history of genetics biology. genetics how characteristics are transmitted from parents to offspring
TRANSCRIPT
History of
Genetics
Biology
Genetics
• How characteristics are transmitted from parents to offspring
Gregor Mendel
• worked with Pisum satium (pea plant)
Gregor Mendel (1822-1884)
• Flower color • Flower position along stem
• Seed color• Seed shape• Pod shape• Pod color• Stem length
Mendel studied 7
characteristics
Mendel’s Experiments
Mendel’s First Cross
• Crossed “purebred” purple with “purebred” white + P (parent) generation
- F1 – purple
• Crossed F1 hybrids + produced F2 generation
- 3 purple : 1 white
• Alternative versions of genes (alleles) account for variations in inherited characters. + each gene resides at a particular location of a chromosome and can exist in variable forms (two different forms for flower color)
Mendel’s Ideas of Inheritance
P
p
Pp
Mendel’s Ideas of Inheritance• For each characteristic, an organism inherits two alleles, one from each parent. + an organism is either homozygous (two of the same alleles) or heterozygous (two different alleles)
Homozygous Heterozygous
• If the two alleles differ, the dominant allele is fully expressed and the recessive allele has no noticeable affect on appearance. + heterozygotes express the dominant trait
Mendel’s Ideas of Inheritance
RR rr
Rr
• The two alleles for each character segregate duringgamete production.
+ ovum/sperm get only one of the two alleles (haploid)
Mendel’s Law of Segregation
P generation Phenotype: Purple/White Genotype: PP/pp
F1 generation Phenotype: Purple Genotype: Pp
F2 generation? Genotype/Phenotype can be predicted using a Punnet Square
Mendel’s Law of Independent Assortment
Each pair of alleles segregates into gametes independently.
WH wHwh Wh
Mendel’s Law of Independent Assortment
Parental Genotypes GGWW ggww
Parental Gametes? GW gw
GgWw
GW Gw gW gw
F1 Genotypes?
F1 Gametes?
Beyond Mendel...
Different Types of Inheritance:
Complete Dominance Incomplete Dominance Mendel’s Traits Snapdragon Color
Incomplete DominanceOne allele does not dominant the other in the heterozygous condition. Both alleles are expressed but a new phenotype appears that is intermediate.
RR rrRr
Codominance
Both alleles in the Heterozygous condition are dominant.
CC Cc cc
Codominance & Multiple Alleles