Genetics Flashcards
What did Mandel do?
Studied genetics
What is a dichotomous trait?
A trait which occurs in one form or another
What is a true breeding line?
Interbred members always produce offspring with the same trait
What is a phenotype?
An organisms’ observable traits
What is a genotype?
The traits which can be passed onto the offspring via the genetic material
What was Mandellian theory?
Two kinds of inherited factors for each dichotomous trait
Each organism possesses two genes for each of its dichotomous traits
One of two kinds of genes dominate
For each trait, each organism randomly inherits one of its father’s alleles and one of its mother’s
What does homozygous mean?
Possesses two of the same allele
What does heterozygous mean?
Possesses two different alleles for a trait
What is a chromosome?
Threadlike structure of the nucleus of each cell
How many pairs of chromosomes does a human have?
23
Where are genes located?
On chromosomes
Two alleles that control each trait are situated where?
At the same locus, one on each chromosome
What are gametes?
The sperm and egg
What is meiosis?
Process of cell division that produces gametes
What does meiosis produce?
Gametes
Process of meiosis
Chromosomes divide
One chromosome from each pair goes to each of the two gametes
How many chromosomes do gametes have?
23
How many chromosomes do humans have?
46 (23 pairs)
What does meiosis account for?
Most of the genetic diversity within a species
How does meiosis account for diversity?
Crossing over
How does crossing over work?
Chromosomes line up in pairs
Cross over one another at random points
Break apart and exchange sections of themselves
Why is crossing over important?
Ensures genetic diversity
First means by which geneticists could construct a gene map
What is mitosis?
Cell division of all other cells in the body
What is linkage?
Clusters of linked genes
If a gene for one trait is inherited from one parent, there is a higher probability (>0.5) of inheriting genes for other traits in the cluster from the same parent
The number of clusters of linked traits is equal to?
The number of pairs of chromosomes
4 DNA bases
Adenine
Thymine
Guanine
Cytosine
DNA replication
DNA starts to unwind
Exposed bases attract complementary loose bases from the fluid of the nucleus
When unwinding is complete, two identical double-stranded DNA molecules are created
Virtually all sex linked traits are carried on what chromosome?
X
If a sex-linked trait is dominant it occurs…
More frequently in females as they have twice the number of X chromosomes
If the sex-linked trait is recessive it occurs…
More frequently in males as they only have one X chromosome and so only have to have one recessive allele compared to women’s two
Example of sex-linked trait
Colour blindness
Rarely occurs in females as it is recessive and the allele is very rare
What is a structural gene?
Genes that contain information necessary for the synthesis of a protein
What is a protein?
A chain of amino acids
What is an operator gene?
Controls a structural gene or a group of structural genes
Determines if structural gene initiates protein synthesis
And at what rate
Operator genes that are regularly on
Are regulated by DNA-binding proteins that turn them up, down or off
Operator genes that are regularly off
Are regulated by DNA-binding proteins that turn them on
Gene expression transcription
Small section of chromosome that contains structural gene unwinds
Unravelled section serves as template for transcription of RNA
mRNA moves out of the nucleus and attaches to a ribosome in the cytoplasm
Gene expression translation
Ribosome moves along RNA strand and translates genetic code
Every 3 bases = codon
Codons code for amino acids
Amino acids are carried to the ribosome by tRNA
Repeats until stop codon reached
Completed protein is released into cytoplasm
Why is mitochondrial DNA of great interest to scientists?
Mutations have been implicated in many disorders
Mutations seem to occur at a consistent rate and so can be used as an evolutionary clock
What is the human genome project?
A map of the sequence of all 3 billion bases that compose human chromosomes
How many protein coding genes do humans have
About 25000 (unexpectedly small in relation to our complexity)
Mice have about the same
Corn have many more
What is alternative splicing?
Mechanism by which information stored in the genes of complex species is edited to make it possible for one gene to specify two or more distinct proteins
What do small RNAs do?
Control DNA
Can turn off genes
Control their level of expression
Cleave DNA into segments
Structural genes constitute how much of the human genome?
<2%
What are genes that appear to have been damaged by mutation over evolution called?
Pseudogenes
Ontogeny
Development of individuals over their lifespan
Phylogeny
Development of species over evolutionary time
Phenylketonuria
High levels of phenylpyruvic acid in urine
Pattern of transmission indicates it is transmitted through a single gene mutation
What do patients with PKU lack?
Phenyalanine hydroxylase
Converts phenylalanine –> tyrosine
Symptoms of PKU
Mental retardation Vomiting Seizures Hyperactivity Hyper-irritability Brain damage
Sensory phase of male songbirds
Several days after hatching
Form memories of adult songs they hear
Genetically prepared to learn songs of their own species
Sensorimotor phase of male songbirds
When juvenile males begin to twitter sub songs
Rambling vocalisations are gradually refined to resemble songs of the adults
Neural circuits that control birdsong
Descending motor pathway
Anterior forebrain pathway
Descending motor pathway
From high vocal centre on each side
To the syrinx
Anterior forebrain pathway
Mediates song learning
What is a heritability estimate?
Numerical estimate of the proportion of variability that occurred in a particular trait in a particular study as a result of the genetic variation in that study
