Chap 9 Sexual Reproduction and Meiosis Flashcards
Asexual reproduction is relatively what?
rare
Which type of organisms reproduce asexually?
single-celled
What is required for sexual reproduction?
meiosis
Meiosis generates what?
a type of cell division that generates sperm and egg cells
Each sperm and egg cell is generally what?
unique
What lies at the heart of sexual reproduction?
specialized sex cells (sperm and egg)
Attracting a mate and producing sex cells requires what?
a lot of energy (which is costly to the organism)
Why is sexual reproduction worth the energy cost?
because it can create or maintain genetic diversity
Worms reproduce how?
sexually or asexually
The percent of worms producing sexually increased or decreased?
increased dramatically
Why did the percent of worms reproducing sexually increase?
the genetic variable offspring were better able to survive the bacterial infections
What are homologous chromosomes?
matched sets
A homologous pair of chromosomes have the same what?
size
structure
contain the same genes
Where do the pairs come from in homologous chromosomes?
one chromosome from father
one chromosome from mother
Diploid cell contain what?
two full sets of chromosomes
A sexually reproducing organism consists mainly of what?
diploid cells
Where do each chromosomes come from in diploid cells?
one full set from each parent
Homologous chromosomes carry the same what?
sets of genes
Are homologous chromosomes identical?
no
Why are homologous chromosomes not identical?
the nucleotide sequence is not the same
Each chromosome in a homologous pair has genes that are…?
for the same traits
arranged in the same order
Life cycles include what?
mitosis and meiosis
In multicellular organisms what is meiosis used for?
reproduce sexually
In multicellular organisms what is mitosis used for?
to grow and develop
Gametes are…?
haploid
Meiosis reduces what?
number of chromosomes by half
Hoe many chromosomes does each gamete have?
only one full set
Gametes are only haploid cells in?
out life cycle; all other cells are diploid
Are zygotes diploid?
yes
What does it mean that a zygote it diploid?
they have two full sets of chromosomes, one from each gamete
Zygotes undergo ? to develop into an adult.
mitosis
All body cells are genetically identical to what?
the zygote
What do haploid gametes give to offspring?
the right chromosome number
How many chromosomes in a sperm cell?
23
How many chromosomes in an egg cell?
23
How many chromosomes in a zygote?
46 (23 from sperm 23 from egg)
Meiosis and mitosis are similar, what are the similar phases each goes through?
interphase (before cell divides)
prophase, metaphase, anaphase, telophase (during cell division)
cytokinesis (at the end of cell division)
In meiosis what replicates once?
DNA
In meiosis what divides twice?
the nucleus
DNA replicates during what phase?
S phase (before cell starts to divide)
What divides in meiosis I?
germ cell
Where is the germ cell located?
testes/ovaries
What happens in meiosis II?
the new cells divide again without copying the DNA again
What happens in prophase I?
spindle forms
chromosomes condense and attach to it
What pairs up in prophase I?
homologous chromosomes
What happens only in meiosis?
each chromosome lines up next to its homolog
What process occurs in meiosis prophase I?
crossing over
What happens during crossing over?
pieces of homologous chromosomes physically change places
What happens in metaphase I?
chromosomes line up in two rows
How are the chromosomes lined up in metaphase I?
the spindle pulls each pair of homologous chromosomes into place
What process happens in metaphase I?
independent assortment
What is independent assortment?
chromosomes pairs align randomly, scrambling the combination of chromosomes for each gamete
How many types of homologous chromosomes?
two
A genotype is made of how many pairs of chromosomes?
3
How many possible versions of gametes are there?
8 (2^3)
What happens in anaphase I?
spindle separates the homologous chromosomes (not the sister chromatids)
What happens in telophase I?
chromosomes move to opposite sides of the cell, new nuclei form
What happens in cytokinesis I?
the cell splits into two new cells
The cells that split after cytokinesis each contain how many sets of chromosomes?
one set
What happens in meiosis II?
like mitosis, with no DNA replication
In meiosis II one diploid cell divides into…?
four haploid cells
Meiosis reduces what?
the number of chromosomes by half
Germ cells have how many sets of chromosomes?
two sets
In total how many chromosomes do germ cells have?
four
Gametes have how many sets of chromosomes?
one set
In total how many chromosomes do gametes have?
two
Random fertilization does what?
multiplies the diversity
Describe random fertilization?
any of the mother’s possible egg cells can combine with any of her mate’s possible sperm cells
What are monozygotic twins?
genetically identical
How is an identical twin formed?
an embryo (early in development) splits in two. each embryo the develops independently
What are dizygotic twins?
have unique DNA
How are fraternal twins formed?
two sperm cells fertilize two separate egg cells in the same pregnancy ( the twins’ DNA is no more similar than siblings that develop during separate pregnancies).
Mitosis and meiosis have different what?
functions
What are the functions of mitosis and meiosis?
mitosis - adds and replaces identical cells
meiosis - produces haploid gametes with unique DNA
When does nondisjunction happen?
anaphase I or anaphase II
What does nondisjunction do in anaphase I?
causes abnormalities in all gametes (e.g. missing or extra chromosome in zygote)
What does nondisjunction do in anaphase II?
causes some abnormalities in some of the gametes (some normal, some have missing or extra chromosome in zygote)
Down syndrome is caused by what?
nondisjunction
What is genetically the cause of down syndrome?
an extra copy of a chromosome (a trisomy)
How many chromosomes too many do individuals with down syndrome have?
one extra (have three copies of chromosome 21 rather than 2)
Which chromosome is there extra of in an individual with down syndrome?
chromosome 21
