SB3 - Genetics Flashcards
What is sexual reproduction?
It is reproduction where genetic information from two organisms is combined to produce offspring that are genetically different to both parents
Define the word ‘haploid’
Cells that have half the number of chromosomes of a normal cell
Define the word ‘diploid’
Cells that have two copies of each chromosome
What word do we use for a fertilised egg?
Zygote
What type of cell division creates egg and sperm cells?
Meiosis
What type of cell division creates body cells?
Mitosis
What do cells have to do before they can undergo meiosis?
Replicate - make copies of their chromosomes
How many daughter cells are made during one cycle of meiosis?
Four
How many daughter cells are made during mitosis?
Two
How many times do cells divide in mitosis?
Once
How many times do cells divide in meiosis?
Twice
Cat sperm cells contains 19 chromosomes. How many chromosomes would you find in the cat’s skin cells?
38
Horse liver cells contain 64 chromosomes. How many chromosomes are found in horse egg cells?
32
Human muscle cells contain 46 chromosomes. How many chromosomes are found in a red blood cell?
None
Spider plants reproduce using runners. Is this an example of sexual or asexual reproduction?
Asexual
What will need to happen before new shoots on the runners for them to become independent plants?
The shoots would need to develop a root system and produce enough leaves to maintain the shoots’ food supply by photosynthesis. To become fully independent of the parent plant the stem connecting the daughter plants to the parent must die and disappear
What name is given to the horizontal stem in this kind of propagation?
The horizontal stem is called a runner
Name a commercially grown fruit whose plants are propagated in this way
The most familiar fruit propagated by runners is the strawberry
Before stem cuttings are planted, the cut end of the stem is often dipped in a hormone powder. What is the point of this?
The hormone powder contains a plant growth substance which promotes the formation of roots. It may also contain a fungicide which reduces the chance of fungus attack on the cut stem
State two advantages of vegetative reproduction
- Reduces competition from other species
- Maintains desirable qualities in the offspring
- Good at colonising favourable areas
State two advantages of sexual reproduction
- Produces greater variety in the offspring
- Good at colonising new areas
- Species more able to survive an epidemic
- Species more able to survive environmental change
What name is given to the population of genetically identical offspring which result from a process of asexual (vegetative) reproduction?
A clone
What is mitosis used for?
Making more body cells, growth
What is meiosis used for?
Making gametes (e.g. sperm and eggs)
Where does meiosis happen?
Ovaries and testes
What is a gamete?
A sex cell (e.g. sperm or egg)
What is differentiation?
When an unspecialised cell becomes specialised
How does differentiation vary in animal and plant cells?
Most plant cells are able to be differentiated throughout their lives. In animals, only embryonic stem cells are able to differentiate into any specialised cell. Adult stem cells can only differentiate into a small number of specialised cells
How many pairs of chromosomes are there in a normal human body?
23
How many chromosomes in a human sperm cell?
23
How many chromosomes in a human egg cell?
23
Who was Mendel?
An Austrian monk who laid the foundations of genetics
What are the three conclusions Mendel made after completing his work on pea plants?
- Characteristics are determines by ‘hereditary units’
- Hereditary units are passed on, unchanged from both parents - one unit from each parent
- Hereditary units can be dominant or recessive. The dominant characteristic will always be expressed when present
Why didn’t Mendel get any credit for his work while he was alive?
Nobody knew about genes, chromosomes or DNA when Mendel was alive
Explain how DNA testing can be used to identify the father of a child
DNA profile of both the baby and its mother must be known. Take a cell sample from the child and father. Isolate the DNA sample from each. Use enzymes to cut up each sample. Place samples in a gel and run a current through the gel. Compare the pattern of DNA fragments from each sample
Give two examples of the advantages of genetic profiling
It is very reliable because no two people have the same DNA (except identical twins), used to determine paternity, used to identify genetic disorders early, used to place suspects at a crime scene
Give two examples of the disadvantages of genetic profiling
DNA data might be stolen and used by insurance / loan / employers, storage of DNW profiles could be seen as an invasion of privacy. Theft of DNA profiles from a database, DNA can be planted at a crime scene causing miscarriages of justice
Name the monomers of DNA
Nucleotides
Describe the general structure of a molecule of nucleotide
A sugar group, a phosphate group and a base
Name the four bases found in DNA
A - adenine, T- thymine, C - cytosine, G - guanine
Which molecules make up the ‘backbone’ of the DNA strand?
