Download chapter 9 regular - Doral Academy Preparatory

Fundamentals of
Genetics
CHAPTER 9
Patterns of Inheritance

The History of Genetics
 Genetics – scientific study of heredity
 Trait – characteristic that can be passed from
parents to offspring
Father of Genetics
 Gregor
Mendel
(born 1822)
 Austrian
Monk
 Studied 7 different
pea plant traits that
are true-breeding
 Produce
offspring
identical to
themselves
Parental Cross
 Cross-pollinated
flowers with
opposite traits (tall, short)
P
generation
 Plants
from the first cross were all
tall- hybrids.
 F1
generation
F1 Cross
 Allowed
f1 plants to self-fertilize
 The recessive trait had reappeared!!
 About 25% of the offspring (F2
generation) were short.
Mendel’s Conclusions


1. Biological inheritance is passed from one generation to the
next- Genes
Alleles- different forms of a gene

2. Some alleles are dominant
Capital Letter -R,D
Some alleles are recessive
Lowercase letters – r, d

3. Principle of Segregation

Alleles separate from each other during formation of sex cells, or gametes.



Genes Represent Traits

Genotype – genes that make up an organism

Includes both genes in a homologous pair

Phenotype – outward expression of the trait

Homozygous – two alleles are identical (AA or aa)

Heterozygous – two alleles are different (Aa)

Also known as a hybrid organism

Purebred – organism receives the same genetic traits form both of
its parents
 Homozygous – AA or aa

Hybrid – organism receives different forms of a genetic trait
 Heterozygous - Aa
Important Terms




Genes – sections of a chromosome that code
for a trait
Allele – distinct form of a gene
Dominant Allele – expressed when two different
alleles are present; represented with capital letter
Recessive Allele – form of gene that is not
expressed when paired with a dominant allele;
represented with lower case letter
Genetics and
Prediction
Predictions for One Trait


Probability – predict likelihood of an event or
outcome
Punnett square – grid for organizing genetic
information
Can be used to make predictions about a cross
between two organsims
 Monohybrid Cross – cross between two parents and
one trait

Monohybrid Cross
Predictions for Two Traits
Dihybrid Cross – cross between
two parents and two traits

Use a 4 x 4
Punnett square
 Sixteen possible outcomes

Incomplete Dominance

Heterozygous offspring show a phenotype that
is in-between the phenotypes of the two
homozygous parents
Blending of traits
 Color in snapdragons;
instead of white or red,
color is pink

Codominance

Both alleles are expressed
 Example: Blood type
 IA, IB, i(O), or IAIB blood type
 Both A and B are dominant so they are both
expressed in the IAIB blood type
Polygenic Trait

Trait controlled by more than one gene
 Example: eye color