Transcript Mendelian Inheritance

Mendelian Inheritance
Terms
 Inheritance patterns – predictable
patterns seen in the transmission of traits
from one generation to the next
 Heredity – the passing of traits from
parents to offspring
 Genetics – is the study of heredity
GREGOR MENDEL





Born in 1822 to peasant parents in Austria
Studied math and science
Failed exam for a teaching certificate
Spent his life in a monastery
Conducted experiments on plant heredity over 7
years
 Developed a set of rules that accurately
explained and predicted patterns of heredity
(results were both qualitative and quantitative)
 His work is considered to be one of the greatest
intellectual accomplishments in science
GREGOR MENDEL
MENDEL’S EXPERIMENTAL
DESIGN
 Mendel identified pea plants that were true
breeding
 True Breeding – plant that produces offspring
identical in appearance to itself generation
after generation, when self fertilized
 Mendel also conducted a series of crossfertilization experiments
 Cross Fertilization – fertilization that occurs
when sperm from the pollen of one plant
fertilize the eggs in the flower of a different
plant
 Mendel chose to work with garden pea
plants for the following reasons:
 They are small, easy to grow, mature quickly
and produce large numbers of offspring
 Earlier results has been done on pea plants
and their results were known to Mendel
 Many variety of peas available
 Pea plants are bisexual and normally self
fertilize but experimental crosses can be
performed
WHAT DID MENDEL FIND?
 To understand Mendel’s findings, we will
follow his study of flower colour.
 He crossed contrasting parents from pure
lines and called this the first parental (P1)
generation.
Purple
x
White
P1
 He found that all of the offspring (first filial
or F1 generation) all resembled one of the
parents.
 He called this the dominant trait.
Purple x
White
↓
All purple
P1
F1
 He then allowed the individuals from the F1
generation to self-pollinate and planted the
resulting seeds to observe their traits.
 This was called the second filial or F2
generation.
Purple hybrid x Purple hybrid
F1
Some purple and some white
F2
Hybrid – offspring that result from crossing two
true-breeding varieties of the same species
 He called the white trait the RECESSIVE
TRAIT.
 He wondered in the proportions of the F2
types (purple vs. white flowers) would give
some clue to the way heredity worked so
he started to count.
 He quantified 929 F2 individuals and
found:
705 purple-flowered plants
224 white-flowered plants
i.e Roughly 24.1% showed the recessive
trait
Monohybrid Crosses
 Hybrids that differ in one trait are crossed
with one another
 Mendel used monohybrid crosses to study
at least 7 categories of pea-plant
Mendelian Model of Inheritance
1. Allele – is an alternative version of a
gene.
Example: seed colour for peas: a yellow
seed allele and a green seed allele
2. For each gene, an individual organism
inherits two alleles, one from each
parent.
If the two alleles are the same, the
individual is said to be homozygous
(AA or aa)
If the two alleles are different, the
individual is heterozygous for that gene
(Aa)
3. An allele may be expressed (appear) as a
trait or else hidden in a heterozygous
individual
Dominant Allele – allele determines the trait
that a heterozygous individual expresses
Recessive allele – allele that is not
expressed in a heterozygous individual
4. Each gamete carries only one allele for
each hereditary trait due to the separation
of allele pairs when the gametes form.
Allele pairs are re-formed in fertilization
Mendel’s Law of Segregation
 Law of Segregation – states that two alleles for a
trait or gene separate during the phases of
meiosis
 With fertilization, each gamete donates one
allele to make up the allele pair
 Alleles like the traits they determine are said to
be heritable because they can be inherited
Homework
 Read pages 127 – 130
 Do page 131 # 1
 Do page 138 # 1, 2, 3, 7, 9