B5.1 Flashcards
What is a gamete?
It’s a mature haploid male or female Germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote
What is a chromosome
It’s a structure of nucleic acids and proteins found in the nucleus of most living cells, carrying genetic information in the form of genes
What is a gene
Short length of DNA on a chromosome which codes for a particular characteristic or protein
What is an allele
It’s each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. It’s a specific variation of a gene or a specific segment of DNA.
What is a dominant allele ?
It’s a variation of a gene that will produce a certain phenotype, even in the presence of other alleles. It’s dominant as one copy produces enough enzymes to supply a cell.
What is a recessive allele?
It’s a variety of genetic code that doesn’t create a phenotype if a dominant allele is present. The recessive allele’s effects are masked by the more dramatic effects of the dominant allele.
What is homozygous
It’s having two identical alleles of a particular gene or genes
What is heterozygous
It’s having two different alleles of a particular gene or genes
What is genotype
It’s the set of genes in our DNA responsible for a particular trait.
What is phenotype
It’s the physical expressions or characteristics of that trait.
What is a genome?
It’s the entire genetic material of an organism
What does the genome influence
The genome and its interaction influence the development of the phenotype of an organism
What’s discontinuous variation
It’s a characteristic that can fall into distinct groups.
What is discontinuous variation caused by
Genetics only and it only involves one or very few genes
What are some examples of discontinuous variation and how can it be displayed?
Gender, eye colour, wrinkled or non wrinkled seeds
Bar chart
What is continuous variation
It’s a characteristic that can be any value between a range
What are the causes of continuous variation
Genetic and environmental
Involves multiple genes
What are the examples of continuous variation and how can it be displayed
Leaf surface area, length of fur, skin colour
Histogram (normally just the line)
How do all variants arise and what do they have an effect on?
Mutations and most have no effect on the phenotype, some influence the phenotype and very few determine the phenotype
What are most phenotypic features results of?
Multiple genes rather than single gene inheritance
What are the advantages of asexual reproduction
Produces lots of offspring very quickly ( E. coli = divides every 30 mins)
Only one parent in needed so organisms can reproduce whenever the conditions are most favourable ( don’t have to wait for mate) (E.g. aphids reproduce in summer when there’s more food)
What are the disadvantages of asexual reproduction
No genetic variation in offspring ( if environment changes then conditions are unfavourable and the whole population is affected)
E.g. the Black Sigatoka = disease which effects banana plants which reproduce asexually. This means of there’s an outbreaks then all will be affected as none are resistant
What are the advantages of sexual reproduction
- Creates genetic variation in the population
- if environment changes then it’s more likely that that some individuals will have characteristics that allow them to survive
- Over time this causes evolution as species become more adapted to the environment
What are the disadvantages of sexual reproduction
It takes more time and energy
Produces fewer offspring ( e.g organisms need to find and attract mates like male bowerbirds build their females an attractive structure and then dance for them)
Two parents are needed to it can be a problem if they are isolated (polar bears live alone so make polar bears have to walk 100 miles to find a mate)
What is a clone
An organism that is genetically identical to its parent
What is asexual reproduction
It is when each organism contains identical genes which are clones of the parent cell
How do bacteria reproduce
They replicate their genetic material and divide in half by mitosis
What is sexual reproduction
It requires 2 parents and they each produce their own sex cells called gametes, the sperm and the ova fuse together in fertilisation to produce the offspring.
How do plants reproduce
To create a new seed the pollen (male) fuses with the egg cell in the ovule .
What does haploid mean
They contain half the number of chromosomes of other body cells (23 in human gametes )
What does diploid mean
They contain 2 sets of each chromosome ( 46 in humans)
This comes form each of the haploid gametes
What is the role of meiotic cell division in halving the chromosome number to form gametes
By the process of meiosis the two haploid sex gametes have 23 chromosomes each so when they fuse they form a diploid cell. It’s also the source of genetic variation
Explain the process of meiosis:
- sexual reproduction so occurs in gonads (texts/ovaries) - the parent cell has 23 chromosomes from the mother and 23 from the father (46 chromosomes and 46 chromatids)
- The DNA unzips and the free mRNA join with the bases to replicate the chromosomes (46 chromosomes and 92 sister chromatids)
- the homologous pairs (similar pairs) of chromosomes go together
- here some sections of the DNA between the chromosomes are crossed and get swapped
- the chromosomes line up along the centre and split apart
- this forms 2 new cells which have a mixture of the mothers and the fathers chromosomes and this mixture creates genetic variation in the offspring (each cell has 46 chromosomes and 46 chromatids)
- in the second division the chromosomes line up in the centre again
- this time the arms of the chromosomes are pulled apart ( arm = 1 chromatid)
- this gives you 4 haploid gametes (germ cells) and each has a single set of gametes (23 chromosomes and 23 chromatids) - half no. Of chromosomes from start
- the cells are not identical but genetically varied
What happens when two sex gametes fuse
They fuse to make a fertilised egg cell which is a diploid cell with 46 chromosomes. This egg cell then divides by mitosis and develops into an embryo. After reaching a threshold, these cells differentiate into specialised cells.
