Transcript 3 Intro to Genetic Crosses

Daily Agenda
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Daily Trivia
Agenda
Check Homework
Notes on Genetic Crosses
Groupwork on HW worksheets
Homework
RR / BIO 137
What is genetics?
• Genetics is the study
of HOW traits are
passed from parents
to offspring.
– Offspring show
some traits of each
parent
– These traits from
parents are passed
onto the offspring
by sex cells
Body Cell vs. Sex Cell
Body Cell
Sex Cell
make up most of the
tissues and organs in
body
Has 23 pairs of
chromosomes
(total=46 chromosomes)
The chromosomes are
paired up
sperm or egg cell only
Has 23 chromosomes
Only 1 of each
chromosome
Chromosomes
BODY CELL
SEX CELL
• A gene is a small
section of
chromosome that
determines a specific
trait
• Genes are arranged
on a chromosome
• Each chromosome
carries specific genes
Chromosome
Genes
gene
Genes
• The genes on
chromosomes in
body cells are
paired
Same Trait
Gene 1
Gene 2
–2 genes
represent a trait
in each body cell
Pair of chromosomes
Fertilization
• FERTILIZATION: we
get genes from each of
our parents
• The only way traits are
passed onto offspring
MOM
DAD
Offspring
Dominant Genes
• Genes that keep
other genes from
showing their
traits
• EX: plant size
• “T” is for the tall
gene for a tree
• Uppercase
letters only
Recessive Genes
• The genes that do not show their traits when
dominant genes are present
• Lowercase letters only
EX: plant size
“t” is the gene for a
short tree
Dominant vs. Recessive
• Pure Dominant – an organism with 2 dominant
genes for a trait
• Pure Recessive – an organism with 2 recessive
genes for a trait
• Heterozygous – an organism with 1 dominant
and 1 recessive gene for a trait
– The dominant gene will overpower the recessive
gene.
– The dominant gene will be expressed
Example: Palm Tree Height
Dominant Recessive
Gene is
depicted by a
lower case
letter
Ex: t
TT = pure
tt = pure
dominant
recessive
Tt = heterozygous
TALL
SHORT
Gene is
depicted with
a capital letter
Ex: T
TT
or
Tt
tt
Punnett Square
Mother’s Genes
Father’s Genes
• A way to show which
genes can combine when
and egg and sperm join
• Letters are used in place
of genes
• Large letter = dominant
gene (F)
• Small letter = recessive
gene (f)
Homework
• p. 11-12
• 211s
Daily Trivia
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Elephants can
“hear” through their
feet.
Agenda
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DT
Agenda
HW Check
Finish Notes
Punnett Squares
Homework
Punnett Square
• Large letter goes first in
heterozygous organisms
(Ff)
• Let’s do a cross between
a pure dominant male
(sperm) for free
earlobes (FF) and a
female (egg) who is
heterozygous for free
earlobes (Ff)
F
f
F
FF
Ff
F
FF
Ff
F is dominant over f
What are the expected results?
F
f
F
FF
Free
Earlobes
Ff
Free
Earlobes
f
Ff
Free
Earlobes
ff
Attached
Earlobes
Expected vs. Observed Results
Expected
Observed
Can be calculated
Actually seen
Predicted
Not Predicted
Genotype: The
combination of genes
one has
What you expect to
observe
Phenotype: the physical
trait that you can see
What you actually
observed
Dominant/Recessive
• One allele is
dominant over the
other (capable of
masking the
recessive allele)
PP = purple
pp = white
Pp = purple
Problem: Dominant/Recessive
• In pea plants, purple flowers (P) are dominant
over white flowers (p) show the cross between
two heterozygous plants.
P
p
GENOTYPES:
- PP (1); Pp (2); pp (1)
P
PP
Pp
- ratio 1:2:1
PHENOTYPES:
- purple (3); white (1)
- ratio 3:1
p
Pp
pp
Punnett Square
• 5 Steps
– Type of cross
– Key
– Cross
– Square
– Answer the question
• Practice Problems on the board
• Pages 13-16
Homework
• 2 Worksheets