Variation and mutations Flashcards
1
Q
Heredity
A
study of inheritance and DNA replication, passing of traits from parent to offspring
2
Q
Eukaryotic cells
A
- complex
- membrane bound organelles
- what humans are made of
- DNA found in nucleus and mitochondria, chloroplasts for plants
- chromatin - complex consisting of DNA and histone proteins
3
Q
Karyotype
A
- complex set of organisms\
- in human cells (somatic) cells 23 pairs of chromosomes - paired and ordered
- matched pairs of chromosomes - autosomes and homologous pairs
- one pair of chromosomes
Visual representation of an individuals complete set of chromosomes
4
Q
Loci
A
a genetic location is called a locus
5
Q
cell division - eukaryotic cells
A
mitosis
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
6
Q
cell cycle
A
continuous
7
Q
mitosis
A
produces two separate, identical, diploid daughter cells
- short part of cell cycle
- 4 stages
- occurs in somatic cells
- for growth and repair
interphase occurs before mitosis
8
Q
interphase
A
prior to any cell division, a doubling of the genetic material needs to take place
9
Q
prophase
A
DNA replication - exchange of genetic material
1. chromatin threads condense to form chromosomes and visible under microscope
2. 2 sister chromatids held together by centromere
3. nuclear membrane disintegrates and the nucleus disappears
4. the mitotic spindle begins to form and is completed by the end of prophase. The spindle fibres attach to each chromosome at its centromere
5. the two centrosomes (each containing two centrioles) move towards opposite poles of the cell
- crossover occurs in prophase 1
10
Q
metaphase
A
- chromosomes move to centre of cell and line up along the equator of the cell
- the centromeres of the chromosomes are aligned on the equator
- the centrioles are located at opposite poles of the cell
- spindle fibres attach to the centromere
- independent assortment starts in metaphase 1
11
Q
anaphase
A
- cell membrane pinches off
1. spindle microtubules shorten and pull on centromere, sister chromatids separate
2. spindle microtubules pull on the sister chromatids to opposite poles of the cell
3. centromere, being attached to the microtubules (spindle fibres), is the first part of each chromosome to be pulled towards the poles. The ‘arms’ of each chromatid follow as they are pulled along by the centromere
4. at the end of this phase, each pole has a complete identical set of material and paternal chromosomes. (the genetic material doubles during the s phase, before the cell division started, so the amount of DNA at each pole is the same as the interphase parent in G1)
5. the sister chromatids are now referred to as chromosomes
12
Q
telophase
A
- chromosomes decondense to form chromatin, can no longer be seen under microscope
- two new nuclear membranes form, one of each daughter cell
- nucleoid reappear and the spindle apparatus disappears
- the cell elongates and a cleavage furrow forms to become ready for cytokinesis
13
Q
cytokinesis
A
completion of cell division
14
Q
cell division types in different cells
A
eukaryotic cells
- mitosis
- meiosis
prokaryotic cells
- binary fission
15
Q
binary fission
A
- simpler than mitosis
1. prior to binary fission, single chromosome is tightly coiled
2. genetic material in the chromosome and the plasmid replicated and separates
3. original and replicate chromosomes attach to cell membrane, are pulled to separate poles as cell elongates
4. new cell wall starts to grow, cleavage furrow develops in cell membrane
5. new cell wall fully develops
6. two cells separate, forming two identical daughter cells: cytokinesis. chromosomes become tightly coiled again - form of asexual reproduction
- far less DNA - much easier, simpler and faster to duplicate a prokaryotic cell
- no membrane bound organelles
16
Q
meiosis
A
17
Q
mutation
A
is a permanent change in the DNA sequence of a gene or chromosome that alters the nucleotide sequence. They are spontaneous, occurs during DNA replication, cell division
18
Q
mutations can occur in:
A
- somatic (body) cells, affecting only the individual
- germ-line (reproductive) cells, which can only be passed to offspring
19
Q
effects of mutations on survival
A
- negative/harmful: causes a change, damages the protein by nonsense or missense or frameshift
- neutral: no impact on phenotype, neither benefits or harms the gene sequence e.g. synonymous/silent mutations
- positive/beneficial: change that’s beneficial, can create new traits that benefit survival
20
Q
causes of mutations
A
- errors in DNA replication
- errors in cell division (mitosis/meiosis)
- mutagens
- biological agents
21
Q
mutagens
A
external physical or chemical factors that induce mutations
22
Q
physical mutagens
A
- UV light
- nuclear radiation
- X rays
23
Q
chemical mutagens
A
- nitric acid
- mustard gas
- colchicine
24
Q
biological agents
A
bacteria and viruses, and horizontal gene transfer
25
gene mutations
point mutations:
- substitution
- insertions
- deletions
26
point mutations in a gene
- single nucleotide within the original DNA sequence is affected by
- substitution
- insertions
- deletions
- a change to the bases in a codon can change the amino acid coded for. This then changed the protein for which the gene codes
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point mutations: substitution
results in either
- synonymous/silent - same amino acid
- missense - different amino acid
- or nonsense mutations - stop codon not supposed to be there - unfunctional
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point mutations: insertion and deletion
- frameshift - where they move from the left or the right meaning they don't match up properly
29
chromosome mutations
can affect many genes simultaneously.
some of the variations that occur with chromosomes, are quite natural in certain situations, therefore continuity of the species.
