Download Ch. 10: Mendel and Meiosis

Ch. 10:
Mendel and Meiosis
What you’ll learn:
-You will identify the basic concepts
of genetics
-You will examine the process of
meiosis.
10.1 Mendel’s Laws of Heredity
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Objectives
Relate Mendel’s two laws to the results
he obtained in his experiments with pea
plants.
Predict the possible offspring of a
genetic cross by using a Punnett
square.
Gregor Mendel

Australian monk that carried on important
studies of heredity
 Heredity-
the passing on of characteristics
from parents to offspring

Characteristics that are inherited = Traits
Why pea plants?

Pea plants reproduce sexually
 Male
and female sex cells = gametes
 Fertilization is the process where the male
gamete unites with the female gamete
 Resulting fertilized cell = zygote
Why pea plants? (Cont.)
Pollination – the transfer of pollen grains
from a male reproductive organ to a
female reproductive organ
 Mendel could cross-pollinate his plants.
He could choose the parents.

Mendel was a careful researcher
Controlled his experiments
 Studied one trait at a time to control
variables.

Mendel’s Monohybrid Crosses

Hybrid – the offspring of parents that have
different forms of a trait
 Ex:
tall and short height
Mono = one
 Monohybrid crosses means the parent
plants differ from each other by a single
trait.

The First and Second Generation
The Rule of Unit Factors
Each organism has 2 factors that control
each of its traits called genes.
 Genes exist in alternative forms called
alleles.

 Ex:
Mendel’s pea plants had two alleles of
the gene that determined height

One allele from the female parent, one
from male parent
The Rule of Dominance
Dominant – the observed trait in an
organism
 Recessive – the trait that disappears, or is
masked by the dominant trait

Dominant vs. Recessive
http://image.tutorvista.com/content/heredity-and-variation/monohybrid-traits-of-mendel.jpeg
The Law of Segregation
States that every individual has two alleles
of each gene and when gametes are
produced, each gamete receives one of
these alleles.
 During fertilization, gametes randomly pair
to produce four combinations of alleles

Phenotype vs. Genotype

Phenotype – the way an organism looks
and behaves
 Ex:

Tall plant
Genotype – the allele combination an
organism contains
 Ex:
TT or Tt
Homozygous vs. Heterozygous

Homozygous – when there are two
identical alleles for a trait
 Ex:

TT or tt
Heterozygous – when there are two
different alleles for a trait
 Ex:
Tt
Mendel’s Dihybrid Crosses
Mendel preformed another set of crosses
in which he used peas that differed from
each other in two traits rather than only
one.
 Di - two

Dihybrid Crosses
The Law of Independent
Assortment

Mendel’s second law states that genes for
different traits (for example, seed shape
and see color) are inherited independently
of each other.
Punnett Squares

Reginald Punnett
 English
biologist
 Devised a way of finding the expected
proportions of possible genotypes in the
offspring
Monohybrid Crosses
Probability
The chance an event will occur
 Punnet squares show all the possible
combinations of gametes and the ratio, or
the probability it will occur

10.2 Meiosis

Objectives
 Analyze
how meiosis maintains a constant
number of chromosomes.
 Infer how meiosis leads to variation in a
species.
 Relate Mendel’s laws of heredity to the events
of meiosis.
Diploid and Haploid Cells
Diploid – a cell with two of each kind of
chromosome, or 2n
 Haploid – a cell with one of each kind of
chromosome, or n

Homologous Chromosomes

Homologous Chromosomes – paired
chromosomes with genes for the same
traits arranged in the same order
Meiosis
Meiosis – type of cell division where one
body cell produces four gametes, each
containing half the number of
chromosomes as a parent’s body cell
 Male gametes = sperm
 Female gametes = eggs
 Sperm + egg = zygote

Phases of Meiosis

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Interphase
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Phases of Meiosis

Think…
 Interphase,
PMAT I, PMAT II
Crossing Over
Occurs during Prophase I
 Non-sister chromosomes can actually
break and exchange genetic material
