week 5 Flashcards
test 2
what are somatic cells
any body cells that do no produce gametes
what are germ cells
a diploid reproductive cell that gives rise to a gamete
what does haploid mean
cells with one set of chromosomes
what does diploid mean
cells with 2 sets of chromosomes
what are homologous chromosomes
inherit one from each parent, a pair of homologous chromosomes consists of one paternal and one maternal chromosome, they consists of alleles of the same types of genes
what’s the difference between mitosis and meiosis
mitosis = normal life cycle
meiosis = for reproduction
explain the structural relationships between chromosomes, chromatids and DNA
DNA makes up chromatids, chromatids make up chromosomes
what do histone proteins do
DNA is wrapped around histones, protecting it from damage
what is methylation
is helps control gene expression by turning genes off, also affects how tightly coiled the DNA is
what are the phases of mitosis
Prophase, metaphase, anaphase and telophase
what happens during prophase
DNA condenses into chromosomes each consisting of two sister chromatids. Nuclear membrane breaks down;
mitotic spindle fibres begin to form and
spindle microtubules extend from the MTOC
by polymerisation and attach to
chromosomes via their kinetochores in the
centromere region (prometaphase)
what happens during metaphase
chromosomes are aligned at
the metaphase plate (equator of the spindle).
each sister chromatid is attached to the microtubules coming from opposite poles
what happens during anaphase
as spindle microtubules shorten
by depolymerisation, sister chromatids are
separated, and the chromosomes are pulled
to opposite poles.
what happens during telophase
the chromosomes decondense
and nuclear membranes are formed around them.
what process precedes mitosis
interphase, starts the process of cell division by replicating DNA
what occurs after telophase
cytokinesis - the formation of daughter cells
what is one difference between the products of mitosis and meiosis
there are two sets of cell divisions - meiosis I and meiosis II
results in 4 daughter cells rather than 2 in mitosis
each resulting daughter cell has half the number of chromosomes as the parent cell
what happens during meiosis I
homologous chromosomes separate
2 haploid daughter cells are formed - reductional division, goes from 2n to 1n
what happens during meiosis II
4 haploid daughter cells are formed from the 2 cells formed from meiosis I, each with a haploid set of replicated chromosomes
what are the benefits of mitosis and meiosis
mitosis: conserves the number of chromosome sets producing cells that are genetically identical to the parent cell
meiosis: reduces the number pf chromosome sets from diploid to haploid, producing cells that are genetically different from the parent cell and from each other
name 3 unique events that occur in meiosis
- at the metaphase plate there are paired homologous chromosomes(tetrads) instead of individual replicated chromosomes
- it is homologous chromosomes instead of sister chromosomes that separate
- synapsis and crossing over: homologous chromosomes physically connect and exchange genetic information
what produces genetic variation and genetic diversity
mutations are an original source of genetic diversity and create different versions of genes called alleles
reshuffling of alleles during mitosis and reproduction produces genetic variation
what is independent assortment and when does it occur
there is an equal chance of the chromosomes from each parent lining up at metaphase I
each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of other cells - allows different combinations
the number of chromosomes possible when chromosomes assort independently into gametes is 2^n (n=haploid number)
occurs during meiosis
what is crossing over
the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis
results in recombinant chromosomes that contain genes from each parent which are new allelic combinations
begins very early in prophase I as homologous chromosomes pair up gene by gene
what is random fertilisation
any eggs can be fertilized with any sperm
each zygote produced has a unique genetic identity
how does genetic variation drive evolution
genetic variation can occur by:
- reshuffling of alleles during sexual reproduction
- independent assortment
- crossing over
this means that certain genetic variations are favoured by the environment through natural selection
what are epigenetics
the study of the chemical modification of specific genes or gene associated proteins of an organism
they do not affect that underlying genome, but involve the attachment of chemical compounds to the DNA like methylation which influences the level of transcription that can occur of particular genes
