Biology 1115 Chapter 13
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Biology 1115 Chapter 13
Meiosis sexual life cycles
Meiosis and sexual life cycles
How are living organisms distinguished?
their own kind
What is genetics?
the scientific study of heredity and variation
What is heredity?
transmission of traits
from one generation to the next
How is variation demonstrated?
differences in appearance
that offspring show from parents and siblings
What is asexual reproduction?
one parent produces genetically
What is a clone?
a group of
individuals from the same organism
what is sexual reproduction?
two parents give rise to offspring that have
unique combinations of genes
inherited from two parents
units of heredity,
and are made up of
How are genes passed to the next generation?
(sperm and eggs)
one set of ___________ is inherited from each parent.
What is karyotype?
ordered display of the
pairs of chromosomes
from a cell
The two chromosomes in each pair are called ______________________.
What makes the two chromosomes in each pair homologous? (3)
controlling the same inherited characters
same banding pattern
What are the sex chromosomes called, who do they represent?
: females (XX)
: males (XY)
The 22 pairs of chromosomes that do not determine sex is called?
Each pair of
one chromosome from each parent
What is a diploid cell (2n)?
two sets of chromosomes
for humans, diploid number is 46
What is a haploid cell(n)?
single set of chromosomes
in humans, diploid number is 23
A gamete, sperm or egg, is haploid or diploid?
, single set of chromosomes
What is fertilization?
is when the
gametes come together
(the sperm and egg)
What is the fertilized egg called and what does it contain?
its called a
one set of chromosomes from each parent
The zygote produces somatic cells by ___________ and develops into an adult. (human life cycle)
At sexual maturity, the ovaries and testes produce what kind of gametes?
Gametes are the
type of human cells produced by ____________.
_________ and _________ alternate in sexual life cycles to maintain chromosome number.
In a cell where DNA synthesis has occurred, each chromosome is ___________.
What does each duplicated chromosome consist of?
It consists of
two identical sister chromatids.
What is the first step of meiosis?
replication of chromosomes
What does the two meiosis stages result in?
How many chromosomes does the daughter cell in meiosis have?
as many chromosomes
In general, what happens in the first cell division (meiosis 1)?
homologous chromosomes separate
What does meiosis 1 result in? what is this division called?
two haploid daughter cells
what happens in the second cell division (meiosis 2)?
sister chromatids separate
What are the results in meiosis 2? What is the division called?
four haploid daughter cells
it's called the
Meiosis 1 is preceded by interphase, what happens in this stage?
to form sister chromatids
What are centrosomes?
microtubules organizing centers
help organize chromosomes
What are two main things about sister chromatids?
and joined at the
What is the main difference between mitosis and meiosis?
conserves the number of chromosomes sets
, producing cells that are
to the parent cell
reduces the number of chromosome sets
from diploid to haploid, producing cells that
from parent cells
What are the three events that are unique to meiosis, and all three occur in meiosis 1?
synapsis and crossing
over in prophase 1
there are paired
, instead of individual replicated chromosomes
homologous chromosomes that are separated
instead of sister chromatids
____________ produces in sexual life cycles contributes to
What are mutations?
in an organisms DNA
Mutations create different versions of genes called?
________________ during sexual reproduction produces genetic variation?
Reshuffling of alleles
What are the three mechanisms that contribute to genetic variation?
independent assortment of chromosomes
How do homologous pairs orient at metaphase 1 of meiosis?
What happens in independent assortment?
the maternal and paternal homologues are separated into different daughter cells independently
What are the number of combinations possible when chromosomes assort independently into gametes?
where n is the
What does crossing over produce?
What is a recombinant chromosome?
combine genes inherited from each parent
Where does crossing over occur?
begins very early in
What happens in crossing over?
homologous portions of
two nonsister chromatids
How does crossing over contribute to genetic variation?
combining DNA from two parents into a single chromosome
How does random fertilization add to genetic variation?
any sperm can fuse with any ovum
How many possible chromosome combinations can the fusion of two gametes without crossing over produce?
What does natural selection results in?
results in the
accumulation of genetic variations favoured by the environment
Sexual reproduction contributes to the
in a population, which originates from _____________.
What is a life cycle?
is the generation-to-generation sequence of stages in the
of an organism
What is common to all organisms that reproduce sexually?
alteration of meiosis
In the animal life cycle, which are the only haploid cells?
The gametes fuse to form a?
The diploid zygote divides by __________ to develop a multicellular organism.
Which organisms exhibit an alteration in generation?
plants and some algae
What are the 2 stages the life cycle of plants and some algae include?
diploid and haploid multicellular stage
What is the
organism in a plant life cycle called? This organism undergoes __________to produce haploid spores.
Each spore in a plant life cycle grows by mitosis to produce a
A gametophyte makes
___________ of gametes results in a
In most fungi and some protists, the only
is the ?
What stage does the fungi life cycle NOT include?
multicellular diploid stage
In the fungi life cycle, the zygote produce haploid cells by?
In the fungi life cycle, each haploid cell grows by
, into a ?
haploid multicellular organism
In the fungi life cycle, the haploid adult produces gametes by?
Only_________ can undergo mitosis.
Which life cycle stage is found in plants but not animals?