Unit 7: Meiosis Flashcards
________ is nulcear division that leads to halving of _____________.
Meiosis is nuclear division that leads to halving of chromosome number.
What is fertilization?
Reproductive cells, sperm, and egg unite to form a new individual.
What are gametes?
They are reproductive cells.
How many chromosomes do gametes have?
Gametes must contain half the chromosome number.
When is the number of chromosomes that gametes have restored?
At fertilization, the full chromosome number is restored.
In meiosis, each diploid cell has ___________ chromosomes.
In meiosis, each diploid cell has two homologous chromosomes.
In meiosis, homologous chromosomes have identical _____ and ______ but may have different ______.
In meiosis, homologous chromosomes have identical genes and gene order but may have different alleles.
What is an allele?
An allele is a version of a gene. Each gene can have many different alleles. (Ex. You inherit two alleles for each gene one from your mother and one from your father. If you inherit a brown eye allele from one parent and a blue eye allele from the other, the brown allele (dominant) will determine your eye color.)
Homologous Chromosomes may contain different __________ of the same _____.
Homologous chromosomes may contain different alleles of the same gene.
What’s an example of alleles versus genes with eye color?
Homologous chromosomes can have two of the same genes that code for eye color. One allele for red eyes, the other gene for purple eyes.
What is a karyotype?
A karyotype identifies the number and types of
chromosomes present in a species.
What are diploid cells?
- They have two homologs of each chromosome.
- They have two alleles of each gene
What are haploid cells?
- They have only one of each type of chromosome.
- They have just one allele of each gene.
What is the purpose of mitosis?
Produce genetically identical cells for growth/maintenance.
Location of mitosis?
Somatic cells.
How many rounds of DNA replication/ cell division occur in mitosis?
One round of division following one round of DNA replication.
In mitosis, when do sister chromatids attach to spindle fibers?
Attach to spindle fibers from opposite poles in metaphase. Separate and migrate to opposite poles at anaphase.
What is the final product of mitosis?
Two genetically identical diploid daughter cells that continue to divide by mitosis.
What is the purpose of meiosis?
To produce gametes four sexual reproduction that are genetically different.
What is the location of meiosis?
Germ-line cells.
How many rounds of DNA replication/ cell division occur in meiosis?
Two rounds of division (meiosis I and meiosis II) following a single round of DNA replication.
In meiosis, when do sister chromatids attach to spindle fibers?
-Attach to spindle fibers from the opposite poles in metaphase I. Migrate to the opposite pole in anaphase I.
-Attach to spindle fibers from opposite poles in metaphase II. Separate and migrate to opposite poles in anaphase II.
What is the product of meiosis?
Four genetically different haploid cells that mature to form gametes and unite to for diploid zygotes.
What are chromosomes?
Structure made up of DNA and proteins; carries the cell’s
hereditary information
(genes).
What are sex chromosomes?
Chromosome associated
with an individual’s sex.
What are autosome chromosomes?
Any chromosome other
than a sex chromosome.
Example of sex chromosomes: _ and _ chromosomes of humans (male are __, females __).
X and Y chromosomes of humans (males are XY, females XX).
Example of autosome chromosomes in humans: Chromosomes _____ in humans.
Chromosomes 1-22 in humans.
What does an unreplicated chromosome look like?
A chromosome that consists of one double-helical molecule of DNA packaged with proteins.
What does a replicated chromosome look like?
A chromosome after DNA replication. Consists of two
identical chromatids, each containing one double-helical DNA molecule packaged with
proteins.
What are sister chromatids?
The two identical chromatids in a replicated chromosome.
What are homologous chromosomes?
Chromosomes that have the same genes in the same position and are
the same size and shape.
Why are homologous chromosomes not called identical chromosomes?
Because the alleles of particular genes are often different between the homologs, homologs are not called identical
chromosomes.
What are non-sister chromatids?
Chromatids on different members of a homologous chromosome pair.
What are bivalent chromosomes?
Paired, replicated homologous chromosomes that exist during prophase and metaphase of meiosis. Cross-over occurs between them.
What’s an example of a haploid cell?
Humans have 23 different types of
chromosomes (n = 23).
What’s an example of a diploid cell?
All human cells except gametes are diploid and contain 46 chromosomes (2n = 46).
What is ploidy?
The number of each type of chromosome.
What’s an example of ploidy?
The number of haploid chromosome sets present; shown by the number in front of n (for example, 2n).
What is haploid?
Having one of each type of chromosome (n).
What is diploid?
Having two of each type of chromosome (2n).
What is polyploid?
Having more than two of each type of chromosome; may be triploid (3n), tetraploid (4n), hexaploid (6n).
What happens in meiosis I?
In Meiosis I, homologous chromosomes pair and one copy gets passed to each haploid daughter cell.
What happens in meiosis II?
In Meiosis II, sister
chromatids separate into 2 new haploid daughter cells.
What are the phases of meiosis I?
- Prophase I (early)
- Prophase I (late)
- Metaphase I
- Anaphase I
- Telophase I
What happens in prophase I (early)?
Prophase I (early)
Synapsis and crossing
over occurs.
