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82 Cards in this Set
- Front
- Back
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What does meiosis mean |
Reduction division |
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Information about chromosomes |
- exist as single stranded structures intertwined to form the chromatin network - occur in homologous pairs called homologues - replicate during interphase of a cell cycle in between cell division to form 2 identical chromatids. These are joined by a centromere. This either takes place before cells divide by either mitosis or meiosis - only become visible when the chromosomes shorten and thicken as a cell divides |
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What is a centromere |
A specialized constricted region of a chromosome where the 2 chromatids are held together and to which spindle fibres attach during cell division |
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What does paternal mean |
Father |
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What does maternal mean |
Mother |
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What is meiosis |
Is a special type of cell division that takes place in the reproductive organs of both plants and animals to produce gametes in animals and spores in plants |
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How many divisions happen in meiosis |
2 |
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What happens during meiosis 1 |
Reproductive division which results in 2 cells being formed each with half the number of chromosomes of the parent cell ie. The haploid number ( n ) |
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What happen during meiosis 2 |
Is a copying division which involves the 2 haploid cells formed, each dividing by mitosis to form 4 daughter haploid cells |
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Steps of meiosis 1 |
reduction division - early prophase 1 - later prophase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - reduction division - early prophase 1 - later prophase 1 - metaphase 1 - anaphase 1 - telephase 1 - metaphase 1 - anaphase 1 - telephase 1 |
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What happens during meiosis 1 |
The first division separates the homologous chromosomes into 2 intermediate cells |
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What happens during early prophase 1 |
Early prophase 1 = the chromosomes condense becoming shorter and fat. They are visible as 2 chromatids joined by a centromere. |
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What happens during late prophase 1 |
- the chromosomes of homologous pairs lie alongside one another in a process called synapsis to form bivalents - the centromere move to opposite poles - a spindle, made up of protein threads develops across the cell from the 2 centrioles - the nuclear membrane breaks down - the chromatids can become entangled and exchange segments of chromosomes in a process called crossing over. |
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What is the process called when the chromosomes of homologous pairs lie alongside one another |
Synapsis to form bivalents |
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Centrioles |
Minute rod shaped bodies formed from the centrosome |
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Draw late prophase 1 |
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What happens during metaphase 1 |
- the bivalents move to the middle of the cell and line up of the equator in a way that is completely random - the centrosomes become attached to the spindle threads |
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Draw metaphase 1 |
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What happens during anaphase 1 |
- the bivalents separate and the homologues are pulled away from each other but the contracting spindle threads. This results in independent assortment of maternal and paternal chromosomes. One chromosome of each pair moves to the opposite poles |
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Draw anaphase 1 |
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What happens during telephase 1 |
The cytoplasm then divides ( cytokinesis) to form 2 haploid cells both of which have only 1 of each homologous pair of chromosomes |
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Draw telephase 1 |
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What happens during meiosis 2 |
Each of the haploid cells will divide again by mitosis so that the chromatids are pulled apart but thr number of chromosomes remains the same. This produces a large number of gametes |
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What happens during late prophase 2 |
- each chromosome is made up of 2 chromatids joined by a centromere - the centriole divides, forming 2 centrioles - a spindle develops between the centrioles which move to opposite poles - the nuclear membrane disappears |
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Draw late prophase 2 |
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What happens during metaphase 2 |
The chromosomes move to the middle of the cell where they line up at the equator. The centromere become linked to the spindle threads |
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Draw metaphase 2 |
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What happens during anaphase 2 |
The centromere split, allowing each chromosome to separate into 2 chromatids. Spindle threads contract and pull the chromatids apart. The chromatids, which are now called daughter chromosomes, move to opposite ends of the cell |
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Draw anaphase 2 |
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What happens during telephase 2 |
Daugheter chromosomes group together at the poles. A new nuclear membrane starts to form around each set of daughter chromosomes. |
