Transcript Chapter 12 PowerPoint

Mendel and Heredity
Standard 3
 Students know and understand the characteristics and
structure of living things, the processes of life, and
how living things interact with each other and their
environment.
 Benchmark 3.13: some traits can be inherited while
others are due to the interaction of genes and the
environment.
 Assessment objective 3.13a: Classify well-known
conditions as being purely genetic or the result of the
interaction of genes and the environment.
Vocabulary
 Character
 Trait
 Hybrid
 Generation
 Allele
 Dominant
 Recessive
 Genotype
 Phenotype
Homozygous
Heterozygous
Punnett square
Probability
Pedigree
Genetic disorder
Polygenic character
Codominance
Linked
Origins of Hereditary Science
 Modern genetics is based on
Mendel’s explanations for the
patterns of heredity in garden
pea plants.
 Seven characters Mendel
studied in his plants
included:
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Flower color
Seed color
Seed shape
Pod color
Pod shape
Flower position
Plant height
Gregor Mendel Introduction (1:30)
Contrasting Traits
 In the study of heredity,
physical features that are
inherited are called characters.
 A trait is one of several
possible forms of a character.
 For example, the color of a
flower is inherited and
therefore a character.
 A variation of the color is a
possible form of a character
and therefore a trait.
 In garden pea plants there
are both male and female
reproductive parts.
 A plant can self-pollinate
(fertilize itself) or crosspollinate with other pea
plants.
 Plants with different traits
that cross-pollinate
produce offspring called
hybrids.
Gregor Mendel Research and Principles (4:30)
A generation is a group of offspring from a
given group of parents.
 Mendel first ensured
that his plants were truebreeding for a certain
trait by letting the plants
self-pollinate for several
generations.
 The first group of
parents that are crossed
are called the parental
generation or P
generation.
 Mendel then crossed two
P generation plants that
had contrasting traits
like white and purple
flowers.
 He called the offspring of
the P generation the first
filial generation or F1
generation.
 Mendel then let the F1
generation plants selfpollinate and produce
new plants. He called
this new generation of
offspring the second
filial generation or F2
generation.
 Notice how many of each
trait was produced—
what’s the deal?
Dominant and Recessive Traits
Punnett Squares Explained (5:00)
Quicklabs
 Go to page 270 and complete table for the QuickLab.
(10 minutes)
 Quicklab pg. 273 add to table: dark vs. light hair and
attached/unattached earlobe. (15 minutes)
Mendel’s Theories
(2:51)
 Mendelian theory explains
 Traits can come from
simple patterns of
inheritance. In these
patterns, two of several
versions of a gene combine
and result in one of several
possible traits.
 An organism’s traits come
from different versions of
genes. Each version is
called an allele.
either parent—because of
meiosis.
 For every pair of traits, only
one expresses itself.
 The allele that expresses
itself is said to be
dominant.
 The other allele is a
recessive allele and its trait
is not expressed.
Dominant Traits
Recessive Traits
Eye coloring
Brown
grey, green, hazel, blue
Vision
Normal vision
Nearsightedness, night blindness, color
blindness *
Hair
Dark hair
Blonde, light, red hair
Non-red
Red hair
Curly hair
Straight hair
Full head of hair
Baldness *
Widow’s peak
Normal hairline
Dimples
No dimples
Unattached earlobes
Attached earlobes
Freckles
No freckles
Broad lips
Thin lips
Immunity to poison ivy
Susceptibility to poison ivy
Normal pigmented skin
albinism
Normal hearing
Congenital deafness
Normal blood clotting
Hemophilia *
Normal hearing and
speaking
Congenital mutism
Facial features
Other
Random Segregation of Alleles
 Even though a gamete
receives an allele from each
parent, only chance (or
fate) determines which one
it will receive.
 The law of segregation
holds that when an
organism produces
gametes, each pair of
alleles is separated and
each gamete has an equal
chance of receiving either
one of the alleles.
 Dominant alleles are
(4:41)
indicated with a capital
letter and recessive alleles
have a lower case letter.
 Given “a” and “A”, which is
dominant and which is
recessive?
Mendel’s Findings in Modern Terms
 The set of alleles that an
individual has for a
character is called the
genotype.
 The trait that results
from a set of alleles is the
phenotype.
 Genotype determines
phenotype.
Homozygous & Heterozygous
 If an individual has two of
the same alleles of a certain
gene, the individual is
homozygous for the related
character.
 If an individual has two
different alleles of a certain
gene, then it is
heterozygous.
 Between pp and Pp, which
is homozygous and which
is heterozygous?
Significance of test cross as genetic tool (1:30)
Mendel’s Second Experiment
 Mendel used dihybrid
crosses which involved two
characters like color and
shape to further test how
patterns appear.
 The Law of Independent
Assortment holds that
during gamete formations,
the alleles of each gene
segregate independently.
 Alleles can mix and match.
Introduction dihybrid crosses (3:15)
Mendel’s Second Law
 Genes are linked to each
other as parts of
chromosomes.
 Genes that are located
close together on the same
chromosome will rarely
separate independently,
thus they are said to be
linked because they’re so
close together.
