Inheritance Flashcards
Give one difference between mitosis and meiosis.
Mitosis leads to genetically identical cells being formed while meiosis leads to non- genetically identical cells being formed.
What does sexual reproduction involve?
The joining (fusion) of male and female gametes.
Give examples of male and female gametes.
-Sperm and egg cells in animals
-Pollen and egg cells in flowering plants
What does the mixing of genetic information lead to in sexual reproduction?
Variety in the offspring.
What does the formation of gametes involve?
Meiosis
What does asexual reproduction involve?
Only one parent and no fusion of gametes.
Only mitosis (a cell dividing in 2)
Why does asexual reproduction lead to genetically identical offspring?
There is no mixing of genetic information hence genetically identical offspring.
Explain how meiosis halves the number of chromosomes in gametes (sex cells).
Each pair of chromosomes replicate and the cell splits in two. There are now two genetically identical cells.
The diploid cells divide again. Chromosomes are distributed between the new cells at random.
This creates four genetically different gametes which each have half the number of chromosomes than in the parent cell.
Explain how fertilisation restores the full (normal) number of chromosomes.
Gametes join/fuse at fertilisation.
The maternal chromosomes from the egg cell and the paternal chromosomes from the sperm cell pair up to form a zygote with the full number of chromosomes.
Cells in reproductive ______ divide by ______ to form ________.
organs
meiosis
gametes
Explain what happens when a cell divides to form gametes.
-copies of the genetic information are made (chromosomes duplicate)
-the cell divides twice to form four gametes, each with a single set of chromosomes
-all gametes are genetically different from each other.
What does the new cell formed by the fusion of two gametes (zygote) do?
Divide by mitosis.
This causes the total number of cells to increase, forming a ball of cells called an embryo.
As the embryo develops, cells differentiate.
List the advantages of sexual reproduction.
-Produces variation in the offspring as the organism inherits alleles from both parents
-If the environment changes, variation gives a survival advantage (increased chance of survival) by natural selection.
Natural selection can be speeded up by humans in selective breeding to produce what?
(Advantage of sexual reproduction)
Animals with desired characteristics.
They are bred to produce offspring which inherit the desired characteristics.
e.g. animals that produce a lot of meat can be selectively bred to increase food production.
Natural selection
Individuals with characteristics that make them better adapted to an environment have a better chance of survival.
They are therefore more likely to breed successfully and pass the genes for the characteristics on.
List the advantages of asexual reproduction.
-Only one parent is needed
-More time and energy efficient as organisms do not need to find a mate
-Faster than sexual reproduction
-Many identical offspring can be produced when conditions are favourable.
Asexual vs Sexual reproduction links to what topics?
-Animal and plant cells
-Cloning
Which organisms can reproduce by both sexual and asexual reproduction depending on the circumstances?
-Malarial parasites
-Fungi
-Plants like strawberries and daffodils
Reproduction in malarial parasites.
Malaria is caused by a parasite that’s spread by mosquitos.
When a mosquito carrying the parasite bites a human, the parasite can be transferred to the human making them sick.
The parasite reproduces sexually in the mosquito (the vector), but asexually in the human host.
Reproduction in fungi
Many fungi reproduce asexually by spores, which can become new fungi when they land in a suitable place.
Spores can also be produced sexually to give variation.
This is usually in response to an unfavourable change in the environment, to increase the chance of the population surviving the change.
Reproduction in plants
Many plants produce seeds sexually (pollen deposited on stigma and egg in pistil), but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
Define genome.
The genome of an organism is the entire genetic material of that organism.
The whole human genome has now been studied and this will have great importance for what in the future?
medicine!!
Describe the structure of DNA
DNA is a polymer made up of two strands forming a double helix.
The strands are made of many repeating monomer units called nucleotides.
Each nucleotide consists of a common sugar and phosphate group with one of four different bases (A,T,C, or G) attached to the sugar.
