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75 Cards in this Set
- Front
- Back
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Meiosis |
- Introduces an enormous amount of diversity - More than 70 trillion different genetic combinations possible from the mating of two individuals - Males/females differ in the way they form gametes - Sperm production begins at puberty, egg production start before birth and ends at menopause |
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Meiosis |
- Special type of cell division - Used only for sexual reproduction - Chromosomes are replicated in S phase of interphase and then halved prior to fertilization - Diploid (2n) parents produce haploid (n) gametes |
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Haploid Cells |
Contain single set of chromosomes - Such as gametes |
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Gametes |
Fuse in fertilization to form a diploid (2n) zygote to become the next diploid generation - Ex: sperm, eggs |
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Gametes contain the wrong number of chromosomes |
If meiosis goes wrong, then what happens to the gametes? |
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Homologues (Homologous chromosomes) |
Chromosomes of the same type - Have the same length - Centromeres are positioned in the same place - One came from the father and other from mother - Show similar banding patterns when stained |
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Chromosomes occur in pairs |
In diploid body cells, chromosomes occur in __________? |
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23 |
Humans have ______ different types of chromosome |
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Two chromosomes of each type |
Diploid (2n) cells have _______ chromosomes of each type |
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Homologous Chromosomes |
- Have genes controlling the same trait at the same position, in which the gene occurs in duplicates, one copy each from mother and father - May encode identical or different genetic information |
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Genes |
- Code for different traits - Exist in several variant forms in a large population |
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Alleles |
Variants that exist for a gene |
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Homozygous for the trait |
Identical alleles for a specific gene on both homologues |
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Heterozygous for the trait |
Maternal allele that differs from corresponding paternal allele |
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Meiosis I Meiosis II |
Meiosis has ______ nuclear divisions |
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Meiosis I |
- Chromosomes are replicated prior to meiosis I in S Phase; consist of two identical sister chromatids - Homologous chromosomes pair up in synapsis and may recombine or exchange genetic material - Homologous pairs align themselves at metaphase plate and then separate so each daughter cell receives one duplicated chromosome from each pair From 2n to n |
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Meiosis II |
- Mitosis of two haploid cells - Gamete formation - DNA is not replicated - Sister chromatids separate and move to opposite poles - 4 daughter cells contain one daughter chromosome from each pair - Each daughter chromosome consist of a single chromatid - Daughter cells are haploid |
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- # Nuclear Division - Synapse - Centromeres - Chromosome Number - # of daughter nuclei - Genetics - Type of reproduction |
Differences between meiosis and mitosis (7) DSCCNGR |
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Synapsis |
Fusion of homologous chromosome pairs at the start of Meiosis I |
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Fertilization |
- Union of male and female gametes - Chromosomes donated by the parents are combined - (2^23)^2 = 70 trillion different zygotes possible without any crossing over |
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Asexual reproduction |
- Produces genetically identical clones - Advantageous when environment is stable - These types of organisms depend on mutations to generate variation in offspring |
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Sexual Reproduction |
- Causes genetic recombinations among members of a population - If environment changes, genetic variability may by advantageous |
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Prophase I |
- Spindle forms - Nuclear envelope fragments - Nucleolus disappears - Homologous chromosomes pair up and physically align themselves against each other side by side (synapsis) - Synapsed homologs are referred to as a bivalent (two homologues) or a tetrad (four chromatids) |
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Metaphase I |
- Homologous pairs are arranged at the metaphase plate by microtubules attaching to kinetochore of one chromosome - Synapsed homologues aka Bivalents (or tetrads) are aligned at the spindle independently of one another |
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Anaphase I |
- Homologous chromosomes of each bivalent separate from one another - Homologues move towards opposite poles - Sister chromatids do not separate - Each is still a duplicated chromosome with two chromatids (Reduction of chromosome number from 2n to n) |
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Telophase I |
Daughter cells have one duplicated chromosome (n) from each homologous pair |
