Topic 3 - Genetics Flashcards
What is sexual reproduction?
Where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
What are the gametes in animals?
Sperm and egg cells
What are gametes?
Reproductive cells
How many chromosomes does a human cell nucleus contain?
46
What is the diploid number of chromosomes for a human?
46
What is the haploid number of chromosomes for a human cell nucleus?
23
What does diploid mean?
Has the full number of chromosomes, normal cells
What does haploid mean?
Contains half the full number of chromosomes of normal cells
Are gametes diploid or haploid?
Haploid
In sexual reproduction what do the father and mother produce?
Gametes
What happens in fertilisation in sexual reproduction?
A male gamete fuses with a female gamete to produce a fertilised egg
What is a fertilised egg also known as?
A zygote
Is a zygote diploid or haploid?
Diploid
How does a zygote develop into an embryo?
By undergoing cell division in the form of mitosis
Why does an embryo inherit characteristics from both parents?
Because it has received a mixture of chromosomes (and therefore genes) from the mother and father
In flowering plants where are the male gametes found?
In the pollen
In flowering plants where are the female gametes found?
In the ovaries at the bottom of the stigma
What is meiosis?
A type of cell division
How is meiosis different to mitosis?
Meiosis doesn’t produce identical cells
In humans where does meiosis occur?
Only in reproductive organs (ovaries and testes)
What happens before the cell starts to divide in meiosis?
The DNA is duplicated so there is enough for each new cell, one arm of each x-shaped chromosome (each chromatid) is an exact copy of the other
How many divisions are there in meiosis?
Two
What happens in the first division of meiosis?
•the chromosomes line up in pairs in the centre (on the equator) of the cell. One chromosome in each pair came from the organism’s mother and one from the father
- the pairs are then pulled apart by spindle fibres so each new cell only has one copy of each chromosome. Some of the mother’s chromosomes and some of the father’s chromosomes go into each new cell.
- each new cell will have a mixture of the mother’s and the father’s chromosomes.
Why is mixing the genes in the first cell division of meiosis important?
To create genetic variation in the offspring
What happens in the second cell division in meiosis?
- the second division is similar to mitosis
- the chromosomes line up again in the centre of the cell and the arms of the chromosomes are pulled apart
- four haploid daughter cells are produced, these are the gametes, the gametes are genetically different
What is the only way in which humans can reproduce?
Sexually
How do organisms pass on their genes?
By reproduction
What happens when cells reproduce asexually?
They divide by mitosis, resulting in two diploid daughter cells which are genetically identical to each other and the parent cell
What does sexual reproduction involve?
Meiosis and the production of genetically different haploid gametes which fuse to form a diploid cell at fertilisation
What are the advantages of asexual reproduction?
- asexual reproduction can produce lots of offspring very quickly because the reproductive cycle is so fast, this allows organisms to colonise a new area very rapidly
- only one parent is needed, meaning that organisms can reproduce whenever conditions are favourable without having to wait for a mate
•
What is the reproductive cycle?
The time it takes to produce independent offspring
What is an example of an organism reproducing quickly
and asexually?
Bacteria such as E.coli can divide every half an hour
What is an example of organisms reproducing asexually when the conditions are favourable and not having to wait for a mate?
Aphids reproducing asexually during summer when there is plenty of food
What is an advantage of sexual reproduction?
- creates genetic variation within the population, different individuals have different characteristics.
- This means that if the environmental conditions change, it’s more likely that at least some individuals in the population will have the characteristics to survive the change
- over time, this can lead to natural selection and evolution as species become better adapted to their new environment
What is a disadvantage of asexual reproduction?
- there’s no genetic variation between offspring in the population
- this means that if the environment changes and conditions become unfavourable, the whole population may be affected
What is Black Sigatoka?
A disease that affects banana plants
What is an example of how a lack of genetic variation is a disadvantage of asexual reproduction?
Bananas reproduce asexually so if there is an outbreak of disease (Black Sigatoka) it’s likely that all the banana plants in the population will be affected as none of the bananas are resistant to it
What are some disadvantages of sexual reproduction?
- sexual reproduction takes more time and energy than asexual reproduction so organisms produce fewer offspring in their lifetime, organisms need to find and attract mates
- two parents are needed for sexual reproduction, this can be an issue if individuals are isolated
What is an example of the disadvantage that sexual reproduction takes time?
