17: Inherited change Flashcards
Define a gene
A small section of DNA that codes for a specific protein
Define a genotype
Genetic makeup of an organism
All the genes an animal can express
Define a phenotype
Observable or biochemical characteristics of an organism
Can be altered by the environment
What does an organisms genotype define?
The limits of the characteristics which an organism can develop
E.g lack of something could mean a person could not grow to max height
Define locus
The position of a gene on a DNA molecule
Define an allele
One of the different forms of a gene
How many alleles can be present at one locus?
One
How many copies of a gene are found in homologous chromosomes?
Two loci each carry one allele of a gene
Define homozygous
When alleles on each of the homologous chromosomes are the same
Define heterozygous
When alleles on each of the homologous chromosomes are different
Define a dominant allele
Allele of a heterozygote that expresses itself in the phenotype
Define a recessive allele
Allele of a heterozygote that does NOT expresses itself in the phenotype
Define homozygous dominant
Homozygous organism with two dominant alleles
Define homozygous recessive
Homozygous organism with two recessive alleles
Define codominant
Two alleles which are both expressed in the phenotype
When is an organism said to have multiple alleles?
Genes that have two allelic forms
What can cause multiple alleles to occur?
Random mutations which occur over long periods of time
Define monohybrid crossing
Crossing of one gene
What is F0, F1, F2?
F0 - parent
F1 - offspring
F2 - offspring of F1 interbred
Define the law of segregation
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete
Define a ratio
Measure of the relative size of two classes
Why are results of genetic crosses rarely the same as predicted?
Predicted results are just predictions of what will occur, does not necessarily occur
Define dihybrid inheritance
Crossing of two different genes located on different chromosomes, result is inherited
What is the standard ratio caused by the breeding of two heterozygous organisms with dihybrid inheritance?
9:3:3:1
What is the law of independent assortment
Each member of a pair of alleles may combine randomly with either of another pair
What are the alleles present which determine blood group?
IA - produces antigen A on cell surface IB - produces antigen B on cell surface IO - does not produce any antigen on cell surface IA and IB are codominant IO is recessive to both
What is the gene combination for blood types?
A - IAIA or IAIO
B - IBIB or IBIO
AB - IAIB
O - IOIO
Why might you not trust the dihybrid inheritance ratio 9:3:3:1?
Alleles are on the same chromosome therefore not independently assorted
What does a 9:7 ratio suggest?
Not 3:1, but probably 9:3:3:1 which is common for a dihybrid
What are the sex chromosomes?
23rd pair of chromosomes
XX in females
XY in males
What is a Y chromosome?
A smaller and different shaped chromosome only found in males
What gametes form from males and females?
Female - All gametes have single X chromosomes
Male - one has X chromosome other has Y
What is a sex-linked gene?
Any gene that is carried on either the X or Y chromosome
What does the extra length of the X chromosome mean?
The corresponding Y chromosome has no equivalent homologous portion
Only one copy of a gene present in males
How do recessive alleles on the non-homologous X chromosome change in frequency?
Recessive X chromosomes will appear more frequently as no homologous portion on Y chromosome could be dominant
What is haemophilia?
Recessive allele on X chromosome which codes for a faulty protein that doesn’t function
Means blood cannot clot
What is standard notation for looking at males and females in genetic diagrams?
Empty square - normal male
Empty circle - normal female
Filled shape - affected
What is an autosome?
All chromosomes other than the sex chromosomes
What are linked genes?
Any two genes that occur on the same chromosome are linked
Linked genes remain together in meiosis, pass onto gametes together
Why are linked genes not separated in meiosis?
They do not segregate by independent assortment
If the question presents you with the genotypes hhgg and HhGg, which alleles go together?
h always goes with g
Diagram is hg hg gametes crossed with HG hg gamets
What is the difference between sex or autosomal linkage?
Sex linkage occurs when a gene is not found on the Y chromosome but is found on X
Autosomal works on the non-sex chromosomes, so no Y chromosomes present
What process in meiosis could cause varieties in ratios when sex-linked genes are crossing?
Crossing over may have occurred
Define epistatis
The allele of one gene affects or masks the expression of another in the phenotype
What is the classic example of epistatis?
Black, agouti, and albino mice
What genes are found in the different colours of mice?
A - agouti a - black B - production of melanin b - no production of melanin If bb is present, the mouse is albino
What is the standard format of a ratio?
A:1
Why would some people not like to take part in testing?
Some embarrassed about
Cannot decide which phenotype is present, as it is subjective
What shows that a phenotype is caused by a recessive allele?
Parents can be carriers but unaffected by the disease
How many different gametes can be produced from Bb Cc Dd?
2^3 = 8
Due to 1 allele from each pair
How many antigen-determining alleles will be preset in a white blood cell?
2 - white blood cells are diploid cells
What is the standard ratio when two AaBb mice mate?
9 - agouti
4 - albino
3 - black
What are the steps in the chi squared test?
Observed (O) and Expected values (E)
Sum of (O-E)^2 / E
If this value is larger than the critical value, then there is enough data to reject H0
When should the chi-squared test be used?
If: the data is in categories
Sample size is large to be representative
Data indicates absolute numbers
If a question asks about a gene coding for enzymes with colours, how do you answer the question?
Gene X allows for the production of the enzyme
Enzyme causes chemical to made, giving the phenotype