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Interkinesis |
- Two haploid (n) daughter cells, each with one duplicated chromosome of each type - Similar to interphase but shorter and no DNA replication |
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Prophase II |
- Nucleolus disappears - Chromosome condense - no longer in homologous pairs - Spindle apparatus forms |
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Metaphase II |
- Chromosomes align at metaphase plate, microtubules attach to kinetochores - They are no longer in homologous pairs |
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Anaphase II |
- Centromere dissolves - Sister chromatids separate toward opposite poles and become daughter chromosomes that are not duplicated |
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Telophase II and Cytokinesis |
- Produces 4 Haploid (n) cells that are all genetically unique - Gametes containing a mixture of maternal and paternal genes (2 Phases) |
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Genetic Variation |
- Essential for a species to evolve and adapt in a changing environment - Asexually reproducing organisms depend on mutations for this - Brought over by meiosis through crossing over between homologous chromosomes and independent assortment of homologous chromosomes |
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Crossing over |
- Exchange of genetic materials between homologous chromosomes- May occur several times in each chromosome - Involves exchange of genetic material between non sister chromatids during Prophase I - At synapsis, the synaptonemal complex appears between homologues that hold them together - Homologues separate and are distributed to different daughter cells |
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Independent assortment |
- When homologous chromosome pairs align at the metaphase plate, they separate in a random manner, may be oriented toward either pole of mother cell - Causes random mixing of blocks of alleles into gametes - Possible chromosome orientations for a cell with 3 pairs of homologous chromosomes is 2^3 combinations of materal and paternal chromosomes |
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Parthenogenesis |
- Form of reproduction in which only one parent contribute genetic information to the next generation - Individuals are produced from unfertilized eggs |
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Parthenogenic Lizards |
- Crossing over occurs during meiosis between sister chromatids (instead of non-sister chromatids) - The species double the number of chromosomes prior to meiosis forming a pair of homologues from a single parent - Because of slight differences in the sister chromatids, small amount of variation is passed on to next generation What type of animal? |
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Mitosis |
- Requires 1 nuclear division - Chromosomes do not synapse or cross over - Centromeres dissolve in mitotic anaphase - Preserves chromosome number - Produces 2 daughter nuclei - Produces genetically identical daughter cells - For asexual reproduction and growth |
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Meiosis |
- Requires 2 nuclear division - Chromosomes synapse and cross over - Centromeres survive Anaphase I - Halves chromosome number - 4 Daughter nuclei - Genetically different daughter cells - For sexual reproduction |
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Stages (Involved in sorting and division of chromosomes) Spindle fibers (Play active role in sorting chromosomes) Cytokinesis (Divide cytoplasm between daughter cells) |
3 Similarities of Meiosis and Mitosis |
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Meiosis II Anaphase II |
Phase of Meoisis II where sister chromatids separate, becoming daughter chromosomes that move to the poles (Same as Mitosis) |
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Life Cycle |
Reproductive events that occur from one generation to the next similar generation |
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Alternation of Generations |
In plants, where haploid "individuals" called gametophytes alternate with diploid "individuals" called sporophytes |
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Gametophyte |
- Haploid individual alternating in plants |
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Sporophyte |
- Diploid individual alternating in plants |
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Mosses |
What type of plant is mostly haploid for their life cycle? |
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Fungi and most algae |
In what plants (2) is the zygote only diploid? |
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Ferns |
Which plant is diploid for most of its life cycle? |
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Plants, algae and fungi gametes |
3 Types of organisms that is produced by haploid individuals |
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Animal Cycle of Life |
- Individuals are diploid and produce haploid gametes - Haploid part of life cycle is the gametes - Products of meiosis are always gametes - Meiosis occurs only during gametogensis |
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Gametogenesis |
Production of gametes (sperm and eggs) |
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Spermatogenesis |
- All 4 daughter cells from meiosis become sperm - Testis contain stem cells called spermatogonia which make spermatocytes that undergo spermatogenesis - After meiosis II spermatids form that differentiate to form sperm |
