Topic 10 - Genetics HL
10.1 - Meiosis
10.1.1 - Interphase
Interphase: period (before meiosis) where cell prepares for meiosis
S phase: chromosomes are replicated (forming sister chromatids)
Sister chromatids: genetically identical strands (same color)
Held together by centromere
S phase is the reason for two divisions in meiosis:
• Suggests meiosis evolved from mitosis
• Bene t: more potential for variation
10.1.4 - Chiasmata - IS ANY OF THIS NEW??
Synapsis: process whereby homologous chromosomes connect to form a bivalent (prophase I)
Connected by the synaptonemal complex (protein-RNA complex)
Sex chromosomes often remain unpaired.
Chiasmata: points of exchange (crossing over) between non-sister chromatids that hold the
bivalent together
fi
, 10.2 - Inheritance
10.2.1 - Dihybrid Crosses
Law of independent assortment (alleles are inherited independently) only applies to unlinked
genes.
Dihybrid cross: cross between two individuals homozygous for two speci c genes
Modeled using punnet squares.
Result in up to four di erent gamete combinations.
P generation: parent genotypes
Phenotypic ratio = 9 : 3 : 3 : 1
Example questions:
Pure breeding = homozygous
Pure breeding horned sheep with black wool: BBHH
Pure breeding hornless sheep with white wool: bbhh
a) F1: BbHh
ff fi
10.1 - Meiosis
10.1.1 - Interphase
Interphase: period (before meiosis) where cell prepares for meiosis
S phase: chromosomes are replicated (forming sister chromatids)
Sister chromatids: genetically identical strands (same color)
Held together by centromere
S phase is the reason for two divisions in meiosis:
• Suggests meiosis evolved from mitosis
• Bene t: more potential for variation
10.1.4 - Chiasmata - IS ANY OF THIS NEW??
Synapsis: process whereby homologous chromosomes connect to form a bivalent (prophase I)
Connected by the synaptonemal complex (protein-RNA complex)
Sex chromosomes often remain unpaired.
Chiasmata: points of exchange (crossing over) between non-sister chromatids that hold the
bivalent together
fi
, 10.2 - Inheritance
10.2.1 - Dihybrid Crosses
Law of independent assortment (alleles are inherited independently) only applies to unlinked
genes.
Dihybrid cross: cross between two individuals homozygous for two speci c genes
Modeled using punnet squares.
Result in up to four di erent gamete combinations.
P generation: parent genotypes
Phenotypic ratio = 9 : 3 : 3 : 1
Example questions:
Pure breeding = homozygous
Pure breeding horned sheep with black wool: BBHH
Pure breeding hornless sheep with white wool: bbhh
a) F1: BbHh
ff fi
