1. California Content Standard
Heredity
LN #18
California Content Standard
Genetics
2g. Students know how to predict possible combinations of alleles in a zygote from
the genetic makeup of the parents.

2. What is Meiosis? fertilization + = Meiosis makes SEX CELLS.
Haploid cells
Gametes
Sperm & egg cells
Diploid is 2n
All of our body cells are diploid.
Haploid is n
ONLY gametes are haploid.
fertilization + =

3. What is a Phenotype? Phenotype = widow’s peak
A phenotype describes what an organism looks like.
In order to determine an organisms phenotype you need to look at it.
Phenotype = free earlobes
Phenotype = attached earlobes

4. What is a Genotype? Gene location for earlobes.
A genotype is the combination of genes in an organism.
Genes are section of DNA that codes for a trait. Genes are located on chromosomes.
Alleles are different forms of a gene.
Genes are labeled by using letters. F
free f
attached
F and f are alleles.
Genotype = Ff
Homologous chromosomes have genes for the same trait.

5. Who was Gregor Mendel?
Mendel carried out the first important studies in heredity.
Mendel studied heredity using pea plants.
Mendel was the first to develop laws and rules for heredity.
One of Mendel’s rules is the rule of dominance.
Some traits are dominant and others are recessive.
(1822 – 1884)

6. Punnett Squares
Punnett squares are used to determine the chance of seeing a trait in the offspring.
Remember every organism has two copies of a gene. Only one of the two is passed to the offspring.
If the genotype of a father is Aa, then he can either pass down A or a.

7. Words to know Monohybrid cross involves studying a single trait.
Homozygous means that both alleles are the same. We can have homozygous dominant, TT or homozygous recessive tt.
Heterozygous means that the alleles are different from one another. We would have Tt.
With the rule of dominance TT and Tt have the same phenotype. The only way to show a recessive trait is to be homozygous recessive, tt.

8. Monohybrid Cross problem
Widow’s peak is a dominant trait (P).
A woman homozygous dominant for widow’s peak marries a man without a widow’s peak. What are the chances that their children will have a widow’s peak?
Parent’s genotype
PP x pp
P P p Pp Pp Pp Pp
100% chance that the children will have a widow’s peak.

9. Summary What is a genotype and phenotype? Who was Mendel?
What are Punnett squares used for?
What are alleles?
How are homozygous and heterozygous different?