The long strands themselves consist of alternating sugar and phosphate sections.
The bases A and T, C and G pair to join the strands.
What does DNA stand for?
Deoxyribonucleic acid
Describe the structure of a nucleotide.
A nucleotide consists of a phosphate group, a pentose sugar, and one of four different bases (A,T,C, or G) attached to the sugar.
What is genetic material in the nucleus of a cell composed of?
DNA (which is a chemical).
Fertilisation
The fusing of male and female gametes.
How does asexual reproduction happen?
By mitosis.
What is sexual reproduction?
Where two gametes combine at fertilisation to produce a genetically different individual.
Genotype
The two alleles present for a particular gene.
(the specific alleles that an individual has)
If a mouse has one allele for brown fur, and another allele for black fur, would they be considered homozygous or heterozygous for that gene?
Summarise the genotype and phenotype of the mouse.
Heterozygous
What is complementary base pairing?
In the complementary strands, a C base is always linked to a G on the opposite strand and a T to an A.
They are linked with weak hydrogen bonds.
Some parts of DNA do not code for proteins.
Describe how the non-coding parts of DNA can affect the expression of genes.
Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed (i.e. how they are used to make a protein).c
A mouse has one allele for brown fur, and another allele for black fur.
The brown fur allele is dominant.
Summarise the genotype and phenotype of the mouse.
Genotype - a brown fur allele and a black fur allele.
Phenotype - brown fur.
Gene
A small section of DNA on a chromosome, which codes for a particular sequence of amino acids, to make a specific protein.
How many bases does DNA contain?
4
A,T,C,G
Where is DNA contained?
Structures called chromosomes in the nucleus of a cell.
Simplest higher tier definition of DNA.
A polymer made from four different nucleotides.
Chromosome
A long molecule of DNA, found in the nucleus.
Each chromosome carries many genes.
Allele
A version of a gene.
Dominant allele
The allele that’s always expressed, even if only one copy is present.
Recessive allele
An allele whose characteristic only appears in an organism if there are two copies present.
(therefore no dominant allele present).
Homozygous
When an organism has two alleles for a particular gene that are the same.
Heterozygous
Where an organism has two alleles for a particular gene that are different.
Phenotype
The characteristics you have as a result of your genotype.
Name some characteristics controlled by a single gene.
-Fur colour in mice
-Red-green colour blindness in humans
Name a characteristic controlled by many genes.
Height
The alleles present, or ________, operate at a ________ level to develop characteristics that can be _________ as a phenotype.
genotype
molecular
expressed
What are most phenotype features the result of?
Multiple genes interacting, rather than a single gene inheritance.
What are inherited disorders caused by?
The inheritance of certain alleles.
What is Cystic fibrosis?
A disorder of cell membranes.
What is Polydactyly?
Having extra fingers or toes.
What type of allele is Polydactyly caused by?
Dominant
This means it can be inherited if just one parent carries the defective allele. (Dd)
What type of allele is Cystic fibrosis caused by?
Recessive.
What are the symptoms of Cystic fibrosis?
-Excess mucus (in the air passages and pancreas)
-Chest infection
-Low weight gain
-Tiredness/low energy
What is the genotype of sufferers of Cystic fibrosis?
Homozygous recessive (ff)
What is the genotype of sufferers of Polydactyly?
Heterozygous or Homozygous dominant
Are there other symptoms of polydactyly other than extra fingers or toes?
No, therefore the genetic disorder isn’t life threatening.
What is a genetic cross?
A diagram used to show the possible genetic outcomes when you cross together different genes.
Alleles are represented as letters.
How many chromosome PAIRS do ordinary human body cells contain?
23
How many chromosome pairs control ONLY characteristics in ordinary human body cells?
22
What does the 23rd chromosome pair carry?
The genes that determine sex.
What are the sex chromosomes in males?
Different (XY)
What are the sex chromosomes in females?
The same (XX)
What is a punnet square?