The sugar and phosphate bases
Describe the complementary pairing found in DNA molecules
Adenine only links to Thymine whilst Cytosine only links to Guanine (A - T, C - G)
What type of bonding occurs between the complementary pairs of DNA?
Hydrogen
Describe how to extract DNA from a banana (4 marks)
- Mash up some banana and mix it into a beaker containing washing up liquid and salt
- Filter the mixture
- Slowly put some ice-cold ethanol to the filtrate
- The DNA will start to precipitate into long white strands which should be removed using a glass rod
What does the washing up liquid do to the banana?
Break down cell membranes to release the DNA
What is the role of the salt in DNA extraction?
Makes the DNA molecules stick together
Why is cold ethanol used?
DNA is not soluble in cold ethanol
What should you see when the cold ethanol is added to the filtrate solution?
White strands of DNA should become visible as they precipitate out of the solution
What risk does the ethanol pose?
It is flammable so could catch light
How is the risk from ethanol reduced?
Keep lit flames away from the ethanol
What term is used to describe a section of DNA that codes for a specific protein?
A gene
What term is used to describe all of an organism’s DNA?
Its genome
What does the DNA control the production of in cells?
Protein
What are proteins made of?
Long chains of amino acids
Explain why each protein has a specific shape
The amino acid chains fold up to give the protein of its shape
What decides the order of amino acids in a protein?
The order of bases on DNA
How many bases make a code for an amino acid?
Three
What do we call the bases that make up a gene?
Base triplet
Some sections of DNA are non-coding. What does this mean?
The DNA does not code for any amino acids
What is a mutation?
A rare, random change of an organism’s DNA base sequence
If a mutation happens in a coding region of DNA, what is produced?
A different version of the gene - a variant
What can non-coding sections of DNA do to genes?
Switch them off and on
What is the first stage of protein synthesis?
Transcription
Where in the cell does the first stage of protein synthesis occur?
The nucleus
Name the second stage of protein synthesis
Translation
Where in the cell does the second stage of protein synthesis occur?
The cytoplasm
Which sub-cellular structures are involved in the second stage of protein synthesis?
Ribosomes
Name the molecule that is needed to make a copy of the DNA bases sequence of a gene
Messenger RNA (mRNA)
How is messenger RNA (mRNA) similar to DNA?
It is a polymer of nucleotides
How is the messenger RNA (mRNA) different to DNA?
It uses Uracil (U) instead of Thymine (T). It is shorter and only a single strand
Name the enzyme that is needed to make mRNA
RNA polymerase
What is the first thing that the RNA polymerase does to start the process of making mRNA?
The RNA polymerase binds to a region of non-coding DNA in front of a gene
Describe what happens next as the two strands of DNA unzip
The RNA polymerase moves along on the strands of DNA, using the code as a template to make mRNA
What ensures that the mRNA is complementary to the gene?
The base pairing between the DNA and RNA
What happens to the mRNA once it is made?
It moves out of the nucleus and binds to a ribosome in the cytoplasm
Name the molecules that bring amino acids to the ribosomes
Transfer RNA (tRNA)
What are the base triplets in mRNA known as?
Codons
Name the part of the tRNA that is complementary to the codon for the amino acid
Anticodon
How is the order of amino acids brought to the ribosomes controlled?
By the pairing of the codon and anticodon
What does the ribosome do to the amino acids?
Joins them together
What is a polypeptide?
A chain of amino acids (another word for a protein)
How do variants in the non-coding DNA at the start of a gene affect an organism’s phenotype?
It affects how well RNA polymerase binds to the DNA
A sample of DNA is analysed and 46% of the base pairs contain thymine (T). If there are 2.16 x 10^6 base pairs in the sample, how many base pairs contain cytosine (C)?
1.17 x 10^6 (1166400)
What are alleles?
