Genetics - Chapter 4 Flashcards
Cell theory
all living things are composed of one or more cells
cells are the smallest units of living organisms
new cells come only from preexisting cells from cell division
Reasons for cell division
for reproduction
for repair
for growth
Heredity Genetics DNA Gene Locus
heredity = the passing of traits from parents to offspring
genetics = the branch of biology dealing with heredity and variation of inherited characteristics
DNA = storage molecule for genetic information
gene = segment of DNA molecule that codes for a particular trait (through proteins), at specific loci on chromosomes
locus (pl. loci) = specific location of a gene on a chromosome
Genetic material
chromosomes = contain the genetic blueprint of an organism, located in nucleus, supercoiled strands of DNA
most chromosomes occur in sets = diploid, haploid, polyploid
mitochondria and chloroplasts also contain small amounts of genetic material
Asexual reproduction
production of offspring from a single parent
genetic makeup of offspring is identical to parent
almost always occurs through cell division
Modes of asexual reproduction
putting out roots and shoots
budding = new individuals develop from outgrowth on body of organism
birth = females give birth to genetically identical offspring
fragmentation = parts of growing mass breaks off, continues to grow independently
Advantages to asexual reproduction
do not need mate
no need to perform specialized mating behaviours
do not need specialized anatomy
Disadvantages to asexual reproduction
may not be able to adapt to dynamic environment
new competitors or diseases can wipe out whole population
Sexual reproduction
offspring is produced from 2 sex cells, usually from 2 different parent organisms
offspring is genetically variable, half genetic info from each parent
Advantages to sexual reproduction
variable offspring with genetic diversity
some can adapt to environment/disease while others may not
Disadvantages to sexual reproduction
must have specialized organs to produce sex cells
specialized mating behaviour can put animal at risk to predators
more energy required to attract mate
offspring can possible inherit unfavourable combination of traits
Mitosis
process where cells reproduce themselves
produces 2 identical daughter cells
ensures genetic continuity within an organism for growth, repair, and development
Interphase
G1 = 1st gap/growth, doing it’s ‘everyday job’, cell grows, signals cell to divide
S = DNA synthesis, copies chromosomes, results in a pair of sister chromatids
G2 = 2nd gap/growth, prepares for division, cell grows, produces organelles, proteins, and membranes
nucleus is well defined, DNA loosely packed in chromatin fibers
Copying and packaging DNA
base pairing allows each strand to serve as a template for a new strand
new strand is half parent template and half new DNA (semiconservative copy process)
Prophase
chromatin condenses, visible chromosomes in the form of sister chromatids
centrioles move to opposite poles of cell
protein fibers cross cell to form spindle fibres (coordinates movement of chromosomes)
nucleolus disappears
nuclear membrane breaks down
Metaphase
spindle fibers begin moving and align chromosomes
chromosomes align along equator of cell
Anaphase
centromeres divide, sister chromatids move to opposite poles of the cell
results in the same number and type of chromosomes at each pole of the cell
Telophase
chromosomes at each end of the cell begin to unwind
spindle fibres dissolve
nuclear membrane start to form around chromosomes (results in two daughter nuclei)
cleavage furrow may start to form
Cytokinesis
cytoplasm of eukaryotic cells and organelles will be divided equally to form two new cells
animals = constriction belt of microfilaments around equator of cell, cleavage furrow forms splitting cell in two
plants = cell plate forms, new cell wall laid down between membranes, new cell wall fuses with existing cell wall
Cloning
cloning = process of producing one individual that is genetically identical to another using a single cell or tissue biotechnology = use and modification of organisms for application in engineering, industry and medicine
Cloning plants
first cloned plant from a single specialized root cell of a carrot
cells return to undifferentiated state and restart process of growth to develop into new plants
Cloning animals
challenge = animal body cells could not be stimulated into restarting process of growth and differentiation that begins with a fertilized egg
technique developed requires 2 cells and 3 adults
Cloning Dolly the sheep
remove cells from original sheep’s body tissue
remove nucleus from an egg cell of another sheep
fuse donor cell into egg cell
implant new embryo into a surrogate mother
surrogate mother gives birth to clone of original
Advantages of animal cloning
preserve endangered species
produce extinct species
offspring will have preferable characteristics
Disadvantages of animal cloning
offspring do not live as long due to health complications
expensive
disease could wipe out whole population
ethical and health concerns
GMOs
genetically modified organisms
carry genes that originated in a different species
commercial insulin is genetically engineered
cost and technological challenges are very high
some moral, ethical, health concerns with GMOs
Meiosis
single replication of nuclear material followed by 2 cell divisions
creates 4 non-identical gametes with haploid number of chromosomes
special type of cell division that occurs in the gonads
purpose = create reproductive cells (gametes)
