Download DNA RNA Protein Trait

Heredity
Patterns of Inheritance
Traits and Genes
• Genes are locations on chromosomes that
control the expression of traits in living
things.
• Remember that DNA makes RNA and RNA
makes Protein.
DNA
RNA
Protein Trait
•Protein is what we are.
•Traits are the physical expression of
protein in living things
Gene Loci
• Heredity is the study of the transmission
of traits from parent to offspring.
• Heredity studies traits that can be
observed at the organism level.
• Traits include things like include facial
features that cause generations to
resemble each other.
Traits and Genes
• All organisms have 2 versions of a trait.
– They get one of each version from each parent (one
from mom and one from dad)
• Alternative forms of a traits are controlled by
genes that have the same position on a pair of
chromosomes and affect the same trait
– Two things to remember here (1. You get one
chromosome from each parent AND each version of
gene on these homologous chromosomes are called
alleles.
• Alleles occur at the same loci (position) on
homologous chromosomes.
Gametes Formation I
• When organisms reproduce to make an
offspring (a baby) they must first reduce their
chromosome numbers in half to form gametes
– A gamete is a sperm or egg
– During gamete formation alleles segregate each
gamete has only one factor from each pair.
– Gametes are also called sex cells.
• Fertilization gives each new individual two
factors again.
– Fertilization is the fusion of sperm and egg to form a
diploid zygote (zygote = offspring).
– The process of gamete formation and fertilization is
called sexual reproduction.
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Gamete Formation II - Meiosis
• The ploidy
number refers to
the number of
chromosomes
found in each
parent somatic
cell.
• Because homologous pairs separate
during meiosis, a gamete has only one
allele from each pair of alleles.
• If the allelic pair is Ww, a gamete would
contain either a W or a w, but not both.
• Ww represents the genotype of an
individual.
• Gametes are represented by W or w.
• A somatic cell
has a diploid
number of
chromosomes
present
• Sex cells have a
haploid #
Expression of Dominance
• Traits can be expressed as completely
dominant, incompletely dominant or even
codominant.
– Complete dominance is when the dominant allele is
expressed over the recessive allele (if it is present in
the genotype of the parent.
– Codominance is when both alleles are equally
expressed in a heterozygote.
– Incomplete dominance is when a heterozygote does
not express the dominant or recessive allele, but
instead shows an intermediate phenotype, or a
blending of the traits
Phenotype and Genotype II
•A capital letter
indicates a
dominant allele.
–An example is W
for a widow’s peak.
•A lowercase letter indicates
a recessive allele.
– Expressed in the absence of
a dominant allele.
–An example is w for
continuous hairline.
Gamete Formation III - Meiosis
Phenotype and Genotype I
• When we track traits, we can predict the
potential of an offspring and what they
will look like.
– A phenotype is the physical trait of the
individual.
– A genotype is the genetic composition of an
individual which can be represented by
letters and short descriptive phrases.
Genotype and Phenotype III
• Homozygous individuals are organisms that
have two alleles that are the same.
– Example, WW stands for homozygous dominant
and ww stands for homozygous recessive.
• Heterozygous individuals are organisms that
have two alleles that are different.
– Example, Ww.
• Both WW and Ww result in widow’s peak,
two genotypes with the same phenotype.
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One-Trait Crosses
One-Trait Crosses
• One-trait crosses are when one trait such as type
of hairline is being considered.
• When performing crosses, the original parents are
called the parental generation
– or P generation
• All of the P1 children are the filial generation
– or F generation (F1, F2, etc).
• If you know the genotype of the parents, it is
possible to determine the gametes and use a
Punnett square to determine the phenotypic ratio
among the offspring
– A punnett square is a prediction of potential offspring and
their statistical ratio of possible occurance
One-Trait Crosses
• Notice the results
are a 3:1 ratio
• The ratio is used to
state the chance of a
particular phenotype
• A 3:1 ratio means
that there is a 75%
chance of the
dominant phenotype
and a 25% chance of
the recessive
phenotype
Pedigrees - Tracking Family Traits
• A pedigree chart shows the pattern of
inheritance of a characteristic within a
family.
• The particular pattern indicates the
manner in which a characteristic is
inherited.
One-Trait Crosses
• In the cross given
here, notice that one
parent is
homozygous
recessive.
• An individual that
is homozygous
(dominant or
recessive) is
considered a
purebred
Pedigrees
• Pedigree charts represent males with
squares and females with circles.
• Recessive and dominant alleles have
different patterns of inheritance.
• Genetic counselors construct pedigrees
to determine the mode of inheritance of a
condition.
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An Example Pedigree
Polygenic Inheritance
• Polygenic traits are governed by more
than one gene pair.
• Several pairs of genes may be involved in
determining a phenotype.
• Such traits produce a continuous
variation
Polygenic Inheritance - Skin Color
• The inheritance of skin color is determined
by an unknown number of genes and is a
classic example of polygenic inheritance.
• A range of phenotypes exist and several
possible phenotypes fall between the two
extremes of very dark and very light.
• Many human traits, like allergies,
schizophrenia, hypertension, diabetes,
cancers, and phobias, appear to be due to
the combined action of many genes plus
environmental influences.
Codominance - ABO Blood Types
Multiple Alleles Traits
• Inheritance of multiple alleles occurs
when more than two alternative alleles
exist for a particular genotype
• A person’s blood type is an example of a
trait determined by multiple alleles.
• Each individual inherits only two alleles
for these genes, but the combination of
the expression of this trait makes the
phenotype different.
Inheritance of blood type
• A person can have an allele for an A
antigen (blood type A) or a B antigen
(blood type B), both A and B antigens
(blood type AB), or no antigen (blood type
O) on the red blood cells.
• Human blood types can be type A (AA or
AO), type B (BB or BO), type AB (AB), or
type O (OO).
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Incomplete dominance
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