biology
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- Created by: ellenrosesenior123
- Created on: 22-04-14 22:36
Describe action of chromosones during phrophase I
Chromatin condenses and supercoils chromosomes shorten + thicken. Chromosomes come together in homologous pairs to form a bivalent. Non sister chromatids attach at points - chiasmata. Crossing over occurs - swap sections of chromatids.
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What happens in metaphase I
Bivalents line up across the equator of the spindle, attached to spindle fibres at the centromeres. Bivalents arranged randomly (random assortment) with each member of a homologous pair facing opposite poles. Chromosomes independently segregate when
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Describe action of nuclear envelope during prophase I
Nucleolus disappears and nuclear envelope disintegrates. A spindle forms made of protein microtubules.
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Describe action of chromosones and centromere during anaphase I
Homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles. Centromeres do not divide. Chiasmata separate and remain attached to chromatid.
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Describe action of nuclear envelope during telophase I
Two nuclear envelopes form - one around each set of chromosomes at each pole - cell divides by cytokinesis.
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Describe action of nuclear envelope and chromosomes during prophase II
If nuclear envelope reformed, it breaks down again. Nucleolus disappears chromosomes condense and spindles form.
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Describe action of chromosomes during metaphase II
Chromosomes arrange themselves on the equator of the spindle. They are attached to the spindle fibres at the centromeres.
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Describe action of chromosomes and spindle fibres during anaphase II
The centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres. Chromatids randomly segregate
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Describe action of nuclear envelope during telophase II
Nuclear envelope reform around the haploid daughter nuceli.
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Give a differnece between plant and animal teleophase II.
In animals the two cells divide giving four haploid cells. In plants a tetrad of four haploid cells form
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4 ways meiosis causes variation:
1. Crossing over. 2 Reassortment of chromosones.3 Reassortment of chromatids. 4. Mutation.
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Describe reassortment of chromatids.
Random distribution on spindle equator of the sister chromatids at metaphase II. due to crossing over sister chromatids no longer genetically identical. How they align at metaphase determines how they divide at anaphase II.
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Describe reassortment of chromasomes.
Random distribution of maternal and paternal chromosomes on spindle equator at metaphase I and segregation of into two daughter nuceli at anaphase I.
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What are three types of epistais
1. Dominant 2. Recessive epistais - 3. Complementary epistasis
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What is Complementary epistasis
One dominant allele for both gene loci have to be present to express a given phenotype.
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What is difference between dominant and recessive epistasis.
Dominant = homozygous recessive allele for a gene masks expression of dominant and recessive allele for another gene. Recessive =(dominant allele at one gene locus masks expression of alleles at a second gene locus.
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What are typical ratio for dominant epistais?
12:3:1 or 13:3
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What are typical ratio for recessive epistais?
9:3:4
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What are typical ratio for complementary epistais
9:7
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What are typical ratio for incomplete and complete codominance
1:2:1
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What is difference between incomplete and complete codominance
Incomplete - two different alleles that result in a third phenotype that is different from what parents originally had. Complete - Both characteristics passed on from parents and are present in phenotype.
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Define term linkage
Two or more genes that are located on the same chromosome - linked alleles normally inherited together because they do not segregate independently at meiosis, unless chiasmata have formed between them
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Other cards in this set
Card 2
Front
What happens in metaphase I
Back
Bivalents line up across the equator of the spindle, attached to spindle fibres at the centromeres. Bivalents arranged randomly (random assortment) with each member of a homologous pair facing opposite poles. Chromosomes independently segregate when
Card 3
Front
Describe action of nuclear envelope during prophase I
Back
Card 4
Front
Describe action of chromosones and centromere during anaphase I
Back
Card 5
Front
Describe action of nuclear envelope during telophase I
Back
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