inquiry question 2 mod 5 Flashcards
cell division
process that cells undergo in order to form new cells
- mitosis
- meiosis
what does DNA stand for
deoxyribonucleic acid
chromosome
- thread like structures made of highly packed DNA around histone proteins
- allows DNA to be accurately copied during cell division
- located inside the nucleus of animal and plant cells
- can be duplicated 92 sister chromatids), unduplicated
- joined at centromere
where are chromosomes found in plants and animals
plants: nucleus, mitochondria, chloroplasts
animals: nucleus, mitochondria
homologous chromosomes
A pair of chromosomes that consists of one maternal and one paternal chromosome that are the same length and carry genes at the same locations
cell cycle
series of events that take place in a cell as it grows and divides
- interphase –> mitosis –> completes division
- mainly interphase
- small part mitosis
mitosis
process of nuclear division in which the replicated genetic material is separated and two new nuclei are formed
- parents cells create 2 identical daughter (2n) cells
eg. binary fission
chromatids
one of two genetically identical halves of a replicated chromosome
sister: identical
non-sister: paternal and maternal
phases of mitosis
(interphase before)
- prophase
- metaphase
-anaphase
- telophase
- cytokinesis (no part of mitosis)
prophase (mitosis)
- chromatin condenses into chromosomes –> chromosomes become visible
- mitotic spindle fibres start to form from centrioles
- nuclear membrane dissolves to allow spindle fibres to attach to chromosomes
interphase
DNA is replicated
- nucelar DNA remaind in semi condensed chromatin configuration
- amount of DNA doubles bu the amount of chromosomes remain the same
metaphase (mitosis)
- chromosomes line up –independent assortment
- centrosomes are at opposite ends of cells –> poles
- spindle fibres attach to centromere of each pair of sister chromatids (makes sure that the chromatins go to different sides)
anaphase (mitosis)
- sister chromatids pulled to opposite ends of the cell
- end: each pole has a full set of chromosomes
telophase (mitosis)
- chromosomes begin to decondense (unravel)
- mitotic spindles break down
- nuclear envelope begins to form around the chromosomes
cytokinesis
Division of the cytoplasm to form two new cells each with their own cell membrane
- Begins in either anaphase or telophase –> doesn’t finish until after telophase.
- Cytoplasm splits equally between the two cells.
- Chromosome unravels to become chromatin
- When cytoplasm divides so each daughter cell has its own cytoplasm
meiosis
process of nuclear division required for the formation of new sex cells (gametes)
- single parent cell divided twice to produce 4 identical daughter cells that contain half the amount of genetic information
- 2n - 2n - nX4
- produces genetically unique gametes
phases of meiosis
interphase
meiosis I
- prophase I
- metaphase I
- anaphase I
- telophase I
cytokinesis
(no interphase)
meiosis II
- prophase II
- metaphase II
- anaphase II
- telophase II
cytokinesis
prophase I meiosis I
- chromosomes condense into x-shaped structures
- two sister chromatids in each chromosome
- pairs may cross over –> exchange DNA to mix maternal and paternal alleles –> increases genetic variability
metaphase I meiosis I
- Homologous pairs of chromosomes line up on the equator randomly –> independent assortment –> increases genetic variability
- centrioles at opposite ends of the cell
- meiotic spindles attach to one chromosome from each pair on each side
anaphase I meiosis I
- cells begin to elongate
- homologous pair of chromosomes are pulled apart by meiotic spindle
- sister chromatids stay attached at centromeres
cytokinesis after meiosis I
- Single cell pinches in the middle→ two new daughter cells
- Each contain a full set of chromosomes within a nucleus
telophase I meiosis I
- Chromosomes complete the move to the opposite poles of the cell
- each pole has a full sett of chromosomes
- chromosomes decondense
- nuclear envelope begins to form around each set of chromosomes
meiosis II
- like mitosis
- no crossing oer
- begins without further replication –> interphase
prophase II meiosis II
- two daughter cells (n)
- Nuclear envelope and nucleoli and membrane dissolve and disappear
- Spindle fibres form and spread across the two daughter cells
(crossing over does not occur)
metaphase II meiosis II
- Chromosomes line up along the equator of the cell → (metaplate) in a single file line different to metaphase I
- law of independent assortment
- meiotic spindles attach to each of the sister chromatids
anaphase II meiosis II
- Sister chromatids are pulled apart to opposite poles due to the meiotic spindle
- one chromatid = one chromosome
telophase II meiosis II
- chromosomes complete their move to opposite poles of the cell
- chromosomes decondense
- nuclear envelope begins to reform around them
cytokinesis (after meiosis II )
- cells physically divide into four daughter cells
- haploid (23 chromosomes)
gene
a distinct sequence of nucleotides on a chromosome which code for some characteristic which is transferred from parent to offspring
allele
each of two or more alternative forms of a gene that are found at the same place on a chromosome
- dominant: when the allele of the gene effectively overruled the other (recessive) allele
genetic continuity
ability to pass on genetic information from one generation to the next
depends on
- large numbers
- stable environment
in changing environment variation helps continuity
why is genetic continuity important
allows for the passage of advantageous traits to ensure species survival
how does sexual reproduction ensure genetic variation and continuity
- crossing over
- law of independent assortment
- law of random segregation
- random fertilisation
crossing over
- Exchange of genetic material between two homologous chromosomes’ non-sister chromatids
- Prophase I or metaphase I
- Leads to new allelic combination in daughter cells
law of independent assortment
- metaphase –> homologous pairs align independently
- Traits are inherited independently
- the allele a gamete receives for one gene does not influence the allele received for another gene
law of random segregation
chromosomes are distributed randomly among the different gametes depending on which way in which chromosome pairs line up during meiosis
- results in unique set of chromosomes
- anaphase I
- Alleles separate/segregate → each gamete is equally likely to receive either on of the two alleles present in the diploid individual
random fertilisation
Random union of gametes during fertilisation → introduces variability
- any sperm can combine with any egg
