# Chapter 11 Introduction to Genetics - PowerPoint by 5CKbcvya

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```									Introduction to
Genetics
Chapter 11
The Work of Gregor Mendel
A. Gregor Mendel’s peas
1. Genetics – study of heredity
2. Mendel studied pea plants
in the monastery gardens
3. Fertilization – male and
female reproductive cells join
Work of Mendel
4. True-breeding – produce
offspring identical to
themselves.
B. Genes and Dominance
1. Trait – specific characteristic,
such as seed color, or plant
height, that varies from one
individual to another.
Work of Mendel

2. Mendel crossed plants with
different traits
a. Example: yellow seed with
a green seed
3. Original pair of plants – P
generation
Work of Mendel

4. F1 – Offspring to the P
generation
5. Hybrids – cross between
parents with different traits
6. Genes – chemical factors
that determine traits.
Work of Mendel

7. Alleles – different forms of
a gene
a. Example: Gene is hair
color, the different alleles
are red, blond, brown,
black, etc.
Work of Mendel

8. Principle of dominance –
some alleles are dominant
and others are recessive
9. Dominant allele for a trait will
always show up.
Work of Mendel

10. Recessive allele will only
show up if the dominant is
not present.
C. Segregation
Work of Mendel

1. Mendel took 2 plants, each
with a different trait and
crossed them
a. Example: tall x short
2. F1 generation had all tall
plants
Work of Mendel

3. Allowed F1 to self-pollinate
4. F2 generation had ¾ tall
and ¼ short
5. Segregation – separation of
alleles
Work of Mendel

6. Gametes – sex cells
7. Capital letter represents a
dominant allele
8. Lower case letter represents
a recessive allele
Probability and Punnett Squares

A. Genetics and Probability
1. Probability – likelihood that
a certain event will occur
a. Example: chances of
flipping heads on a coin is
50%
Probability and Punnett Squares

b. Chance of tails three
times in a row?
½ x ½ x ½ = 1/8
2. Past outcomes do not
affect future ones.
Probability and Punnett Squares

B. Punnett Squares – diagram
that shows gene combinations
1. Types of gametes produced
by the parent are on the top
and left side.
2. Possible gene combinations
appear in the squares.
Probability and Punnett Squares

3. Punnett squares are used
to predict and compare the
genetic variations that will
result from a cross.
4. Homozygous – organism that
has 2 identical alleles for a
particular trait
Probability and Punnett Squares

a. Example: TT or tt
5. Heterozygous – organism
that has two different alleles
for the same trait
a. Example: Tt
Probability and Punnett Squares
6. Phenotype – Physical
characteristic
7. Genotype – genetic makeup
C. Probabilities predict averages
1. More likely to get the expected
ratio the more times the test is
done.
Mendelian Genetics

A. Independent Assortment
1. Two-Factor cross (F1)
a. Crossed true breeding
round yellow peas (RRYY)
with wrinkled green (rryy)
Mendelian Genetics

b. All offspring were round
and yellow (RrYy)
2. Two-Factor Cross (F2)
a. Mendel wanted to know
what these heterozygous
F1 plants would produce.
Mendelian Genetics

b. Crossed RrYy x RrYy
c. Independent assortment –
alleles for one trait are not
influenced by the other
alleles.
Mendelian Genetics

B. Summary of Mendel’s
Principles
1. The inheritance of
characteristics is determined
by genes. Genes are passed
from parent to offspring.
Mendelian Genetics
2. Some forms of the gene are
dominant and others recessive.
3. Organism has 2 copies of each
gene – one from each parent.
Genes are segregated during
gamete production.
Mendelian Genetics

4. Alleles for different genes
usually segregate
independently of one
another.
C. Beyond Dominant and
Recessive Alleles
Mendelian Genetics

1. Some alleles are neither
dominant or recessive.
Many traits are controlled by
multiple alleles or multiple
genes.
Mendelian Genetics
2. Incomplete Dominance – one
allele is not completely
dominant over another,
heterozygous shows a blending
a. Example: four o’clock flowers
b. RR (red) x rr (white)
Mendelian Genetics
3. Codominance – both alleles
contribute to the phenotype,
heterozygous shows both
phenotypes
a. Example: chicken feathers
b. BB (black feathers) x bb
(white feathers)
Mendelian Genetics
4. Multiple Alleles – more than 2
alleles exist to form several
different combinations of genes
a. Example: coat color in
rabbits, blood types
b. Each organism only has 2
alleles, but more than 2
alleles exist in a population.
Mendelian Genetics
c.   I       – Type A
AIA, IAi

IBIB, IBi – Type B
IAIB – Type AB
ii – Type O
d. Heterozygous type A x type
AB
Mendelian Genetics

5. Polygenic Traits – traits
controlled by 2 ore more
genes
a. Example: more than 4
different genes control
skin color
Mendelian Genetics

D. Genetics and The
Environment
1. Genes provide a plan, but
how it unfolds depends on the
environment.
Meiosis

A. Chromosome Number
1. Homologous – 2 sets of
chromosomes (one set from
a. Humans – 23 mom, 23 dad
Meiosis

2. Diploid – a cell that
contains both sets of
homologous chromosomes
a. Humans 2N = 46
Meiosis

3. Haploid – a cell that
contains only a single set of
chromosomes
a. Humans N = 23
b. Sperm and egg cells
Meiosis

B. Phases of Meiosis
1. Meiosis – process of
reduction division in which
the number of chromosomes
per cell is cut in half.
Meiosis

a. Has 2 divisions – Meiosis
I, Meiosis II
end each cell has N
Meiosis

2. Meiosis I
a. Chromosomes have been
doubled
b. Homologous chromosomes
pair up and form a tetrad
Meiosis

c. Crossing over – parts of
homologous
chromosomes are
exchanged
i. Crossing over increases
genetic variety
Meiosis

d. Homologous
chromosomes separate
and from two cells
e. Each cell only has half
the genetic information
Meiosis

3. Meiosis II
a. The chromosomes have
sister chromatids
b. The chromosomes line up
down the middle
c. Sister chromatids break
apart
Meiosis

d. Produces 4 cells with the
haploid number of
chromosomes
C. Gamete Formation
1. Male animals – produce
sperm cells
Meiosis

2. Plants – pollen contains
sperm cells
3. Female plant and animal –
egg cells
Meiosis

a. In female animals the cell
divisions are uneven in
Meiosis, producing one
egg and three polar
bodies (not used in
reproduction)
Meiosis

D. Comparing Mitosis and
Meiosis
1. Mitosis – 2 cells – identical
Meiosis – 4 cells – different
2. Mitosis – 2N (diploid)
Meiosis – N (haploid)
Meiosis

3. Mitosis – Cells used in
asexual reproduction
Meiosis – cells used in
sexual reproduction

1. In flies for example:
reddish-orange eyes and
miniature wings are almost
always found together.

2. Chromosome is a group of
3. Chromosomes are
associated independently,
not individual genes