Chapter 7: The Cellular Basis of Inheritance Flashcards
define asexual reproduction
- produces genetically identical offspring
- binary fission, mitosis, budding, cloning, etc
define sexual reproduction
- produces genetically different offspring
- meiosis and fertilization: production and fusion of haploid cells into single diploid cell
define diploid life cycle
- haploid gametes undergo fertilization to create diploid zygote
- zygote undergoes mitosis to grow
- meiosis creates haploid gametes from diploid cells
advantages of asexual reproduction
- faster
- no mate needed
- population size increases rapidly
how does asexual reproduction introduce genetic variation
mutations
disadvantages of asexual reproduction
- no genetic variation
why do most eukaryotes reproduce sexually
- evolutionary success
- advantage of genetic variation outweighs all disadvantages
advantages of sexual reproduction
- genetic variation
how does sexual reproduction introduce genetic variation
- mutations
- meiosis: shuffling of genetic information
disadvantages of sexual reproduction
- requires mate
- energy spent in the process
- only 1/2 of the population is capable of producing offspring
what are the 4 main differences between mitosis and meiosis
- number of divisions: mitosis=1, meiosis=2
- number of cells and their ploidy: mitosis=2 diploid, meiosis=4 haploid
- genetics: mitosis=genetically identical, meiosis=genetically unique
- type of cell: mitosis=somatic, meiosis=sex
describe the level of organization of a genome
- DNA makes genes
- genes make chromosomes
- chromosomes make a genome
define autosomes
- all except sex chromosomes
- homologous pairs: one similar chromosome from each parent
define sex chromosomes
- determines biological sex of individual
- heterologous chromosomes: differ in shape and organization
- X and Y in humans
define allele
- different variations of the same gene
- more than 2 alleles often exist for 1 gene
- creates genetic variation
do X and Y chromosomes share any similar regions
- yes
- pseudo autosomal regions
define ploidy
- measure of number of sets of chromosomes
- diploid: 2 sets (somatic cells)
- haploid: 1 set (gametes)
- polyploid: more than 2 sets (common in plants)
describe the ploidy of human somatic cells and gametes
- somatic cells: diploid, 2 sets of chromosomes (one from each parent), 46 chromosomes
- gametes: haploid, 1 set of chromosomes, 23 chromosomes
what ploidy do most animal cells have
diploid
what animals are haploid
- very rare
- male bees
- wasps
- ants
what animals are polyploid
- 2 species of birds
- 1 species of rat
- most common in insects, crustaceans, fish, reptiles, and amphibians
is there a correlation between genome number and organism complexity
no
do all animals have the same number of chromosomes
- no
- chromosome number is characteristic of a particular species
can species with different diploid numbers interbreed
- unlikely
- if they can the offspring are usually infertile due to uneven chromosome numbers
example of interbreeding species
- horse and donkey breed and produce a mule
- mule is infertile
- horse: 2n=64
- donkey: 2n=62
- mule: 2n=63 –> cannot form functional gametes
describe interphase in meiosis
- same as mitosis
- has G1, S, and G2 phase
- S phase replicates chromosomes and creates identical sister chromatids
what does meiosis result in
- reduction of chromosome number
- produces 4 haploid gametes: have single set of chromosomes
which part of meiosis do homologous chromosomes separate
meiosis 1
which part of meiosis do sister chromatids separate
meiosis 2
which part of meiosis reduces the cell from diploid to haploid
meiosis 1
explain prophase 1
- chromosomes condense and pair up
- synapsis: each chromosome aligns with its homologous partner so corresponding positions along chromosome are matching
- crossing over: homologues exchange part of their DNA
explain the process of crossing over in prophase 1
- homologous chromosomes pair up
- synaptonemal complex holds them together in synapsis: physical connection of chromosomes
- segments are exchanged through crossing over
what does the process of crossing over result in
- exchange of genetic information
- recombinant chromosomes: carry genes from two parents
what is the physical point where homologues are connected during crossing over in prophase 1 called
chiasmata
during which step in meiosis does crossing over occur
prophase 1
what is the group of 2 homologous pairs of chromosomes during meiosis 1 called
tetrad
explain prometaphase 1
- spindle fiber microtubules attach to the kinetochore proteins at the centromeres