How does genetic variation occur
You have 2 copies of genes for each characteristic (one from each parent). These 2 copies may be different or the same (different forms of a gene = alleles)
What type of characteristics does BB have
Homozygous dominant
Both are copies of same allele
What type of characteristics does Bb have
Heterozygous
Different versions of a gene - capital letter is written first
What type of characteristics does bb have
Homozygous recessive
Give examples of dominant characteristics
- dark wavy hair
- brown eyes
- straight nose
- free ear lobes
- freckles
- ability to roll tongue
- projecting chin
Give examples of recessive characteristics
- straight blonde hair
- blue eyes
- joined ear lobes
- upturned nose
- inability to roll tongue
- receding chin
- no freckles
How can predicting how the parents’ alleles might combine during fertilisation be useful?
Scientists can work out the possible characteristics of the offspring
How can you predict the outcome of a genetic cross?
- state the phenotype of both parents
- state the corresponding phenotype (CAP = DOMINANT lower = recessive)
- state the gametes for each parent and circle the letters
- Use a Punnett square to show the results and put the possible ones together
- state the proportions of each type of genotype produced
- state the corresponding genotype for each of the possible genotypes
What happens when two homozygous dominant and recessive alleles are crossed?
All of the offsprings are heterozygous. This means all the organisms will have the characteristics of the dominant allele.
What happens when two heterozygous individuals are crossed?
There is a 75% or 3 in 4 probability chance that the offsprings will have the characteristics of the dominant allele.
There is a 25% or 1 in 4 probability chance that the offsprings will have the characteristics of the recessive allele.
What happens when you cross a heterozygous individual and a homozygous individual?
There is a 50% or 2 in 4 probability chance that the offsprings will have the characteristics of the dominant allele.
There is a 50% or 2 in 4 probability chance that the offsprings will have the characteristics of the recessive allele.
What do the last pair of chromosomes represent?
The 22 pairs are identical in appearance but the 23rd one is known as the sex chromosome.
What type of chromosomes do you have to have to be male or female?
- if your cell has 2 large X chromosomes = female
- if your cell has 1 large X chromosome and 1 small Y chromosome = male
Why does XY mean it’s a male offspring?
The Y chromosome has a gene that results in a male offspring
What are the chances of the offspring being male or female and why?
Male gametes (sperms) can either have an X or Y chromosome, so it’s the father that determines the sex of its offspring. All the female gametes (eggs) have an X chromosome.
Due to this there is a 50 : 50 chance of conceiving a boy or a girl during pregnancy. In a larger population this will result in in equal numbers of boys and girls
What type of inheritance refers to the inheritance of traits determined by a single gene?
Monohybrid inheritance (study of one characteristic)
What is a mutation and when does it occur?
A mutation occurs when the sequence of DNA bases is altered and they can occur spontaneously. They can be inherited.
What can increase the chances of mutation of occurring?
Some substances such as benzene and ethanol and ionising radiation such as UV can greatly increase the chance of mutation occurring
What is a genetic variant and what is it caused by?
Genetic variant is a different version of an allele which is caused by the change in DNA.
What determines the effect that mutation will have on the organism
The position of the mutations in the DNA sequence determines the effect that will have on the organism
Give examples of harmful mutations
- cancer
- production of abnormal protein channels ( channels that allow molecules to be transported through the cell membrane) that do not function properly (such as cystic fibrosis)
- cause different shaped protein molecules to be made (people with sickle anaemia have unusually shaped haemoglobin molecules and this makes their blood cells sickle shaped)
What is cancer the result of?
It’s when the cell grows and divide uncontrollably
Give an example of a neutral mutation
Ability to roll your tongue as a result of a gene mutation which does not affect you significantly
Give an example of a beneficial mutation
Mutations in some bacteria enable them to be resistant to antibiotics which increases their chance of survival
Why does smoking significantly increase your risk of cancer
This is because the substances produced when cigarettes burn increase the chance of mutations occurring in your DNA
How is a DNA strand organised?
It is organised into sections of coding DNA (genes), which are separated by sections of non-coding DNA
What three things can happen to a DNA base when mutations occur?
The bases may be changed or added or deleted. This changes the sequence of bases so the order of the bases (in mRNA) produced during transcription may be different.
How much does changing a base, adding a base and deleting a base change the amino acid coded for the triplet sequence.
- changing = changed the amino acid coded for by the 1st triplet only
- adding = changed the amino acid code for the 1st triplet in sequence and all that follows it after
- deleting = Changed 1st triplet and all triplets
What effect does the sequence of the bases changing have?
The amino acids may be assembled into a different order, the wrong protein may be produced, or it may fold incorrectly and form a different shape.
What will happen when a protein that is an enzyme mutates?
It’s active site might change shape and it will be no longer able to bind to a substrate and catalyse the specific chemical. This can result in metabolic diseases such as Phenylketonuria (PKU). In this condition, phenylalanine cannot be broken down by the body, which can lead to brain damage. This is how genetic variants may influence the phenotype in coding sections of DNA as they alter the activity of a protein.
What specific sequences of DNA bases that are found before each gene and what do they do?