Different versions of a gene
How many alleles of a gene do nerve cells contain?
Two
How many alleles of a gene do egg cells contain?
One
Define heterozygous
When an organism has two different alleles for a specific gene
Define homozygous
When an organism has two alleles that are the same for a specific gene
What type of allele always controls a characteristic?
Dominant
What type of allele needs to have two copies for it to be shown?
Recessive
Define the term ‘genotype’
The alleles that make up an organism’s genome
Define the term ‘phenotype’
The physical characteristics that are controlled by alleles
What are the sex chromosomes for a male?
XY
What are the sex chromosomes for a female?
XX
Define the term ‘monohybrid inheritance’
A characteristic that is controlled by a single gene
How is monohybrid inheritance studied?
Using monohybrid crosses - crossing (breeding) two parents to look at just one characteristic
Define the term ‘carrier’
A person who has one copy of a faulty allele that causes a disorder but doesn’t have any symptoms
What is the chance of a child having a disorder if both parents are carriers?
1 in 4 chance - 25%
What is the chance of a child being a carrier if both parents are carriers?
1 in 2 chance / 2 in 4 chance - 50%
What can genetic diagrams, like the Punnet square, be used for?
To predict and explain the outcomes of monohybrid crosses
In genetics, what does a family pedigree show?
How a characteristic or disorder is inherited in a group of related people
Why will you only inherit cystic fibrosis if you get the cystic fibrosis allele from both parents?
Cystic fibrosis is controlled by a recessive allele so two copies are needed for the characteristic to be displayed
Why can one parent of polydactyl pass the condition on?
Polydactyl is controlled by a dominant allele
Why are carriers of cystic fibrosis not affected by the disorder?
The cystic fibrosis allele is recessive. Carriers have one normal copy of the allele as well as one cystic fibrosis allele. The normal copy is dominant so it controls the phenotype
A couple have a baby with cystic fibrosis yet neither parent has the condition. Draw a diagram to show how this happened and give the probability of this happening again
25% risk
A plant with red flowers is crossed with a white-flowered plant of the same species. All the seeds, when grown, produce plants with red flowers. Assuming that the flower colour is controlled by a single pair of alleles, which allele is dominant and which is recessive?
The allele for red-coloured flowers must be dominant if no white flowers appear in the first generation (assuming a very large sample)
If a dominant allele for tall plants is represented by the letter D, what letter should represent the corresponding recessive allele?
The recessive allele is d
In cats, the allele (S) for short fur is dominant to the allele (s) for long fur. What is the genotype of a true-breeding, long-furred cat?
A true-breeding, long-furred cat has the genotype ss
In cats, the allele (S) for short fur is dominant to the allele (s) for long fur. What is the phenotype of a cat with genotype Ss?
The Ss genotype will produce a short-furred phenotype
In cats, the allele (S) for short fur is dominant to the allele (s) fro long fur. In the Ss genotype, which allele is expressed in the phenotype?
In the Ss genotype, the dominant allele (S) will be expressed
Which of the following genotypes is (i) heterozygous: SS, Ss, ss?
Ss
Which of the following genotypes is (I) homozygous dominant: SS, Ss, ss?
SS
In rabbits the dominant allele (B) produces black fur. The allele (b) for white fur is recessive. What colour fur will a rabbit with BB alleles have?
Black
In rabbits the dominant allele (B) produces black fur. The allele (b) for white fur is recessive. What colour fur will a rabbit with Bb alleles have?
Black
In rabbits the dominant allele (B) produces black fur. The allele (b) for white fur is recessive. What colour fur will a rabbit with bb alleles have?
White
In rabbits the dominant allele (B) produces black fur. The allele (b) for white fur is recessive. What colour fur will a rabbit with bB alleles have?
Black
Which rabbits are homozygous for coat colour: BB, Bb, bB, bb?
BB, bb
If rabbits BB and bb were mated together and had 12 babies, how many of these would you expect to be black?
All 12 - they all have one dominant allele
If rabbits Bb and bB were mated together and had 48 babies, how many of these would you expect to be white?
