Inheritance Flashcards
What is monohybrid inheritance?
Inheritance of a single characteristic, controlled by one gene
What is genetics?
The study of mechanisms by which an organism inherits characteristics from its parents.
Define gene
A length of DNA that codes for one polypeptide chain
Define allele
A version of a gene
Define locus
The position of a gene on a chromosome
Define a recessive allele
An allele that is only expressed in the phenotype if there is no dominant allele present
Define a dominant allele
An allele that is always expressed in the phenotype if present
Define codominant alleles
Both alleles are expressed in the phenotype of a heterozygote
Define phenotype
The characteristics of an organism resulting from both genotype and the environment
Define genotype
The alleles possessed by an organism
What do homozygous and heterozygous mean?
Homozygous means having two of the same alleles, heterozygous means having two different alleles
What are the sex chromosomes and what are autosomes?
The sex chromosomes are X and Y. Biological females are XX, males are XY. Autosomes are any of the other 22 pairs of chromosomes
What is a test cross and why are they done?
A test cross is done to identify the genotype of an individual that shows the dominant characteristic. They are crossed with a homozygous recessive individual
Why are males more likely to have sex linked recessive diseases?
Sex linked diseases have their loci on the X chromosome. Males only have one copy of the X chromosome, so if they inherit the recessive allele they will express it. Females must inherit two copies to express it.
What does a chi squared test show?
If there is a significant difference between observed and expected results
What are the differences between a chi squared test and a t test?
In chi squared data is categorical T it is continuous. In chi squared data is not normally distributed, in T it is. They both determine if there is a significant difference, but chi squared is between observed and expected, T test is between the means of two sets of data.
What is the null hypothesis in a chi squared test?
That there is no significant difference between observed and expected results
When would you reject the null hypothesis of a chi squared test?
When the calculated chi squared value is higher than the critical value found in the probability table for the correct degrees of freedom
What are multiple alleles?
When there are more than two alleles of a gene that can code for a characteristic, such as blood types
What is dihybrid inheritance?
The inheritance of two characteristics coded for by two separate genes. We assume these are on different chromosomes
What is autosomal linkage?
When the genes in a dihybrid cross are both on the same chromosome, so cannot assort independently at metaphase of meiosis. This is the explanation if observed results do not match expected results in a dihybrid inheritance question
If two genes are autosomally linked, how could you still get phenotypic combinations that are not the parental combinations?
By crossing over of non parental chromosomes in prophase 1 of meiosis to produce recombinants
When do most gene (point) mutations occur in meiosis and mitosis?
Interphase, when the DNA is replicated
When do most chromosome mutations occur?
During crossing over in prophase 1, or non-disjunction in anaphase 1 or 2 (where the chromosomes/chromatids do not separate correctly)
Give one example of a gene (point) mutation and one example of a chromosome mutation
Sickle cell anaemia is a gene mutation. Down’s syndrome is a chromosome mutation
What are silent mutations?
Mutations that have no effect on the phenotype
What is a mutagen?
A factor that can increase the rate of mutation, such as ionising radiation. A mutagen that causes cancer is a carcinogen
Which genes can mutate to cause uncontrolled cell division leading to cancer?
Either tumour suppressor genes, that normally decrease cell division. Or proto-oncogenes, which mutate to form oncogenes and increase cell division
What is epigenetics?
Control of gene expression by addition or removal of tags from the DNA, without changing the DNA sequence
What is the effect of adding methyl groups to the DNA?
The DNA becomes more tightly coiled around histone proteins, meaning it is transcribed less and less of the polypeptide chain is produced. The gene is silenced
What phenotypic ratio would you see in the offspring when two heterozygotes are crossed in a simple monohybrid cross
0.12569444444444455
What phenotypic ratio would you see in the offspring when two heterozygotes are crossed in a monohybrid cross with codominance
0.043067129629629664
What phenotypic ratio would you see in the offspring when two heterozygotes are crossed in a dihybrid cross?
9:3:3:1
