GENETICS
GENETICS
• Study of heredity
• What we inherit from our parents
Gregor Mendel (1822- 1884)
• Father of Genetics
• Studied pea plants
• Grow rapidly
• Have 7 contrasting traits
which are easy to observe
• Can self-pollinate
7 Contrasting Traits of Pea Plants
Mendels’ Experiment
• Self-pollinated plants (true-breeding)-
sperm cells fertilize egg from the same
flower
• would produce offspring with identical
traits to themselves
Mendel’s Experiment
• Cross – pollinated plants – sperm from one
plant used to fertilize egg from different
flower
• Offspring of this crosses are known as hybrid
Mendels’ Experiment continues….
Mendels’ Conclusion
• Traits are controlled by genes, that occur
in pairs
Remember a gene…..
• It’s a segment of DNA (bases) that codes
for trait
• DNA + protein Chromosome
• We have 23 pairs of homologous
chromosome
• Therefore, genes also occur in pairs
Law of Dominance
• Some traits hide the effect of others
• Allele – different form of a gene
• 2 alleles trait
• Alleles maybe:
• Dominant – hides the other trait
• Recessive – trait seems to disappear
Ex: Tall x short = all tall
Law of Dominance
Law of Segregation
• only one of the two gene copies present
in an organism is distributed to each gamete
(egg or sperm cell) that it makes, and the
allocation of the gene copies is random
Monohybrid Cross
• Involves 1 pair of allele - 1 trait
Monohybrid Cross
Problem Set 1: In pea plants, flower color is
determined by a single gene with two alleles.
The dominant allele (F) produces purple flowers,
while the recessive allele (f) produces white flowers.
Parent 1: Homozygous dominant
Parent 2: Heterozygous
Monohybrid Cross
a. Determine the genotype of each parent.
b. Set up a Punnett square to show the possible
genotypes of the offspring.
c. Calculate the phenotypic ratio of the offspring.
Monohybrid Cross
Problem Set 2: In guinea pigs, coat color is
determined by a single gene with two alleles.
The dominant allele (C) produces black coat color,
while the recessive allele (c) produces white coat
Parent 1: Homozygous dominant guinea pig
Parent 2: Homozygous recessive guinea pig
Monohybrid Cross
a. Determine the genotype of each parent.
b. Set up a Punnett square to show the
possible genotypes of the offspring.
c. Calculate the phenotypic ratio of the offspring.
Law of Independent Assortment
• Genes for different traits can separate
independently during the formation of gametes
•DIHYBRID CROSS → 2 pairs of alleles
• Ex. RrYy X RrYy (2 traits)
Dihybrid Cross Example
• R = round
• r = wrinkled
• Y = yellow
• y = green
PHENOTYPIC RATIO =
9 ROUND YELLOW:
3 ROUND GREEN:
3 WRINKLED YELLOW:
1 WRINKLED GREEN
Dihybrid Cross
• Involves 2 pairs of allele - 2 traits
Dihybrid Cross
• Pure-breeding lines are
crossed to produce
dihybrids in the F1
generation. The cross
of these particular
dihybrids produces
four phenotypic
classes.
Dihybrid Cross
1. In rabbits, gray hair is dominant to white hair. Also in
rabbits, black eyes are dominant to red eyes. These
letters represents the genotypes of the rabbit.
GG = gray hair BB = black eyes
Gg = gray hair Bb = black eyes
Gg = white hair bb = red eyes
Dihybrid Cross
What are the phenotypes of rabbits that have the
following genotypes?
Ggbb = ____________________________________
ggbb = ____________________________________
ggBB = ____________________________________
GgBb = ____________________________________
Dihybrid Cross (Try this)
2. A male rabbit with the genotype GGbb is crossed
with a female rabbit with the genotype ggBb. Fill out
the square and determine the phenotypes in the
offspring.
a. How many have gray fur and black eyes?
b. How many have gray fur and red eyes?
c. How many have white fur and black eyes?
d. How many have white fur and red eyes?
