Chapter 13: Meiosis and the Sexual Cycle Flashcards
The study of heredity and hereditary variation
genetics
coded information
genes
segments of DNA
genes
similar to our
written language and passes specific information
from parent to child
sequence of nucleotides
how many genes are in chromosome?
100’s – 1000’s
The specific location of a gene on a
chromosome is known as its
locus
are the cells which transmit genes from one generation to the next
The gametes (sperm and ova)
characteristic of Asexual Reproduction
- Only 1 parent produces offspring
- Offspring are genetically identical to the
parent - Cloning via Mitosis
what type of cells use Asexual Reproduction
- Single-celled eukaryotes
- Multicellular organisms = budding
when an egg cell develops as an embryo without the need for any genetic material from a sperm cell
parthenogenesis
characteristic of Sexual Reproduction
- Meiosis
- fertilization
- Increases genetic diversity
- Creates unique individuals
what type of cells use Sexual Reproduction
most eukaryotic organisms.
Chromosomes that look alike , they
have the same length and shape
Homologous chromosomes
the shared genes that homologous chromosomes have that control the same inherited traits
alleles
the sex chromosomes
X and Y
determine the sex of an individual
the sex chromosomes
what chromosomes do females have?
homologous X sex chromosomes
what chromosomes do males have?
1 X and 1 Y chromosome
pair up
non homologous chromosomes
autosomes
how many autosomes and sex chromosomes not including sex chromosomes do gametes have?
22 = autosomes
1 = sex chromosome
how many chromosomes are in haploids?
23(only one set)
cells with only one set of chromosomes
haploid
cells with two sets of chromosomes
diploid
what is the fused gametes called?
zygote
The process in which the nucleus of a cell completes 2 successive divisions that
produce 4 nuclei, each with a chromosome number that has been reduced by half.
meiosis
the formation of gametes
meiosis
fusing of the nuclei of 2 gametes
fertilization
two divisions of meiosis
– Meiosis I
– Meiosis II
at stages are in Meiosis I and Meiosis II
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
what happens in meiosis I
homologous pairs separate
what happens in meiosis II
The 2 sister chromatids of each
chromosome are separated from each other
what happens in prophase I
– chromosomes condense
– nuclear envelope breaks down
– homologous chromosomes pair up = Synapsis
and form a tetrad
what happens in Metaphase I
- Pairs of homologous chromosomes are
moved to the equator of the cell. - The homologues, each made of 2 chromatids s
stay together.
what happens in Anaphase I
- Homologues separate
- The chromosomes of each pair are “pulled” to opposite ends of the cell.
- BUT (unlike in mitosis) chromatids DO NOT
separate at their centromeres. Each chromosome
is still composed of 2 chromatids joined by the
centromere - Non-disjunction could occur
An accident in chromosome separation
when one daughter cell receives both pairs
of chromosomes and the other daughter cell
receives none.
Non-disjunction
what happens in Telophase I
- Individual chromosomes gather at each pole of
the cell (2). In most cases, cytoplasm then
divides (cytokinesis) forming 2 new cells.
-reductive division.
Each of the cells produced
contain half the number of
chromosomes as the original cell. this is known as what?
reductive division.
what happens in Prophase II
- Each chromosome becomes attached to the
microtubules and starts moving toward its equator
what happens at Metaphase II
All chromosomes are now positioned at the equator
what happens in Anaphase II
Centromeres divide and the chromatids
NOW called chromosomes move to
opposite poles of the cell
what happens in Telophase II
- Four daughter nuclei form. When the cytoplasm divides each new cell is haploid (n). The original chromosome number has been reduced by half.
- One or all of these cells may become
gametes.
3 sources of genetic variation
- Independent Assortment
- Crossing-Over
- Random Fertilization
when is independent assortment done?
Metaphase I
the homologous pairs of chromosomes line up at the metaphase plate
-orientation random
Independent Assortment
when is crossing over (homologous chromosomes) happening
Meiosis (Prophase I)
segments of the chromosomes can exchange
segments of DNA.
-recombinant chromosomes
crossing over (homologous chromosomes)
genes inherited from both parents combined onto one chromosome
recombinant chromosomes
Area where crossover occurs is known as the
chiasmata
how many possible chromosome combinations are possible for a human ovum and sperm?
8.4 million
how many diploid combinations for the resulting zygote is possible
70 trillion
