genetics quiz jan 23

8/2/2019 Genetics Quiz Jan 23

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4.1.1 State that eukaryote chromosomes are made of DNA & protein

Eukaryote chromosomes are made of DNA & protein

4.1.2 Define gene, allele & genome

Gene: a heritable factor that controls specific characteristics

Allele: one specific form of a gene, differing from other alleles by one or a few bases only &

occupying the same gene locus as other alleles of that gene

Genome: the whole genetic information of the organism

4.1.3 Define gene mutation

Gene mutation: a randhom rare change in the base sequence of an allele. This change in the DNA

base sequence can result in an alteration of mRNA during transcription.

4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of

transcription & translation, using the example of sickle cell anaemia

Consequences of base substitution mutation means that the wrong amino acid is placed on the

growing polypeptide chain

Sometimes this mutation is found in the gene that creates hemoglobin

The shape of the molecule changes, they look pinched in the middle

The codon GAG becomes GTG, during translation instead of adding glutamic acid, valine is

added instead = different shape

4.2.1 State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei

Meiosis is a reduction division of a diploid nucleus to form haploid nuclei

4.2.2 Define homologous chromosome

Homologous chromosome: are similar in shape & size & they code for the same gene. Two exist

because one comes from the father & one comes from the mother.


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4.2.3 Outline the process of meiosis, including pairing of homologous chromosomes & crossing

over, followed by two divisions, which results in four haploid cells

Meiosis involves two divisions. Meiotic cells have an interphase stage before the start of meiosis I

which is similar to mitosis. It includes G1, S and G2 phases. (See notes on mitosis) After meiosis I

there is another brief interphase stage, which is followed by meiosis II.


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4.2.4 Explain that non-disjunction can lead to changes in chromosome number, illustrated by

reference to Downs syndrome (trisomy 21)

Trisomy 21: three copies of chromosome 21 During meiosis the sister chromatids have not been separated (non-disjunction) so that the

gamete has had 24 chromosomes (23 + i extra chromosome number 21)

At fertilisation when the chromosomes form new homologous pairs the 21stpair actually isa triplet

Chromosome 21 shows trisomy4.2.5 State that, in karyotyping, chromosomes are arranged in pairs according to their size &

structure

In karyotyping, chromosomes are arranged in pairs according to their size & structure

4.2.6 State that karyotyping is performed using cells collected by chorionic villus sampling or

amniocentesis, for pre-natal diagnosis of chromosome abnormalities

Karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for

pre-natal diagnosis of chromosome abnormalities

4.2.7 Analyse a human karyotype to determine gender & whether non-disjunction has occurred

Karyotyping can be carried out when chromosomes from metaphase are available Y chromosome is smaller than X XX= female, XY= male

4.3.1 Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus,

homozygous, heterozygous, carrier & test cross

Genotype: the alleles of an organism.

Phenotype: the characteristics of an organism.

Dominant allele: an allele that has the same effect on the phenotype whether it is present in the

homozygous or heterozygous state.

Recessive allele: an allele that only has an effect on the phenotype when present in the

homozygous state.

Codominant alleles: pairs of alleles that both affect the phenotype when present in a

heterozygote.

8Locus: the particular position on homologous chromosomes of a gene.


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Homozygous: having two identical alleles of a gene.

Heterozygous: having two different alleles of a gene.

Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in

individuals that are homozygous for this allele.

Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive.

4.3.2 Determine the genotypes & phenotypes of the offspring of a monohybrid cross using a

Punnett grid

4.3.3 State that some genes have more than two alleles (multiple alleles)

Some genes have more than two alleles (multiple alleles)

4.3.4 Describe ABO blood groups as an example of codominance & multiple alleles

Phenotype Genotype

A IAIA

or IAi

B IBIB

or IBi

AB IAIB

O ii


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4.3.5 Explain how the sex chromosomes control gender by referring to the inheritance of X&Y

chromosomes in humans

Sex chromosomes determine gender the X and the Y chromosome Therefore gender depends on whether the sperm which fertilizes the egg is carrying an X or a Ychromosome.

