Download HEREDITY

HEREDITY
A. Def. = the study of genetics
B. Most traits / characteristics are decided by two genes – one from the male
parent, one from the female parent.
C. Most genes come in two forms:
1. Dominant – symbolized with a capital letter. It is the stronger gene.
2. Recessive – symbolized with a lower case letter. Gets masked / hidden by
the dominant gene.
D. Terms to know
1. Phenotype – what trait is actually showing (what you see)
2. Genotype – what genes are actually there (you cannot see this)
3. Homozygous (“purebred”) – has two of the SAME gene (allele); TT or tt
4. Heterozygous (“hybrid”) – has two DIFFERENT genes (alleles); Tt
5. Allele – a form of a gene (T or t). You can only get TWO alleles for each
gene (one from mom, one from dad)
EXAMPLE
Pea Plant: tall = dominant trait (T)
short = recessive trait (t)
Plant 1:
TT
=
(genotype)
tall plant
(phenotype)
PUREBRED / HOMOZYGOUS
Plant 2:
tt =
(genotype)
short plant
(phenotype)
PUREBRED / HOMOZYGOUS
Plant 3:
Tt
=
(genotype)
tall plant
(phenotype)
HYBRID / HETEROZYGOUS
EXAMPLE
Punnett Square = shows the possible outcomes in a cross between the male parent
and the female parent.
Tall Mom
(Tt)
Mom’s genes
Dad’s genes
X
Tall Dad
(Tt)
T
t
T
TT
tall
Tt
tall
t
Tt
tall
tt
short
Genotypic percent
Phenotypic percent
¼ or 25% - TT – purebred dominant
¾ or 75% - tall
2/4 or 50% - Tt – Hybrid
¼ or 25% - short
¼ or 25% - tt – purebred recessive
“ADVANCED” HEREDITY
A. Incomplete Dominance – Genes are neither dominant, nor recessive. They end
up blending or mixing their traits.
*This is always symbolized with 2 capital letters, but they use different letters.
Example : Four o’clock flowers
1) Red (RR) X White (WW)
R
R
W
RW
RW
W
RW
RW
Red = RR
White = WW
Pink = RW
2) Pink (RW) X Pink (RW)
R
W
R
RR
RW
W
RW
WW
B. CO – DOMINANT (Both genes are dominant)
Example: Blood Types (this is also an example of multiple alleles)
Allele A, Allele B, Allele O
AA= Type A
BB = Type B
AB = Type AB
AO = Type A
BO = Type B
OO = Type O
C. SEX-LINKED TRAITS (The trait is “linked” onto the X chromosome)
Examples: Color blindness and Hemophilia
Female
XX = not colorblind
XcX = “carrier” (not colorblind)
XcXc = colorblind
Male
XY = not colorblind
XcY = colorblind