Transcript Genetic Notes

Mendelian Genetics
How Genetics Began
• A monk named Gregor Mendel first studied
how certain traits could be passed on by
studying his pea plants.
Heredity (or inheritance): the passing of traits
to the next generation
What Mendel did in his experiments:
• He found two plants that were “pure-breds” or
true-breeding of certain traits.
• Those two plants were called the parent or “P”
generation
• Once he pollinated those two plants, he waited
until seeds were produced, planted them and
then observed what characteristics they had
• The seeds from the parent plants make up the
“F1” generation
Traits in pea plants that Mendel
studied
• Allele: two forms of one trait
(example #1 : seed color could be yellow or green
example #2: plants could be tall or short)
• Dominant traits- the trait that shows through in the
organism
• Recessive Trait- the trait that is “masked” (doesn’t
show)
Dominance
• Homozygous- an organism with two of the
same alleles for a particular trait
• Heterozygous- an organism with two different
alleles for a particular trait
*The outward appearance of an organism does
not always indicate which pair of alleles is
present
Genotype: the organism’s allele pairs
Phenotype: the observable characterisitics
(what the organism actually looks like)
Mendel’s Genetic Laws
1. Law of segregation: the 2 alleles for each trait
separate during meiosis
2. Law of Independent Assortment: a random
distribution of alleles occurs during gamete
formation.
Practice: Monohybrid Crosses
• Tongue rolling is a dominant trait. Suppose both parents
can roll their tongues and are heterozygous (Tt) for the
trait. What possible phenotypes and genotypes could
their children have?
Practice: Monohybrid Crosses
• A person with a widow's peak (Pp) is married to a
person with a straight hairline (pp), what percentage
of their children will have a straight hairline?
Practice: Monohybrid Crosses
Two people who are both heterozygous for the
widow's peak trait are married. What percentage
of their children will have a straight hairline?
Review: Monohybrid Crosses
• Gregor Mendel is out working in his pea
garden one day and decides to cross a plant
that is homozygous for round seeds (RR). He
crosses this plant with one that is
heterozygous for round seeds (Rr).
• Create a Punnett Square that shows the
possible genotypes that could be seen in the
F1 generation.
What if you wanted to look at TWO
traits at one time???
You do a dihybrid cross:
• Example: Mendel crossed two pea plants,
both were heterozygous for yellow color and
round seeds (YyRr) and wanted to see the
chances that the offspring would have green,
wrinkled seeds?
Complex Patterns of Inheritance
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Incomplete Dominance
Codominance
Mulitple Alleles
Epistasis
Sex Determination
Incomplete Dominance
• Heterozygous phenotypes is an intermediate
phenotype between two homozygous
phenotypes
• Example: A red-flowered plant (RR) is crossed
with a white-flowered plant (rr) produces pink
flowered plants that are heterozygous (Rr).
• How do you know for sure you’re seeing
Incomplete Dominance? Look for a “new color
phenotype” that’s in the middle of the parents.
Codominance
• Both alleles are expressed in the heterozygous
condition
• Example: A white cow mates with a red bull.
The offspring has a mixture of red and white
fur
• How do you know? Both alleles are expressed
Codomanice: Roan coloration
Multiple Alleles
• More than two alleles can influence the trait.
• Example: Human blood groups (three forms of
blood alleles: IA IB i). A, B, AB, or O
Sex Determination
• There are two types of sex chromosomes: X
and Y
• Individuals with two X chromosomes are
female
• Individuals with an X and a Y chromosome are
male
Karyotype: Chromosomes are
arranged by size and structure
• Pairs 1-22 are called autosomes
• The 23rd pair are called sex chromosomes: They
control what sex the organism will be
• What is the
sex of the
karyotype
on this slide?