Transcript Introduction to Genetics and Heredity

Introduction to Genetics and Heredity
Hypotheses about genes
 1800’s - scientist argued between two hypothesis regarding
genes and how they are passed on to offspring
Blended hypothesis - traits from 2 parents are mixed to
become a 3rd trait
Particulate hypothesis – traits from 2 parents are joined
but remain separate, and can be separated back to the
original forms
Which hypothesis seems more logical to you?
Who was Gregor Mendel?
-Austrian monk
-Did work with pea plants
-Know as the “Father of Genetics”
Genetics – the scientific study
of heredity
Mendel’s work
-Mendel
selectively bred
pea plants
What is Selective breeding?
 True-breeding – if
plants were allowed to selfbreed they would have
identical offspring
 Self-breeding – Sperm
and egg from the same
flower fertilize
 Selective breeding
 Cross-pollination
o Mendel took sperm
from one plant and
fertilized eggs from
other plants
What Mendel found…..
 Mendel and Pea Plants:
 Tall is dominant to short.
 Gene for tallness = “T”
 Gene for shortness = “t”.
Dominant Trait v. Recessive Trait
 Dominant Trait
 the observed trait that masks another trait
 written as an upper case letter (X)
 Recessive Trait
 trait that can be masked by a dominant trait
 written as a lower case letter (x)
Phenotype & Genotype
 Phenotype
 The way an organism looks and behaves
 Ex. Humans- Tall, yellow, blonde, blue eyes
 Ex. Pea- Smooth, Green,
 Genotype
 The gene combination an organism contains
 Ex. TT or Tt for tall
 Ex. tt for short
 Homozygous – 2 alleles are the same, TT
or tt
 Heterozygous – 2 alleles are different, Tt
Mendel’s Results and Punnett Squares
Punnett Square Practice!!
Remember from Meiosis
 All organisms pass on inherited information using haploid
gametes.
XX
XX XX XX XX
XX
XX XX X
XX
XX
X XX
XX
XX
XX
XX XX
XX
XX
XX
Human zygotes have 23 pairs of chromosomes
Some Words to Know!
 Fertilization – male and female
reproductive cells join
 Gamete – sex cells
 Male – pollen or sperm
 Female – eggs
 Zygote (Seed) – fertilized egg or new cell
Genes and Dominance
 Parental generation (P) – Original pair of plants
 Filial generation (F1) – offspring, progeny
 Traits – a specific characteristic (ex. Brown hair)
 Seed color
 Plant height

Remember from Meiosis
 Genes – chemical factors that determine traits
(Hair color)
 Alleles – different forms of traits
(Brown hair, blonde hair)
(Tall(T) or Short(t) pea plants)
Mendel's observations from these
experiments can be summarized in
two principles:
 The principle of segregation
 A parent passes on at random only one allele for
each trait to each offspring
 The two alleles for each trait separate during
meiosis.
 The principle of independent assortment
 A random distribution of alleles occurs during
gamete formation. Genes on separate
chromosomes sort independently during meiosis.
Diploid – A cell with two of
each kind of chromosome
(1 from each parent)
We say the cell is a diploid cell
or 2n
(This supports Mendel’s conclusion
that organisms have two factors –
alleles – for each trait)
Haploid – A cell with one of
each kind of chromosome
(gametes)
We say the cell is a haploid or n
(This supports Mendel’s conclusion
that parents give one allele for each
trait to their offspring)