They are start codons which are found before each gene in the non-coding section of DNA, which triggers transcription. If a mutation occurs within the sequence the gene may not be transcribed into a mRNA. This means no protein will be made. This is how genetic variants may influence the phenotype in non-coding sections of DNA as they alter how genes are expressed.
When was the discovery that certain characteristics are inherited carried out?
- 1866
Who discovered that certain characteristics are inherited
Gregory Medel
What did Mendel experiment with to show that certain characteristics are inherited?
He carried out experiments on peas and observed that characteristics such as height and colour are passed on from parents and to their offspring
What are the three things that Mendel noticed in his experiment with peas?
- characteristics in plants were determined by hereditary units which were now called genes
- hereditary units are passed on from both parents, one unit from each
- hereditary units are dominant or recessive
When was Nuclein discovered?
1869
Who discovered Nuclein?
Friedrich Meischer
What did Miescher discover?
He discovered that there is an acidic substance present in the nucleus of a cell which is the DNA
When was it discovered that genes could be transferred from one generation to the next
1944
Who discovered that genes could be transferred from one generation to the next
Oswald Avery
How did Avery discover that genes could be transferred from one generation to the next?
- Avery transferred DNA between bacteria
- passed the ability to cause disease from one strain of bacteria to another
- bacteria passed on the treat to the offspring
- showed that genes were made up of DNA
When we DNA base pairs discovered?
1950
Who discovered DNA base pairs?
Erwin Chargaff
What did Chargaff discover about DNA base pairs?
- found that even though different organisms have different amounts of DNA, all DNA have equal quantities of adenine and thymine and of cytosine and guanine
When where DNA crystals photographed?
1952
Who photographed DNA crystals and how?
Maurice Wilkins and Rosalind Franklin images DNA crystals using X -rays
When was the double helix structure of DNA identified?
1953
Who identified the double helix structure of DNA?
James Watson and Francis Crick
What did Watson and Crick discover about the DNA?
- published their description of DNA
- described it as a double helix
- (2 spirals held together by complementary base pairs)
How did genetics advance between 1953 - 2000?
- scientists identified genes that code for genetically inherited disorders such as cystic fibrosis
- scientists altered an organism’s characteristics by adding genetic material ( genetic engineering developed)
When was the Human genome project completed?
2003
What was the Human genome project?
- project lasting over 20 years
- scientists working across the globe identified and sequences around 24 000 genes = the complete set of genes in the human body
What current research is happening relating to genetics?
Gene Therapy:
- currently scientists are trying to replace faulty genes (mutated genes) with normal copies of the gene. This may be able to cure genetic diseases such as cystic fibrosis
Why should we carry on researching?
further scientific breakthroughs = more diseases may be cured or prevented in the future
Name in order, the name of the key scientists that helped us understand genetics over time?
Mixed = Mendel Martial = Miescher Arts = Avery Can = Chargaff Foster = Franklin World = Wilkins Wide = Watson Carnage = Crick
Name 2 genetic inherited disorders:
- polydactyly
- cystic fibrosis
What is polydactyly?
- condition where baby is born with extra fingers or toes
- cased by dominant allele
- Aa + aa = 50% of having an offspring with polydactyly
What is cystic fibrosis?
- disorder of cell membrane which results in lots of sticky mucus being released in different parts of the body ( particularly in airways of lungs and pancreas)
- caused by recessive allele Ff + Ff = 25% chance of getting cystic fibrosis
- most poeple have homozygous dominant genotype but 1 in 25 people are heterosygpus = called carriers = possibility of passing onto offspring
What is embryo screening?
- IVF embryos can be screened before implanting back into mother’s uterus
- Embryo screening = look at embryo’s genes to see if it’s carrying any genetic disorders (polydactyly and cystic fibrosis)
- if alleles that could cause a disorder found = might discard that embryo and use a different one instead
What are the advantages and disadvantages of embryo screening?
Advantages
- reduce overall amount of suffering
- save money (treatment is expensive)
Disadvantages
- implies that people with genetic problems are less desirable than healthy individuals = increase prejudice
- future = people might screening for other traits (Laws to prevent)
What are the 2 types of mutation?
- pointe = has no effect
- chromosomal = has effect
How can mutations lead to a change in the phenotype?
- mutations change the sequence of bases in the DNA, which can produce a genetic variant
- this can alter the sequence of amino coded for by a gene, changing the structure of the protein produced
- this may affect the protein’s ability to perform its function by a small or large amount, leading to changes in the phenotype of an organism
- mutations can also affect non-coding sections of DNA
- mutations in these sections affect wether the genes are expressed or not. They can stop the transcription of mRNA so the so the protein coded for by that genes isn’t produced at all.
- mutations that prevent protein from being expressed can have a large or small effect on phenotype of an organism
What are the key differences between mitosis and meiosis?
- mitosis = body cells, 2 diploid cells, body cells produced, 1 division, 2 sets of chromosomes (diploid), identically/ clones of parent cell
- meiosis = reproductive organs, 4 haploid cells, gametes produced, 2 divisions, 1 set of chromosome (haploid), not identical to parent cell
