Our genes determine our traits or characteristics Your genotype Dd or genetic makeup for a particular trait determines your phenotype dimples or physical appearance for that trait ID: 265450
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Slide1
The Basics of Genetics…the passing of traits
Our genes determine our traits or characteristics.
Your
genotype
(
Dd
) or genetic makeup for a particular trait determines your
phenotype
(dimples) or physical appearance for that trait.
Alleles
are different forms that a gene may have for a single trait. For example, having dimples or not having dimples. Slide2
Alleles
can be represented by letters. You get one allele from each parent; that’s why there are 2 letters.
Alleles
can be
dominant
, represented by a capital letter or
recessive
, represented by a lowercase letter.
Homozygous
(pure) = 2 of the same alleles for a trait; for example:
dd
or DD
Heterozygous
(hybrid) = 2 different alleles for a trait; for example:
DdSlide3
Punnett squares and Pedigree ChartsSlide4
Punnett squares
A chart that shows the chances or probability of a particular trait being expressed in offspring.
Each box of the Punnett square represents a 25% chance for that
trait being expressed.
Example: Cross
Tt
and
ttT = dominant allele = tallT = recessive allele = shortThe Tt and tt along the top and sides of the Punnett square are the genotypes for the parents.
The genotypes for the offspring are inside of the Punnett square.Slide5
Interpreting Punnett squares
Remember that T is dominant over t, which is recessive.
Parent 1’s genotype =
tt
; phenotype = short
Parent 2’s genotype =
Tt
; phenotype = tallThere is a 50% chance of producing short offspring = tt because there are 2 boxes with that trait.There is a 50% chance of producing tall offspring = Tt.Slide6
Pedigree Charts (also see Pedigree notes)
There are four generations shown on this pedigree chart.
Squares = males and circles = females; if the shape is totally shaded then he/she has the condition; if the shape is shaded ½ way then he/she is a carrier for that condition.
Generation I parents had 2 boys and 3 girls of which only 1 has the condition.