Prophase I
nuclear membrane dissolves
chromosomes are attached to their copy by a centromere
centrioles appear and move to the poles
all of the chromosomes of the same chromosome number (homologous) join together to form a tetrad (bundle of four chromosomes, 2 from each parent)
during the tetrad formation, non-sister chromatids can exchange genes to create unique allele combinations that are not seen in the parent, called synapsis/crossing over
Metaphase I
the tetrads align themselves at the equator
all tetrads align independently of one another, called independent assortment
once aligned, the tetrads are held in place by spindle fibers released from the centrioles at the poles
the spindle fibers attach to the centromeres of the sister chromatids
Anaphase I
the spindle fibers contract and pull apart each tetrad such that one pair of sister chromatids goes to each pole
centromere does not split, it still holds the sister chromatids together
Telophase I and Cytokinesis
a nuclear membrane reforms around each new nucleus and the cytoplasm is divided by cytokinesis creating 2 non-identical cells
these two cells immediately proceed into next stage, no interphase
in some cell types, telophase I does not occur
Prophase II
the chromosomes become more visible and are still attached by centromere
centrioles move towards poles of the cell
nuclear membranes dissolve
Metaphase II
sister chromatids line up at the equator of the cell
spindle fibers emerge from centrioles and attach to the centromeres of each chromosome pair
Anaphase II
spindle fibers constrict, breaking centromeres, and pull apart sister chromatids
one copy of the chromosome pair goes to one pole while the other copy goes to the other pole
Telophase II
nuclear membrane starts to reform around chromosomes
cell membrane starts to pinch inwards at the equator, signaling the end of meiosis and beginning of cytokinesis
Genetic variability
very large number of possible chromosome combinations in meiosis
number of possible combinations = 2n
n is the number of chromosome pairs
processes that lead to genetic variability = synapsis, independent assortment
Gametogenesis
the production of gametes through the process of meiosis
Spermatogenesis
meiosis in males, occurs in the testes
starts with a diploid cell called a spermatogonia
occurs all of the time from puberty until death
Oogenesis
meiosis in females, occurs in the ovaries and oviducts
starts with a diploid cell called an oogonia
egg production starts before a female is born, but pauses in Meiosis I
the meiotic process resumes at puberty with ovulation for 1 cell every month
after telophase I and II, only one of the cells receives the majority of the cytoplasm, resulting in one egg cell and three polar bodies
allows the egg cell to have sufficient nutrients to support a zygote
Chromosome pairs
humans have a total of 23 chromosome pairs
number of chromosomes in daughter cell of mitosis = 2n
number of pairs of homologous chromosomes = n
beginning of prophase I = 2n
beginning of telophase I = n
beginning of telophase II = n
one chromosome pair determines the sex of the offspring
XX = female, XY = male
Nondisjunction
error during chromosomal division
when a gamete that has experienced nondisjunction fertilizes another gamete, it results in monosomy or trisomy
Nondisjunction in Meiosis I
homologous pairs travel to the same daughter cell
2 daughter cells have 2 copies
2 daughter cells have 0
nondisjunction in Meiosis I impacts all daughter cells
Nondisjunction in Meiosis II
error occurs when sister chromatids don’t separate, but travel to the same daughter cell
2 daughter cells have 1 copy (not affected by nondisjunction)
1 daughter cell has 0
1 daughter cell has 2
nondisjunction in Meiosis II impacts half of the daughter cells
Karyotype charts
pictures of chromosomes arranged in homologous pairs by number, size, shape
banded region = contains potentially hundreds of genes
prepared by staining and photographing chromosomes under a microscope
Impacts of nondisjunction
leads to abnormalities and often zygote death since the resulting embryo will have too little or too much genetic information
examples = Down’s (trisomy 21), Klinefelter’s (XXY), Turner’s (X0)
Cytoplasmic DNA
the genes in mitochondria contain information related to cellular respiration
the genes in chloroplasts contain information related to photosynthesis
both organelles were thought to have been ancient prokaryotic organisms that were then engulfed by a eukaryotic cell (endosymbiosis)
Types of cytoplasmic inheritance
maternal inheritance = a zygote inherits cytoplasmic DNA from only the female gamete
paternal inheritance = a zygote inherits cytoplasmic DNA from only the male gamete
Genetic variation within organelles
genetic variation occurs within organelles as the different types of organelles are randomly separated during cell division
example = variegated leaves
Mitochondrial disease
a genetic disorder related to energy
process of DNA egg swapping =
if mother is at risk for passing on a mitochondrial disease, remove nucleus of fertilized egg, transfer nucleus to an unfertilized and enucleated egg from donor
resulting cell is transplanted back into mother
Horizontal gene transfer
horizontal gene transfer = the transfer of genetic information from one species to another, allows one organism to exhibit the characteristics of an entirely different organism
example = green sea slug
green sea slug feeds on algae, but instead of digesting it completely, it keeps the chloroplasts intact, then incorporates into DNA