Male bowerbirds build structures out of twigs and then dance to impress females
What is an example of the disadvantage that sexual reproduction requires two parents?
Polar bears often live alone so male polar bears may have to walk up to 100 miles to find a mate
What are DNA strands?
Polymers made up of lots of repeating units called nucleotides
What does each nucleotide in a DNA stand consist of?
One sugar molecule, one phosphate molecule and one ‘base’
What do the sugar and phosphate molecules in the nucleotides form for the DNA strands?
A ‘backbone’, the sugar and phosphate molecules alternate
One of how many bases joins to each sugar in a DNA strand?
One of four bases
What are the four potential bases in DNA strands?
A, T, C and G
What does the base A stand for?
Adenine
What does the base T stand for?
Thymine
What does the base C stand for?
Cytosine
What does the base G stand for?
Guanine
What is the structure of a DNA molecule?
Two strands coiled together in the shape of a double helix, each base links to a base on the opposite strand in the helix
What base does A pair with?
T
What base does T pair with?
A
What base does C pair with?
G
What base does G pair with?
C
What are the pairings of bases called?
Complementary base pairs
What are the complementary base pairs joined together with?
Weak hydrogen bonds
What are chromosomes?
Long, coiled up molecule of DNA
Where are chromosomes found?
In the nucleus of eukaryotic cells
What is a gene?
A section of DNA on a chromosome that codes for a particular protein
What makes up an organism’s genome?
All of an organism’s DNA (including the non-coding regions)
Describe the practical to extract DNA from strawberries.
1) mash some strawberries and then put them in a beaker containing a solution of detergent and salt. Mix well
2) filter the mixture to remove the froth and the big insoluble parts of the cell
3) gently add some ice-cold alcohol to the filtered mixture
4) the DNA will start to come out of the solution due to it being insoluble in cold alcohol
5) the DNA will appear as a stringy white precipitate that can be carefully removed from the solution with a glass rod
Why is detergent used when extracting DNA from strawberries?
To break down the cell/nuclear membranes to release the DNA
Why is salt used when extracting DNA from strawberries?
To make the DNA stick together
Who were the people awarded a Nobel Prize for their work in determining the structure of DNA in 1962?
Crick, Watson, and Wilkins
What do DNA molecules contain that determines which proteins are built?
A genetic code
What do proteins (made by a genetic code) do?
Determine how all the cells in the body function
What does DNA control?
The production of proteins (protein synthesis) in a cell
What is protein synthesis?
The production of proteins
What are proteins made up of?
Chains of amino acids, each protein has its own particular number and order of amino acids
Why does each protein have a different function?
The amino acid chains fold up to give each protein a different, specific shape which means that each protein can have a different function, this is why enzymes have active sites with a specific shape and so only catalyse a specific reaction
Why do enzymes have active sites with a specific shape and only catalyse a specific reaction?
Because the amino acid chains in proteins fold up to give each protein a different, specific shape, meaning that each protein can have a different function
What decides the order of amino acids in a protein?
The order of the bases in a gene
What is a base triplet?
Each amino acid is coded for by a sequence of three bases in a gene
What is a code based on base triplets?
A triplet code
How are amino acids joined together to make proteins?
Following the order of the bases in the gene: if one base triplet in DNA is “T C G” for example and the other base triplet next to this is “T G G” the cell will read the genetic code to match the amino acid to the base triplet (so the amino acids would be “T C G” and “T G G”) to put the amino acids together.
What allows a gene to code for a particular protein?
Each gene contains a different sequence of bases
What does it mean when regions of DNA are non-coding?
They don’t code for any amino acids, although some of the non-coding regions are still involved in protein synthesis
What is a mutation?
A rare, random change to an organism’s DNA base sequence that can be inherited
What happens if a mutation happens in a gene?
A genetic variant is produced which is a different version of the gene
How can a mutation in a gene affect the activity of a protein?
The genetic variant produced may code for a different sequence of amino acids which may change the shape of the final protein and so it’s activity. the activity of the enzyme may increase, decrease or stop altogether. This could result in a change in the characteristics of the organism
What are genetic variants also called?
Alleles
What is an example of how a mutation in a gene can change the characteristics in an organism?
XDH is an enzyme, fruit flies with normal XDH activity have red eyes, fruit flies with no XDH activity have brown eyes because they can’t produce the red pigment
Can mutations happen in non-coding regions of DNA?
