Transcript Mendel’s Laws of Heredity-Why we look the way we look

Mendel’s Laws of
Heredity-
Why we look the way we look...
EQ: What is the
significance of
Mendel’s
experiments to the
study of genetics?
WHAT
IS HEREDITY?
The passing on of characteristics
(traits) from parents to offspring
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Genetics is the study of biological
inheritance and variation in
organisms.
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MENDEL USED PEAS...
Mendel’s Pea Plants
They reproduce sexually through
self-pollination
●Have both sex organs with two
distinct, male and female, sex
cells called gametes
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Fertilization = sperm + egg
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MENDEL CROSSED THEM
Cross - combining gametes
from parents with different
traits
● Line of plants (offspring)
became purebred, genetically
uniform
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Genes and Alleles
Genes - located on chromosomes, they
control how an organism develops and
looks
●Each organism has two alleles for each
trait
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Alleles - different forms of the same gene
WHAT DID MENDEL
FIND?
He discovered three laws
and rules that explain
factors affecting heredity.
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1. RULE OF DOMINANCE
The trait that is observed in the
offspring is the dominant trait
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expressed no matter what when
present***
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The trait that disappears in the
offspring is the recessive trait
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only expressed when two copies of
the allele are present**
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RULE OF DOMINANCE
2. LAW
OF
SEGREGATION
Organisms inherit two copies of
each gene, one from each parent.
●The two alleles for a trait must
separate when gametes are formed
during Meiosis
●A parent randomly passes only one
allele for each trait to each
offspring **
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3. LAW OF INDEPENDENT
ASSORTMENT
The genes for different
traits are inherited
independently of each other.
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PHENOTYPE & GENOTYPE
Phenotype - the way an organism
looks
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red hair or brown hair
Genotype - the gene combination
of an organism
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AA or Aa or aa
HETEROZYGOUS & HOMOZYGOUS
Heterozygous - if the two
alleles for a trait are different
(Aa) (one dominant & one recessive )
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Homozygous - if the two alleles
for a trait are the same (AA
or aa) (both dominant Or both recessive)
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