- homologs still held together at chiasmata
- nuclear membrane completely broken down
explain metaphase 1
- spindles attached to chromosomes
- chromosomes line up in the center of the cell along the metaphase plate
- independent assortment of chromosomes along metaphase plate
define independent assortment in meiosis
- sister chromatids separate without influence from another chromosome
- random assortment of chromosomes (maternal and paternal) along metaphase plate during metaphase 1
during which phase of meiosis does independent assortment take place
metaphase 1
explain anaphase 1
- microtubules pull tetrads apart
- homologous pairs move toward opposite poles of the cell
- tetrads separate as chiasmata is broken but sister chromatids remain attached at the centromeres
define telophase 1
- separated chromosomes arrive at opposite poles
- nuclear membrane sometimes reforms and chromosomes decondense (depends on organism)
what is the result of meiosis 1
two haploid cells
explain meiosis 2
- division of sister chromatids
- very similar to mitotic division except sister chromatids are not genetically identical and resulting cells are haploid
what are the products of meiosis 2
- 4 haploid cells
- genetically unique
what are the two types of chromosome abnormalities
- disorders in chromosome number
- structural rearrangement of chromosomes
are chromosomes abnormalities typically severe or mild
- severe
- fatal
- result in miscarriages
define karyotype
- number and appearance of chromosomes
- length, banding pattern, centromere position
define nondisjunction
- occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis
- results in duplication or loss of chromosome
if there is nondisjunction during meiosis 1, how will the final cells be affected
- all will be affected
- 2 will have extra chromosome
- 2 will have one less chromosome
if there is nondisjunction during meiosis 2, how will the final cells be affected
- 2 cells will be affected
- 1 will have extra chromosome
- 1 will have one less chromosome
- 2 will be unaffected
define euploid
individuals with the appropriate number of chromosomes
define aneuploid
- individual with an error in chromosome number
- includes monosomy and trisomy
define monosomy
- loss of one chromosome
- lethal for all autosomes
define trisomy
- gain of extra chromosome
- most are lethal, some are not
describe x inactivation
- in each cell only one x chromosome is activated (only traits on that chromosome are expressed)
- tortoiseshell cats fur color
- allows nondisjunction with extra x chromosome to be less fatal
describe triple x syndrome
- XXX
- females with three x chromosomes
- 1 in 1000 births
- 90% undiagnosed due to x silencing/inactivation
symptoms of triple x syndrome
- taller than average
- increased risk of learning disabilities
- weak muscle tone
- behavioral and emotional difficulties
- cardiovascular and reproductive issues
describe turner’s syndrome
- X0
- females with only 1 x chromosome
- 1 in 2500 births
- more severe than triple x syndrome (95% don’t survive to birth)
symptoms of turner’s syndrome
- heart and kidney issues
- short stature
- webbing of neck
- infertility
describe kleinfelter syndrome
- XXY
- male with extra x chromosome
- 75% undiagnosed
- usually diagnosed when seeking medical advice for infertility issues
- can be treated with testosterone therapy
symptoms of kleinfelter syndrome
- infertility
- sparse facial hair
- enlarged breasts
- small testicles
- narrow shoulders
describe jacob’s syndrome
- XYY
- male with extra y chromosome
- 1 in 1000 males affected
- often diagnosed along with autism
symptoms of jacob’s syndrome
- attention difficulties
- delayed motor skills
- involuntary muscle movement
- emotional or behavioral issues
- taller than average
- prone to acne and skin irritation
what are the 4 types of chromosome structural rearrangements
- duplications
- deletions
- inversions
- translocations
explain chromosome duplications
- extra copy of a small piece of a chromosome
- ex: potocki-lupski syndrome
explain chromosome deletions
- deletion of segment of a chromosome
- ex: cri-du-chat
explain chromosome inversions
- detachment, 180-degree rotation, and reinsertion of part of a chromosome
- changes orientation of gene
- usually mild unless gene sequence is interrupted during detachment
explain chromosome translocations
- segment of chromosome breaks off and reattaches to different chromosome
- can be benign or devastating
- can be reciprocal: two non-homologous chromosomes exchange genetic information, no loss or gain of genetic information
