Transcript Document

Introduction to
Genetics Notes
CH 11
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Section:
Introductory Vocabulary
1.Trait: observable, inheritable characteristic eye
color. Example of traits in pea plants: Plant
height, flower color, seed color, seed shape
2. Gene: region of a chromosome that controls a
particular trait
Character
Traits
Height
Tall
or
Short
Flower Color
Purple
or
White
Seed Color
Yellow
or
Green
Seed Shape
Round
or
Wrinkled
3. Allele: a different form of a gene
(ex:eyecolor gene: alleles are blue,
Trait: Stem height
green, brown…)
Alleles: T (Tall) or t
4. Pure bred: organism that would
produce identical offspring as itself (AA or aa)
5. Hybrid: organism produced by crossing parents
with differing traits (Aa or “mix”)
6. Homozygous: Organisms that have 2 identical
alleles for a particular trait (AA or aa)
7. Heterozygous: Organisms that have 2 different
alleles for a particular trait (Aa)
9. Genotype: genetic makeup (represented by 2
letters)
10. Phenotype: physical characteristics (word used to
describe – blue, green, brown)
11. Gametes: sex cells (egg or sperm)
12. Gregor Mendel: in 1843 he became
a monk in an Austrian monastery
13. Heredity: passing on characteristics
from parent to offspring
14. Genetics: study of heredity
Gregor Mendel:
The Father of Genetics
1. Gregor Mendel: 1822-1884
Austrian monk
a.Did genetics (breeding)
experiments on garden pea
plants.
b.1866: Published paper on
experiments
Gregor
Mendel
d. Mendel can control the
fertilization
(pollination) or mating of
these plants. Fertilization:
the joining of
gametes.
Two types of fertilization:
1. self-fertilization – the pollen
fertilizes the ovule on
the same flower
2. cross-fertilization – the pollen
of
one plant is used
fertilize the ovule of another
plant.
Cut stamens (holds pollen)
off of one flower
Brushed pollen from a
2nd flower onto carpel
(holds eggs) of 1st flower
Carpel
develops
into a pea
pod.
Slide # 9
Conclusions made by Mendel:
1. Each parent MUST contribute one gene for
each trait to the offspring.
– Evidence: F2’s had white flowers (present but
hidden in F1 generation.)
2. Each parent must have two copies of a
gene; and can have two different versions
of that gene called alleles at the same
time.
-- Evidence: F2’s had white flowers both parents
must have had at least one white allele!
 Dominant: allele that is expressed when 1
or both are present (capital letter)
 Recessive: allele that is masked by
presence of dominant allele (lower case)
a. The individual MUST have both recessive
alleles to show the recessive trait
The F1 purple
flowering plants
must have a second
hidden gene for
white flowers!
Slide # 8
Alleles
Homologous
Chromosomes
1. Alleles: alternate forms of
a gene or trait
FROM MOM
a. Parents may have two of
the same alleles or two
different alleles
b. Homozygous: having 2 FROM DAD
identical alleles
c. Heterozygous: having 2
different alleles
Every organism has two copies of
the same gene. One copy came
2. Alleles are located on
from MOM in her egg, the other gene
chromosomes
copy came from DAD in his sperm.
This plant has 2 different alleles
for the flower color character.
Homologous Chromosomes:
-are similar gene carrying chromosomes
from the opposite-sex parents .
Slide # 10
Mendel Solves the Genetics Puzzle
Phenotypes: Purple & White
Genotypes: PP
x
pp
1. Mendel reasoned that each
parent must have 2 possible
alleles to contribute
– Genotype: the alleles the
organism has (two letters)
Gametes: P
~ p
– Phenotype: physical
appearance of an organism
2. Mendel reasoned that the two
alleles separated when gametes
Fertilization:
Pp
(sex cells like eggs) formed.
3. Mendel also reasoned that the
alleles paired up again during
Phenotype of F1: All Purple
fertilization (joining of egg &sperm)
Genotype of F1: All Pp
Gene Diagram – Flower color
Alleles-
P = Purple flower
p = White flower
All genes occur in pairs – so 2 alleles affect a
characteristic – possible combinations are;
genotypes
PP
Phenotypes PURPLE
Pp
PURPLE
pp
WHITE
Punnett Square
1.
Determine what the alleles are. P=purple
p=white
2. Parent genotypes are determined. --Both are Pp
3. Parent’s possible gametes are determined and placed one
next to -or above each box.
Complete the Cross
Pp
purple
female
P
p
Pp Purple male
P
p
PP
Pp
Pp
pp
3 purple and 1
white offspring
3:1 chance with
these parents