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Chapter 10
Sexual Reproduction
and
Genetics
Sexual Reproduction and Genetics
Section 1:
Meiosis
Section 2:
Section 3:
Mendelian Genetics
Gene Linkage and Polyploidy
Section 10.1 Meiosis
1.
Objective: Understand meiosis is an early
step in sexual reproduction that produces
haploid gametes.
2.
Essential Question: At the end of meiosis
are there n or 2n number of
chromosomes?
(13 slides)
Karyotype Diagram
Human Karyotype- 23 pairs of chromosomes
(46 total)
What is meiosis?

Meiosis = a type of cell division that reduces
the number of chromosomes in half.

Meiosis produces four haploid daughter
cells that are not identical
Spermatogenesis = 1 sperm cell  4 sperm cells
Females: Oogenesis = 1 egg cell  1 egg cell & 3 polar
bodies (total 4)
Males:
Which cells go
. through meiosis?
What are gametes?
Only the gametes
undergo meiosis
Gametes are the sex
cells, which are the
egg (ovum) and
the sperm. [pollen
for plants]
Meiosis produces haploid cells.
What does that mean?
= (n) a cell that has half the
number of chromosomes as a diploid cell.
“half”
 Haploid

In humans the haploid # is 23
What is diploid?
= (2n) a cell that has 2 copies of
each chromosome “double”
 Diploid

In humans the diploid # is 46.
What are homologous chromosomes?
Homologous chromosomes —one of
two paired chromosomes, one
from each parent. They have:
 Same length
 Same centromere position
 control the same inherited
traits

Meiosis separates homologous
chromosomes
What are the steps of meiosis?
There are 2 divisions – Meiosis I and II. Each has the PMAT
steps.
.
What are the steps of Meiosis I?
Prophase I - Homologous chromosomes pair.
Synapse & crossing over occurs
Metaphase I - Homologous chromosomes
(pairs) line up at the equator randomly. This
increases genetic variation, too.
Anaphase I - homologous chromosomes
separate and move to opposite poles
Telophase I Chromosomes uncoil and form
two nuclei
Meiosis II – DNA is NOT duplicated again!
Prophase II –second phase begins,
chromosomes condense again
Metaphase II- chromosomes line up
individually at the equator.
Anaphase II- The sister chromatids separate
bringing the cells to a haploid number.
Telophase II- four nuclei have formed.
Cytokinesis -four haploid cells (gametes –egg
or sperm-) have formed. (n number of
chromosomes)
Why is meiosis important?

The gametes need
to reduce their
chromosome
number in half so
that when there is
fertilization the
diploid number
(2n) is restored.
For humans:
23 + 23 = 46
.
How Does Meiosis Provide Genetic Variation?
1.
Random assortment
when chromosomes
line up at the
equator
2.
Crossing over
3.
Random combination
of gametes during
fertilization.
What is synapsis?

Synapsis = a process that binds together a pair of
homologous chromosomes
What is crossing over?
Crossing over = homologous chromosomes
exchange segments.
 This increases genetic variation.
What about asexual reproduction?
 The offspring receive ALL
the genes from one parent.
This is why the offspring
look EXACTLY alike.
Example: bacteria
10.2 Mendelian Genetics
1.
Objective:
•
2.
Predict combinations of alleles (genotype and
phenotype) from the genetic makeup of the
parents.
Essential Question:
•
What are the rules for the inheritance of traits
with Mendelian genetics?
•
(10 slides)
Who was Gregor Mendel?
(1822-1884)
The “father” of genetics
 Austrian Monk
 Experimented with pea
plants
 Compared 7 contrasting
traits.


(Ex:height = tall and short)
Mendel studied seven different traits
 Seed or pea color
 Flower color
 Seed pod color
 Seed shape or texture
 Seed pod shape
 Stem length
 Flower position
What is heredity?
Heredity = passing of traits to the next generation.
How do we name generations?

The parent generation is
also known as the P
generation.

The offspring of this P
cross are called the first
filial (F1) generation.

The second filial (F2)
generation is the offspring
from the F1 cross.
What did Mendel conclude?

Allele = An alternative
form of a single gene
passed from generation to
generation



example: alleles for pea
color are yellow & green
Dominant factor –
dominates or masks all
other factors
Recessive factor – does
not show if a dominant
factor is present
What are Mendel’s Laws?
Law of Segregation –a
pair of alleles is
separated during the
formation of gametes
(meiosis)
Law of independent
assortment – alleles
are distributed to
gametes
independently or
randomly
What are Genotype and Phenotype?
We use Mendel’s discoveries to predict
genotype and phenotype probabilities.
 Genotype – the allele pairs (genetic
makeup) of an organism


Phenotype – the observable physical
characteristics (appearance) of an allele
pair.


Ex: PP or Pp
Ex: Purple flowers
Phenotype depends on Genotype
What are homozygous & heterozygous?

Homozygous – both alleles are the same
for a trait (AKA purebred)


Ex: (homozygous dominant- PP) or
(homozygous recessive -pp )
Heterozygous (AKA hybrid)– allele are
different for a trait

Ex: Pp (heterozygous)
Which pair of alleles is heterozygous?
A. RR
B. Rr
C. rr
D. yR
Describe:

Phenotype =


Genotype =


Purple flower
PP or Pp (if purple
is dominant)
What is the
genotype if it is a
recessive trait?
How do we predict genotype and phenotype?

Punnett Squares
 Monohybrid Cross (1
trait)

Be able to identify both
the phenotype and
genotype ratios
Sample Problem

A.
B.
C.
D.
In rabbits, gray fur (G) is dominant to
black fur (g). If a heterozygous male is
crossed with a heterozygous female,
what is the phenotypic ratio of the
possible offspring?
1:1
1:2:1
2:1
3:1
Monohybrid Cross (1 trait)
How do we predict genotype &
phenotype for two traits?
Use FOIL from math
to set up gametes!

Dihybrid cross (2
traits)
Example: YyRr x YyRr
produces the phenotypic
ratio of 9:3:3:1.

10.3

Gene Linkage and Polyploidy

(5 slides)
What is Genetic Recombination?

Genetic recombination = the new
combination of genes produced by
crossing over and independent assortment
 Combinations of genes in a gamete due to
independent assortment can be calculated
using the formula 2n where n is the
number of chromosome pairs.
 Pea Plants 27 = 128 combinations
Examples of Possible Combinations

For pea plants there are 7 pairs of
chromosomes

The possible combinations for each off-spring
are 27 (x) 27 = 16,384 possible combinations
For humans there are 23 pairs of chromosomes
 Since any possible male gamete can fertilize any possible
female gamete, then the possible combinations are
(x) X
= more than 70 trillion
(without considering the effects of crossing over)

What is Gene Linkage?
 The linkage of genes on a chromosome results
in an exception to Mendel’s law of independent
assortment because linked genes usually do not
segregate independently.
What is polyploidy?

Polyploidy is the
occurrence of one
or more extra
sets of all
chromosomes in
an organism
Polyploidy **
Occurs in
plants—rarely
animals**

A triploid organism, for
instance, would be
designated 3n, which
means that it has three
complete sets of
chromosomes.