Transcript WARM UP - Ms. Chambers' Biology

WARM UP
January 3, 2011
Warm Up
• If you are acquainted with your birth
parents, list 4 physical traits you share,
and from which parent you acquired that
trait from.
• If you are not acquainted with your birth
parents, think of one of your friends that is,
and pick out 4 traits he or she shares with
them.
Introduction to
Genetics
Genetics Terms to know:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Gamete
Gene
Allele
Dominant
Recessive
Heterozygous
Homozygous
Hybrid
Genotype
Phenotype
What is genetics?
•
Genetics: The study of heredity
– All things seem to inherit traits from
their “parents”
– Trait: a characteristic based on
heredity
• i.e. hair color, plant flower color,
number of wings on a fly…
Understanding Heredity
• For centuries humans
have known that
offspring inherit traits
from their parents.
• However it is the work
of a monk, named
Gregor Mendel that
greatly increased
knowledge of
genetics!
Watch this clip about Mendel
• “Thread of life”: Gregor Mendel’s
experiments
http://www.youtube.com/watch?v=pkYxEy9g
F1w
• 23 and me: “What is a gene?”
Go Go Gregor cont..
• The monastery had several
true-breeding pea plants
– meaning that they only selfpollinate
• One stock of true breeding
plants only bred tall plants
• One stock of true breeding
plants only bred short plants
every time
Tall
Short
Go Go Gregor cont..
• So Gregor
decided to
cross pollinate
the tall plants
with the short
plants, and do
you know what
he got?
• All tall plants!!!
Go Go Gregor cont..
• So he crossed the offspring of the first cross (the
two new tall plants) and what did he get?
• About ¾ tall and ¼ short!
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
So what did this mean?
• Mendel drew a couple of conclusions from his
experiments.
– 1st conclusion: Biological inheritance is determined by
factors passed from one generation to the next. (We
call these factors GENES)
– The different forms of a gene are called alleles.
• Example: tall pea plant allele and short pea plant allele
– Every organism that reproduces sexually gets two
alleles (genes) for each trait, one from each parent.
So every organism has two alleles for a certain trait,
one from each parent.
So what did this mean? Cont.
• 2nd conclusion: THE PRINCIPLE OF
DOMINANCE
– This means that alleles can come in a dominant or
recessive form. Dominant traits mask recessive traits
when they are expressed.
– Example: tall is dominant over short pea plants.
Yellow seeds is dominant over green seeds, etc…
etc..
– Letter size signifies dominant (CAPITAL) or recessive
(lower case)
• T = tall height
• t = short height
– TT, Tt, tt ? Are these tall or short?
Phenotype Vs. Genotype
• Phenotype – outward physical appearance
Example: Tall pea plant or blue eyes
Pheno-physical!!!!
• Genotype – genetic composition (what
alleles are in DNA) Hh or bb
Wow! what are some dominant
and recessive traits in humans?
• Tongue rolling is dominant of non tongue
rolling
• Widow’s peak is dominant
Wow! what are some dominant
and recessive traits in humans
• Free earlobe is dominant over attached
earlobe
Alleles and Punnett squares
• Homozygous – individuals that have 2
identical alleles for a given trait. Example
genotypes: HH (homozygous dominant)
or hh (homozygous recessive).
• Heterozygous – individuals with 2
different alleles for a given trait. Example
genotype: Hh
• http://www.mcgrawhill.ca/school/schoolGr
aphics/biology6_1.mpg
Go Go Gregor cont..
• Mendel did this with several other true breeding
traits as well.
Seed
Shape
Seed
Color
Round
Yellow
Seed Coat
Color
Gray
Pod
Shape
Pod
Color
Smooth
Green
Flower
Position
Plant
Height
Axial
Tall
Short
Wrinkled
Green
White
Constricted
Yellow
Terminal
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Review
• dominant – only one copy of the allele is
present for the trait to be “shown”
• recessive – absence of a dominant allele
required (2 copies of recessive allele) to
“show” trait