Download Ch. 8 Heredity

Ch. 8 Heredity
GLE 0707.4.3 Explain the relationship among
genes, chromosomes, and inherited traits
TB 234-240
What You’ll Learn…
• Explain how traits are inherited
• Identify Mendel’s role in history of genetics
• Use Punnett Squares to predict the results of the
crosses
• Compare and contrast the difference between an
individual’s genotype and phenotype
Why You Need To Know It…
• Heredity and genetics help explain why people
are different
I. Inheriting Traits
1. Heredity – passing of traits from
parent to offspring
A. What is Genetics?
1. Genes on chromosomes control
organism’s form, function, and
traits
2. Different forms of traits that make
up a gene pair = alleles
3. Meiosis = pair of chromosomes
separate, alleles also separate into
different sex cells
4. Every sex cell has 1 allele for each
trait
5. Study of how traits are inherited
through interactions of alleles =
science of genetics
II. Mendel: Father of Genetics
1. Gregor Mendel
a. Austrian Monk
b. 1865- studied pea plants to
predict possible types of
flowers and fruits resulting
from cross breeding
c. 1st to trace on trait through
several generations
d. 1st to use math = probability to
explain heredity
http://www.brainpop.com/science/c
ellularlifeandgenetics/heredity/
III. Genetics in a Garden
1.
a.
b.
c.
Mendel studied specific traits
Crossed 2 plants with different expressions of that trait
New plants all looked like one of the 2 parents
New plants called hybrids = received different genetic information (Diff.
Alleles) for a trait from each plant
2. Organism that always produces the same trait generation to generation =
purebred
EX: Tall plants that always produce tall plants = purebred
III. Genetics in a Garden
A. Dominant and Recessive Factors
1. Cross pollination- pollinate one trait with opposite trait
Ex: Purebred tall plants with purebred short plants
2. Dominant Allele = trait that covers up/dominants other
form of that
trait
Ex: Tall gene covered short gene in plants
3. Recessive Allele = trait that is covered by the dominant
trait
http://www.brainpop.com/health/geneticsgrowthanddevelop
ment/genetics/
Dominant and Recessive
Factors
III. Genetics in a Garden
B. Using Probability to Make Predictions
1. Probability- math that helps you predict
the chance of something happening
Ex: Coin toss – heads or tails – 50/50
chance
2. Mendel worked with a large number of
plants – helped make predictions more
accurate. Also increased the chances of
seeing a repeatable pattern
3. Valid science conclusions need to be
based on results
III. Genetics in a Garden
C. Punnett Squares
1. Letters represent dominant and
recessive alleles
2. Uppercase letter = dominant allele
3. Lowercase letter = recessive letter
4. Letter – A code (genotype) =
Genetic make-up
5. The way an organism looks or
behaves is a result of genotype =
phenotype
Ex: Brown hair = phenotype of hair
color = brown
III. Genetics in a Garden
D. Alleles Determine Traits
1. Most cells have 2 alleles for every
trait
2. Alleles are located on
chromosomes in nucleus of the
cell
3. Organism with the same 2 alleles
= homozygous trait
EX: both tall alleles ( TT )
4. Organism with that has 2 different
traits
EX: 1 tall and 1 short ( Tt )
5. Mendel produced heterozygous
hybrids for height = Tt
III. Genetics in a Garden
E. Making a Punnett Square
1. Letters representing 2 alleles
from 1 parent are written along
the top of the grid
2. Those of the 2nd parent are
placed down the side of the grid
(1 letter per section )
3. Each square of the grid is filled
with 1 allele donated by each parent
4. Letters represent genotypes of
possible offspring that parents
could produce
T
T
T
t
III. Genetics in a Garden
F. Principles of Heredity
1. Traits are controlled by alleles on chromosomes
2. An allele’s effect is dominant or recessive
3. When a pair of chromosomes separates during
meiosis, the different alleles for a trait move into
separate sex cells
https://www.khanacademy.org/science/biology/heredit
y-and-genetics/v/punnett-square-fun