Yes
Where are proteins made and what by?
In the cell cytoplasm and by ribosomes
Where is DNA found in the cell?
The nucleus
Why can’t DNA move out of the cell nucleus? What does this mean?
Because DNA is very big. This means that the cell needs to get the information from the DNA to the ribosomes in the cytoplasm
How is the information from the DNA in the nucleus communicated to the ribosomes in the cytoplasm?
By using messenger RNA (mRNA)
What is mRNA?
Like DNA mRNA is a polymer of nucleotides but it’s shorter than DNA and only a single strand.
What does mRNA use as a base instead of thymine?
Uracil (U), uracil still pairs with adenine
What is RNA polymerase?
An enzyme involved in joining together RNA nucleotides to make mRNA
What is transcription?
When mRNA is made as part of protein synthesis (transcription is part of protein synthesis)
What happens in transcription?
1) RNA polymerase binds to a region of non-coding DNA
2) the two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA
3) the RNA polymerase uses coding DNA in the gene as a template to make the mRNA.
4) base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene
5) once made, the mRNA molecule moves out of the nucleus DNA joins with a ribosome, once the mRNA is bound to a ribosome, the protein can be assembled in translation.
What is translation?
When the protein is assembled in protein synthesis
What happens in translation?
1) Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA)
2) the order in which the amino acids are brought to the ribosome matches the order of the base triplets in mRNA.
3) part of the tRNA’s structure is called an anticodon - it is complementary to the codon for the amino acid. The pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the correct order.
4) the amino acids are joined together by the ribosome. This makes a polypeptide
What are the base triplets in mRNA also known as?
Codons
What is a polypeptide?
A protein
If a mutation happens in the area of non-coding DNA which the RNA polymerase has to bind to before transcription what would happen?
The ability of the RNA polymerase to bind to the region of non-coding DNA could be affected, the mutation could make the non-coding region of DNA easier to bind to or more difficult to bind to
How can a mutation in the region of non-coding DNA the RNA polymerase has to bind to affect the phenotype of an organism?
- the mutation could affect how easily the RNA polymerase binds it the region of non-coding DNA
- the ability of how well the RNA polymerase can bind to the non-coding region of DNA affects how music mRNA is transcribed and so how much protein is produced.
- depending on the function of the protein the phenotype of the organism may be affected by how much of it is made
- this means that genetic variants in non-coding regions can still affect the phenotype of an organism, even if they don’t code for proteins themselves
Who was Gregor Mendel?
An Austrian monk who trained in mathematics and natural history. On his garden plot at the monastery in the mid 19th century, Mendel noted how the characteristics of plants were passed on from one generation to the next.
When were Gregor Mendel’s results of his genetic experiments with plants published?
In 1866 and they eventually became he foundation of modern genetics
What is an example of one of Mendel’s experiments?
- Mendel crosses two pea plants of different heights, a tall pea plant and a dwarf pea plant. The offspring produced were all tall pea plants
- he then bred two of these tall offspring together, he found that when the offspring from the first cross were crossed with each other, three tall offspring were produced for every dwarf offspring overall. He produced a 3:1 ratio of tall: dwarf plants
What does ‘cross’ mean?
To breed
What had Mendel shown in his example with pea plants?
- That the height characteristics in pea plants was determined by separately inherited ‘hereditary units’ passed on from each parent.
- The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants, T, was dominant over the unit for dwarf plants, t.
What do we now know about the pea plants in Mendel’s experiment?
The pea plants in the first cross were homozygous for their trait and the offspring were heterozygous for their trait.
What is another way in which Mendel showed that other characteristics of pea plants were inherited in the same way as height?
He found that a purple flower colour was dominant over a white colour.
What were the three conclusions that Mendel reached about heredity in plants?
- characteristics in plants are determined by hereditary units
- hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
- hereditary units are dominant or recessive - if an individual has both the dominant and recessive unit for a characteristic, the dominant characteristic will be expressed
Does hereditary work the same as plants? Why?
Yes, although Mendel didn’t perform experiments on animals, similar experiments have since shown that hereditary in animals works the same as in plants
What are what Mendel referred to as “hereditary units”?
Genes
After Mendel’s death what’s was realised about his work? Why hadn’t it been realised before?
