D3.2 Inheritance Flashcards
How much genetic material comes from each parent?
The offspring produced have 50% of the genetic material from each parent.
Is your genetic material specific to you or not?
Your genetic makeup is specific to you and not the same as that of your sibling, even with the same parents. Unless you are a monozygotic twin (Produced from a single fertilised egg).
What happens when an individual is sexually matured?
Cells within specialised organs called gonads will start to undergo a certain kind of cell division called meiosis. The gonads contain cells whose nuclei have pairs of chromosomes. The cells divide twice during meiosis and the unique cells produced are given the term gametes. These are known as haploid (n) as they have only one copy of each chromosome from one of the parents.
What is special about gametes?
The gametes are highly specialised with specific features. On their own, these gametes cannot generate a new individual. Two gametes (one from the male parent and one from the female parent) fuse together to form a diploid (2n) zygote that now contains an equal amount of genetic information from both parents.
What is hermaphroditic?
Hermaphroditic is when the male and female gametes are often present in the same plant e.g. pea plant.
Who was George Mendel? And why is he famous?
A monk named Gregor Mendel (1822–84) from an area now found in the Czech Republic, conducted numerous plant-breeding experiments over many years using the humble pea (Pisum sativum). He observed flower colour along with the texture and colour of pea seeds and pods. His experiments are so important that he is often referred to as the ‘father of genetics’.
What was Mendel’s experiment?
In his experiments, Mendel crossed many pea plants by selecting the pollen from one plant and brushing it onto the stigma of another plant. He was able to first observe and later predict the inheritance of different pea flower and pea seed traits. For example, he showed that when true-breeding parents for traits such as round seeds were bred with true-breeding parents for wrinkled seeds, they would result in offspring that produced only one form of these traits (e.g. round seeds).
What is the P generation?
Parent generation of a genetic cross. (Parental generation)
What are offspring called in genetic crossing?
The offspring are called the filial (F) generation.
What is F1 generation?
F1 are the offspring from the P generation (First generation).
What is F2 generation?
If two members of the F1 generation are subsequently bred together, this would give rise to the F2 generation which would then possess some physical characteristics not seen in the F1 generation. ( F2 are the offspring produced from crossing F1 parents)
How can genetic breeding be linked to solution for UN SDG 2 zero hunger and climate change?
Genetic breeding experiments between two related species are commonly used to generate new varieties of crops. Specific individuals can be carefully selected to ensure that the offspring have desired characteristics. Scientists around the world are focused on breeding plants that are able to cope with climate change, extreme weather, drought or flooding.
What are homologous chromosomes?
A pair of chromosomes of the same type (one comes from the mother and one comes from the father).
What is a gene?
Along the length of the chromosome are stretches/ a segment of DNA that codes for a specific protein.
What is the relationship between location and the gene on homologous chromosomes?
These genes are in identical positions on each of the chromosomes and so an individual will therefore have two copies of the gene (one from each parent).
Do genes need to be identical on the homologous chromosomes?
However, the two genes may differ from each other by a few bases. These different forms of a gene are called alleles.
What is an allele?
A variant or version of a gene.
What happens when the alleles combine?
This allele combination is called the genotype.
What is a genotype?
The specific set of DNA that an organism possesses.
What is it called when a gene has two identical alleles?
Homozygous
What is homozygous?
Both alleles for a trait are the same, for example, FF or ff.
What is it called when the two alleles are different from one another?
Heterozygous
What is heterozygous?
The alleles for a trait are different e.g. Ff.
How are genotypes determined?
Genotypes can be hard to determine but some physical traits are easily visualised and are caused by the genotype an individual possesses e.g. hitchhikers thumb.
What is a phenotype?
The outward expression of the combination of the alleles along with the influence of environmental. (Physical traits and characteristics of a cell or organism)
Are phenotypic traits always determined by environment or genotype?
Some traits, like our skin colour, are a combination of both genetics and environment; in this case, how much we expose our skin to the sun.
Can genes effect the way you taste?
Yes, the ability to taste the bitter chemical is controlled by one gene called TAS2R38 which codes for a protein for a taste receptor on the tongue. There are two common forms of the allele: one allele is the ‘tasting allele’ and one the ‘non-tasting’ allele.
What is a dominant allele?
A dominant allele masks the presence of the recessive allele.
What is a recessive allele?
A trait that is only expressed when it is in the homozygous form.
What is homozygous dominant?
Both alleles for a trait are dominant, for example, FF.
What is homozygous recessive?
Both alleles for a trait are recessive, for example, ff.
What is phenotypic plasticity?
The ability of an organism to express different phenotypes depending on the abiotic or biotic environment
This involves regulatory genes that switch on structural genes given the appropriate stimulus.
What does phenotypic plasticity allow an individual to do?
