Meiosis Flashcards
Chromosomes contain the genetic information which is passed from
generation to generation as genes
Each gene is a short length of a
chromosome
A gene is a
short length of a chromosome
A gene has an effect on the cell by
having the information to cause a protein to be made
What effect does the gene have on a cell
It provides the cell with information to make a protein
How many chromosomes do humans have?
46
Chromosomes can be ordered in pairs by
size and shape
ordered pairs of chromosomes are called
homologous pairs
Homologous pairs of chromosomes are called this because
they both have genes for the same characteristic
Pair 23 does what?
Determines the sex of the person
Pair 23 is called the
Sex chromosomes
If a person has two X chromosomes they are
female
If a person has an X and a Y chromosome they are a
male
The other 22 chromosome pairs that aren’t sex chromosomes are called
autosomes
Mitosis: Before a cell division every chromosome
replicates to give two chromosomes which are identical
Mitosis: Replication before mitosis ensures that
both daughter cells get a copy of every gene
Mitosis: Replication begins by unzipping the DNA molecule by
breaking the hydrogen bonds between the bases
This process of breaking the hydrogen bonds requires
Enzymes and Energy from ATP
Mitosis: Free DNA nucleotides join to the
exposed bases on both strands
Mitosis: The new nucleotides join with each other by
phosphate to deoxyribose sugar
Mitosis: This process produces two chromosomes that are
identical to each other
Meiosis is a type of cell division in which a gamete mother cell with 46 chromosomes produces
four cells with 23 chromosomes
Cells with only 23 chromosomes are called
haploid cells
When a haploid sperm fertilizes a haploid ova resulting in a
diploid zygote
Before meiosis each chromosome replicates to give
two identical chromatids joined by centromere
At the start of the first meiotic division the nuclear membrane
disappears to allow easy chromosome movement
At the same time the chromatids
shorten by coiling to prevent tangling
The spindle arranges the chromosomes along the
equator in homologous pairs
The homologous pairs may cross over points this is called
chiasmata
The spindle pulls one member of each homologous pair to
each pole at random
The random way in which 23 pairs of chromosomes are pulled to the poles is known as
independent assortment
Independent assortment leads to
great variation in the gametes produced
The cytoplasm is divided by a membrane giving two cells with
23 chromosomes, each made up of two chromatids
In the second meiotic division the chromosomes in both cells are lined up singly along the
equator by the spindle fibers
The chromatids are separated by the spindle fibres and
pulled to the poles of the cells
Cytoplasmic division by membranes gives
4 cells
Variation in gametes results from
the independent assortment of homologous chromosome pairs in the 1st division
Extra variation in gametes results from
chromosomes breaking at chiasmata and rejoining with a different chromosome
What processes ensure that every gamete used in conception is genetically unique?
Independent assortment and crossing over