Ratio of 3 black to 1 white baby, which is 36 black and 12 white
If rabbits Bb and bb were mated together on several occasions and had a total of 50 babies, how many of these would you expect to be black?
50% black and 50% white, (i.e. 25 of each)
The alleles controlling the ABO blood groups are given the letters IA (group A), IB (group B) and i (group O). What alleles could be found on the chromosomes for a person with Type A blood?
IA, IA or IA, i
What alleles could be found on the chromosomes for a person with Type B blood?
IB, IB or IB, i
What alleles could be found on the chromosomes for a person with Type O blood?
IA, IB
What alleles could be found on the chromosomes for a person with Type AB blood?
i, i
Give three examples of human disorders which are caused by the action of a single pair of alleles. In each case say whether the harmful allele is dominant or recessive to the non-harmful allele
Any three from haemophilia (recessive), albinism (recessive), phenylketonuria (recessive), red-green colour blindness (recessive), sickle-cell anaemia (partially recessive), polydactyl (recessive)
What is the genotype for human males?
XY
What is the genotype for human females?
XX
In humans, is it the sperm or the ovum which determines the sex of the offspring?
The sperm determines the sex of the offspring
Give a reason for why the sperm determines the sex of the offspring
All the ova contain an X chromosome. Half the screens carry an X chromosome and half carry a Y chromosome
When a particular gene is said to be ‘sex-linked’, on which chromosome is that gene usually present?
A sex-linked gene is usually carried on the X chromosome and is absent from the Y chromosome
One form of colour-blindness is a sex-linked inherited condition controlled by a recessive allele. Use the symbols X and Y for the sex chromosomes and N and n for the alleles for normal or defective colour vision to show the genotype of a normal male
XN, Y
Show the genotype of a colour-blind female
Xn Xn
Show the genotype of a colour-blind male
Xn Y
Show the genotype of a normal (carrier) female
XN Xn
Show the genotype of a normal (non-carrier) female
XN XN
What is the chance of a carrier female and non-colour-blind male having a colour-blind child?
25% / 1 in 4
What is the chance of a carrier female and non-colour-blind male having a colour-blind son?
25% / 1 in 4
How do we classify blood types?
ABO blood group system
Explain why ABO blood groups show codominance
Both alleles present affect the phenotype
What are the possible genotypes of a person with Type AB blood?
AB
What are the possible genotypes of a person with Type O blood?
OO
What are the possible genotypes of a person with Type A blood?
AO / OA
What are the possible genotypes of a person with Type B blood?
BO / OB
What do we call disorders that show a different pattern of inheritance in women and men?
Sex-linked genetic disorders
Explain why men are more likely to have red-green colour blindness compared to women
Need to have not of red-green colour genes because it is recessive. It is found on the X chromosome. Men only have one X chromosome and therefore if they have the recessive allele they will definitely be colour-blind. However, women have two X chromosomes and therefore have to have two copies to have the disorder
Use a Punnett square to calculate the probability of having a boy or a girl who is colour blind if the father is NOT colour blind and the mother is a carrier of the allele
Boy - 50% / Girl - 0%
Using a Punnett square explain why a mother who is blood group A and a father with blood group B could have children who are any of the four blood groups
Mum - AO, Dad - BO, Offspring AB - 25%, A - 25%, B - 25%, O - 25%
What type of variation is caused by different alleles?
Genetic variation
What type of variation is caused by interacting with your surroundings?
Environmental variation
Explain what type of variation controls the length of hair
Environmental - you can cut your hair
Explain what type of variation controls blood group
Genetic
Explain what type of variation controls height
Genetic and Environmental - genes control the possible growth, the amount of nutrition can also stunt growth
What type of chart would you use to show variation in leaf length?
Frequency chart
What type of chart would you use to show variation in the numbers of leaves on a plant?
Bar chart
What type of chart would you use to show the growth of a plant over a month?
Line graph
What shape of graph is made by continuous variation?
Bell chart
What type of distribution is shown by the shape of graph that is made by continuous variation?
Normal distribution
Where is the most common value on a continuous variation graph?
The middle
What happens to the number of individuals as the values move away from the median?
There are fewer individuals