X chromosome is bigger than the Y Y chromosome contains a few genes, X contains many The female always passes on to her offspring the X chromosome from the egg (female gamete).The male can pass on either the Y or the X chromosome from the sperm (male gamete).4.3.6 State that some genes are present on the X chromosomes & absent from the shorter Y

chromosome in humans

Some genes are present on the X chromosomes & absent from the shorter Y chromosome in humans

4.3.7 Define sex linkage

Sex Linkage: when the gene controlling the characteristic is located on the sex chromosome and so we

associate the characteristic with gender

4.3.8 Describe the inheritance of colour blindness & haemophilia as examples of sex linkage

4.3.9 State that a human female can be homozygous or heterozygous with respect to sex-linkage

genes

A human female can be homozygous or heterozygous with respect to sex-linkage genes

4.3.10 Explain that female carriers are heterozygous for X-linked recessive alleles

Females that carry X-linked recessive alleles are always heterozygous (one dominant allele, andone recessive)

Recessive from one parent, and dominant from another Hemopheliao Carrier mother + unaffected father, father passes on dominant allele to female offspring. Mothercan either pass on the dominant (female offspring = hemophiliac) or the recessive (female offspring =

carrier)

4.3.11 Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any

of the above patterns of inheritance.

4.3.12 Deduce the genotypes and phenotypes of individuals in pedigree charts.


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4.4.1 Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.

Polymerase chain reaction is used to copy and amplify minute quantities of DNA.

Useful when only a small amount of DNA is available but a large amount is required to undergo testing.

We can use DNA from blood, semen, tissues and so on from crime scenes for example.

The PCR requires high temperature instead of helicase to open up DNA

Temperature increases

Primers are hydrolysed, and added to match the ends of the target sequence

DNA polymerase enzyme from Thermus aquaticus (a bacterium that lives in hot springs)

new complimentary strands are replicated exponentially

4.4.2 State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated

according to their size.

In gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size

4.4.3 State that gel electrophoresis of DNA is used in DNA profiling .

Gel electrophoresis of DNA is used in DNA profiling

4.4.4 Describe the application of DNA profiling to determine paternity and also in forensic investigations.

Organisms have short sequences of bases which are repeated many times.

These repeated sequences vary in length from person to person.

The DNA is copied using PCR and then cut up into small fragments using restriction enzymes.

Gel electrophoresis separates fragmented pieces of DNA according to their size and charge.

This gives a pattern of bands on a gel which is unlikely to be the same for two individuals.

This is called DNA profiling (used to determine paternity or CSI)

4.4.5 Analyse DNA profiles to draw conclusions about paternity or forensic investigations.

Look for similarities between the bands from the sample obtained and collected sample After Electrophoresis

4.4.6 Outline three outcomes of the sequencing of the complete human genome.

Can study how genes influence human development

Helps Identify genetic diseases

Advances studies of evolution and migration of humans

4.4.7 State that, when genes are transferred between species, the amino acid sequence of

polypeptides translated from them is unchanged because the genetic code is universal.

When genes are transferred between species, the amino acid sequence of polypeptides translated from

them is unchanged because the genetic code is universal.

4.4.8 Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or

other cell), restriction enzymes (endonucleases) and DNA ligase.

1) Restriction enzyme (after the gene has been located) to isolate gene2) Take out a plasmid from a bacterium3) Cut it using the same restriction enzyme (so sticky ends match)4) Use ligase to attach the sticky ends together5) Put the plasmid back into the bacteria, and the plasmid will replicate4.4.9 State two examples of the current uses of genetically modified crops or animals.

Retinol in rice, from daffodil Herbicides


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4.4.10 Discuss the potential benefits and possible harmful effects of one example of genetic modification.