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Oogenesis |
- Production of eggs - One of the 4 daughter cell's nuclei receives the majority of the cytoplasm and becomes the egg or ovum - The others wither away as polar bodies - Ovaries contain stem cells called oogonia which produce primary oocytes which begin oogenesis but only a few continue at sexual maturity- Secondary oocyte begins meisosis II but stops at metaphase II, leaves ovary, and enters uterine tube- If there is no sperm, degenerates- If there is sperms, triggers oocyte to ccomplete meiosis II and another polar body forms |
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Human Life Cycle |
- Sperm and egg produced by meiosis in spermatogenesis and oogenesis - Gametes fuse at fertilization - Results in zygote (Which undergoes mitosis for growth) - Each somatic cell in body thus has same number of chromosomes and genetic makeup as original zygote |
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True |
Meiosis almost always proceeds normally. True/False? |
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Euploidy |
Correct number of chromosomes in species |
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Aneuploidy |
- Change in chromosome number - Results from nondisjunction, failure of chromosomes to separate |
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Karyotype |
Display of chromosomes arranged by size, shape, and banding pattern for observing aneuploidies |
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Nondisjunction |
- Failure of chromosomes to separate - Can occur in meiosis I or meiosis - May result in gain or loss of chromosomes - Ex: Monosomy, Trisomy |
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Monosomy |
- Type of nondisjunction where there is only one of a particular type of chromosome |
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Trisomy |
- Type of nondisjunction where there are three of a particular type of chromosome - 3 Autosomal ___________s are possible beyond birth - Most common in humans is __________ 21. |
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Trisomy 21 |
- Also called down syndrome - Changes increase with mother's age (Since oocytes are stored longer - nondisjunction) - Recognized by the following characteristics: Short stature, eyelid fold, flat face, stubby fingers, wide gap between first & second toes |
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Changes in sex chromosome number |
- Results from inheriting too many or too few X or Y chromosomes - Extra copies of sex chromosomes more easily tolerated than autosomes - Nondisjunction during oogenesis or spermatogenesis - Ex: Turner Syndrome, Klinefelter syndrome |
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Turner Syndrome (XO) |
- Female with single X chromosome - Short with broad chest and widely spaced nipples - Can be of normal intelligence and function with hormone therapy |
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Klinefelter syndrome (XXY) |
- Male with underdeveloped testes and prostate; some breast overdevelopment - Long arms, legs; large hands - Near normal intelligence unless XXXY, XXXXY, etc - No matter how many X chromosomes, SRY gene results in maleness as a testis determing factor |
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SRY gene |
- The presence of this gene determines maleness, testis determining factor and male genital development |
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Mutation |
Environment agents like radiation, organic chemicals or certain viruses can cause chromosome breakage, which, if they don't rejoin, results in ________________ |
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Deletion Duplication Translocation Inversion |
Changes in chromosome structure (4) |
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Deletion |
- One or both ends of a chromosome breaks off - Two simultaneous breaks lead to loss of an internal segment - Change in chromosome structure |
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Duplication |
- There is a presence of a chromosomal segment more than once in the same chromosome - Change in chromosome structure |
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Translocation |
- Segment from one chromosome moves to non-homologous chromosome - Follows breakage of two non-homologous chromosomes and improper re-assembly - Change in chromosome structure |
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Inversion |
- Occurs as a result of two breaks in chromosome - Internal segment is reversed before reinsertion - Genes occur in reverse order in the inverted segment - Change in chromosome structure |
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Human syndromes |
- Changes in chromosome structure can cause various _______________ and can be detected in a karyotype or by studying an inheritance pattern in a family |
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Williams Syndome |
- Type of deletion syndrome where there is a loss of the end of chromosome 7, which contains the gene for elastin - Children resemble pixies |
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Alargile Syndrome |
- Type of translocation-caused syndrome where a translocation between chromosome 2 and 20 which can lead to a congenital heart defect called tetralogy of fallot |
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Chronic myelogenous leukemia |
- Type of translocation caused syndrome that is a blood cancer caused by a translocation between chromosomes 22 and 9 |
