Transcript Heredity/Genetics

Heredity/Genetics
Heredity – passing of
traits from parents to
offspring
Genes – section of
DNA that contain a
trait.
- each gamete
contains one gene for a
trait.
Alleles – different
forms of a gene
Egg – gene for white
flower (r )
Sperm – gene for red
flower (R )
Genetics – study of how
traits are inherited
through the action of
alleles.
Gregor Mendel
Austrian monk
Worked with pea
plants to predict
offspring
Father of Genetics
Mendel’s experiment
Two purebred tall pea
plants
both alleles – T T
All offspring – tall
Two purebred short
pea plants
All offspring – short
tt
Purebred plant/ animal
– both alleles are the
same for the trait
TT
Tall
tt
short
1. Pollinated plants by
putting male gametes
on female gametes of
1 TT plant onto 1 tt
plant.
Result: 4 tall plants
but are NOT purebred.
They have an allele for
shortness. Tt
2. Took two hybrid
pea plants (Tt) and
pollinated them.
Result: 3 tall plants
1 short plant
TT Tt Tt tt
Hybrid – organism that
contains alleles of
opposite traits.
Homozygous – trait
with two alleles that
are alike TT
tt
Heterozygous – trait
with two different
alleles
Tt
Dominant trait – trait
that overpowers its
opposite trait.
Recessive trait – trait
that is being
overpowered Tt
except if homozygous
tt
Genotype – the
genetic make up of a
trait RR Rr rr
Phenotype – the
physical appearance of
a trait.
Red pink white
Copy in notebook
Write a genotype for every
phenotype listed.
NOTE: use S for
spherical
Y for yellow
P for color
I for inflated
G for green
Complete this punnett square
1. Homozygous tall with
homozygous short
2. Homozygous tall with
heterozygous tall
3. Heterozygous tall with
heterozygous tall
4. Heterozygous tall with
homozygous short
Incomplete Dominance
Mendel’s experiement
with peas does not work
for all kinds of plants.
With incomplete
dominance, a cross
between organisms
with two different
phenotypes
produces offspring
with a third
phenotype that
shows a blending
of the parental
traits.
The trick is to recognize
when you are dealing
with a question involving
incomplete
dominance. There are
two steps to this:
1) Notice that the
offspring is showing a
3rd phenotype. The
parents each have one,
and the offspring are
different from the
parents.
2) Notice that the trait in
the offspring is a blend
(mixing) of the parental
traits.
Questions:
1. A cross between a blue blahblah bird & a white
blahblah bird produces offspring that are
silver. The color of blahblah birds is determined
by just two alleles.
a) What are the genotypes of the parent blahblah
birds in the original cross?
b) What is/are the genotype(s) of the silver
offspring?
c) What would be the phenotypic ratios of
offspring produced by two silver blahblah birds?
2. The color of fruit for plant "X" is determined
by two alleles. When two plants with orange
fruits are crossed the following phenotypic ratios
are present in the offspring: 25% red fruit, 50%
orange fruit, 25% yellow fruit. What are the
genotypes of the parent orange-fruited plants?
Multiple genes
Shades of colors of
eyes – produced by a
combination of many
genes
Polygenic inheritance
– group of gene pairs
act together to produce
a single trait
Produces a wide
variety of phenotypes
Skin color, height,
weight, shape of eyes,
ears and ear lobes, hair
color – result of
polygenic inheritance.