A type of genetic cross diagram.
What MUST we do when drawing punnet squares to work out probabilities?
Draw a grid, with a cross in the top left corner.
Fill in the parents’ genotypes.
Fill in the possible genotypes for the offspring.
Circle the genotype that would lead to the characteristic (phenotype) you’re looking for.
Discuss the importance of understanding the human genome.
Knowledge of the human genome can be used to:
-search for genes linked to different types of disease
-understand and treat inherited disorders
-trace human migration patterns from the past
Using knowledge of the human genome to search for genes linked to different types of disease.
Carrying some genes increases the risk of developing a non- communicable disease e.g. having the BRCA gene increases the risk of developing breast cancer.
Using knowledge of the human genome to understand and treat inherited disorders.
Certain genes cause inherited diseases.
Doctors use this information to choose effective treatments and scientists develop better ones.
Using knowledge of the human genome to trace human migration patterns from the past.
The human genome is mostly identical in all individuals.
This is because we are all descended from a common ancestor who lived in Africa.
However, as different populations migrated away from Africa, tiny differences developed in their genomes.
By studying these differences, scientists can work out when populations split off in different directions, and what route they took.
Why do red blood cells need lots of the protein haemoglobin?
Haemoglobin binds to oxygen to transport it around the body to be used in aerobic respiration.
How many amino acids can genes code for?
20, however these can make up thousands of proteins.
What does DNA determine?
-What order amino acids are bonded together in
-(So) What proteins the cell produces
-(So) What type of cell it is e.g. RBC, skin cell
Name a protein
Haemoglobin
Keratin
What is keratin? (not on spec but its interesting)
-A protein found in epithelial cells
-It helps form skin/ hair/nails
-It has a role in healing wounds
In a question about Asexual reproduction, what should you mention, even if it seems way too obvious?
-In asexual reproduction, there’s only one parent
-There is no fusion of gametes, no mixing of chromosomes, and no genetic variation between parent and offspring (making the offspring clones)
To find out the parents’ genotype, you sometimes have to do what? (mostly if the dominant characteristic is expressed in all offspring).
Breed the offspring together and see the ratio of different phenotypes.
If the ratio is 3:1 the parents, genotype is likely both heterozygous .
What ratio of phenotypes for the offspring would you expect if a heterozygous (Dd) parent is crossed with a homozygous recessive (dd) parent?
1:1
dominant allele expressed: no dominant alleles
What is a carrier?
A heterozygous person who carries a recessive allele that causes an inherited disorder, but doesn’t have it themself due to the presence of the dominant allele. (which will always be expressed!)
e.g. for cystic fibrosis
FF- doesn’t have Ff-carrier ff-has
For a child to have cystic fibrosis, what must their parents’ phenotypes be?
-Both heterozygous (so carriers)
-Homozygous recessive(so have the disorder themselves)
From a family tree diagram, how do you tell if an inherited disease is dominant/recessive?
If it’s recessive, plenty of the family will carry the allele but won’t have the disorder.
If you get a family tree showing the inheritance of a dominant allele, what will not be shown?
Carriers because the dominant allele is always expressed.
What is the probability of each gender?
50%
Use a punnet square - parents XX and XY
Practice your…
family tree diagrams mwahahaha
What is embryo screening?
Removing a cell from an embryo and analysing its genes, after fertilisation in the lab but before the embryo is implanted into a mother’s womb during IVF.
It is also possible to get DNA from an embryo in the womb and test for genetic disorders.
What can embryo screening be used for?
To detect genetic disorders such as cystic fibrosis.
