Inheritance Flashcards
What is mono hybrid inheritance?
Inheritance of a single characteristic controlled by one gene (each parent having two alleles for that gene)
What is a gene
Length of DNA which codes for one polypeptide
What is an allele
One version of a particular gene
What is a locus
Location of a gene on a chromosome
What is a genotype
The allele possessed by an organism
What is a phenotype
Characteristics of an organism often resulting from an interaction between its alleles and the environment.
What is meant by dominant?
An alleles affect on the phenotype of a heterozygote is identical to its effect in a homozygote, when present it is always expressed.
What is meant by recessive?
An allele which is only expressed were no dominant allele is present.
What is meant by codominant?
When both alleles have an effect on the phenotype of a heterozygous organism
What is heterozygous
Having two different alleles of a gene
What is homozygous
Having two identical alleles of a gene
What does F1 stand for?
First generation (first filial generation)
What does F2 stand for?
Second generation (second filial generation)
What is sex linkage
The inheritance of a gene only present on the X chromosome no allele present on the Y
What is genetics
Study of mechanisms by which an organism inherit characteristics from its parent.
What is Mendels first law?
The characteristics of an organism are determined by alleles which occur only in pairs. Only one of a pair of alleles can be present on a single gamete.
What are the Mendel first law rules?
- Both parents donate one copy of a gene to each offspring.
- A characteristic appearing in the phenotype must have at least one appropriate allele in the genotype.
- A recessive characteristic must be homozygous in order to express the phenotype.
- If two parents show a given characteristic which is not shown in the offspring the parents are heterozygous and the offspring is a homozygous recessive.
How is a test cross carried out?
Using a homozygous recessive.
What happens if the unknown is homozygous?
Oh offspring will express the dominant phenotype
If the unknown is heterozygous what happens?
Half of the offspring will show the recessive phenotypes.
What are the steps when carrying out a punnet square?
P.phenotypes p.genotypes gametes F1 genotype F1 phenotype.
What is pure breeding?
It refers to a variety bred for several generations will itself so that all individuals are homozygous. All offspring have the same Geno/phenotype as their parents.
What are multiple alleles?
When one when more than one allele can code for one particular gene.
What chromosome is no alleles found?
y
Describe sex linkage?
The sex linked genes have their Loci on the X chromosome.
Males have only one copy of these genes whereas females have two.
In the male phenotype if the recessive allele is present then it will be expressed. In XX individuals there is a second copy of the allele which if its dominant will prevent an expression of the recessive allele (carrier). Sex linked recessive phenotypes are more common in males than females.
What are three sex linked traits?
Red green colour blindness.
Haemophilia.
Duchennes muscular dystrophy
Explain red green colour blindness?
The recessive allele lead to the failure to produce a functional cell cone pigments for either red or green detecting cone cells.
Explain haemophilia?
Recessive allele which leads the failure of producing a blood clotting protein factor eight.
Females act as carriers.
What is DMD?
Sex linked disorder in which females are carriers. 2/3 of cases are inherited from parents one third is due to mutations. It affects 1/5000 males at birth. Mutation occurs on the X chromosome affecting the production of dystrophin.
Who can act as carriers?
Only females, if the male has the gene they will express it.
What is dihybrid inheritance?
Inheritance of two species/gene is located on two different chromosomes. Each gene will have two alleles.
What is Mendels second law?
Law of independent assortment. Either one of a pair of contrasted characters may combine with either of another pair. E.g. alleles of different genes assort independently of one another during gamete formation.
What was found out about Mendels peas?
That the round shaped piece was dominant to wrinkled and yellow seed colour was dominant to green.
How do you workout phenotypic ratios?
The total number of offspring is divided by the number of homozygous recessive individuals.
What is the phenotypic ratio for a dihybrid cross between a heterozygous and a homozygous?
1:1:1:1
What is the phenotypic ratio for a dihybrid cross between a heterozygous and a hetrozygous?
9: 3: 3: 1
How do you carry out a dihybrid cross?
The unknown individual with a pea plant is crossed with a homozygous recessive for both traits (rr yy)
What is Chi squared?
It is a statistical test which enables you to establish if there is a significant difference between two sets of data: observed and expected. It is used to determine the number of offspring with particular phenotypes and if it is significantly different to the expected phenotypic ratios according to Mendels laws of inheritance.
If there is not a significant difference between observed and expected what is the difference due to?
Chance
What is the null hypothesis?
No significant difference between observed and expected results any difference is due to chance Mendels laws of inheritance applies.
What is the experimental hypothesis?
There is a significant difference between observed and are expected
How do you workout the degree of freedom?
Number of categories - 1
What happens if the calculated value is greater than the critical value?
Reject the null hypothesis
What happens if the calculated value is less than the critical value?
Accept the null hypothesis
If you reject the null hypothesis what doesn’t apply?
The Mendels ratios
When are genes linked and not linked?
If genes A and B occur on separate chromosomes they aren’t linked. If genes A and B occur on the same chromosome they are linked.
What is autosomal linkage?
When two or more genes are carried on the same chromosome.
What happened to chromosomes in autosomal linkage?
If A is inherited then b will be inherited. If a is inherited then B will be inherited. two gene loci on the same chromosome. Inheritance of Aa and Bb are dependent on one another. Certain alleles are inherited.
