genetics, populations, evolution and ecosystems- topic 7 Flashcards
Genotype
Genetic constitution of an organism, determines variation
phenotype
Observable characteristic; expression of genotype and affected by the environment
gene
Length of DNA that codes for a polypeptide/protein/rRNA
or tRNA
Locus
Position of a gene on a piece of DNA or chromosome
allele
different forms of a gene
Homologous chromosome
Pair of chromosomes, one maternal and one paternal in origin. They contain the same genes at the same loci, although alleles can vary
Homozygous
Identical alleles at the same locus on homologous chromosomes
heterozygous
different alleles at the same locus on homologous chromosomes
dominant allele
Allele that is expressed in the phenotype of an organism. Only 1 copy is needed. It masks any recessive allele
recessive allele
Only expressed in the phenotype when both alleles present are recessive. Not expressed if dominant allele present
codominant alleles
In a heterozygous genotype, both forms of the allele are expressed resulting in a phenotype that is a mixture
multiple alleles
Three or more allelic forms of which only two can exist in a diploid individual at any one time, e.g. ABO blood groups
Monohybrid inheritance
Inheritance of a single pair of alleles e.g. Bb or Gg
dihybrid crosses
Dihybrid crosses are those where we consider the inheritance of two characteristics at the same time. For example brown hair and blue eyes together, so a person could be genotype HhEe
dihybrid cross 2 heterozygotes ratio
9:3:3:1
gametes for HhEe
HE, He, hE, he
Gametes for HHEE
HE
gametes for hhee
he
what can be used to determine deviation between observed and expected values
chi squared
why can chi squared be used for codominance
because the data is discrete
homozygous dominant
2 dominant alleles
homozygous recessive
2 recessive alleles
how are codominant alleles shown in a punnet square
C^allele letter eg:C^w
how are blood group alleles shown
I^blood group eg: I^A
male sex chromosomes (humans)
XY
female sex chromosomes (humans)
XX
are X linked conditions always dominant or recessive
recessive (expressed in males as no equivalent genes on Y)
do sex linked disorders predominantly affect men or women in humans, why
men as there are no equivalent genes on the Y chromosome to prevent the recessive allele from being expressed
How are sex linked chromosomes shown
X^allele letter or Y^allele letter
autosome
any chromosome which is not a sex chromosome
autosomal linkage
2 or more genes are carried on the same chromosomes. Therefore dominant alleles are paired together and recessive alleles are paired together
reason for autosomally linked chromosomes to not remain together
crossing over
crossing over
process where a chromatid breaks during meiosis (prophase 1) and re-joins to the chromatid of its homologous chromosome so that their alleles are exchanged
epistasis
when the allele of one gene affects or masks the expression of another in the phenotype. usually happens with colours eg: colour arrangement being masked by being albino
gene pool
all the alleles of all the genes of all the individuals in a population of a single species at a given time. It includes both genes
that are expressed, and those that are not.
hardy weinberg principle
predicts that the frequency or proportion of alleles (of a particular gene) will stay constant from one generation to the next
assumptions of hardy weinberg principle
no selection, no mutation, no migration, large population, random mating
p + q=
1
p=
dominant
q=
recessive
p^2 + 2pq +q^2=
1
