Meiosis I
Meiosis II (same as mitosis)
Prophase
//Spindle forms
Nuclear envelope disappears
- Chromosomes shorten/thicken/condense
- Form bivalents/tetrads
- Crossing-over of homologous pairs
//Spindle forms
//Nuclear envelope disappears
Metaphase
//Spindle complete
- Bivalents at equator
- Join to spindle (fibres) via centromere
//Spindle complete
- Chromosomes at equator
Anaphase
//Cytokinesis begin
Random segregation of homologues
- Intact centromeres
- Two chromatids on one chromosome
//Cytokinesis begins
Random segregation of chromatids
- Chromatids are pulled to opposite poles
- Centromeres divide
Telophase
//Spindle disappears
//Nuclear envelope reforms
- 2 haploid cells
- Chromosomes still duplicated
//Spindle disappears
//Nuclear envelope reforms
- 4 haploid daughter cells
Principles of Mendelian Inheritance
Mendel's 1st Law of Segregation (Anaphase I and II)
During gamete formation, allele pairs (Gg) of one gene separate
(G)(g)
Thus, only one of the alleles of one gene is present in a
single gamete
Monohybrid inheritance (single gene - 3:1 ratio)
Recessive alleles can cause genetic disorders (e.g. cystic
fibrosis)
Mendel's 2nd Law of Independent Assortment (Anaphase I and II)
Alleles for one gene segregate independently with the alleles
of another gene (GgBb)
Two genes for each characteristic segregate during gamete
production (GB)(gb)(Gb)(gB)
Independent assortment means either G / g can go with either of
B / b
Meiosis separates alleles / homologous chromosomes
Dihybrid inheritance (two genes - 9:3:3:1 ratio) →
occurs at different loci
Multiple Alleles
Human ABO group is controlled by the immunoglobulin gene I
The immunoglobulin gene has 3 alleles IA, IB, I0
These alleles code for antigen A, B, neither A/B, respectively
Only 2 alleles can be present in a diploid cell →
IAIB is codominant, I0 recessive
Codominance (1:2:1)
Heterozygous allele is neither dominant nor
recessive → both alleles are expressed
Sex Linkage
e.g. Haemophilia → clotting time of blood is longer
than usual
Inheritance of sex in humans
Females are homogametic sex (X: or XX)
Males are heterogametic sex (XY) / Y chromosome is shorter
Involves whole chromosomes instead of individual genes
Phenotypic characteristic is inherited on X, not on Y
chromosome
Thus, more common in males / females can be heterozygous (XAXB)
Thus, sex linked characteristic is never passed from father to
son
Evidence from a tree diagram which suggests that a disease is
Sex linked: only seen in males / not in females
Recessive: unaffected parents
Application of Chi-Squared Test (x²) to Data Obtained
Observed Expected value
IMG 5-14-1
Degree of freedom = n - 1
Shows if differences between sets of data are significant or
not
Null hypothesis states that there are no significant
differences between sets of data
Small value / probability higher than the level of significance
0.05/5%
Little difference between observed and expected value
Likely to be extremes of the same population
Null hypothesis accepted
Large value / probability is less than the level of
significance 0.05/5%
Significant difference between observed and expected data
Likely to be two distinct populations
Null hypothesis rejected
Ecosystem
Ecosystem
Five Kingdoms
Human Activity
Inheritance
Nutrient Cycle
Photosynthesis
Selection
Variation
Content
Stages of Meiosis
Principles of Mendelian Inheritance
Multiple Alleles
Codominance (1:2:1)
Sex Linkage
Application of Chi-Squared Test (x²) to Data Obtained
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