- people realised how significant his work was and that the mechanism of inheritance could be fully explained
- at the time this wasn’t realised because scientists didn’t have the background knowledge to properly understand Mendel’s findings.
- at the time there was no understanding or knowledge about genes, DNA and chromosomes
How can you use genetic diagrams?
To predict how different characteristics will be inherited
What are alleles?
Different versions of the same gene
What controls the characteristics you develop?
What genes you inherit
How many genes control each different characteristic?
Some characteristics are controlled by a single gene. Most characteristics are controlled by several genes interacting
How many versions of every gene is in he body?
Two versions of every gene (two alleles) is in the body.
How many alleles are on chromosomes?
One allele on each chromosome in a pair
If two alleles for a particular gene that are the same what is the organism?
Homozygous for that trait
If two alleles for a particular gene are different what is the organism?
Hererozygous
How are dominant alleles different to recessive alleles?
Dominant alleles overrule recessive alleles so if an organism has one dominant and one recessive allele for a gene, then the dominant allele will determine what characteristic is present
To display a dominant characteristic what alleles must be present in an organism?
Either two dominant alleles for a particular gene or one dominant and one recessive allele for that gene.
To display a recessive characteristic what alleles must be present in an organism?
Both alleles must be recessive
What is a genotype?
The combination of alleles in an organism
What is a phenotype?
The characteristic, the alleles determine what characteristic will be present - the alleles determine the phenotype
How are different phenotypes formed?
Different combinations of alleles form different phenotypes.
What is the inheritance of a single characteristic called?
monohybrid inheritance
what can you use to show how recessive and dominant traits for a single characteristic are inherited?
a monohybrid cross
what can be used to show how sex is determined in humans?
a genetic diagram
how many pairs of chromosomes are there in every human cell?
23 matched pairs
which pair of chromosomes determines the sex of humans (the chromosomes being XX or XY)?
the 23rd pair
what pair of chromosomes is exclusive to males?
XY
what pair of chromosomes is exclusive to females?
XX
what chromosome causes male characteristics?
Y
what combination of chromosomes causes female characteristics to develop?
XX
what are the chances of a baby being either male or female when born?
50%
what chromosome do all egg cells have?
an X chromosome
what chromosome does a sperm cell have?
either an X chromosome or a Y chromosome
what does sex determination in humans depend on?
whether the sperm that fertilises an egg carries an X or a Y chromosome
what is a family pedigree?
a family tree of genetic disorders
what is an example of a genetic disorder?
cystic fibrosis
what is cystic fibrosis?
a genetic disorder of the cell membranes
is the allele that causes cystic fibrosis dominant or recessive?
recessive
how many people carry the allele that causes cystic fibrosis?
1 person in 30
what are people with only one copy of the recessive allele which can cause a genetic disease called?
carriers
how can the probability of a person being unaffected, being a carrier or having the disorder be expressed from a genetic diagram?
in a ratio, percentage or fraction
e.g. unaffected : carrier : disorder
when is a characteristic sex-linked?
if the allele that codes for the characteristic is located on a sex chromosome
where are most genes on sex chromosomes located? why?
on the X chromosome because the Y chromosome is smaller than the X chromosome and carries fewer genes
why do men often only have one allele for sex-linked genes?
because men only have one X chromosome
as men only have one allele what does this mean about the characteristic shown of a sex-linked genetic disorder?
the characteristic of the allele is shown even if the characteristic is recessive. this makes men more likely than women to show recessive characteristics for genes that are sex-linked
what are sex-linked genetic disorders?
disorders caused by faulty alleles located on sex chromosomes
what is colour blindness caused by?
a faulty allele carried on the X chromosome
how is a genetic cross of a sex-linked disorder different to a normal genetic cross/
both the chromosome and the allele are written in the genetic diagram, e.g. X^n where X represents the X chromosome and n represents an allele, unless the chromosome doesn’t have an allele linked to the genetic disorder (e.g. Y chromosome would just be Y, not Y^n or Y^N
why is colour blindness more common in men than women?
women need two copies of the recessive allele to be colour blind while men only need one copy of the allele to be colour blind. therefore colour blindness is rarer in females than males
what are two examples of sex-linked genetic disorders?
colour blindness and haemophilia
what is haemophilia?
a disease where the blood doesn’t clot properly
what is haemophilia caused by?
a faulty allele carried on the X chromosome
how many potential blood types do humans have?
