Genetic Processes - 2 Flashcards
What are nucleotides?
The basic structural units of a molecule of DNA
What are nucleotides made of?
Each nucleotide consists of:
Phosphate group
Deoxyribose sugar (pentose sugar)
Nitrogenous base
What are the types of nitrogenous base?
There are four types of nitrogenous base:
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
What is a base pair? Which nitrogenous bases form them?
Each base will only bond with one other specific base; A/T and C/G. This means there is always equal numbers of A and T in any given molecule of DNA, and there is always equal numbers of C and G.
These pairings of nitrogenous bases are called base pairs.
What shape is a strand of DNA?
2 strands of DNA wrap around each other, forming a double helix structure.
There are roughly 10 base pairs per helical turn.
What is a codon?
To look at differentiating genetic code, we need to look at the sequence of bases.
These bases are arranged in triplets called codons.
Ex.,
AGG-CTC-CTG-GGG
TCC-GAG-GAC-CCC
Mutations in nucleotides
A mutation is a change to the nucleotide sequence in DNA.
Mutations can be caused by environmental agents such as radiation or certain chemicals, or by errors made in DNA replication/cell division.
Mutations can occur as the DNA in an organism’s cell is replicated
Most mutations occur in parts of DNA that do not code for genes and most are immediately corrected
Mutations that occur in mitosis affect the autosomes (body cells) and are not passed on to offspring
Mutations that occur in meiosis affect the gametes (sex cells) and can be passed on to offspring
What are the different types of mutations?
Base pair substitution
When one nitrogenous base is substituted for another (e.g., a T substituted for an A)
Insertion
When one nitrogenous base is added to a nucleotide sequence (e.g., a T added to a sequence it wasn’t originally in)
Deletion
When one nitrogenous base is deleted from a nucleotide sequence (e.g., an A completely deleted with no replacement)
What traits are typically coded for in the Y chromosome?
In the Y chromosome, nearly all traits coded for are sexual. It is shorter, leaving less room for other traits.
What traits are typically coded for in the X chromosome?
In the X chromosome, nearly all traits coded for are nonsexual. It is much longer than the Y chromosome.
Why are women less likely to inherit X linked recessive traits than men?
Women would need both X chromosomes to carry the recessive trait, whereas men only have one X chromosome, meaning they will show the trait if one X chromosome has it.
What are women “carriers”
Women who have 1 recessive defective gene are called carriers.
Because the X chromosome codes for many non-sexual traits, it’s more likely to carry sex-linked inheritances.
Writing genotypes in relation to sex chromosomes
When writing genotypes in relation to sex chromosomes, the allele becomes a superscript to the base letter, which is the sex chromosome (X or Y).
e.x., a woman carrying colourblindness would be written X^b X^B, and a colourblind male would be written X^b Y, as the Y chromosome does not carry any alleles for this trait.
What is incomplete dominance? What is Codominance?
Incomplete Dominance:
Heterozygous phenotype is expressed as an intermediate of the homozygous phenotypes.
Codominance:
Both phenotypes are independently present and expressed in the heterozygotes.
Incomplete dominance in snapdragons:
In snapdragon flowers, the red colour (expressed as C^rC^r) is homozygous, and so is the white (C^wC^w). The heterozygous, however (C^rC^w), are incomplete dominants, and are expressed as pink!
Although this looks similar to the idea of blending, both alleles are still distinct and can result in offspring which are fully white or red.
