This document summarizes key concepts in genetics and inheritance, including Mendel's experiments with pea plants, his laws of segregation and independent assortment, genetic crosses, and degrees of dominance. It discusses how Mendel used pea plants to discover the basic principles of heredity, including that alleles segregate independently and traits are inherited according to dominant and recessive genes. The summary also outlines monohybrid and dihybrid crosses, dominant and recessive alleles, and degrees of dominance like complete, incomplete, and codominance.

1. LIFE SCIENCES GRADE 12
UNIT 5
GENETICS AND INHERITANCE
By Vilakazi N.S
216010009

2. THE PROCESS OF HYBRIDIZATION
 Genetics: the study of heredity
 Heredity: relations between successive generations. Gregory Mendel was the father of
genetics.
 Mendel discovered the basic principles of heredity by breeding garden peas in
carefully planned experiments.
 Advantages of pea plants for genetic study: Cross-pollination (fertilization
between different plants) can be achieved by dusting one plant with pollen from
another.
 True breeding : breeding varieties of organisms with only one variety of type.

3. LAW OF SEGREGATION
 P-generation – true breeding parents
 F1-generation- hybrid offspring of the P-generation
 F2-generation- hybrid offspring of the F1 generation
 Alleles-alternative versions of a gene
 Locus- position of a gene in a chromosome
 Homozygous- identical alleles e.g(BB)
 Heterozygous- different alleles e.g(Bb)

4. LAW OF INDEPENDENT ASSORTMENT
 Two alleles for a heritable character separate during gamete formation
and end up in different gametes.

5. GENETIC CROSSES
 Each pair of alleles segregate independently of each other pair of alleles
during gamete formation. (applies to different non-homologous
chromosomes)
 Genotype-genetic composition of a gene
 Phenotype- physical appearance of a gene

6. DEGREES OF DOMINANCE
 1. MONOHYBRID CROSS-cross between 2 organisms where we look at
one pair of contrasting traits.(determine outcome of F1 generation)
 2. DIHYBRID CROSS- cross between 2 organisms where we look at
two pairs of contrasting traits at the same time.

7. SUMMARY OF GENETICS
 Complete dominance One allele suppresses the expression of the other allele.
 Incomplete dominance: phenotype of F1 hybrids is somewhere between the
phenotypes of the 2 parental varieties – neither allele completely dominant (White x
Red = Pink)
 Codominance, 2 dominant alleles affect the phenotype in separate, distinguishable
ways. (Red and white flowers = White and red visible.)

8. REFERENCES
 Chromosomes carry hereditary info (genes)
 Chromosomes (and genes) occur in pairs
 New combinations of genes occur in sexual reproduction
 Monohybrid vs. Dihybrid crosses
 Mendel’s Principles:
 Dominance: one allele masks another
 Segregation: genes become separated in gamete formation
 Independent Assortment: Members of one gene pair segregate independently
from other gene pairs during gamete formation
 ADDITIONAL RESOURCES
 https://www.youtube.com/watch?v=ya7h-Y-9l8c
 https://www.youtube.com/watch?v=bVk0twJYL6Y

9.  Hartwell, L. (2010). Genetics: From Genes to Genomes 4th Edition.
McGraw Hill. London.
 Available from slide share:
https://www.slideshare.net/rspawar007/genetics-70106620
Assessed: 13 December 2016