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6.3 Mendel and Heredity
1. How did Mendel “take
control” over breeding his pea
plants?
2. What were Mendel’s “key
three decisions” he used in his
experiments?
6.3 Mendel and Heredity
1. Mendel interrupted the self-pollination
process by removing male flower parts. He
then took control of the pollination by
fertalizing the plants himself.
2. Mendel made three key decisions in his
experiments.
• use of purebred plants
• control over breeding
• observation of seven“either-or” traits
6.3 Mendel and Heredity
• Get out your Flash Cards
– Initial ALL of them
• Get in pairs
• One person place flashcards out with vocab word facing
up
• One person’s flashcards are facing with definition facing
up
• Please match up all cards
• Like “Memory”- if you match wrong. Turn them back
over. Return to them later
Set
Cornelland
Notes
on pg.
6.3 up
Mendel
Heredity
81
6.4 Genes,
2.1 Atoms,
Ions, Traits, Alleles
and Molecules
•Topic: 6.4 Genes, Traits,
Alleles
1. Explain why an organism’s genes may be
•Essential Questions:
1. Explain why an
organism’s genes may
be homozygous
dominant,
homozygous
recessive, but never
heterozygous
recessive.
•Don’t forget to add it to
your T.O.Contents!
homozygous dominant, homozygous
recessive, but never heterozygous
recessive.
6.4 Traits, Genes, and Alleles
KEY CONCEPT
Genes encode proteins that produce a diverse range
of traits.
6.4 Traits, Genes, and Alleles
The same gene can have many versions.
• A gene is a piece of DNA that directs a cell to make a
certain protein.
• Each gene has a locus, a
specific position on a pair of
homologous chromosomes.
*homo =same
6.4 Traits, Genes, and Alleles
• An allele is any alternative form of a gene occurring at a
specific locus on a chromosome.
– Each parent donates one allele for every gene.
X
Y
X XX
XY
X XX
XY
6.4 Traits, Genes, and Alleles
– Homozygous
describes two alleles
that are the same at a
specific locus.
*homo=same
– Heterozygous
describes two alleles
that are different at a
specific locus.
*Hetero=different
6.4 Traits, Genes, and Alleles
• Alleles can be represented using letters.
– A dominant allele is
expressed as a phenotype
when at least one allele is
dominant.
–(AA or Aa)
– A recessive allele is
expressed as a phenotype
only when two copies are
present.
–(aa)
6.4 Traits, Genes, and Alleles
• A genotype refers to the makeup (alleles) of a specific set of
genes.
Genotype: BB or Bb
Genotype: bb
6.4 Traits, Genes, and Alleles
• A phenotype is the physical expression of a trait. You can
see it!
Phenotype: Brown Eyes
Phenotype: Blue Eyes
6.4 Traits, Genes, and Alleles
*Both homozygous dominant (AA) and
heterozygous (Aa) genotypes yield a
dominant phenotype.
• Most traits occur in a range
and do not follow simple
dominant-recessive patterns.
6.4 Traits, Genes, and Alleles
6.4 Traits, Genes, and Alleles
Genes influence the development of traits.
• All of an organism’s genetic material is called the genome.