What sort of genes don’t follow the expected ratios?
Linked genes
Describe crossing over and autosomal linkage?
In some cells crossing over occurs in prophase one of meiosis. Formation of a bivalent by synapsis leads to production of recombinant genotypes. Further apart the autosomally linked genes are on the chromosome the more likely crossing over is to occur.
Expected mandolin ratios will be reflected in the subsequent generations/
What is a mutation?
Something which happens in somatic cells during mitosis (won’t be inherited). They are spontaneous events which provide a source of material for natural selection and evolution.
For the mutation to be an inherited it must affect the DNA of gametes (change in DNA).
What sort of mutation occurs in Down syndrome?
Change in the amount of DNA it is a chromosome mutation
What sort of mutation occurs in cystic fibrosis?
Change in the arrangement of the bases.
What are mutagens?
Chemicals or radiation which increase the rate of mutation e.g. ionisation radiation, chemicals
What is the mutagen called which causes cancer?
Carcinogen
What are the two types of mutation?
Chromosome- affect many genes and gene mutation - affect single bases
When does most mutations occur?
During crossing over in prophase and non-disfunction in anaphase one and two. Mutations can affect protein synthesis and can change the phenotype of an organism some mutations have no effect on the phenotype.
What is chromosome mutation?
Large changes in chromosome number and offspring affecting many genes and visible under light microscope in the Karyo type. The results of non-dysfunction in meiosis e.g. down syndrome
What is gene mutation?
Small changes in base sequence which only affects single genes no visible change in karyotype, the result of a fault in DNA replication.
Sickle cell anaemia – a substitution of one base during interphase. The DNA changes the protein structure changing the phenotype.
What is substitution?
It when one base is changed to another base.
“Silent” mutation as the code is degenerate. Neutral change if the amino acid altered is not essential to the tertiary or Quaternary structure. If the change results in functionally different protein the different allele is formed.
What is sickle cell anaemia?
It is when a single base in the gene is substituted.
In the beta haemoglobin the CTT is replaced by CAT causing glutamic acid to be replaced with Vaseline. Primary structure is then changed causing subsequent structures of the haemoglobin to change.
What happens to the haemoglobin molecule in sickle cell anaemia?
HB molecule becomes insoluble at low partial pressures and haemoglobin tends to stick to Adam molecules forming long fibres. The fivers to store a blood cells making them sickle-cell shaped. Mutation has led to put oxygen binding.
In a homozygous individual how many molecules are affected by the sickle-cell gene?
all
How many molecules are affected by the sickle-cell gene in a heterozygous?
Half the molecules are affected and oxygen binding is reduced by 20% – sickle trait
What is deletion and insertion/addition?
Its a frameshift mutation which affects all the subsequent codons it’s likely to cause the protein to be non-functional (recessive allele) any mutation which results in the terminator: will have a similar result
Invert THE FAT CAT SAT
THE FAT TAS TAC
What is cancer?
The uncontrollable division of cells which produces a tumour. Malignant tumours can break off and travel in the blood to form secondary tumours.
What is cancer caused by?
A mutation in the gene which control cell division. Tumour suppressor genes lead to a lack of protein which halts cell division causing a lack of receptors. Proto-oncogenes mutate producing oncogene which releases proteins and excess which stimulate cell division/excess protein receptors
What happens if the mutation causes a lack of protein synthesis?
It causes cell death
What are oncogenes?
Mutated genes which produce unspecialised and simple cells they have no edge affects so can grow over existing tissue which interferes with the normal function.
Where do most mutations occur?
In the junk DNA so don’t affect the phenotype – genetic fingerprinting.
How is down syndrome caused
By the non-dysfunction of chromosome 21 during anaphase resulting oocytes with an extra chromosome.
What is Epigenetics?
It involves heritable changes in the gene function without changing the base sequence of the DNA.
Changes occur after DNA replication this is due to variation in the environment which then alters the gene expression.
What are the two ways of inhibiting transcription?
Increased methylation of DNA.
Decrease acylation of associated histones.
The affect the ability of it being transcribed
Name epigenetic modifications?
diet seasonal correlations disease exposure toxic chemicals drugs of abuse finance status exercise microbiome therapeutic drugs alternative medicine social interaction psychological state.
Whats the function of histones?
They package DNA and help condense into chromosomes they are covered in tags which accumulate through life, the tags are epigenome.
What is epigenetic silencing?
It’s when inactive jeans can be wrapped tightly and become inaccessible ensuring that they aren’t transcribed.
What are inactive genes?
They are looser and easy to read
What happens when more more acylation of histones occurs
It causes gene activation. The DNA becomes looser so more transcription can occur.
What is DNA methylation?
It’s when methyl groups are added to the DNA or removed the group is added to the cytosine nucleotides in DNA.
What happened in over methylation?
Gene silencing. More methyl groups causes DNA to be tightly wound around histones inhibiting transcription as it reduces its ability to be expressed prevents the bases from being recognised.
What happens in undermethylation?
Gene activation. If you are meet our groups so there is less tightly wound DNA so more transcription.
What happens if the histone close tightly?
It prevents gene expression. If it is coiled loosely increases gene expression.
What can epigenetic changes do to whole chromosomes?
Switch them off