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Draw telephase 2 |
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What is cytokinesis? |
Its the process whereby The cytoplasm starts to divide forming 2 new daughter cells, each with the haploid number of chromosomes. A new nucleolus forms and the daughter chromosomes form the chromatin network |
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Draw cytokinesis |
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What happens at the end of meiosis |
For new, non identical haploid gametes are formed from one parent cell each with half the original number of chromosomes. The gametes are not identical to the parent cell |
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2 sister chromatids make up what |
Chromosome |
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2 chromosomes make up what |
Homologous pairs |
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A pair of homologous chromosomes make up what |
A bivalent |
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Draw a picture of meiosis 2 |
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What is crossing over |
It is the mutual exchange of pieces of chromosomes so that the whole groups of Gene's are swapped between maternal and paternal chromosomes |
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When does crossing over take place |
- late prophase 1 - early metaphase 1 |
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Explain the process of crossing over |
- the replicated homologous pairs of chromosomes comes together in a process called synapsis to form bivalents. They swap pieces of their inner chromatids by breaking and rejoining their dna while they are paired up - the points of crossing over where the chromatids break are called chiasmata - in this way some Gene's frol a maternal chromatids change place with some Gene's from a paternal chromatid, forming a recombinant chromatid. Recombinants will result in offspring with genotypes unlike either parent. The outer, unchanged chromatids are called parentals |
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What is chiasmata |
When the points of crossing over where the chromatids break |
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What is the outer, unchanged chromatids called |
Parentals |
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Draw a picture of crossing over |
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Why is crossing over important |
- the exachnge of genetic material produces chromatid with a unique combination of genes. This increases genetic variation among individuals - during this exchange process, mistakes may occur which lead to mutations. |
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What is it called when the cells making up the body of an organism |
Somatic cells |
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In somatic cells these cells contains 2 sets of chromosomes for example |
Diploid ( 2n ) |
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In humans the diploid number is |
46 chromosomes |
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Why is meiosis called reduction division |
Because during the first meiotic division, the number of chromosomes is reduced from 2 sets ( diploid ) in the parent cell to one set ( haploid ) in each of the daughter cells ( gamete ) formed |
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What is gametogenesis |
When most animals and seed bearing p km ants are made by meiosis so that the number of chromosomes is halved |
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Formation of sperm is called and occurs where |
Spermatogenesis and occurs in testes |
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Formation of egg cells is called and where is it |
Oogenesis and in the ovaries |
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In seed bearing plants where does meiosis take place |
In the nathers and ovaries to produce haploid gametes |
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How do mosses and ferns differ |
an exception is found in primitive plants such as mosses and ferns where haploid spores are formed by meiosis in a diploid sporophyte generation. The spores develop into a haploid gametophyte plants. Specialized cells in the Male and female organs of this plants produce haploid gametes by mitosis. On fertilization the zygote develops into a diploid sporophyte |
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Importance of meiosis |
- in sexual reproduction, during the process of fertilization, the haploid egg cell fuses with a haploid sperm cell to form a diploid zygote with 2 sets of chromosomes. Therefore meiosis prevents the chromosome number doubling after fertilization
- various processed in a meiosis produce chromatids with a unique combination of Gene's. This provides genetic variation among individuals In a population |
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Variation? |
The difference which exist between organisms belonging to the same species |
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This variation of the offspring is caused by differences in their genetic code as a result of |
- crossing over of pieces of chromatids which causes a reshuffling of the Gene's in the gametes found
- the random lining up of maternal and paternal chromosomes on the equator of the cell during metaphase of meiosis - the sheer chance as to which particular sperm fertilizes an egg cell during fertilization - mutations which are sudden and unpredictable changes in the genetic code if an organism |
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What is independent assortment |
The random lining up of maternal and paternal chromosomes on the equator of the cell during metaphase of meiosis |
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What does abnormal meiosis result in |
