Transcript IN SEXUAL REPRODUCTION TO GENES ARE PASSED FROM

LIVING THINGS INHERIT
TRAITS IN PATTERNS
• PARENTS & OFFSPRING ARE SIMILAR
• GENES ARE ON CHROMOSOME PAIRS
• GREGOR MENDEL MADE SOME
IMPORTANT DISCOVERIES ABOUT
HEREDITY
– A monk, Gregor Mendel, who lived in Austria in mid1800’s, did first major experiments on heredity.
– Began studying inheritance of traits among pea plants
in monastery’s garden.
– Took detailed notes & worked with several traits
(plant height, flower position, seed shape, seed color,
flower color, etc.)
• ALLELES INTERACT TO PRODUCE TRAITS
PARENTS & OFFSPRING ARE
SIMILAR
• Inherited Traits are
characteristics passed on
from your parents
• Acquired Traits are
developed during your
life (riding bike)
• During SEXUAL
REPRODUCTION, a
mom’s cell with genetic
data combines with a
dad’s cell with different
genetic data, to create a
new, unique cell, which
becomes the offspring.
GENES ARE FOUND ON
CHROMOSOME PAIRS
• GENE: unit of heredity
found at a specific spot on
a chromosome, codes for
a particular product (that
causes traits).
• HEREDITY: passing of
genes from parent to
offspring.
• Cells have PAIRS of
chromosomes, (one part
of pair from each of 2
parents). Chromosomes in
a pair are called
HOMOLOGS (same size
& shape)
GENES FOUND ON
CHROMOSOMES PAIRS cont.
• On each homolog, are sites where specific genes
are located, used to determine specific traits (like
height).
• Both homologs may have gene for height at spot
“A”, but one may be for tall, the other short. The
various forms of the same gene are called
ALLELES.
• The alleles on a pair of homologs may or may not
be different.
• Human chromosomes are numbered 1-22; the
23rd pair are the SEX CHROMOSOMES.
• Female has XX, and Males have XY.
GREGOR MENDEL
• Took TRUE BREEDING (always produces
offspring with a particular trait if self-pollinated)
plants for tall & true breeding plants for short &
cross bred.
• All offspring tall, then let them self-pollinate, and
the second generation were 75% tall & 25%
short; the trait that seemed to disappear (short) in
the first generation, reappeared in the second.
• Mendel realized there must be 2 “factors” for
each possible trait (one from each parent)
• He felt some of these factors may be “masked” or
overpowered by the other (short factor
overpowered by tall factor).
• Today we call his “factors” genes & alleles.
ALLELES INTERACT TO
MAKE TRAITS
• PHENOTYPE: observable characteristics of an
organism (what they look like)
• GENOTYPE: actual genes an organism has for
specific traits.
• DOMINANT ALLELE: is expressed in the
phenotype even if only 1 is present in the
genotype (eyefold allele)
• RECESSIVE ALLELE: is expressed in
phenotype only when 2 copies are present on the
homologs/chromosomes (no eyefold)
• Hair & skin color as well as other traits, are
determined by multiple genes, not just 1 pair.