Genetic diversity and adaptation

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What is mutation?
Any change to the quantity or the base sequence of the DNA of an organism
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What is a gene mutation?
Any change to one or more nucleotide bases, or change in the sequence of the bases
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What happens if a mutation occurs during formation of gametes?
May be inherited
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Remember:
Sequence of triplets on DNA is transcribed into mRNA & then translated into a sequence of amino acids that make up a polpeptide. Follows that any changes to one or more bases in DNA triplets result in change in the amino acid sequence of polypeptide
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Remember:
Gene mutations can arise spontaneously during DNA replication and include base substitution and base deletion.
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What is substitution?
Type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base.
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Give an example of substitution
Consider DNA triplet of bases (G,T,C) that codes for amino acid glutamine. if final base Cytosine replaced by Guanine then becomes GTG. GTG is 1 of the DNA triplet codes for the amino acid histidine & then replace the original amino acid: glutamine.
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The polypeptide produced will differ in a single amino acid. The significance of this difference will depend upon what?
The precise role of the original amino acid.
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What would happen to the amino acid sequence if the role of it was to form bonds to determine the tertiary structure of the final protein?
replacement of the amino acids may not form the same bonds, protein may then be a different shape and not function properly.
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What would happen to an enzyme if a mutation occurred?
As its a protein the amino acid sequence affects it tertiary structure so the active site may no longer fit the substrate and it will no longer catalyse the reaction.
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The effect of the mutation is different if the new triplet of bases still codes for the same amino acid before, why does it?
Degenerate nature of the genetic code, most amno acids have more than one codon?
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Define codon
Sequence of 3 bases on mRNA that codes for a single amino acid.
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Here is an example of how the mutation doesn't affect the DNA triplet code?
If 3rd base is replaced by thymine, then GTC becomes GTT. However, both DNA triplets code for glutamine, there is no change in the polypeptide produces and the mutation has no effect.
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When does a deletion arise?
A nucleotide lost from normal DNA sequence, loss of single nucleotide from the 1000s in typical gene may seem a minor change but consequences can be considerable. Usually the amino acid sequence of polypeptide is entirely different unlikely 2 functio
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What happens to sequence bases in the deletion?
Sequence of bases in DNA is read in units of triplets. One deleted nucleotide causes all triplets in a sequence to be read differently because each has been shifted to the left by one base.
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what are chromosome mutations?
Changes in the structure or number of whole chromosomes.
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Chromosome mutations can arise spontaneously and take 1 form which are and explain?
Changes in whole sets of chromosomes- occur when organisms have 3> sets of chromosomes rather than the usual 2. Condition called polyploidy and occur mostly in plants.
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Chromosome mutations can arise spontaneously and take 1 form which are and explain?
Changes in the number of individual chromosomes- sometimes individual homologous pairs of chromosomes fail to separate during meiosis- non disjunction and results in a gamete having either one more or one fewer chromosome.
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Define homologous pairs
1 chromosome of each homologous pair comes from mother ( a maternal chromo) and one comes from father (paternal chromo). Homologous chromosomes are similiar but not identical. Each carries the same genes in the same order, but different alleles.
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Example of non- disjunction
Down Syndrome where individuals have an additional chromosome 21.
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What is non-disjunction?
On fertilisation with a gamete that has the normal complement of chromosomes, the resultant offspring have more or fewer chromosomes than normal in all their body cells.
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Add purple box on page 221-223
Learn and remember
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2 ways of cell division
Mitosis produces 2 daughter cells with the same number of chromosomes as the parent cell and as each other.Meiosis usually produces 4 daughter cells, each with half the number of chromosomes as the parent cell.
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Define chromosomes
is a strand of DNA that is encoded with genes
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Whats the process of meiosis 1?
1st division homologous pair up & chromatids wrap around eachother.Equivalent portions of these chromatids maybe exchanged in process-crossing over. By end division the homologous pairs have separated, with 1 chromo from each pair going 1of2 daughter
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Whats the process of meiosis 2?
the chromatids move apart, at the end of meiosis 2, 4 cells have usually been formed. In humans each of these cells contain 23 chromosomes.
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Halving number of chromosomes, meiosis produces genetic variation among offspring, which may lead to adaptations that improve survival chances. Meiosis bring about this genetic variation in 2 ways what are they?
1) independent segregation of homologous chromosomes 2) new combinations of maternal and paternal alleles crossing over.
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What is a gene?
A length of DNA that codes for a polypeptide.
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What is a locus?
The position of a gene on a chromosome or DNA molecule.
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What is a allele?
