Chapter 13 Flashcards
gentics
the scientific study of heredity and variation
heredity
The transmission of traits from one generation to the next
variation
demonstrated by the differences in appearance that offspring show from parents and siblings
true or false: it is genes that are actually inheritied
TRUE
genes
units of heredity, are made up of segments of DNA
how are genes passed on to the next generation?
via reproductive cells called gametes
locus
the specific location a gene has on a certain chromosome
DNA is packaged into…
a chromosome
asexual reproduction
a single individual passes genes to its offspring without the fusion of gametes
clone
a group of genetically identical individuals from the same parent
sexual reproduction
two parents give rise to offspring that have unique combinations of genes inherited from the two parents
life cycle
the generation to generation sequence of stages in the reproductive history of an organism
somatic cells have how many pairs of chromosomes?
23 pairs
karyotype
an ordered display of the pairs of chromosomes from a cell
homologous chromosomes
two chromosomes in each pair
-same length, shape, and carry genes controlling the same inherited characters
sex chromosomes
determine the sex of an individual, called x and y
- females have pair of x chromosome
- males have one x chromosome and one y chromosome
the remaing 22 pairs of chromosomes apart from the sex chromosomes are called
autosomes
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 _____ and one from _____
mother
father
diploid cell
has two sets of chromosomes
for humans the diploid number is 46
haploid cell
this is a gamete that contains a single set of chromosomes
- from humans, the haploid number is 23
- -22 autosomes and 1 sex chromosome
an unfertilized egg always has the chromosome..
x
true or false;
a sperm cell, may have either x or y chromosome
true
fertilization
the union of gametes (sperm and egg)
zygote
fertilized egg
- has one set of chromosome from each parent
- zygote produces somatic cells by mitosis and develops into an adult
when do people start to produce haploid gametes?
at sexual maturity
meiosis
results in one set of chromosome in each gamete
alternation of generations (by plants and some algae)
- includes both a diploid and a haploid multicellular stage
- the diploid organism, called the sporophyte, makes haploid spores by meiosis
- ea. spore grows by mitosis into a haploid organism called a gametophyte
- a gametophyte makes haploid gametes by mitosis
- fertilization of gametes result in a diploid sporophyte
alternation of generations (by fungi and protists)
- 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
true or false: only diploid cells can divide by mitosis
FALSE
depending on the type of life cycle, either haploid or diploid cells can divide by mitosis
true or false: only diploid cells can undergo meiosis
true
meiosis takes place in two sets of cell divisions….
- Meiosis 1
2. Meiosis 2
the two cell divisions result in ___ daughter cells
and each daughter cell has _______
- four
- only half as many chromosomes as the parent cell
what happens in Meioisis 1:
(reductional division): homologous chromosomes pair up and separate, resulting in two haploid daughter cells with replicated chromosomes
what happens in Meiosis 2:
(equational division) sister chromatids separate
—the result is four haploid daughter cells with unreplicated chromosomes
what happens in the interphase of meiosis?
- pair of homologous chromosomes in diploid parent are duplicated
- starts as / / and now is // //
- two pairs of sister chromatids
what are the four phases of meiosis 1
prophase 1
metaphase 1
anaphase 1
telophase 1 and cytokinesis
what happens in prophase 1 of meiosis?
- crossing over and synapsis
- homologous chromosomes loosley pair up, aligned gene by gene
synapsis
homologous chromosomes loosely pair up, aligned gene by gene
crossing over
- nonsister chromatids exchange DNA segments
- each pair of chromosomes form a tetrad, a group of four chromatids
chismata
x shaped regions where crossing over occured
what happens in Metaphase 1 of meiosis 1
- tetrads line up at the metaphase plate, with one chromosome facing each pole
- microtubules from one pole are attached to the kinetochore of one chromosome at each tetrad
- microtubules from the other pole do the same
what happens in anaphase 1 of meiosis 1
- pair of homologous chromosomes separate
- one chromosome moves toward each pole, guided by the spindle aparatus
- sister chromatids remain attached at the centormere and move as one unit toward the pole
what happens in telophase 1 and cytokinesis
- each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids
- cytokinesis happens simultaneously
- no chromosome replication occurs between the end of meiosis 1 and the beginning of meiosis 2 because the chromosomes are already duplicated
what are the four phases of meiosis 2
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2 and cytokinesis
what happens in prophase 2
- a spindle apparatus forms
- chromosomes move toward metaphase plate
what happens in metaphase 2
- sister chromatids are arranged at the metaphase plate
- The kinetochores of sister chromatids attach to microtubules extending from opposite poles
because of crossing over in meiosis 1 the two sister chromatids of each chromosomes are ….
no longer genetically identical
what happens in anaphase 2
- sister chromatds separate
- The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles
what happens in telophase 2
- the chromosomes arrive at opposite poles
- nuclei form, and chromosomes begin decondensing
what do you have at the end of meiosis 2
- 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
where does DNA replication occur in mitosis versus meiosis
both occur in interphase
number of divisions in mitosis versus meiosis
one in mitosis
two in meiosis
when does synapsis of homologous chromosomes occur in mitosis versus meiosis
does not occur in mitosis
-Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion
number of daughter cells and genetic composition in mitosis versus meiosis
two daughter cells in mitosis and genetically identical to the parent cell
-in meiosis it is four,ach haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other
what is the role in the animal body of the final product of mitosis versus meiosis
- in mitosis it enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction
- in meiosis it produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes
what are three events that are unique to meiosis (and all three occur in meiosis 1)
– Synapsis and crossing over in prophase I:
Homologous chromosomes physically connect and exchange genetic information
– At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes
– At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate
what allows sister chromatids of a single chromosome stay together meiosis 1
- sister chromatid cohesion
- -protein complexes called cohesins are responsible for this cohesion
when is the sister chromatid cohesion split? (mitosis versus meiosis)
In mitosis, cohesins are split at the end of metaphase
• In meiosis, cohesins are split along the chromosome arms in anaphase I (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids)
alleles
mutations (changes in an organism’s DNA) create different versions of genes which are alleles
-shuffling of alleles during sexual reproduction produces genetic variation
what three things contribute to genetic variation?
- independent assortment of chromosomes
- crossing over
- random fertilization
homologous pairs of chromosomes orient randomly at ______ of meiosis
metaphase 1
when does crossing over occur?
begins very early in prophase 1, as homologous chromosomes pair up gene by gene
