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Vocabulary, Punnett Squares
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#1 #2
#3 What is
happening here? These are
called ______ _________
#4
#5 Diploid or Haploid ?
#6 Diploid or Haploid?
Completely Random!!!!!!
• Genes – determine the characteristics of an organism.
• Alleles – alternate forms of genes– Ex. Gene = seed color
Green or Yellow Alleles
*Remember*Only 1 allele for each trait is passed on to
the offspring from each parent!
The Terms…• Genotype – genetic make-up of an individual– Ex. T T = genotype (letter combination)
Each letter is inherited from different parents.Dad Mom T T
Genotype Possibilities
• Homozygous (purebred) – An organism with genes that are alike.
• Ex. BB or bb
• Heterozygous (hybrid)
– An organism with genes that are different• Ex. Bb
DOMINANT TRAITS!!!• Homozygous Dominant Genotype
-Both alleles are the same.
-Both are capital letters.
Ex. TT• Heterozygous Genotype
-Different alleles.
Ex. Tt
Recessive Traits • recessive genotype– Both alleles are the same
– Both represented by lower case letters
•Example = tt
**For an organism to show a recessive phenotype, the genotype must be homozygous recessive.• Example: tt = short
Mendel’s 1st Law• Law of Segregation
A) Hereditary characteristics are determined by factors called genes.
B) For each characteristic, an offspring gets 2 genes, one from each parent.
C) The 2 genes of each pair segregate from each other and end up in separate gametes.
Genotype and Phenotype• Letters represent traits– Capital letter = dominant trait– Lower case = recessive trait
• Ex. HEIGHT• Tall = T (dominant)• Short = t (recessive)
TT, Tt Tall tt short
Gene Expression
• Phenotype– Expression of an individual’s genes…what it
looks like.• Ex. Tall = phenotype (physical appearance)
Ww 2 wings
Solving Genetics ProblemsIf you know the genotype of the parents, it is
possible to predict the likelihood of an offspring inheriting a particular phenotype.
- Probability – the chance that a given event will occur
- Punnett Square – named for R.C. Punnett, British biologist and mathematician
- Probability is shown through monohybrid crosses – genetic cross involving only 1 trait of the parents.
Examples• Homozygous tall plant (TT) with
homozygous short plant (tt).
100% Tt 100% Tall heterozygous tall
Examples…• Heterozygous long hair female with
homozygous short hair male (long is dominant). L l x l l
50% Ll = long hair 50% ll = short hair 1 : 1 ratio (1Ll to 1ll)