate
Metaphase II
Metaphase II
§The sister chromatids are arranged at the metaphase plate
§Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical
§The kinetochores of sister chromatids attach to microtubules extending from opposite poles
Anaphase II
Anaphase II
§In anaphase II, the sister chromatids separate
§The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles
Telophase II and Cytokinesis
Telophase II and Cytokinesis
§Nuclei form, and the chromosomes begin decondensing
§At the end of meiosis, there are four daughter cells, each with a haploid set of unduplicated chromosomes
§Each daughter cell is genetically distinct from the others and from the parent cell