others arise because of anomalies that occur during the formation of the gametes
- variation in chromosome structure and number
30
variation in chromosome structure
abnormalities caused by chromosomal mutations may arise by:
- deletion
- inversion
- translocation
- duplications
31
deletion
part of strand removed
32
inversion
section of DNA been swapped/inverted (reversal of codon structure)
33
translocation
piece of one chromosome attached to another chromosome
34
duplications
codon attached to the end of it
35
variation in chromosome number
non-disjunction can occur through them all
- monoploidy
- polyploidy
- aneuploidy
36
monoploidy
involves a haploid number of chromosomes that act as a complete set, instead of diploid
- honey bees
37
polyploidy
occurs when an organism acquires one or more complete extra sets of chromosomes
38
aneuploidy
results of either a loss of one or more chromosomes due to an addition of one of more chromosomes
39
non-disjunction
- is the failure of chromosomes to separate properly during cell division
- when the two identical chromosomes do not separate, but go into the same cell
- occurs either during the first or second meiotic division - results in the formation of two types of gametes in equal proportions, but one type has two copies of a particular chromosome, and the other type has none
40
traits influenced by the environment
some traits that have the range of a phenotype given the same genotype
- height
- size
- skin colour
- flower colour
41
environmental factors that influence a phenotype
- temperature
- pH
- availability of food
- light exposure
- wind exposure
42
genetic variation
foundation of evolution
creates differences between individuals
- meiosis and sexual reproduction allow for genetic variation
- allows species to adapt to their environment through evolution
- 3 sources of genetic variation in sexual reproduction
- mutations - gene mutations and chromosome mutations
43
3 sources of genetic variation in sexual reproduction
Changes to the combination of maternal and paternal genes in the gametes during the meiosis process of cell division
- crossing over
- independent assortment
- random fertilisation
44
Crossing over
- during prophase 1, when the genetic material is condensing, and homologous chromosomes are close to each other. Non-sister chromatids (one maternal and one paternal join at a chiasma to switch sections of DNA strands. Results in 4, non-identical chromatids that will each go to a separate gamete
45
Independent assortment
- during metaphase 1, the homologous chromosome pairs align along the equator independent of other chromosomes. This means that anaphase 1, different amount of maternal and paternal chromosomes are separated to each side during the first division
46
Random fertilisation
The fusing of a male and female gamete to form a zygote. Given the large number of gametes produced (especially from males), any gamete (that has been individualised during the meiosis process) can join with each other
47
Fertilisation
Occurs in sexually reproducing organisms and is the joining of a male and female gamete. It results in a zygote that has gained one of each of its pairs of chromosomes from each parent
48
sources of genetic variation (not limited to sexual reproduction)
- mutations - gene and chromosome
- nondisjunction
49
allele
- different forms of a gene
- pairs of alleles are found on set of maternal and paternal homologous chromosomes
- a set of alleles (one from each parent) - genotype
50
dominant allele
(represented by a capital letter)
- always expressed in the phenotype
- mask a recessive allele
- same effect on the phenotype whether it is paired with another dominant allele of a recessive one
51
recessive allele
(represented by a lower case)
- only expressed in phenotype when present with the same allele (homozygous) e.g. ww
- masked by a dominant allele
52
Pure breed
- a pair of alleles - are identical (it is homozygous)
- either both dominant or both recessive
- pure breeds are used when studying inheritance and can be identified by a test cross
53
homozygous
- both alleles are the same (RR or rr)
- can be either dominant or recessive
54
heterozygous
- when both alleles are different (Rr)
55
genotype
- gene combination for a trait (e.g. RR, Rr, rr)
56
phenotype
- the physical feature resulting from a genotype (e.g. brown eyes)
57
Autosomal trait
- inherited on an autosome - a chromosome that is not a sex chromosome
- a gene on an autosomal - called autosomal
58
sex-linked trait
- inherited on a sex-chromosome (X or Y)
- a gene on a sex chromosome is called a sex-linked
- Y chromosome is short and contains relative few genes, most code for sex- related traits
- X chromosomes are longer and contain more genes, they carry genes for sexual development as well as for certain other traits
59
mendel's experiments
- he took a pure-breeding tall pea plant and crossed it with a pure-breeding short pea plant
- pure-breeding plants are ones that, when crossed among themselves, always give rise to offspring that are like parents
- was able to study the principles of genetics through careful observation of the phenotypes of pea plants and using selective breeding techniques. He found dominant traits masked recessive traits
60
punnet square
- table that displays all the possible offspring genotypes (given the parental alleles)
- can predict likelihood of producing a child with particular traits
61
monohybrid cross
involves a single trait which is controlled by only 1 pair of alleles at a single gene loci (monogentic inheritance) e.g. pea plant height
62
test cross
- if an organisms genotype is unknown, and is displaying a dominant phenotype, the genotype can be determined by performing a test cross
- the cross is usually with an organism that is homozygous recessive at the locus in question
- the ratio of phenotypes in the offspring reveals the unknown genotype
63
multiple alleles
- for most traits, there are more than two forms of alleles for a gene. This is known as multiple alleles
- in any one individual, only two alleles are normally present, a monohybrid. A multiple allele system is present when three or more alleles of a gene exist among the membranes of a population
- an example of this is seen in the ABO blood group system in humans. In the human population, there are three alleles possible for one gene
- there are four possible phenotypes, with no variation in between each blood group. This leads to discontinuous variation, because only one set of discrete phenotypic categories controlled by a single gene and its set of alleles
64
polygenetic inheritance
- for one characteristic, two or more genes and therefore two or more sets of alleles contribute to a phenoytype
- a characteristic controlled by more than one gene is known as a polygenetic characteristic, and its transmission is called polygenetic inheritance
