Meiosis/Genetics
Topic 4
Stages of Meiosis
Meiosis Stage 2
Genes and Chromosomes
• Terminology:
• Genotype – genetic constitution of a gene/org
• Phenotype – physical expression of a gene
• Dominant allele – form of the gene that is
expressed even when only 1 is present
• Recessive allele – form of the gene that is only
expressed when both alleles are recessive
Terminology cont’d
• Codominant allele – when two two forms of a
gene are both expressed when paired together
• Locus – the location of a gene/allele on a
chromosome
• Homozygous – when both alleles of a gene are
the same (ex. aa, AA)
• Heterozygous – when both alleles of a gene
Terminology cont’d
• Carrier – an individual of heterozygous makeup that carriers, and therefore can pass on, a
disease causing allele but doesn’t express that
trait
• Test cross – when an individual of known
phenotype but unknown genotype (AA or Aa)
is crossed with a homozygous recessive
individual in order to determine its genetic
make-up.
Mendelian Genetics – Monohybrid Cross
Classical Punett's Square is a way to determine ways traits can
segregate
parental P cross
a
a
A
Aa
Aa
F1 cross
A
Aa
Aa
A
a
A
AA
Aa
testcross: mating F1 generation to the parental (usually
recessive) strain
a
a
A
Aa
Aa
?
aa
aa
a
Aa
aa
Some genes have more than two
alleles- Blood surface antigens
Blood type also and ex. Of
Codominance
Sex-linkage basics
Sex-linkage notes page
Pedigree basics
Pedigrees and pedigree
analysis
Sex-linked Pedigree