Download Genetics

Genetics
Basic rules…
Lots of info is being researched by the
Human Genome Project….
• Genetics ~
the study of traits or genes that are passed
from parent to offspring
• Each parent gives 1 gene to the child for a total of 2
genes per trait
Ex: hair color: B from mom
+ B from dad
BB for child
Blood type: A from mom
+ B from dad
AB for child
http://www.ornl.gov/sci/techresources/Hum
an_Genome/posters/chromosome/chooser.
shtml
• Dominant ~ the gene that “shows up”, or takes over
(dominates)
• Recessive ~ the gene that does not “show up”, or is
hidden. Unless there are 2 of them together.
Ex: eye color
Dominant: Brown (B)
Recessive: Blue (b)
http://faculty.southwest.tn.edu/jiwilliams/Hu
man_Traits.htm
BB - brown
bb - blue
Bb - brown
• Genotype: genetic make up of a trait;
gene pair (2 letters that represent genes)
• You receive 1 gene from each parent for a
total of two genes per trait
Ex: AA
Bb
tt
• Phenotype:
physical appearance, as a result of the
gene pair (genotype)
Ex: type A blood
Type B blood
Brown hair
blue eyes
Genotypes vocabulary:
•
Heterozygous – a gene pair with two different genes; one
dominant and one recessive
Ex: Aa, Rr, Bb, Pp
•
Hybrid – a synonym for heterozygous
Ex: Aa, Rr, Bb, Pp
•
Homozygous – a gene pair with two of the same genes; either 2
recessives, or 2 dominants
Ex: aa, AA, RR, rr
•
Pure – a synonym for homozygous
Ex: aa, AA, RR, rr
•
Writing a key: for each genetics problem, start by writing the key for
the traits. You ALWAYS use the letter of the dominant trait for both
dominant and recessives.
Ex: Trait: Yellow – dominant
key: Y – yellow
Green – recessive
y- green
• Punnett Square ~ a tool used to determine probability of
offspring traits
1. Put mom’s 2 genes in the spaces on top of the square (1
gene over each square)
2. Put dad’s 2 genes in the spaces along the side of the
square (1 gene next to each square)
3. Bring down the genes in mom’s column 1 to both
squares underneath, then column 2 to both squares
underneath
4. Bring over the genes in dad’s column 1 to both squares
next to it, then column 2 to both squares next to it.
Punnett Square practice
B – black fur (dominate)
b – brown fur (recessive)
B
B
Mom’s
genotype: BB
phenotype: black
Dad’s
Genotype: Bb
phenotype: black
Possible offspring:
Genotype:
_BB____ % __50_____
__Bb___ % __50 ___
__bb___ % ___0____
Phenotype:
black___ % ___100_____
brown___ % ____0____