Download - Summing up Mendel’s Laws
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…