What happens in prophase I (late)?
Chromosomes condense,
become visible. Spindle
forms. Nuclear envelope
fragments. Spindle fibers attach to each chromosome.
What happens in metaphase I?
Paired homologous
chromosomes align
along equator of cell.
What happens in anaphase I?
Homologous
chromosomes
separate to opposite poles of cell.
What happens in telophase I?
Nuclear envelope assembles around chromosomes. Spindle disappears.
Cytokinesis divides cell into two.
What is synapsis?
Synapsis results in crossing over during Meiosis. Synapsis is the process in which homologous (bivalent) chromosomes pair up during Prophase I of Meiosis I.
In Meiosis I, homologous chromosomes pair
and _______ gets passed to each ______ ______cell
In Meiosis I, homologous chromosomes pair
and one copy gets passed to each haploid daughter cell.
In Meiosis II, _________ separate into 2 new _____________ cells.
In Meiosis II, sister chromatids separate into 2 new haploid daughter cells
What are the phases of meiosis II?
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
What happens in prophase II in meiosis II?
Prophase II Nuclear envelope fragments. Spindle forms and fibers
attach to both chromosome.
What happens in metaphase II in meiosis II?
Metaphase II Chromosomes align along equator of cell.
What happens in anaphase II in meiosis II?
Anaphase II Sister chromatids separate
to opposite poles
of cell.
What happens in telophase II in meiosis II?
Nuclear envelopes assemble around two daughter nuclei. Cytokinesis divides cells.
What is the result of meiosis II?
Four non-identical
haploid daughter
cells.
Fertilization _______ a
_______ Set of
Chromosomes.
Fertilization Restores a
Diploid Set of Chromosomes
What does ovulation have to do with meiosis?
All human eggs are arrested at an
early stage (prophase I) of the first meiotic division as a primary oocyte (cell in ovary before meiotic division).
Meaning: in human females, all eggs (oocytes) are paused in Prophase I of Meiosis I from before birth until they are selected for ovulation.
What hormone stimulates the completion of meiosis I of eggs?
Following puberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis I the day before ovulation.
When does an egg undergo meiosis II?
Only upon fertilization: If a sperm penetrates the egg, Meiosis II resumes and completes. If fertilization does not occur, the oocyte remains arrested and is eventually lost during
menstruation.
What are the critical periods of development and how do pharmaceutical drugs affect physical structures of development?
Ears, eyes, arms, legs, heart develop around 1-2 months same time drugs like thalidomide, accutane, and DES are recommended affecting development of fetal limb growth.
What percent of fetuses successfully come to term?
31%
What is the main cause why fertilized eggs don’t survive?
Of the fertilized eggs that do not survive, over half have chromosomal
abnormalities.
What is segregation in meiosis?
The process of separating homologous chromosomes in the first division and sister chromatids in the second division.
What is independent assortment?
Pairs of alleles for different genes will be sorted independently of one another when gametes are formed (inheritance of one trait doesn’t influence inheritance of another).
How many different chromosome combinations would there be for humans?
2^23 = 8,388,608
What results in various combinations of alleles?
Independent Assortment of Homologous Chromosomes.
What is down syndrome (trisomy 21)? How common is it?
Down syndrome is seen in about 1/700 live births in the United States. Caused by an extra copy of chromosome 21
What causes nondisjunction in meiosis?
If both homologs or both sister chromatids move to the same daughter cell, products of meiosis will be abnormal
What is trisomy as it relates to nondisjunction?
Gametes with an extra chromosome are n + 1 (trisomy)
What is monosomy as it relates to nondisjunction?
Gametes with a missing chromosome are n − 1 (monosomy).
What are haploid gametes?
Meiosis produces haploid gametes (egg & sperm) with half the
chromosomes.
What is genetic recombination?
Genetic recombination reshuffles DNA, creating unique individuals.
What does meiosis increase?
Meiosis increases variation, which drives adaptation & evolution
What is the purifying selection hypothesis?
Natural selection against deleterious alleles is called purifying selection.
What does purifying selection have to do with asexual reproduction?
In asexual reproduction, purifying selection is less efficient because offspring inherit all the mutations of the parent, making it harder to eliminate harmful mutations from the population.
What is the changing-environment hypothesis?
Offspring that are genetically identical to their parents are unlikely to thrive if the environment changes.
What does asexual reproduction have to do with changing environment hypothesis?
- Asexually produced offspring will be equally susceptible to that new strain.
- If offspring are genetically varied, some of them will likely have allele combinations to better resist the new strain and produce offspring.
Between the changing-environment hypothesis and the purifying selection hypothesis, which do studies support?
Studies support the changing-environment hypothesis: Genetic variation promoted by sexual reproduction may be favored in certain environments
How can we calculate the possible number of different gametes with different chromosome combinations?
The possible number of different gametes an individual can produce is given by: Numberofdifferentgametes =
2^𝑛 where 𝑛 is the haploid number of homologous chromosomes (the number of chromosome pairs).
Ex. if you had the chromosomes RR and rr and YY and yy, 2^2=4 possible combinations.