4
what are the potential blood types in humans?
O, A, B and AB
how many alleles does the gene for blood type in humans have?
three
what are the alleles for the gene for blood type in humans?
I^O, I^A, I^B
what two alleles for the gene for blood type in humans are codominant?
I^A and I^B
what does codominant mean?
when an individual has both of the codominant alleles then one allele isn’t dominant over the other
which allele for the gene for blood type in humans is recessive?
I^O
what does I^O being recessive mean for blood type if paired with I^A or I^B?
only the effect of the more dominant allele will be presented, e.g. I^O and I^A to make the genotype I^AI^O then only the effect of I^A will be seen so the blood type will be blood type A
why is blood ground O common in Britain despite being recessive?
recessive blood groups are usually rare but it is coincidence that many people of Britain are descended from people with the genotype I^OI^O to make the O blood type
how can you draw genetic diagrams for codominant alleles?
in the same way as for alleles which are recessive and dominant, however predicting the phenotypes of the offspring once the genotype has been calculated is more difficult
what are the two types of variation within a species?
genetic or environmental
what is genetic variation within a species caused by?
organisms having different alleles which can lead to differences in phenotype
what can genetic variation be caused by?
- new alleles arising through mutations
- sexual reproduction
how does sexual reproduction cause genetic variation?
sexual reproduction results in alleles being combined in lots of different ways in offspring - sexual reproduction means that no two members of species are genetically identical (apart from identical twins)
what is genetic variation within a population of a species mostly due to?
neutral mutations
what are environmental variations in phenotype also known as?
acquired characteristics
what are acquired characteristics?
characteristics that organisms acquire during their lifetimes
what is an example of how phenotype is determined by a mixture of genetic and environmental factors?
the maximum height that an animal or plant could grow to is determined by its genes, but whether the plant or animal actually grows to the maximum height depends on its environment (e.g. how much food it gets)
how do alleles arise?
due to genetic mutations within a gene
what are mutations?
changes to the base sequence of DNA
how common is it that a single mutation will have a big effect on the phenotype of an organism?
very rare
what causes cystic fibrosis?
a mutation causes a protein that controls the movement of salt and water into and out of cells to stop working properly. this leads to the production of thick, sticky, mucus in the lungs and digestive system, making it difficult to breathe and digest food
what was the Human Genome Project?
A project to find every single human gene
when did the Human Genome Project start?
in 1990
what was the end result of the Human Genome Project?
a map of the human genome including the locations of around 20500 genes was completed in 2003
so far how many genes has the Human Genome Project been able to identify related to disease?
1800 genes
how has the Human Genome Project helped in the prediction and prevention of disease?
- if doctors knew what genes predisposed people to what diseases, everyone could receive individually tailored advice on the best diet and lifestyle to prevent the likely problems.
- doctors could also check regularly to ensure early treatment if the diseases caused by the genes develop
what diseases are caused by the interaction of different genes?
many common diseases like cancers and heart disease (which are also caused by lifestyle factors)
how has the Human Genome Project helped in the testing and treatment for inherited disorders?
- scientists are able to identify the genes and alleles that are suspected of causing an inherited disorder more quickly than in the past
- once an allele that causes an inherited disorder has been identified then people can be tested for it and it may be possible to develop better treatments or even a cure for the disease eventually
how has the Human Genome Project helped in the production of new and better medicines?
- genome research has highlighted some common genetic variations between people, some variations affect how our individual bodies will react to certain diseases and to the possible treatments for them
- scientists can design new drugs specifically tailored to people with a particular genetic variation and can also determine how well an existing drug will work for an individual and what dosage is most appropriate for certain drugs in different patients
what are some disadvantages of the Human Genome Project?
- increased stress
- gene-ism
- discrimination by employers and insurers
how can the Human Genome Project lead to increased stress as a disadvantage?
if someone knew from an early age that they were susceptible to a certain disease then this could cause panic and stress if minor potential symptoms occur
how can the Human Genome Project lead to gene-ism as a disadvantage?
people with genetic problems could come under pressure not to have children
how can the Human Genome Project lead to discrimination by employers and insurers as a disadvantage?
life insurance could become impossible or extremely expensive to get if a person has a genetic likelihood of serious disease. employers may discriminate against people who are genetically likely to get a disease
what does DNA stand for?
deoxyribonucleic acid
