9 - Inheritance (C2) Flashcards
What is the definition of a gene?
A sequence of DNA that codes for a polypeptide and which occupies a specific locus on a chromosome
What is the definition of an allele?
A variant nucleotide sequence for a particular gene at a given locus, which codes for an altered phenotype
What does homozygous mean?
The alleles of a particular gene are the same
What does heterozygous mean?
The alleles of a particular gene are different
What is the genotype of an individual?
The alleles that they contain
What is the phenotype of an individual?
A description of their appearance, including characteristics that can’t be seen, e.g. their blood group
What is a dominant allele?
An allele that has the same effect on the phenotype of a heterozygote as a homozygote
What is a recessive allele?
An allele is only expressed when in a homozygous pair and when no dominant allele is present
What is co-dominance?
When both alleles contribute to the phenotype
What is monohybrid inheritance?
The inheritance of a single gene
Why are peas useful to be used in inheritance experiments?
- They’re easy to grow
- Their flowers can self-fertilise and cross-fertilise
- They make flowers and fruit in the same year
- They make a large number of seeds from each cross
Why did Mendel chose to study pairs of contrasting characteristics e.g. tall or dwarf plants?
- They’re controlled by single genes
- They’re controlled by genes on different chromosomes
- Easy to tell apart
What is continuous variation?
Variation with a range of values that’s controlled by a number of genes e.g. height
What is incomplete dominance?
When neither allele is dominant so the offspring phenotype is intermediate between that of the 2 homozygotes e.g. red flower + white flower -> pink flower
What are linked genes?
Genes that are on the same chromosome and therefore are not separated at meiosis
What increases the likelihood of crossing over of genes?
The further apart 2 genes are on a chromosome, the more opportunity there is for crossover to occur between them
What number is the degrees of freedom?
1 less than the number of classes of data
Why are the sex chromosomes called heterosomes?
Because they’re different sizes
What are the autosomes?
The 22 pairs of identical genes in humans (non-sex chromosomes)
What is a sex-linked gene?
A gene on the X chromosome that gives rise to a sex-linked condition
What are 2 features of mutations?
- Spontaneous
- Random
What is a mutation?
The change of the structure of a gene resulting in a variant form
What mutations are inherited?
Only those that occur in gametes
What can mutation rates be increased by?
- Ionising radiation
- Mutagenic chemicals e.g. those in cigarette smoke
What can cause gene or point mutation?
DNA not being copied accurately in S phase
What can cause chromosome mutation?
When chromosomes get damaged and they repair themselves incorrectly, altering their structure and affecting lots of genes
What is aneuploidy and what causes it?
- Chromosome being lost or added
- When chromosomes fail to separate to poles of dividing cells
- Or when chromosomes fail to separate at anaphase 2
What is polyploidy and what causes it?
Number of chromosomes doubling if the cell fails to divide following the first nuclear division after fertilisation
Why are bacteria often used in mutation experiments?
They have:
- Short life cycle
- High rate of mutation
What is non-disjunction?
When a faulty cell division in meiosis causes 1 of the daughter cells to receive 2 copies of the chromosome whilst the other receives none
What are hermaphrodite organisms?
Those that produce both male and female gametes
What is a carcinogen?
An agent that causes cancer
What are tumour suppressor genes?
Genes that regulate mitosis and prevent cells dividing too quickly
What is an oncogene?
A proto-oncogene with a mutation that results in cancer
How can proto-oncogenes cause cancer?
Mutations can cause them to be switched on permanently causing rapid, repeated mitosis
What is epigenetics?
The control of gene expression by modifying DNA or histones, but not by affecting the DNA nucleotide sequence
What is the epigenetic modification of DNA methylation?
- Cytosine can have a methyl or hydroxymethyl group added
- Areas of DNA that are heavily methylated are less likely to be transcribed
What is the epigenetic histone modification following translation?
- e.g. attaching an acetyl group to the amino acid lysine
- These changes to histone proteins alter their interaction with DNA and changes the arrangement of the nucleosomes
- Coiling is more relaxed and transcription factors and RNA polymerase have access to the DNA, so transcription is increased
What is genomic imprinting?
If genes are activated into gametes, the inactivation may be transferred to the next generation
When do you accept the null hypothesis in a chi squared test?
- If chi squared value < critical value
- This means there’s no sig diff between observed and expected
- Accept null
What is complete/total linkage?
- When 2 genes have their loci close together on the same chromosome so tend to occur in gametes in parental combinations
- Causes 3:0:0:1
What is the locus?
The position of a gene on a chromosome
What is a benign tumour?
One that is not growing in size
What is a malignant tumour?
A cancerous one
What is a monohybrid cross?
A cross in which only one gene is being considered e.g. TT x tt
What is a dihybrid cross?
A cross in which 2 genes are considered e.g. TTRR x ttrr
