diversity and selection (p1) Flashcards
include meiosis and mutations
diploid body cells
normal body cells have a diploid number of chromosomes (2n). two of each chromosome one from mum and one from dad. .
Gene __________ involve a change in the base sequence of
chromosomes. They can arise spontaneously during DNA
__________ and include base deletion and base substitution. Due to
the ______ nature of the genetic code, not all base
substitutions cause a change in the sequence of encoded amino
acids.___________ agents can increase the rate of gene mutation.
Gene mutations involve a change in the base sequence of
chromosomes. They can arise spontaneously during DNA
replication and include base deletion and base substitution. Due to
the degenerate nature of the genetic code, not all base
substitutions cause a change in the sequence of encoded amino
acids. Mutagenic agents can increase the rate of gene mutation.
Mutations in the number of chromosomes can arise spontaneously
by chromosome ______-__________ during meiosis.
Mutations in the number of chromosomes can arise spontaneously
by chromosome non-disjunction during meiosis.
Meiosis produces daughter cells that are genetically __________ from
each other.
Meiosis produces daughter cells that are genetically different from
each other.
The process of meiosis only in sufficient detail to show how:
*_____ nuclear divisions result usually in the formation of four
_________ daughter cells from a single diploid parent cell
* genetically _________ daughter cells result from the
independent _________ of homologous chromosomes
* ________over between homologous chromosomes results in
further genetic variation among daughter cells
The process of meiosis only in sufficient detail to show how:
* two nuclear divisions result usually in the formation of four
haploid daughter cells from a single diploid parent cell
* genetically different daughter cells result from the
independent segregation of homologous chromosomes
* crossing over between homologous chromosomes results in
further genetic variation among daughter cells
homologous pairs
chromosomes that make up a pair are same size and have same genes although may have different alleles these pairs of matching chromosomes are homologous pairs
gametes
sperm cells in males egg cells in females. have a haploid number of chromosome (n). one copy of each chromosome . Haploid number in humans is 23.
in sexual reproduction 2 gametes fuse together to form a ______ which divides and develops into a new organism
in sexual reproduction 2 gametes fuse together to form a zygote which divides and develops into a new organism
at fertilisation ______ sperm fuses with ______ egg forming a cell with a diploid number of chromosomes. Half from father half from mother
at fertilisation haploid sperm fuses with haploid egg forming a cell with a diploid number of chromosomes. Half from father half from mother
during sexual reproduction any sperm can fuse with any egg (its ________). It produces zygotes with a random combination of chromosomes from the parents .mixing of genetic material in sexual reproduction increases genetic _________ within a species.
during sexual reproduction any sperm can fuse with any egg (its random). It produces zygotes with a random combination of chromosomes from the parents .mixing of genetic material in sexual reproduction increases genetic diversity within a species.
meiosis vs mitosis
meiosis: produces haploid cells, daughter cells genetically different from eachother and parent cell,produces 4 daughter cells
mitosis:produce diploid cell, daughter cells are genetically identical to each other and the parent cell,produces 2 daughter cells
meiosis
1.before meiosis starts DNA replicates, forming 2 copies of each chromosome called chromatids
2.DNA condenses to form a double armed chromosome,made of two sister chromatids, that are joined by a centromere.
3.Meiosis I-chromosomes arranged themselves in homologous pairs
4. these homologous pairs are then separated halving the chromosome number.
5.meiosis II-pair of sister chromotids that make up a pair are separated (centromere is divided.)
6.2 haploid cells that are genetically different are produced
what happens in first meiotic division
chiasmata are formed (cross overs)
gamete mother cell is present
homologous chromosomes form pairs
what happens in the second meiotic division
haploid gametes are produces
chromatids separate
what 2 main events during meiosis lead to genetic variation
1.crossing over of chromatids
2. independent segregation of chromosomes.
crossing over of chromatids
.during meiosis I chromosomes come together and pair up. the chromatids twist around eachother and bits of the chromatids swap over
.chromatids still contain the same genes but a different combination of alleles.
.means each of the 4 daughter cell produced in meiosis II contain chromatids with different alleles.
dependant segregation of chromosomes.
-each homologous pair is made from one chromosome from mum and one from dad
-when homologous pairs are separated in meiosis I it is completely random what chromosome ends up in what daughter cell
-so each each of the 4 daughter cells produced in meiosis have completely combinations of maternal and paternal chromosomes.
-this is independent segregation of chromosomes
-this shuffling of chromosomes leads to genetic variation in any potential offspring
Gene mutations
invlove a change in the DNA base sequence of chromosomes and include
substitution,deltion,addition,duplication,inversion and translocation.
order of DNA bases in a gene determines the order of amino acids in particular protein. if a mutation occurs in a gene it can effect the amino acid it codes for
substitution
one base substituted with another
deletion
one or more bases are deleted
what can cause DNA mutations
errors in DNA replication
addition
one or more bases are added.
duplication
one or more bases are repeated
inversion
sequence of bases are reversed