BENEFITS DISADVANTAGES

- Increased amount of crops in regions with

food shortages

- Foods (animal and plant) are considered

unnatural and unsafe for human

consumption

- Increased amount of crops with specific

dietary requirements such as vitamins andminerals

- Risk of developing a risk gene that could

escape into the environment and haveunknown effects

- Longer shelf lives of crops - Humans feel uneasy about eating food that

is able to last for so long

4.4.11 Define clone.

Clone: An organism that has the same DNA as another organism.

4.4.12 Outline a technique for cloning using differentiated animal cells.

1) Udder cells from Animal A, are fused with an egg that has no nucleus from Animal B 2) The new cell is implanted into a surrogate mother3) The offspring has the same DNA as Animal A, whom donated the udder cells. They are

clones.


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4.4.13 Discuss the ethical issues of therapeutic cloning in humans.

Benefits Harms

Could be used to study the effect that

environmental factors have on humans

You can create a very large army (mass

production of humans)

Harvest stem cells to study human development

and treat disease

When does life start? Killing an embryo after it

has been used for stem cells is sad to somepeople...

You have an extra set of body parts Psychological harm to the cloned one

No danger of rejection of the transplant because

the organ's DNA would match the patient's DNA

exactly

Opportunity for parents with genetic diseases to

have normal children

10.1.1 Describe the behaviour of the chromosomes in the phases of meiosis.

Two divisions occure during meiosis, these are termed meiosis I and meiosis II. Each division

involves the four stages of prophase, metaphase, anaphase and telophase.

Meiosis I

Prophase I

Chromosomes coil up tightly and become visible under a light microscope Homologous chromosomes pair up and crossing over occures (the point of cross over is

known as the chiasma)

Nuclear membrane disintgrates and the centrioles travel to the poles of the cellMetaphase I

Microtubules form a spindle and the spindle fibers attach to the centromeres of thechromosomes

Pairs of homologous chromosomes align along the equatorAnaphase I

Spindle fibers shorten pulling paired homologous chromosomes in opposite directions Paired homologous chromosomes are seperated and pulled to opposite poles so that each

pole contains one chromosome of each pair.

Telophase I

A nuclear membrane forms around the chromosomes at each pole and chromosomes uncoil The cell undergoes cytokinesis to form two daughter cells Forms two haploid cells At the end of telophase I the cells may enter a short interphase period or proceed directly to

meiosis II

DNA is not replicated


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Meiosis II

Prophase II

Chromosomes coil up again Centrioles move to the cell poles Nuclear membrane disintergratesMetaphase II

Spindle fibers attach to the the centromeres Chromosomes align along the equatorAnaphase II

Spindle fibers shorten Centromeres split Chromatids of each chromosome travel to opposite polesTelophase II

Nuclear membrane forms around the chromatids at each pole, once the membrane is formed,each chromatid is then called a chromosome.

Both cells undergo cytokinesis to form four cells Chromosomes uncoil Nucleoli form


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10.1.2 Outline the formation of chiasmata in the process of crossing over.

In prophase I the four sister chromatids of a pair of homologous chromosomes become tightly

linked in a process called synapsis. A cut is made in the DNA molecule of one of the chromatids.

Following this another cut is made at the same point in the DNA molecule of a non-sister

chromatid. The DNA of the one chromatid binds to the DNA of the non-sister chromatid. Paternal

and maternal chromosomes can then exchange genetic material. This is called crossing over. Once

crossing over is finnished the homologous chromosomes are no longer tightly linked however the

connection between the non-sister chromatids remains, forming an X - shaped structure called a

chiasma. The chiasma links homologous chromosome pairs together and remains until late

metaphase I.


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10.1.3 Explain how meiosis results in an effectively infinite genetic variety in gametes through

crossing over in prophase I and random orientation in metaphase I.

Two processes result in the infinite genetic variety in gametes. These are crossing over in

prophase I and the random orientation of chromosomes in metaphase I.