One of the different forms of a particular gene.
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What is homologous chromosomes?
A pair of chromosomes, one maternal and one paternal, that have the same gene loci.
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What happens during sexual reproduction with gametes?
2 gametes fuse to give rise 2 new offspring. Each gamete has full set of chromosomes-dip, then the cell produce double.Dip num of chromo 46, which means that their would be 92 chromos. Doubling the num of chromos would continue at each generation
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In order to maintain a constant number of chromosomes in the adults species what happens to chromosomes?
the number of chromosomes must be halved at some stage in the life cycle. this halving occurs as a results of meiosis.
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when does meoisis occur in animals?
occurs in the formation of gametes.
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when does meoisis occur in plants?
gametes are produced by mitosis, in fern meiosis occurs in the formation of spores.
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Remember: Every diploid cell of an organism has 2 complete sets of chromosomes: one set from each parent.
During Meiosis, homologous pairs of chroms separate, so that only one chromosome from each pair enters a daughter cell. Haploid number of chromosomes which in humans 23. 2 haploid gametes fuse at fertilisation, diploid number of chromosome is restore
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Remember: Every diploid cell of an organism has 2 complete sets of chromosomes: one set from each parent.
During Meiosis, homologous pairs of chroms separate, that only one chromosome from each pair enters a daughter cell. Haploid number of chromosomes which in humans 23. 2 haploid gametes fuse at fertilisation, diploid number of chromosome is restored.
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Explain independent segregation of homologous chromosomes?
Meiosis 1 each chromo lines up alongside its homologous partner. Humans- 23 homologous pairs of chromosomes lying side by side. When homologous pairs arrange themselves in this line they do so at random. 1 of each pair will pass to each daughter cell
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Explain independent segregation of homologous chromosomes? (part 2)
1 of the pairs go into daught cell, with which one of any of the pairs, depends on how the pairs are lined up in the parent cell. Since the pairs lined up at random, the combination of chromos of maternal & paternal origin that go into daughter cell
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Explain how there is a variety from new genetic combinations?
Each member of homopair of chromo has exactly same genes & determines same characteristics- tongue rolling/ blood group.However alleles of genes may differ (code for roller/nonroller/ blood group A/B), independent assortment produce new genetic combo
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Explain the examples of chromosomes and the alleles of it?
1 of the pair chromosomes includes the gene for tongue tolling and carries one allele for roller and one for non. other chromo include gene for blood group and carries allele for group A and B.
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What happens to the homologous pairs in meoisis 1?
2 possible arrangements P&Q of 2 chroms at start meiosis. Both are equally probable, but each produces a different outcome in terms of characteristics may be passed on via gametes. End meiosis 1 the **** chromos have segregated into 2 separate cells
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arrangement of P produces the following types of gamete with alleles for:
roller and blood group B. non-roller and blood group A.
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Arrangement Q produces the following types of gamete with alleles for:
non roller and blood group B. roller and blood group A.
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Why does cells produces in meiosis are gametes that are genetically identical different? part 1
Result of different combins of maternal & paternal chromos/ alleles contained. Haploid gametes fuse randomly at fertilis. Haploid gametes produced by meiosis fuse to restore the diploid state. Each gamete has different makeup & their random fusion.
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hy does cells produces in meiosis are gametes that are genetically identical different? part 2
Therefore produces variety in the offspring. where the gametes come from different parents, 2 different genetic make ups are combined and even more variety results.
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Genetic recombination by crossing over, during meiosis 1 each chromosome lines up alongside its homologous partner. What will the following happen? (just 1 and 2)
Chromatids of each pair become twisted around one another. During twisting process tension created and portions of chromatids break off. the broken portions might then rejoin with chromatids of homologous partner.
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Genetic recombination by crossing over, during meiosis 1 each chromosome lines up alongside its homologous partner. What will the following happen? (just 3 and 4)
usually it is the equivalent portions of homologous chromsoe that are exchanged. in this wat new gentic combination of maternal and parternal alles are produced
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what is crossing over?
chromatids cross over one another many times.
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what is recombination?
The broken off portions of chromatid recombine with another chromatids.
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what is the effect of this recombination by crossing over on the cells produced at the end of meiosis?
all 4 cells produced have a different genetic composition, increasing genetic variety.
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If there is no recombination by crossing over what happens to the cells?
only 2 different cells are produced.
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How to calculate possible chromosome combinations following meiosis?
2n if 4 homologous pairs of chromsomes can produce 2(4)= 16 possible different combinations of chromosomes of maternal and paternal origin in its daughter cells as a result of meiosis.
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