GeneticsThe study of heredity…whatever that means.
Heredity-The passing of traits from parents to progeny (offspring…ummm…kids…do flowers have kids?).
Who was Gregor Mendel?
He was a dude who studied peas in the 1850’s…WOW…that sounds exciting!
Actually, he experimented with pea plants to see how traits were inherited (passed from parent to offspring).
Mr. Blacher's 7th Grade Biology
What did he do…exactly?
Well…he crossed purebred plants (that means the parents have similar traits so the offspring always have the same trait as the parent…blue eyed parent…blue eyed kid).
Then he started crossing different types (like green with yellow instead of green with green).
He figured out that individual factorswere controlling what he saw in the plants.
These are called…GENES!
Mr. Blacher's 7th Grade Biology
Genes
Remember that a GENE is a specific sequence of nucleotides within the DNA molecule.
So…a GENE contains the “code” for a particular trait (like blue hair and blonde eyes).
Also remember that when cells are dividing (MITOSIS in the cell cycle), the DNA is packed together forming a structure we call a CHROMOSOME.
Mr. Blacher's 7th Grade Biology
Alleles These are the various forms of a gene
(remember…genes control traits).
Alleles control the inheritance of traits. There are two forms and they’re represented by letters of the alphabet.
Some traits are determined by one allele and some are multi-allelic.
In sexual reproduction, one allele come from the male and one comes from the female, so…there will be two (2) alleles.
Mr. Blacher's 7th Grade Biology
Let’s Start with the Simplest Type…
Complete Dominance…one allele is dominant over another.
DOMINANT (capital letters): If this allele is there…the trait shows up.
Recessive (lower case letters): If this allele is there…the trait won’t show up if a dominant allele is also there.
Mr. Blacher's 7th Grade Biology
Huh?
Ok, let’s say that B = Brown fur and b= white fur. What organism? Doesn’t matter…let’s say the Alaskan ShortnoseSqueezle.
If mom and dad each contribute a B gene, then the squeezle offspring has brown fur (BB)
If mom gives up a B and dad a b, then the squeezle kid still has brown fur…why?
Mr. Blacher's 7th Grade Biology
As long as the is a B…there will be brown fur, because B is DOMINANT.
Now…if mom gives up a b and so does dad (bb), then bingo…white furred squeezle (and we all know how good those are grilled).
bb…two recessive alleles.
Unfortunately…all of this junk has names that you gotta know.
Fortunately…you already know a bunch of them
Mr. Blacher's 7th Grade Biology
Phenotypes & Genotypes
Phenotype: the physical
characteristics of offspring (blue eyes, straight hair, blood type).
Genotype: the actual genetic
makeup of the offspring (Bb, rr, TT). Genotypes can be as follows…
Mr. Blacher's 7th Grade Biology
Genotypes: Combinations of Alleles
Homozygous: two of the same alleles…BB, RR, rr, ss…get it?
Homozygous Dominant…two dominant alleles…QQ, LL, DD.
Homozygous Recessive…two recessive alleles…dd, ss, ff.
Heterozygous: one of each allele, one dominant and one recessive…Ff, Bb, Aa
Mr. Blacher's 7th Grade Biology
Punnett Squares Used to determine the possible
outcomes based upon the GENOTYPE of the parents.
You can determine the GENOTYPIC RATIO & PHENOTYPIC RATIO from this information.
They look like this:
Mr. Blacher's 7th Grade Biology
Try These …
Red flowers are dominant (R)
Yellow flowers are recessive (r)
1. Homozygous Dominant x Heterozygous
2. Homozygous Recessive x Homozygous Dominant
3. Heterozygous x Heterozygous
Mr. Blacher's 7th Grade Biology
