17.Inherited Change Flashcards
What is a genotype
Describes the alleles the organism has, what its inherited
What’s a phenotype
The observable characteristic of organism, it’s the result of interaction between genotype and environment
What’s a gene
Length of dna that’s a sequence of nucleotide bases that code for a particular protein/polypeptide
What’s an allele
Variation or different form of a gene
What’s a locus
Postiiton of a gene on a particular DNA molecule
What’s homozygous and heterozygous
When each allele of gene is same
When each allele of gene is different
What is dominant alleles
Dominant means the allele that expresses itself in the phenotype
What’s codominant
When two alleles contribute to the phenotype
What is monohybrid inheritance
Inheritance of single gene
What does a monohybrid cross look at
Gametes of female and gametes of male
Eg G G and g g
What is the common ratio when breeding a homozygous dominant and a homozygous recessive
Gg, Gg, Gg, Gg
4:0
What’s common ratio when breeding two heterozygous
GG, Gg, Gg, gg
3:1
What is the basic law of genetics
In diploid organisms, characteristics are determined by alleles that occur in pairs, only one of each pair of alleles can be present in single gamete
What is a dihybrid
Inheritance of two characteristics at once
What is the theoretical ratio of a dihybrid between two heterozygous cells
9:3:3:1
What is sex linkage
A gene carried on the X or Y chromosome
Where does the gene for haemophilia lie
On X chromosome
Males only get X chromosome from mum
What’s autosomal linkage
Two or more genes carried on same autosome
When do you use chi squared
Used to test null hypothesis, suggesting that no significant difference, any difference is due to chance
Sample size larger than 20
Data must be discrete
Only raw counts not percentages
Compare experimental rates with theoretical rates
What are multiple alleles and what’s their nature
When gene has two or more allelic forms
As only two chromosomes in homologous pair, only 2 out of 3 or more will be present in single organism
Explain how to make genetic diagram
Example - Green or yellow pea
- if letters not given, choose single letter for each characteristic (G)
- higher case is dominant and lower case is recessive G-green g-yellow
- label parents and state their phenotypes (GG and gg)
- state gametes produced by each parent (G) (G) (g) (g)
- use punnet square to show results of random crossing of gametes
- state phenotype of each genotype (Gg is green)
- indicate numbers of each genotype
Explain how single gene is inherited
Mendel peas
- Green pods repeatedly bred with each other they are pure breeding for green
- said to be homozygous (two green alleles)
- if pure breeding green pod crossed with pure breeding yellow pod, first filial will be green pods
- green is dominant
- is heterozygous pods crossed together, f2 generation is 3:1 green:yellow
What is 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 single gamete
Why are actual results of genetic crosses rarely same as predicted
- Chance determines which gametes fuse with which gamete
- larger samples more likely to show results near theoretical ones
Explain dihybrid inheritance
Mendel peas
- round and yellow seeds (both dominant features)
- wrinkles and green seeds (both recessive features)
- crossed RRGG with rrgg (R-round or wrinkles, g-yellow or green)
- gametes are RG and rg
- offspring is RrGg
- intercross of offspring gametes ( RG, Rg, rG, rg) gave 9:3:3:1
Law of independent assortment
Each member of pair of alleles may combine randomly with either of another pair
How do you write codominance
-Different letter for each characteristic eg fur coat brown, white, black
-written as power (superscript) to letter C
C^W (white fur)
If a genetics question gives you a ratio that is not 3:1, or 9:3:3:1 what do you consider?
Co dominance
How does multiple alleles affect inheritance
For blood groups, only two out of three alleles can be present
I^A is dominant or co dominant with I^B and I^o is recessive
How is sex determined genetically
Female gametes are X and X
Male gametes are X and Y
Inherit one from each parent XY is boy, XX is girl
How are sex linked diseases like haemophilia inherited
- X linked genetic disorder that’s caused by defective gene on X chromosomes
- only shown as a superscript on X
- H is dominant, for production of protein in blood clotting
- h is recessive, for haemophilia
- Males only inherit X from mother, father can pass on X to daughter
What is haemophilia
When recessive allel with altered sequence of dna nucleotides bases codes for a faulty protein which does not function,
Individual unable to produce functional protein required in blood clotting, leads to slow and persistent bleeding internally
-confined to males as many women die when reach menstruation
How many homologous pairs are needed to show all 4 alleles are present
When autosomal linked
When not linked
Linked - one homologous pair
Unlinked - two homologous pairs
Genes A and B, if on separate chromosomes 4 possible combos of Ab AB aB ab
Genes A and B in same chromosome, 2 possible combos of AB ab
What does not occur if genes are linked
Assuming no crossing over, all linked genes remain together during meiosis and pass into gametes together , don’t segregate in accordance with mendels law of independent assortment
What is epistasis
When allele of one gene affects or masks expression of another in phenotype
What’s example of epistasis
Mice
- gene a controls distribution of black pigment in hairs, domintnat A leads to black bands on hair, recessive a leads to uniform black hairs
- gene b controls colour by determine expression of gene A, dominant B leads to production of melanin, recessive b leads to no pigment of hair therefore white coat
- if mouse is brown/grey it’s got black banded hair
Formula for chi squared
Sum of ( (O-E)^2 divided by E)
