Meiosis and mutations Flashcards
What does diploid mean?
cells where the nucleus has two sets of chromosomes
What does haploid mean?
cells that only have one copy of each chromosome
What is a homologous pair?
a pair of chromosomes, one maternal and one paternal, that have the same gene loci and determine the same features
What is meiosis?
the type of cell division where the number of chromosomes is halved- results in 4 non- genetically identical daughter cells
What is a chromatid?
one of the arms of a chromosome
What is a centromere?
joins the chromatids together to make a chromosome
What is independent segregation?
randomly shuffled homologous pairs- each chromosome is inherited randomly, and independent of each other- inheritance of one does not impact inheritance of another
What is recombination/crossing over?
happens when the chromatids of a bivalent get twisted, and breaks occur, meaning parts of the chromatids are exchanged between homologous pairs. it happens at random and is very rare/infrequent
What is a mutation?
a change in the amount or structure of DNA
What is acquired mutation?
occurs in cells after conception
What is hereditary mutation?
a gene change in a gamete that becomes incorporated into the DNA in every cell of the body of the offspring
What are the two types of mutation?
a gene mutation- a change in the base sequence of the gene, which can cause a change in the polypeptide chain. it is caused by errors during DNA replication
a chromosome mutation- a change in the number or structure of the chromosomes. it is caused by errors during cell division
What is substitution?
when one of the bases is swapped for a different base- DOES NOT RESULT IN FRAME SHIFT- but could change the amino acid it codes for
What is deletion?
the removal/deletion of a base in a sequence, causing a frame shift to the left
What is addition?
the addition of a base in a sequence, causing frame shift to the right
What is frame shift?
when, due to the addition or deletion of a base, the subsequent triplet codes are all altered, due to it being read in 3s
What is a mutagenic agent?
a chemical, biological, or physical agent that causes changes to the DNA of a cell
Name 4 mutagenic agents
-x-rays
-gamma rays
-benzene derivatives
-mustard gas
What are the stages of meiosis?
prophase I
metaphase I
anaphase I
telophase I
prophase II
metaphase II
anaphase II
telophase II
What happens in interphase?
DNA is replicated, the cell grows, and organelles are synthesised
What causes variation in a species?
crossing over
independent segregation
What is the chiasma?
the point of crossing over
When does crossing over happen?
only in prophase I
How does independent segregation happen?
homologous pairs attach to spindle fibres opposite each other in a random order, and the maternal and paternal chromosomes are not always on opposite sides. it only happens during metaphase I.
How does independent segregation lead to variation?
the daughter cells will contain different, random assortments of the randomly separated chromosomes, so the gametes aren’t genetically identical
How do you calculate how many variations there could be in meiosis due to independent segregation?
2^n –> where n equals the number of pairs
example- 2 pairs - 2 ^2 = 4 variations
What is the point of meiosis I?
to separate the homologous pairs
What is the point of meiosis II?
to separate the chromatids of the chromosomes
What happens in prophase I?
chromosomes condense and shorten, and homologous chromosomes pair to form a bivalent
CROSSING OVER CAN HAPPEN HERE
Compare meiosis to mitosis
meiosis-
-2 cell divisions
-4 daughter cells produced
-not genetically identical daughter cells
-gametes created
-crossing over can occur
mitosis-
-1 cell division
-2 daughter cells produced
-genetically identical daughter cells
-sematic cells created
-crossing over cannot occur
When presented with a life cycle question, what is happening when it goes from 2n –> n?
meiosis, it is going from diploid to haploid
When presented with a life cycle question, what is happening when it goes from n–> 2n?
fertilization, it is going from haploid to diploid
How do you calculate the number of possible chromosome combinations produced from the fertilization of two gametes?
(2n)^2
where n equals the haploid number/ how many pairs there are
you must square it as you are joining gametes together
What is non-disjunction?
when chromosomes fail to separate correctly during meiosis
What is it called when you have extra whole sets of chromosomes?
polyploidy
What happens when an organism has odd numbers of chromosomes?
the organism tends to be infertile as you cannot evenly half the them to form gametes
When can’t you form gametes?
if you can’t form homologous pairs
When could non-disjunction happen?
in meiosis I during the splitting of the homologous pairs
or
in meiosis II during the splitting of the chromosomes into chromatids
What increases the chance of non-disjunction?
older age
