Download Genetics and Inheritance

04/17/2017
Bill Nye Genes video
– Complete the handout as the video plays.
What are traits?
– A trait is a characteristic that an
organism exhibits, such as the shape
of your ears or the color of your eyes.
– The traits we exhibit are determined
by our DNA (an organism’s genetic
material)
Genetics and
Inheritance
How does DNA determine
what we look like?
– All of the DNA in your
cells exists as
chromosomes.
– Chromosomes are tightly
coiled strands of DNA
that carry genetic
information.
Ch 12 Genetics Goals
– SC.7.L.16.1: Understand and explain that every organism requires a set of
instructions that specifies its traits, that this hereditary information (DNA)
contains genes located in the chromosomes of each cell, and that heredity is
the passage of these instructions from one generation to another.
– SC.7.L.16.2: Determine the probabilities for genotype and phenotype
combinations using Punnett Squares and pedigrees.
– SC.7.L.16.4: Recognize and explore the impact of biotechnology (cloning,
genetic engineering, artificial selection) on the individual, society and the
environment..
– Every human has 46
individual chromosomes,
23 pairs.
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Asexual Reproduction
– Each chromosome is
made of multiple genes.
- In asexual reproduction, one organism makes a
copy of itself.
- The “daughters” are exact copies of the “parent”.
– A gene is a section on a
chromosome that has
genetic information for
one trait.
Where do Genes Come
From?
– All living organisms inherit their genes
from their parents through
reproduction.
Reproduction
- There are two ways that organisms can reproduce:
- Sexually, with two parents or
- Asexually, with one parent
- In both forms of reproduction, the parent’s genes are
passed from parent(s) to child.
Asexual Reproduction
- Both multicellular organisms like us, and
unicellular organisms like bacteria use mitosis to
make new cells.
- Mitosis is the process by which one cell divides to
make two identical cells.
Mitosis:
- During mitosis, one cell makes a copy of each
chromosome (its DNA ), then it split into two cells.
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Mitosis:
- Mitosis produces genetic copies of the parent cells.
- The “daughter cells” have the same DNA as the
“parent cells”.
Mitosis:
- Unicellular organisms use mitosis to reproduce
asexually.
- Multicellular organisms use mitosis to grow (by
making more cells) and replace old or damaged
cells.
Mitosis:
- Because all new cells are copies of old cells,
mitosis DOES NOT increase genetic diversity in a
species that uses it to reproduce.
Sexual Reproduction
- In sexual reproduction, two
parents donate half of their
DNA to make offspring that
are different than themselves.
- Child receives ½ of their
chromosomes from each
parent.
- Chromosomes are passed on
through sex cells
– eggs and sperm
known as gametes.
How are sex cells (eggs
and sperm) made?
- Gametes (sex cells) for sexual reproduction are made
through a process called meiosis.
- Meiosis is the process by which one cell divides to
create 4 cells, each with half of the DNA of the
original parent.
How are sex cells (eggs
and sperm) made?
- During meiosis, one sex cell doubles its number of
chromosomes (DNA) and divides twice so it only has
half of the DNA of the original cell.
- This makes 4 gametes (eggs or sperm)
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Fertilization
Inheritance
- In order for offspring to form, the gametes of male
and female must join and combine their DNA. This
process is called fertilization.
1. Traits are passed on from parent to child.
2. Cell nucleus controls inheritance.
3. Genes for traits are on chromosomes and are
located inside the nucleus
How it Works
- The offspring then has a full compliment of DNA
and can grow.
- Sexual reproduction in this manner is only used by
multicellular organisms, like humans.
-
-
- Because the parents donate a mix of their DNA,
sexual reproductions increases genetic diversity in a
species.
Recall that each human has 46
chromosomes.
Each chromosome has one other
chromosome that carries the same
genes as it does.
These are homologous
chromosomes: pairs of
chromosomes (one inherited from
each parent) that have genes for
the same traits arranged in the
same order
Humans have 23 pairs of
homologous chromosomes.