It allows individuals with the same genome to adapt when exposed to different environmental conditions. These changes may involve an alteration in behaviour, physiology or morphology. This is not caused by changes in the genotype and these changes do not even need to be permanent; the changes might be reversed during the individual’s lifetime depending on the situation.
Why is phenotypic plasticity important?
Phenotypic plasticity is important as a means to increase the chances of survival in a changing global climate.
What is an example of phenotypic plasticity?
An example of this phenotypic plasticity is the seasonal polyphenism of the butterfly Bicyclus anynana. When it is cooler, the adults take on the form of ‘dry-season’ adults that live for a longer time and breed at the end of the season. Their wing patterns are similar to dry foliage so that they can escape predators. However, when the weather is warmer, the adults look more like ‘wet-season’ adults. These have a shorter life span but breed many times during this season. Their wing patterns have distinctive eye spots that prevent predation. As the seasons change, so does the butterfly’s physical form.
What is a recessive genetic condition?
A recessive genetic condition means the individual would need to be homozygous recessive with two copies of the recessive allele to have the trait. The presence of one correct allele is sufficient to generate the functioning enzyme and results in a healthy individual.
What is an example of a recessive genetic condition?
One such recessive disorder is phenylketonuria or PKU. PKU is caused by a mutation in a gene on chromosome 12, This gene codes for an enzyme used in metabolism called phenylalanine hydroxylase (PAH) that converts the amino acid phenylalanine (Phe) into tyrosine (Tyr). In a child that is homozygous recessive for this allele, the Phe in the cell is not broken down and so toxic levels build up.
What the symptoms of PKU?
The baby may initially seem healthy but within a few months, symptoms can develop, such as a musty odour from the skin and urine, fair skin, eczema, seizures, tremors and hyperactivity.
How is PKU tested?
In most countries around the world, babies are tested for PKU at 1–2 days of age. A simple heel stick gives a drop of blood that can be tested on a filter paper for the Phe:Tyr ratio. If the test reveals a high level of Phe, then further testing is conducted.
What happens if PKU is not treated? And what is treatment?
If the condition is left untreated, brain damage can occur. Unfortunately, there is no quick treatment, but this condition can be well managed if a life-long dietary plan that keeps protein levels low is maintained, along with frequent blood tests.
What is a single nucleotide polymorphisms?
Single nucleotide polymorphisms (SNPs, pronounced snips) are the most common variation in humans. They are caused by a single nucleotide change.
What is a mutation/variation in human genome?
Sometimes, a single nucleotide in the DNA gets randomly changed for another one. This is called a mutation
Where can SNP be found?
They can be in a gene that codes for a protein or in parts of the DNA that are non-coding and are responsible for other functions.
What does SNP result in?
SNPs can then result in many different alleles for a single gene. The more SNPs within a gene, the more different alleles there will be. These multiple alleles available in a gene pool all add to the genetic variation possible. The different allelic forms of a gene are not necessarily permanent and can appear, and equally as easily disappear, in a population of organisms. To increase variation even further, each individual only inherits two alleles for a gene and so the combination of the alleles it possesses also relates to the variation.
What are multiple alleles?
Many allele options for a gene. E.g. Blood type is a human trait controlled by multiple alleles and inherited from parents.
Where is allele blood type found?
The allele for blood type is found on chromosome 9 in the human genome and the gene is called the ABO gene.
What are the allelic forms for blood type?
The three allelic forms A, B and O are each responsible for making their own type of enzyme (glycosyltransferase).
What is the role of the type of enzyme (glycosyltransferase) in blood types?
This enzyme catalyses the production of specific carbohydrate chains (sugars) on the outside of the red blood cells. These sugars are capable of producing an immune response and so are referred to as antigens. So, it is the ABO type of gene that determines which kind of sugar (antigen) is made. However, each individual only has the possibility of two alleles for blood type.
How blood type A written in alleles?
type A (IAIA or IAi)
Someone that has one IA allele and one i will have blood type A, as the IA allele is dominant over i; they will have the A antigen on the surface of their red blood cells.
How blood type B written in alleles?
type B (IBIB or IBi)
An individual with one IB allele and one i will have blood type B, as blood type B is dominant over O; they will have the B antigen on their red blood cells.
How blood type O written in alleles?
type O (ii)
However, a person that has two ii alleles (type O) will express neither antigen.
How blood type AB written in alleles?
blood type AB (IAIB)
Individuals that have alleles for glycosyltransferase A and glycosyltransferase B will express both antigen A and B on their red blood cells as both of these genes are equally dominant (codominant)
What is codominance?
Two alleles are both expressed equally.
Why must blood transfusions be done carefully?
When giving blood transfusions, care must be taken, as it is the presence of antibodies in the plasma of the recipient that might result in clotting of the received blood. Clots are dangerous as they can break free and move into other parts of the body; for example, they could block the blood flow to the brain or move into the lungs.