Results in chromosome abnormalities and it can take place in several different ways |
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What is it called when the sex chromosomes fail to separate correctly during meiosis |
Chromosome non - disjunction |
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What is the condition called when fertilization involving one these abnormal gametes results in a zygote with either an extra or missing chromosome |
Aneuploidy |
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What does aneuploidy cause |
Causes various physical ams mental characteristics called syndromes |
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What is polyploidy |
Is a condition in which am organism has more than 2 complete sets of chromosomes in a cell |
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An example of aneuploidies |
Down syndrome |
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What is it called when children who are born with an extra copy of chromosome number 21 in their cells |
Trisomy |
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Who was down syndrome named after |
John langdon |
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How does down syndrome come about |
- during oogenesis, the 2 number 21 chromosomes do not separate properly during anaphase 1. This results in a egg with 2 number 21 chromosomes instead of 1 - if this egg is fertilized, the zygote will have 3 number 21 chromosomes and a total of 47 chromosomes in each cell instead of 46 - as the new embryo develops by mitosis, all the cells will have 47 chromosomes |
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The characteristics of down syndrome |
- mental retardation - distinctive flattened facial features with slightly slanting eyes - short stubby finger and toes - heart defects |
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What is maternal age effect |
With age the chromosomes seem to have more difficulty In separating |
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What problems do down syndrome children encounter |
- tend to grow and develop slower - some may need special classes - patronizing attitudes |
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What about aborting the fetus |
A new test, taken early in the pregnancy combined blood tests with and ultrasounds examination. This can identify whether the fetus has down syndrome 11 weeks after conception |
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What is amniocentesis |
A process whereby a small sample of fluid is removed from the amniotic cavity in the uterus |
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What is karyotype |
Is a computerized diagram of all the chromosomes in a cell during metaphase 1 |
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In the human karyotype in the next column |
- non sex chromosomes, autosomes, of a similar size are grouped together and places in groups A - G according to their length - sex organisms, gonosomes ( X - female, Y - Male ) are place separately |
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The normal human female contains 23 pairs of homologous chromosomes: |
- 22 pairs of autosomes - 1 pair of X chromosomes |
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The normal male contains |
- 22 pairs of autosomes - one Y chromosome - one x chromosome |
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Karyotypes are useful as they can show |
- whether a cell comes from a male or female - if there are abnormal chromosomes |
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Difference between mitosis and meiosis |
- where and when the process occurs - the purpose of the process - the difference in the process |
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Explain the difference where and when the process occurs for mitosis and meiosis |
MITOSIS: - takes place in plants and animals in the development of a zygote to an embryo and then cells continue to divide by mitosis to form a mature organism
- plants = takes place in meristemmatic tissue to bring about growth
- animals = takes place in many places, like the skin
MEIOSIS: - plants =takes place in the spotangia of the sporophyte generation
- animals = takes place in the reproductive organs, testes, ovaries in the formation of gametes |
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Explain the difference for the purpose of the process between mitosis and meiosis |
MITOSIS: - the purpose of mitosis is to keep the number of chromosomes in the daughter cells the same as the number of chromosomes in the parent MEIOSIS: - the purpose of meiosis is to halve the number of chromosomes, ie. The diploid number of chromosomes in the parent cells is reduced to the haploid number in the gametes or spores found. This is to prevent chromosome numbers doubling after fertilization in sexual reproduction |
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Mitosis cell division is involved in ? |
- development of an adult organism from a single zygote - growth and repair of tissues - regeneration of body parts - asexual reproductive |
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Difference in the process between mitosis and meiosis |
MITOSIS: - involves 1 cell division - in prophase: no bivalents formed and no crossing over - in anaphase: the centromere split and the chromatids of each chromosome separate and move to opposite poles of the cell - 2 daughter cells are formed with the same number of chromosomes - somatic cells are formed that are similar genetically to the parent cell MEIOSIS: - involves 2 cell divisions - in prophase 1: bivalents formed and crossing over takes place - in anaphase 1: centromeres do not split and the chromosomes of each homologous pair move to opposite poles - 4 daughter cells are formed, each with half the number of chromosomes of the parent cell ie. Haploid number - gametes are formed that are genetically different to each other and to the parent cell |