- Homologous
chromosomes carry
the same genes, but
may have different
alleles.
- An allele is a different
form of a gene.
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Example:
- Chromosome 1 came from
the father.
- Chromosome 2 came from
the mother.
- Each chromosome carries
the gene for ear shape.
- Chromosome 1 has the
allele for attached ear lobes.
- Chromosome 2 has the
allele for free-hanging ear
lobes.
Gregor Mendel
•Austrian Monk that lives in the1800s
•He is known as the Father of Modern Genetics
•Observed inherited traits.
•He asked: Why did some traits found in the parent
plants show up in offspring while others did not?
•experimented with pea plants
ie. Height, color, covering type
•Experiments lead to development of the
Principals of Genetics WHICH STILL
HOLDS TRUE
Mendel’s Work
- When this child is
grown and is ready to
pass on their genetic
traits, they will pass
on either chromosome
1 OR chromosome 2.
• In his experiments, Mendel
took pollen from the flowers
of purebred pea plants to
pollinate the flowers of other
purebred pea plants by using
a paint brush to transfer the
pollen.
• This process is called crosspollination.
How did we discover genes
and how they are passed on?
https://www.youtube.com/watch?v=Mehz7tCxjSE
Why Peas?
Mendel’s Work
Pea flowers are constructed in such a
way that they typically self fertilize.
Because of this, it is relatively easy to
control crosses in peas.
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Crossing Pea Plants
Mendel’s Work
Gregor Mendel crossed pea plants that had different traits.
Crossing Pea Plants
Mendel’s Work
Mendel’s Work
In all of Mendel’s crosses, only one form of the trait appeared
in the F1 generation. However, in the F2 generation, the “lost”
form of the trait always reappeared in about one fourth of the
plants.
Mendel’s Experiments
Mendel’s Work
• F1 generation was a
cross between a pea
plant with purple
flowers and a pea
plant with white
flowers.
• All plants of the F2
generation had purple
flowers.
• He bred the F2
generation plants
together and found
that ¼ of the plants
had white flowers.
The illustrations show how he did this.
Mendel’s Experiments
Mendel’s Experiments
Mendel’s Work
- Mendel called the original purebred parent plants the P1
generation.
- The offspring were called the F1 generation.
- He then crossed (bred) the F1 generation together. This
produced the F2 generation.
Dominant and Recessive Factors
• Mendel called the purple flower form the
dominant (DAH muh nunt) factor because it
dominated, or covered up, the white flower
form.
• He called the
form that seemed
to disappear the
recessive (rih SE
sihv) factor.
Click image to view movie.
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Dominant and Recessive Alleles
- Mendel’s Work
Mendel studied several traits in pea plants.
Mendel's observations from these experiments can
be summarized in two principles:
1. the principle of segregation - for any particular trait,
the pair of alleles of each parent separate and only one allele
passes from each parent on to an offspring.
Which allele in a parent's pair of alleles is inherited is a matter
of chance.
2. the principle of independent assortment - different
pairs of alleles are passed to offspring independently of each
other. The result is that new combinations of genes present
in neither parent are possible.
Law of Independent Assortment
• When Mendel crossed peas and looked at two different
traits, he discovered that the traits assorted
independently
• In other words, if he was looking at the height of the
plants and the color of the flowers, all four possible
combinations of height and flower color were produced:
• Tall Purple
• Tall white
• dwarf Purple
• dwarf white
Other things
•Pure trait – inherits 2 of same gene = homozygous
•Hybrid – inherits 1 dominant and one recessive = heterozygous
•No organism is pure in every trait.
An individual is a mix of pure and hybrid.
Genotype - what the 2 alleles are
Phenotype – what the organism looks like
Menedel’s Law of Dominance:
1. An organism receives 2 genes for each trait.
One from each parent.
2. One of the genes may be stronger than the other.
The trait of the stronger is expressed.
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