What blood type is a universal donor?
The O blood type is known as the universal donor as this blood type has no antigens on the surface and so regardless of the blood type of the recipient, the antibodies would have nowhere to bind, and therefore would not cause clotting.
What blood type is a universal recipient?
A person with blood type AB is known as the universal recipient. Their red blood cells have both surface antigens, but these individuals have no antibodies in their plasma, and so can receive all blood types without hindrance.
What is incomplete dominance?
A third phenotype that is intermediate between the dominant and recessive can be produced. This is when two parents with different phenotypes give rise to offspring with a phenotype that is intermediate between the two parental types.
What is an example of incomplete dominance?
In the flower called the Marvel of Peru (Mirabilis jalapa), the allele for red flowers is not entirely dominant over the allele for white flowers. Therefore, in heterozygotes, a third phenotype – pink – results that is intermediate between the red and white flowers.
How do you write incomplete dominance?
The convention for incomplete dominance is to use a capital letter with a superscript letter for the allele. In this example, CW is the white allele and CR is the red allele. Using this notation, white flowers would have the genotype CWCW, red flowers would have the genotype CRCR and pink flowers would have the genotype CWCR.
What is the chance of either sex?
50/50 chance of either gender
How is sex determined?
Sex determination is inherited. In humans, the 23rd pair of chromosomes are the sex chromosomes. A haploid egg contains one copy of all 23 chromosomes. The 23rd chromosome will be an X chromosome. A haploid sperm also has one copy of all 23 chromosomes but in this case the 23rd chromosome will be either an X or a Y chromosome. Either could fertilise the egg, and therefore it is the sperm that ultimately determines sex. When fertilisation occurs, the zygote will contain the chromosomes that were carried within the gametes.
What is chromosomes are required for female and male sex in humans?
XX=female
XY=male
What is the gene that is important on the Y chromosome?
A particular gene on the Y chromosome called the SRY gene is important in allowing the zygote to develop into a male embryo. This gene encodes for a sex-determining region Y protein which acts as a transcription factor and binds to particular parts of the DNA to control the expression of certain genes. This factor enables a foetus to develop male gonads and prevents the development of female organs.
What is non-disjunction?
Sometimes the meiotic division responsible for making eggs or sperm at oogenesis or spermatogenesis goes wrong. (The failure of homologous chromosomes or sister chromatids to separate during cell division.) If this happens in the 23rd pair, an incorrect number of sex chromosomes can result.
What is an example when non-disjunction occurs on chromosome 23?
Klinefelter syndrome is one of the most common example of aneuploidy (Figure 2). Aneuploidy is when an individual has an extra chromosome(s) or is missing a chromosome. This is different from polyploidy where there are extra complete sets of chromosomes in the nucleus. Klinefelter syndrome occurs in about 85–250 cases for every 100 000 males born and can result in a person having 47 (XXY), 48 (XXXY) or 49 (XXXXY) chromosomes.
Why are there sex-linked disorders?
The X chromosome is about three times larger than the Y chromosome and has about 900 genes compared with the 55 genes found on the Y chromosome. With a greater number of genes comes a greater possibility of mutations, and therefore disorders. Due to the difference in sizes, there are portions of the X chromosome that have no homologous Y counterpart. This means that if an allele is present for a disorder on the X chromosome only, the individual would then be positive for that disorder.
What are sex-linked genetic disorders? And what are two examples?
Certain alleles that confer inherited conditions are found on the long arm of the X chromosome. These are called sex-linked genetic disorders and include colour blindness and haemophilia.
What is haemophilia?
In haemophilia, blood-clotting factors known as Factor XIII or Factor IX are made in insufficient quantities. This is often caused by a mutation in a gene for one of these clotting factors. This means that when an individual is cut, they can bleed excessively, even after a relatively small trauma. Bleeding might not be visible and can be internal, which is when damage occurs to the blood vessels inside the body; this can be equally life threatening.
Why is haemophilia know as the king’s disease?
It has been called the ‘disease of the kings’ as Queen Victoria of England was a carrier, however no living member of the current royal family carries the defective gene. New gene therapy technology has been used with success for haemophilia. The gene that makes Factor IX has been inserted into a virus that infects humans but does not cause disease. This virus is called a vector and can be used to infect liver cells that are responsible for making the clotting factor. Functional protein is then generated by these cells and so this removes the need for injections of Factor IX every three to four days for life.
What are pedigree charts?
Diagrams used to show the inheritance of a trait through a family’s history.
How females and males represented in pedigree charts?
Female=circle
Male=square
How carriers, affected, unaffected represented in pedigree charts?
Carriers=half-coloured
affected=fully coloured
unaffected=not coloured/blank
How is family and marriage represented in pedigree charts?
family=lines that link down
marriage=lines that link across
What happens when breed in small population or within family?
