Inheritance of Traits
Lab 6 - Inheritance of Traits: the Dragon Genetics Lab
#NSB20141Students will be able to:Define the terms heredity,
traits, karyotype, autosome, Punnett square, allelesDetermine the
difference between dominant and recessive genes.Compare homozygous
and heterozygous traits.Demonstrate how alleles affect the
inheritance of traits in a model organism.#NSB20142The passing of
characteristics from parent to offspring is called heredity.Before
DNA and chromosomes were discovered, the mechanism of heredity was
one of the greatest mysteries of science.It was once believed (in
the 16th century) that a sperm contained a fully formed, miniature
human being (called preformationism).
#NSB20143Terminology to knowDNA - deoxyribonucleic acid, a
self-replicating material present in nearly all living organisms as
the main constituent of chromosomes. It is the carrier of genetic
information.Chromosomes - a threadlike structure of nucleic acids
and protein found in the nucleus of most living cells, carrying
genetic information in the form of genes.Genes - a distinct
sequence of nucleotides forming part of a chromosome, and
determines some characteristics of offspringAllele - one of two or
more alternative forms of a gene#NSB20144Autosomal Chromosome pairs
1 22 in humans, contain all the instructions for the bodys anatomy
and functionSex Chromosome 23rd pair in humans, contain the sex
instructions, xx or xy
#NSB20145
Gregor MendelAn Austrian monk named Gregor Mendel, who is known
as the Father of Genetics, pioneered the study of heredity in the
late 1800s.
#NSB20146Mendels HypothesesFor each inherited character, an
individual has two copies of the gene -one from each parent.These
are called alleles
#NSB20147Mendels HypothesesThere are alternative versions of the
gene - for example, the alleles (big) Y and (little) y, (big) T and
(little) tThe combination of these alleles is the organisms
genotype for that gene
#NSB20148Mendels HypothesesOf the two alleles, one of them may
be completely expressed (dominant), while the other one may have no
observable effect (recessive) on the organisms phenotype
(appearance).
#NSB20149Mendels HypothesesWhen gametes are formed, the alleles
for each gene in an individual separate independently of one
another. Thus gametes carry only one allele for each inherited
trait.Gametes are the sex cells the egg or sperm
#NSB201410MEIOSISTwo Laws of HeredityThe law of segregation
states that the two alleles for a character segregate (separate)
when the gametes are formed.The law of independent assortment
states that the alleles of different genes separate independently
of one another during gamete formation. For example, the alleles
for the height of a plant separate independently of the alleles for
its flower color.
#NSB201411The Human Karyotype22 pairs of autosomes
1 pair of sex chromosomes
Female = XXMale = XY
#NSB201412For autosomal genes:
If an individuals genotype is homozygous dominant or
heterozygous, their phenotype will show the dominant allele. Ie.
HH, Hh
If an individuals genotype is homozygous recessive, their
phenotype will show the recessive allele. Ie. hh#NSB201413
#NSB201414Autosomal or Sex Linked?If a gene is autosomal (found
on the autosomes), it will appear in both sexes equally.A
sex-linked genes allele is located on the X or Y (sex)
chromosome.Most sex-linked traits are carried on the X chromosome
and are recessive.If a trait is sex-linked, its effects are usually
seen only in males.Color-blindnessMale-pattern
baldnessHemophilia
#NSB201415Sex-Influenced TraitsA sex-influenced trait is a
phenotype that is expressed differently in males and females.While
sex-linked genes are only found on the sex chromosomes,
sex-influenced genes can be autosomalExample:Male pattern baldness
(due to high testosterone; males have more testosterone than
females, so baldness is much more common in males)Also called a
sex-limited trait (trait is found in only one sex)
#NSB201416Complex Patterns of HeredityNot all traits that are
inherited are controlled by one set of genes. When several genes
influence a character, this is called polygenic inheritanceeye
color, weight, height, skin color (this is why we have so many
different eye colors, weights, skin colors, etc)In Mendels crosses
there was either a dominant or a recessive trait. In some
organisms, an individual displays a phenotype that is intermediate
between the two parents, a condition known as incomplete
dominance#NSB201417Examples of Incomplete DominanceWhen a
snapdragon with red flowers is crossed with a snapdragon with white
flowers, a snapdragon with pink flowers is produced. Neither the
red nor the white allele is dominant over the other.
In humans, the child of a straight haired parent and a
curly-haired parent will have wavy hair.
#NSB201418Incomplete Dominance v. CodominanceExample: flower
color in CarnationsHomozygous dominant (AA) = RED
phenotypeHomozygous recessive (aa) = Heterozygous (Aa) =
PINKCodominance: both alleles are equally dominant and both alleles
are visible in the hybrid genotypeExample: feather color in
chickensHomozygote 1 (F1F1) = BLACK feathersHomozygote 2 (F2F2) =
Heterozygote (F1F2) = Black and patternIncomplete dominance: one
allele is only partially dominant to the other; the heterozygote
exhibits a phenotype that is intermediate relative to the dominant
and recessive phenotypes
WhiteWhiteWhite#NSB201419Characters Influenced by the
EnvironmentSome phenotypes depend on environmental
conditionsHydrangea flowers of the same genotype can exhibit
different phenotypes based on the environment (soil pH) Plants in
acidic soil have blue flowers, while plants in neutral or basic
soil have pink flowers
#NSB201420Temperature-dependent Sex DeterminationThis is the
condition where the sex of the offspring is influenced by the
prevailing temperatures during embryonic development. In sea
turtles, warmer temperatures produce more or all females, cool
temperatures produce more or all males, and thepivotal
temperatureis the constant incubationtemperature that produces
equal numbers of males and females. #NSB201421
Example from lab#NSB201422
FfLong neckGGNo back humphhBack spikesiiShort tailJJFlat
feet