Crossing over is important for genetic variety as it allows the exchange of genetic material

between the maternal and paternal chromosomes. This forms chromatids with new combinations

of alleles (recombination of linked genes). The chromatids which have a combination of allele

different to that of either parent are called recombinants. It is also important to note that crossing

over occures at a random point and more than one chiasma can form per homologous pair. This

means that meiosis can result in almost an infinite amount of genetic variety.

The random orientation of homologous chromosomes at the equator in metaphase I also plays a

vital role in genetic variety. Since the homologous pairs of chromosomes are orientated randomly

at the equator, either maternal or paternal homolgue can orient towards either pole. The number

of possible orientations is equal to 2 raised to the power of the number of chromosome pairs. For

example, for a haploid number of n, 2n

is the number of possible outcomes. Humans have a

haploid number of 23. 223

gives a value of over 8 million. This means that there are over 8 million

possible combinations just through the radom orientation of the homologous chromosmes. If we

add the effects of crossing over, the number of combinations increases even further. Therfore,

these two processes allow infinit genetic variety in gametes.

10.1.4 State Mendels law of independent assortment.

Allele pairs seperate independently during gamete formation which means that the transmission

of traits to offspring are independent to one another.

10.1.5 Explain the relationship between Mendels law of independent assortment and meiosis.

During metaphase I of meiosis the homologous pairs of chromosomes align along the equator. The

orientation of the chromosomes is random. This means that when the pairs of homologous

chromosomes move to opposite poles during anaphase I, either chromosome can end up at either

pole. This depends on which way the pair is facing (occurs randomly). Also, which ever way the

pair is facing does not affect which way the other homologous chromosome pairs are facing. This

is known as idenpendent orientation and forms the basis of Mendel's law of independent

assortment. Unlinked genes are found on different chromosomes so when the homologous

chromosome pairs seperate it allows the formation of daughter cells with random assortemnets

of chromosomes and alleles.

10.2.1 Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses

involving unlinked autosomal genes.

Ratios from a 4x4 dihybrid cross Punnett grid are 9:3:3:1

PARENTS = RrYy x RrYy

RY Ry rY ry

RY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy Rryy

rY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

10.2.2 Distinguish between autosomes and sex chromosomes.

Sex chromosomes are chromosomes 23

They determine gender

Chromosomes 1-22 are autosomes, and contain genes for other characteristics


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10.2.3 Explain how crossing over between non-sister chromatids of a homologous pair in prophase I

can result in an exchange of alleles.

Maternal chromosomes can cross with a paternal chromosome, and a recessive allele can contain adominant trait

After crossing over has occurred the maternal and paternal chromosomes are no longer 100% pure,they are now heterozygous alleles

During any crossing over event, thousands of genes can be traded in this way between non-sisterchromatids.

A single bivalent can have several chiasmata producing crossing over in more than one chromatid10.2.4 Define linkage group.

A group of genes on the same chromosome, and are usually passed onto the next generation

together

10.2.5 Explain an example of a cross between two linked genes.

Fruit flies have the gene for body colour grey (G) or black (g) in the same linkage group as wing

length, short (l) or long (L)

The Genotype for true breeding parents are GGLL, and ggll. These genotypes dont show that the

genes must be linked so another notation to show this is; G L

======

G L

The two horizontal lines symbolize homologous chromosomes, and show that the locus of G is on

the same chromosome as L

One G is on the maternal homologue and the other on the paternal

The alleles are read vertically

10.2.6 Identify which of the offspring are recombinants in a dihybrid cross involving linked genes.

10.3.1 Define polygenic inheritance.

Involves two or more genes influencing the expression of one trait

10.3.2 Explain that polygenic inheritance can contribute to continuous variation using two examples,

one of which must be human skin colour.

Continuous variation: A great amount of genes making up the genotype can produce an array of

possible phenotypes.

Skin colour for example is determined by the inheritance of many genes

Another example is height and body shape

genetics quiz jan 23

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