Transcript Section 10.1 Summary – pages 253


Genetics—Branch of biology that
studies heredity

Heredity – the passing on of
characteristics from parents to offspring

Gregor Mendel--Austrian monk who
used pea plants to study how traits are
passed from one generation to the next

Traits—characteristics that are inherited

Hybrid—offspring of parents (pea plants) that
have different forms of a trait

Ex.—tall pea plant bred with short pea plant
Mendel’s Experiment

Cross-pollination—using pollen from one plant to
pollinate a different plant

Mendel bred tall pea plants with short plants

The offspring in the 1st generation were all tall

The offspring in the second generation were 75% tall and
25% short

The short trait disappeared in the 1st generation and
reappeared in the 2nd generation
•P generation—original
parents
•F1 generation—offspring of
the parent plants (filial)
•Ex.Your parents are P and
you are F1
P1
Short pea plant
Tall pea plant
F1
All tall pea plants
F2
3 tall: 1 short

Alleles—Different forms of the same gene,
each one located on different copies of the
same chromosome (1 from mother and 1 from
father)

Ex. T is allele for tall plant, t is allele for short plant
•Dominant—trait that covers
over another trait, capital letter
•Ex. T (tall) is a dominant
allele
•Recessive—trait that is
covered over by another trait,
lower case letter
•Ex. t (short) is the recessive
allele
T-tall
t-short
The second generation
Pod
color
Pod
Plant
shape height
purple
axial
(side)
green
inflated
tall
white
terminal
(tips)
yellow
constricted
short
Seed Seed Flower Flower
shape color color position
Dominant
trait
round yellow
Recessive
trait
wrinkled
green
•Phenotype—physical appearance
•Ex. Phenotype is tall
•Genotype—genetic makeup
•Ex. Genotype can be TT for a tall
plant
Tall pea plant
•Homozygous—2 same alleles
for a trait
•Ex. TT-tall tt-short
•Heterozygous—2 different
alleles for a trait (carrier)
•Ex. Tt-tall
TT, Tt-tall tt-short
Simple Genetic Human Traits
Tongue Rolling (R)
 Dimples (D)
 Freckles (F)
 Eye Color: Brown is dominant to blue (B)
 Hitchhiker’s Thumb (h)


Law of segregation—Each gene has 2 alleles
for a trait, after meiosis each gamete receives
one of these alleles

Law of Independent assortment – genes
for different traits are independently inherited
of each other

Punnett square--A tool used to
predict the possible offspring of a cross
between 2 parents

Monohybrid cross--crossing a single
trait between 2 parents
 Genotype
of the parents along top and side
of square
 Cross each trait individually

1. Cross TT x tt
T
T
t
Tt
Tt
t
Tt
Tt
Genotypic ratio
100% Tt
Phenotypic ratio
100% tall

2. Cross Tt x tt
T
t
t
Tt
tt
t
Tt
tt
Genotypic ratio
50% Tt 50% tt
1 Tt : 1 tt
Phenotypic ratio
50% tall 50% short
1 tall : 1 short
3. Cross Tt x TT
T
t
T
TT
Tt
T
TT
Tt
Genotypic ratio
50% TT 50% Tt
1 TT : 1 Tt
Phenotypic ratio
100% tall

4. Cross Tt x Tt
T
t
T
TT
Tt
t
Tt
tt
Genotypic ratio
25% TT 50% Tt 25%tt
1 TT : 2 Tt : 1 tt
Phenotypic ratio
75% tall 25% short
3 tall : 1 short
Sex Chromosomes
Female (eggs): XX
 Male (sperm): XY

•Every time a female has a
baby, what percent chance do
they have of having a boy?
A girl?
•If a female has 5 boys in a
row, what percent chance do
they have to have another
boy?
A girl?
•Which parent determines the
sex of a baby? WHY?