Breeding within a small population reduces a species’ variation. Any genetic diseases within a smaller gene pool will then be more likely to be observed. Throughout history, many human cultures have favoured consanguineous marriage (marriage between two blood relations that are second cousins or closer) as this is seen to help retain a strong lineage. This cultural practice can lead to the increased presence of autosomal recessive disorders, as well as congenital abnormalities. Many societies now have restrictions over close family marriage for this reason.
What is a discrete variation?
Phenotypes that have distinct categories, for example, blood type A, B, AB or O. There are no gradual changes between these types and no in-betweens.
What is continuous variation?
Phenotypes that show a wide variety between two extremes in a population, for example, height. Human height for example, where there are no specific groups, but show a gradual change between two extremes in a population.
What is polygenic inheritance?
When more than one gene controls a characteristic, for example, the inheritance of skin colour or height. Also when environment affects the phenotype.
What would graph be like for continuous?
This continuous variation results in a spread called a normal distribution and, when plotted, results in a bell-shaped curve. All continuous variation in a population can be seen to have a normal distribution.
How is different ski coloured produced?
The vast range of skin colours in the human population is due to the presence or absence of melanin. Some genes encode for melanin and some do not. It is the additive effects and combination of all these alleles in an individual that means they have the skin tone that they do. Even siblings with the same parents can have quite different skin colours purely because the combination of alleles they inherited from their parents is unique to them. Examination of people that are originally from various parts of the world helps to explain why skin colour has evolved. The more genes that express melanin, the darker the skin colour. This melanin protects the nucleus from dangerous UV wavelength. Where UV is strong, the skin is dark. Where the UV is less strong, skin is lighter.
What are linked genes?
When genes are found on the same chromosome, and are close together, they are said to be linked. (Genes on the same chromosome that are usually inherited together)
What are unlinked genes?
If they are on different chromosomes, they are unlinked. (Genes on different chromosomes that assort independently.)
What is independent assortment?
When the gametes are being made in meiosis, pairs of alleles for these different genes will separate (segregate) and then join together (assortment) independently from one another. We can say that the inheritance of one allele is independent of the inheritance of the other. (The separation of homologous chromosomes and sister chromatids being independent of their pair during meiosis due to random orientation)
When do we use monohybrid cross and a dihybrid cross?
Monohybrid=linked chromosomes
Dihybrid=unlinked chromosomes
What is the location of a gene called?
The genes within a human population are located in the same position called loci (singular locus) on specific chromosomes.(The position of a gene on a chromosome.)
What are the short and long arm called on the chromosomes?
Chromosomes have a short arm (p for petit) and a long arm (q).
What does each gene with a specific locus have the ability to do?
Each gene with its specific locus encodes for a polypeptide product.
Why do linked genes no follow Mendel’s law?
Linked genes can fail to assort independently and so do not follow Mendel’s laws. This may be because they are close to each other on the chromosome and therefore the genes travel together as a unit.
What happens to gene when they are further apart?
However, if the genes are further apart on the chromosome, then there may be some exchange of material between the paternal and maternal chromosomes. This happens when the non-sister chromatids come close to each other in prophase I of meiosis during a process called synapsis. The corresponding parts of the non-sister chromatids might break and then reattach to the sister chromatid from the other parent. This is called crossing over and gives rise to more genetic variation.
What does distance between genes lead to?
If they are very close, then they are likely to be inherited together. The further apart they are from one another, the more likely it is that crossing over happens at least once. The distance between genes can be calculated based on the number of crossing overs. The further apart the genes are, the more crossing over episodes will likely have occurred. As the gametes are made in meiosis II, the haploid cells may contain the same combination of genes as the parent or, if crossing over has taken place, they may have a combination not found in either of the parents. Rather, it is a recombination of both of the parents’ chromosomes. The frequency of recombinant genes is greater when the genes are further apart.
Definition: Genotype
the alleles of an organism
Definition: Phenotype
the characteristics of an organism
Definition: Dominant allele
an allele that has the same effect on the phenotype whether it it present in the homozygous or heterozygous state
Definition: Recessive allele
an allele that only has an effect on the phenotype when present in the homozygous state
Definition: Codominant alleles
pairs of alleles that both affect the phenotype when present in a heterozygote
Definition: Locus
the particular position on homologous chromosomes of a gene
Definition: Homozygous
having two identical alleles of gene
Definition: Heterozygous
having two different alleles of gene
Definition: Carrier
an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele
Definition: Test cross
testing a suspected heterozygote by crossing it with a know homozygous recessive
What affects the phenotype?
The phenotype can be shaped by a combination of the genotype plus the particular environment an organism is exposed to.
What is Rheus factor (blood type)?
Rh determines the absence or presence of D antibodies. Rh += dominant, Rh-= recessive
