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Ch. 9 Heredity & Genetics
I.
Basics
A. Genetics- Study of heredity
B. Heredity- transmission of traits from parent to
offspring
C. Inheritance- passing of traits by heredity
II.
Gregor Mendel- A monk from Brunn Austria trained
in math + science
A. His work- Identified seven diff. characteristics that
occurred in one from or another (Pea plants)
Ex. Tall vs. short pg 167
B. Conclusions- His work found the basis for our modern
knowledge of genetics today!!
* Key words in understating his work
1. Pure- Plants that are pure for a trait always produce
offspring w/that trait
2. Pollination- Transfer of pollen from the anther (male) to
the stigma of the female
3. Self Pollination- Transfer of pollen from anther to stigma
in the same plant
Know parts labeled on the picture below
4. Cross Pollination- Pollen form one plant anther to
another plants stigma
5. Gene- Segment of DNA that controls a certain trait
6. Alleles (factors)-Contrasting form of a gene represented
by letters
7. Probability- The likelihood that an event will occur
8. Punnet Square- A diagram that aides in determining
probability in genetics
9. Monohybrid Cross- 1 pair of contrasting traits are
crossed. (4 square PS)
Ex. TT X tt
**Know how to set up and figure
out G and P ratios of the F1 and F2 generations
10. Dihybrid Cross- 2 pair of contrasting traits are crossed
(16 square PS)
Ex. RRYY x rryy **Know how to set up and
figure out G and P ratios of the F1 and F2 generations
11. Homozygous- when both alleles (factors) are the same in
a gene pair
Ex. TT or tt (homozygous dominant or homozygous
recessive)
12. Heterozygous- When both alleles are different in a gene
pair
Ex. Tt (Heterozygous dominant)
13. Dominant- The trait that is expressed
14. Recessive- “ “ “ “ hidden/ masked
15. Genotype- Actual genes that are present in its cell
(LETTERS)
Ex. TT, Tt, tt (Can Not See!!)
16. Phenotype- What traits are shown, what you actually see
(WORDS)
Ex. Tall, Tall, Short (Can See)
17. Parent Generation (P1)- original pure plants
18. First filial generation (F1)- the offspring of the P1
19. Second filial generation (F2)- the offspring of the F1
20. Incomplete dominance- 2 alleles are neither dominant
nor recessive. They both
contribute to the phenotype
In 4 O’clock flowers
Ex. Red x white flowers = pink
RR = red
Rr =pink
rr = white
21. Co-dominance- Occurs when both alleles for a gene are
expressing in a heterozygous offspring
In horses
Ex. Red x White fur color = Roan
III. The sex chromosomes
A. How sex is inherited
1. Determined by DNA- Specifically the x and y
chromosomes.
2. Females are XX
Male’s XY
Therefore
x
y
x x
xx xx
xy xy
50% chance
of either having
a boy or a girl.
B. Twins
1. Identical- 1 egg and 1 sperm that divided after
fertilization
2. Fraternal- 2 eggs and 2 sperm. No more closely related
than brothers or sisters
except they are the same age and developed
under the same conditions.
C. x- linked Traits- Traits that are carried on the Xchromosome
These genes are carried by women and passed on to the
male offspring
Ex. Muscular dystrophy , color blindness, hemophilia,
pattern baldness
X-linked recessive example
XH-No MD
Xh-MD
Female
Male
Expression
XhXh
XhYRecessive
XHXh
XHY
Dominant
XHXH
Dominant
Male only needs one recessive allele to express the
recessive trait
Example
XHXh x XHY  make a punnett square and find
possible offspring
1. Carriers- have one normal allele that dominates
the recessive allele
2. Pedigree- a chart or diagram that shows the passing of traits
in a family by marriages and births.
Provides scientists a way to determine if traits are
dominant, recessive, or x- linked.