Arguments for embryonic screening:
It will help to prevent people from suffering. (ethical)
It will save the government (and hence the taxpayers) money because they won’t have to pay for treatment of disorders. (economic)
There are laws to prevent the selection of ‘desirable’ characteristics - parents cannot select sex etc. (social)
Arguments against embryonic screening:
-For embryos produced by IVF, embryos with ‘bad’ alleles would be destroyed after screening
-For embryos in the womb - screening could lead to the decision to terminate a pregnancy
-This implies people with genetic problems are ‘undesirable’ and could increase prejudice
-There may come a time where everyone wants to screen their embryos to pick the most ‘desirable’ one e.g. blue eyed blonde intelligent boy
(all ethical)
-Screening is expensive (economic)
Describe the process of protein synthesis.
-A gene on DNA is copied into mRNA
-mRNA leaves the nucleus and binds to a ribosome
-At the ribosome, every three bases are read.
-Carrier molecules bring specific amino acids to the ribosomes in the correct order
-These join to form a protein chain
Explain simply how the structure of DNA affects the protein made.
The order of bases in a gene controls the order in which amino acids are assembled to produce a particular protein.
Describe how genetic variants may influence phenotype in coding DNA.
-If the order of bases changes, the order in which amino acids are assembled will also change
-This can lead to changes in the protein that it codes for
Describe how genetic variants may influence phenotype in non-coding DNA .
-Non-coding parts of DNA can switch genes on and off
-So variations in these areas of DNA may affect how genes are expressed.
Explain how a change in DNA structure may result in a change in the protein synthesised by a gene
-If the order of bases changes, the order in which amino acids are assembled will also change
-This can lead to changes in the protein that it codes for (different shape)
What does a protein chain do when complete?
It folds up to form a unique shape.
Mutations occur ____________. They can occur _____________ e.g ________
continuously
spontaneously e.g. when a chromosome isn’t replicated properly
What would the effect of a serious mutation be?
A few mutations code for an altered protein with a different shape.
This could affect the protein’s ability to carry out its function.
For example, An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
What codes for a particular amino acid?
The sequence of the three bases (a codon)
Codon
A sequence of 3 bases.
Each codon codes for one amino acid.
What are some roles of proteins?
-as enzymes
-as hormones
-as structural proteins
What does the unique shape of proteins allow them to do?
Their job as enzymes, hormones or forming structures in the body such as collagen.
What are structural proteins?
Strong proteins like collagen (which strengthens connective tissues like ligaments and cartilage).
Mutation
A random change in the base sequence of DNA.
Can mutations be inherited?
Yes.
What do most mutations do?
Most do not alter the protein, or only alter it slightly
Therefore its appearance or function is not changed.
How might a protein’s ability to carry out its function be affected by a change in shape?
-An enzyme may no longer fit the substrate binding site
-A structural protein may lose its strength (so be no use in providing structure and support)
What are the 3 different types of mutation?
-Insertions
-Deletions
-Substitution
Insertions
-A new base is added to the DNA sequence.
-This changes the way the codons are read
-Which can change the amino acids they code for
-They can change more than one amino acid (in a knock-on effect)
Deletions
-A random base is deleted from the DNA base sequence
-This changes the way the codons are read
-Which can change the amino acids they code for
-They can change more than one amino acid (in a knock-on effect)
Substitutions
-A random base in the DNA base sequence is changed to a different base
-This changes the way one codon is read
-Which can change the amino acids it codes for
Transcription
The copying of a single gene of DNA, to mRNA.
Why does a gene of DNA have to be copied to mRNA (transcription)?
DNA is too large to leave the nucleus.
How is mRNA different to DNA?
-mRNA is single stranded, but DNA is double stranded
-mRNA is shorter than DNA
Translation
The combination of amino acids to form a polypeptide.
Polypeptide
A chain of amino acids.
Mutations can occur spontaneously in our _____, but certain factors can ________ ___ ____.
cells
increase the risk
What factors increase the risk of a mutation?
-Ionising radiation such as x-rays and gamma rays
-Carcinogens like those found in cigarette smoke
Deletion and insertion mutations have a larger impact on the protein than substitution mutations. Explain why.
They disrupt all of the codons after the mutation.