 QUIZ # 2
Simulating a dihybrid cross (2:57)
Punnett Squares
 Punnett squares show all
the genotypes that could
result from a given cross.
 As shown, the simplest
box is 4 squares with the
parent’s traits on the top
and side of the square.
 Watch the video
 Do the Test Cross
QuickLab on page 277
(10 minutes).
Punnet Square (4:49)
Using Probability
(7:04)
 Probability is the likelihood that a specific event could
occur.
 Punnett squares predict probability
 Probability can be calculated using the formula:
Number of one kind of possible outcome
 Probability = Total number of all possible outcomes
 Probability formulas can be used to predict the
probabilities that specific alleles will be passed on to
offspring.
Using a Pedigree
 A pedigree is a family
history that shows how a
trait is inherited over many
generations.
 Genetic disorders or
diseases can be inherited.
 Pedigrees can answer
questions associated with
sex linkage, dominance,
and heterozygosity.
Sex linked inheritance (29:06)
Sex-Linked Genes
 The Y and X chromosomes carry more genes than just
gender.
 Because the Y chromosome is shorter than the X
chromosome, it holds fewer genes.
 A recessive allele on a female’s X chromosomes will often
have a corresponding dominant allele on the other X
chromosome, thus the trait is not expressed on the female
but can be passed on to a male offspring because their Y
chromosome may lack a corresponding allele for the
recessive gene.
 These are sex-linked traits which are commonly seen more
in males than females such as colorblindness.
Dominant/Recessive
Heterozygous/Homozygous
 If a person has a trait that is
autosomal and dominant and
has even one dominant allele,
he/she will show the trait.
 If a person has a recessive trait
and only one recessive allele,
he/she will not show the trait
but could pass it on.
 Quiz # 3
 If a person is either
heterozygous or
homozygous dominant for
an autosomal gene, their
phentoype will show the
dominant trait.
 Homozygous recessive
shows the recessive trait.
 If a child shows the
recessive trait, that means
that both parents are
heterozygous carriers of
the recessive allele.
 When several genes affect a
character, it is called a polygenic
character.
 Examples are eye color, skin color
and height.
 Most characters are polygenic.
 Human eye color is more complex
than two genes. It is known that
three genes are involved in eye color
that explain inheritance of brown,
green and blue, but it does not
explain grey, hazel, or multiple
shades of blue, brown, green and
grey. The molecular basis of these
genes is not known.
 Incomplete dominance occurs when
an offspring has a phenotype that is
in-between the traits of its two
parents.
 An example is when a red and white
snapdragon flower is crossed and a
pink offspring results. It shows that
neither the red or the white is
completely dominant.
 Incomplete dominance in
snapdragons (2:07)
 Incomplete dominance in humans
and plants (2:01)
Blood types and Rh factor
 In humans, blood types are determined by 3 alleles: IA, IB, and i.
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These can produce blood types of A, B, AB and O
The Rh agglutinogen (Rh antigen) was discovered and named for
rhesus monkeys.
A person whose RBCs carry the Rh agglutinogen is Rh positive,
while a person lacking it is Rh negative.
Most people are Rh positive.
If an Rh negative mother has an Rh positive baby, the mother
recognizes the Rh agglutinins and produces anti-Rh agglutinins
to fight them. This usually doesn’t affect the first child, but
subsequent children that are Rh positive can be subject to the
anti-Rh agglutinins from mom attacking the fetus’s red blood
cells causing anemia and possible death.
Multiple alleles, Codominance and
Incomplete Dominance
(3:27 Khan Academy)
 Multiple alleles are genes
that have three or more
possible alleles.
 Codominance is a
condition in which both
alleles for the same gene
are fully expressed.
 Human blood groups are
examples of codominance.
 Incomplete dominance is
when an individual
displays a trait that is
intermediate between the
two parents. Skin color.
Multiple Alleles and
Codominance in Blood (11:09)
Genes affected by environment
and genes linked within chromosomes
 Phenotype can be affected by
conditions in the
environment such as
nutrients and temperature.
 Many arctic animals have
genes that cause their fur to
be dark in the summer and
light in the winter in order to
increase chances of survival
through camouflage.
 Environmental Factors
Which Influence the
Expression of Traits (02:02)
 During meiosis, genes that
are close together on the
same chromosome are less
likely to be separated than
genes that are far apart.
 Genes that are close together
as well as the traits they
determine are said to be
linked.
Dihybrid Punnett Square
 Make a dihybrid punnett
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square for the possible
genotypic possibilites:
F free earlobes
f attached earlobes
B brown eyes
b blue eyes
Write down the ratios for:
Free earlobe, brown eyes
Free earlobe, blue eyes
Attached earlobe, brown eyes
Attached earlobe, blue eyes
Quiz # 4
FB
FB
Fb
fB
fb
Fb
fB
fb
Review
 Page 287 Review: numbers 3-18, 23,24
 Page 289 Test Prep pretest, 1-11 (including essay)
 For the multiple choice, write out the question as well
as the letter and answer for the correct answer to each
question.