Do you look exactly like either one of your parents? What about your siblings? Why is

this & how do you explain it???

Summing up Mendel’s Laws

The Key Terms!!

What is Genetics?• Study of heredity from generation

to generation AND variation of organisms

–Heredity – passing of characteristics: parents → offspring

– Traits – characteristics received by offspring (Ex: color, size)

Somatic Cells vs. Gametes

A quick review of cells…

A quick review of reproduction

• Sexual reproduction – Sex cells (gametes) from male & female

come together

Sperm Egg

• Fertilization – fusion of gametes;individual traits passed to fertilized cell (zygote)

• DNA in sperm & egg cells carry genes on chromosomes–Genes – sections of DNA that code

for traits (proteins); come in different forms called alleles

– Allele – located on 2 different copies of a chromosome, 1 inherited from mother, 1 from father

Examples: Plant Height – Tall/Short Plant Color -

Purple/White

Law of Dominance–Dominant allele – masks recessive

trait

–Recessive allele – trait that can be masked

Example: Can you roll your tongue? Tongue rollers are dominant. Let’s symbolize the tongue rolling trait using a letter code – let’s use “T.”

If dominant is TThen recessive must be t

Genotypes and Phenotypes

• Letter codes can be joined together in various combinations…what are they?

TT – tongue rollers Tt – tongue rollers tt – non-tongue

rollers

Phenotype:

observable character-

isitics

Genotype: gene

combos

How do we categorize these combinations???• Homozygous – same 2 alleles

→ recessive alleles are ALWAYS homozygous

TT, tt

• Heterozygous – different alleles

Tt

Mendel’s Laws1. Law of Segregation – – Because each organism has 2

alleles → TWO different types gametes can be produced

– During fertilization, gametes randomly pair → produce combinations of alleles

2. Law of Independent Assortment– Genes for different traits inherited

independently of each other

– Genes separate and recombine

– This accounts for variation in genotypes/phenotypes!

Mendel’s Laws cont…