Mrs. Ruhlig's Biology B PowerPoint Chapter 6 &7

1. BIOLOGY CHAPTER 6 &
7
Meiosis and Mendelian Genetics

2. 6.1 & 6.2 CHROMOSOMES AND
MEIOSIS
6.6 MEIOSIS AND GENETIC VARIATION
Mitosis
Somatic cells undergo mitosis
One diploid cell produces 2 genetically
identical, diploid cells
There are 4 stages (prophase, metaphase,
anaphase, telophase)
DNA is copied once and divided once
Mitosis is used for development, growth, and
repair

3. Meiosis
Germ cells produce gametes (sex cells) during
meiosis
One diploid cell produces 4 genetically
different haploid cells
There are 8 stages (prophase I, metaphase I,
anaphase I, telophase I, prophase II,
metaphase II, anaphase II, telophase II)
DNA is copied once and divided twice

4. Homologous Chromosomes
Half of an organism’s chromosomes come from the
mother, and half from the father. The chromosomes
pair up to form homologous chromosomes
Homologous chromosomes are two chromosomes
with the same length, general appearance, and the
same type of genes
The pairing of the genes on the homologous
chromosomes are what code for all of an organism’s
traits (see examples in section 6.4)

5. All humans have 23 total pairs of
chromosomes, for a total of 46 chromosomes.
22 of the pairs are autosomes (body
chromosomes)
1 pair is the sex chromosomes (XX= female,
XY=male)

6. Meiosis I
Same steps as mitosis, except during
Prophase I crossing over can occur(see
below),
during Metaphase I homologous chromosomes
pair up in the middle and
during Anaphase I, the sister chromatids DO
NOT separate
By the end of Meiosis I, there are 2 haploid
cells

7. Crossing Over
Homologous chromosomes exchange genes
This results in a new combination of genes
(called recombination)
Genes that are located near each other on a
chromosome are more likely to be moved (or
crossed over) together. This is called genetic
linkage (refer to page 191)
Meiosis II
This is exactly the same as mitosis

8. 6.3 MENDEL AND HEREDITY
Gregor Mendel
An Austrian monk who is known as the “father
of genetics”
He discovered that traits (genes) are inherited
from parents by working with pea plants
He made both purebred plants and crossed
plants to see what the results would be.

9. WHY PEA PLANTS?
They reproduce quickly
They can both self-pollinate(creating
purebreds) and cross-pollinate(creating a mix
of traits)
They have “either-or” traits (the traits do not
mix to make a 3rd trait, ex. The purple flowers
and white flowers don’t mix to make a pink
flower)
(refer to page 179 to see the traits and results
of Mendel’s experiment)

10. MENDEL’S CONCLUSIONS
Mendel’s Law of Segregation:
 Organisms inherit two copies of each gene,
one from each parent
Organisms donate only one copy of each gene
in their gametes. Thus, the two copies of each
gene segregate, or separate, during gamete
formation (Law of Independent Assortment)
In other words, the Law of Ind. Assortment is
saying that traits are inherited separately.

11. 6.4 TRAITS, GENES, AND ALLELES
6.5 TRAITS AND PROBABILITIES
Genes
Each gene has a specific locus, or place on
the chromosome
A gene is a piece of DNA that provides a set of
instructions to make a certain protein. The
proteins then code for traits.
Each trait is represented by alleles.

12. Letters are used to represent different alleles.
There are two alleles per trait (one from
mother, one from father)
Dominant alleles are represented by capital
letters and Recessive alleles are represented
by lowercase letters
Dominant alleles will always overpower the
recessive alleles.

13. EXAMPLE: P= purple flowers
p= white flowers
PP=purple flowers (homozygous)
pp= white flowers (homozygous)
Pp= purple flowers (heterozygous)
Genotype-the alleles/genetic code (PP or Pp)
Phenotype-the physical trait (purple or white)

14. PUNNET SQUARES
Punnet squares are used to predict the outcome of
genotypes when crossing two organisms
Monohybrid cross- crosses one trait (always yields a
3:1 phenotypic ratio)
Dihybrid cross- crosses two traits (always yield
9:3:3:1 phenotypic ratio)

15. CHAPTER 7
EXTENDING MENDELIAN GENETICS
Complex Patterns of Inheritance
Incomplete Dominance—the trait is in between
the dominant and recessive
Ex. RR=red rr=white Rr=pink
Codominance—both traits are expressed at the
same time
Ex. RR=red rr=white Rr= both red and white

16. Polygenic Traits—when two or more
genes influence a trait
Ex. Human eye color(at least 3 different
genes), human skin color (4 different genes)
Environmental factors—when the
environment plays a role in gene
expression
Ex. Sea turtle eggs become female in warmer
temps and male in colder temps

17. SEX-LINKED TRAITS—TRAITS CAUSED
BY GENES LOCATED ON THE SEX
CHROMOSOMES
The X contains many genes
The Y only determines sex (male)
A male is XY, so all of the alleles on the X are
expressed in a male, even the recessive ones
A female is XX, so dominant alleles can mask
the recessive ones
Carriers—those who carry a recessive genetic
disorder, but do not express the phenotype. They
can pass on the disorder to their offspring