Cell Reproduction

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what is an allele?
an allele is a version of a gene, a gene is a section of DNA that codes for a polypeptide chain. An allele of a gene translates into a slightly different polypeptide
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What is crossing over?
occurs during ptophase 1, homologous chromosomes pair up to form bivilents. The chromatids on each chromosome twist around each other, and swap over sections of DNA so sections contain the same genes but different alleles.
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how does crossing over lead to variation
genetic material is exchanged creating new versions of the gamete due to new combinations of alleles
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what is independant assortment?
occurs during metaphase 1, at the equator, homologous pairs of chromosomes arrange themselves in random order.
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what occurs during prophase 1?
chromatids condense to get shorter and thicker, synapsis occurs where sister chromatids come together to form bivilants(one paternal, one maternal chromosome) the nucleus disappears and nuclear envelope disintergtates centromeres move spindles form
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Metaphase 1
independant assortment occurs,where chromosomes line up on on the equator randomly. Spindle fibres attatch to centromeres. Microtubules attach to whole chromosomes
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Anaphase 1
homologous pairs in each bivalent are pulled apart to opposite poles by the contraction of spindle fibers. each chromosochromatidsme consists of 2 sister that may not be genetically identical due to crossing over.
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Telophase 1
2 nuclear envolopes form arounf each set of chromosomes at each pole, cells divide by cytokinesis and there is a breif interphase.
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Prophase 2
nuclear envelope breaks down, chromatids condense to descrete chromosomes. Spindle fibres form
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Metaphase 2
chromosomes line up on the equator, spindle fibres attatch to chromosomes by the centromeres. Chromosomes are randomly assorted
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Anaphase 2
chromatids are pulled apart centromere first, causing chromosomes to divide.
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Telophase 2
the nuclear envelope forms around haploid daughter chromosomes. Nucleoli reform and cytokineses occurs. Chromatids decondense,
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What is a genotype?
the genotype is the genetic make up of a organism in terms of the alleles it contains the phenotype is the observable characteristic e.g. eyecolour
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What is a dominant allele?
an allele is dominant if it is expressed in the phenotype, even in the presence of another allele
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What is a recessive allele?
an allele if recessive if it is only expressed int the phenotype in the absence of a dominant allele for the same gene
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What are co-dominant alleles?
alleles are co-dominant if they both contribute to the overall phenotype. No one is dominant or recessive.
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what is linkage?
refers to 2 or more genes that are located on the same chromosome, so the linked alleles are normally inherited together as they do not segregate unless crossed over. Reduces the number of phenotypes after a cross.
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What is sex linkage?
a characteristic is sec-linked if the gene that codes for it is found on one of the sex chromosomes. As males are semizygous, they only need one X to suffer some diseases. If the characteristic is on the non homologous region they only need 1>suffer
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Why are there no male tortie shell cats?
The co-dominant alleles for ginger and black colour are found on the homologous region of the X chromosome, so the male will only ever have one.
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What is epistasis?
the interaction of different gene loci so that one gene locus masks of suppresses the expression of another gene locus
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How can genes work antagonistically?
the homozygous presence of a recessive allele may prevent the expression of another allele at a second gene locus. Those that are dominant are epistatic, those that are masked are hypostatic,
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what is Recessive epistasis ?
If the recessive allele is epistatic, a 2 copies of the gene will block the expression of the other gene. Produces a 9:3:4 ratio. If there is no dominant allele, neither characteristic is shown.
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What is dominant epistasis?
If an epistatic allele is dominant, at least one copy of the allele will mask the espression of the other gene. Produces a 12:3:1 ratio
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Other cards in this set

Card 2

Front

What is crossing over?

Back

occurs during ptophase 1, homologous chromosomes pair up to form bivilents. The chromatids on each chromosome twist around each other, and swap over sections of DNA so sections contain the same genes but different alleles.

Card 3

Front

how does crossing over lead to variation

Back

Preview of the front of card 3

Card 4

Front

what is independant assortment?

Back

Preview of the front of card 4

Card 5

Front

what occurs during prophase 1?

Back

Preview of the front of card 5
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