Download alleles - Jordan High School

Chapters 11, 14 & 15
The Experiments of Gregor Mendel
• Genetics—the study of heredity
• Gregor Mendel carried out his genetics studies
on pea plants
• Pea plants self-pollinate (offspring have only 1
parent)
• Trait—specific characteristic of an individual
• Mendel cross-pollinated pea plants to
determine how traits were inherited
• Dusted the female parts of the flower with pollen
from a different plant
• Produces plant with 2 different parents
• Hybrid—the result of crosses between parents
with different traits
• Generations identified by P (parents), F1 (first
generation), F2 (second generation), etc.
• Mendel found that an individual’s
characteristics are determined by genes
passed from one generation to the next
• Ex: Height, flower color, seed color
• Genes are found in different forms called
alleles
• Ex: tall or short, pink or white flower, yellow or
green seed
• Mendel also formed the principle of
dominance—some alleles are dominant &
some are recessive
• Dominant trait will be exhibited
• Recessive trait is exhibited if dominant is not
present
Segregation
• P generation: Tall x
Short
• F1 generation: all Tall
• Mendel allowed F1 to
self-pollinate for F2
• F2 generation: 3 Tall, 1
Short
• Mendel suggested that alleles separate
(segregation) during the formation of sex cells
(gametes)
• Alleles separate so that each gamete has only
one allele for each trait
Probability & Punnett Squares
• Probability—the likelihood that a particular
event will occur
• Allele segregation defines probability of
genetics
• Gametes have 1 in 2 chance of getting allele
• Alleles indicated by letters (TT, Tt, tt)
• Dominant traits are capital letters (T)
• Recessive traits are lower-case letters (t)
• Organisms with 2 identical alleles for a gene
are homozygous (homozygote)
• Ex: TT or tt
• Organisms with 2 different alleles for a gene
are heterozygous (heterozygote)
• Ex: Tt
• Genotype—genetic makeup of an organism
• Ex: TT, tt, GG, gg
• Phenotype—physical traits of an organism
• Ex: tall, short, green seed, yellow seed
• Determined by genotype
• Punnett squares predict the outcome of a
genetic cross
• Alleles of 1 parent across the top of the square
• Alleles of the other parent down the side of the
square
9: 3: 3: 1 ratio
3: 1 ratio
Beyond Dominant & Recessive Alleles
• Incomplete
dominance—one
allele is not completely
dominant over the
other
• Phenotype is a blend of
the alleles
• Codominance—alleles of both alleles are
shown
• Phenotype shows both traits of alleles
• Multiple alleles—a gene that has more than 2
alleles
• Organism only gets 2 alleles
Genes & the Environment
• Environmental conditions can affect gene
expression & influence traits
• Cool temperatures cause less pigment, warm
temperatures cause more pigment
Chromosome Number
• Chromosomes in an organism are
homologous—each chromosome from father
has matching chromosome from mother
• Cells containing both sets of chromosomes are
diploid (2N)
• Cells containing single set of chromosomes are
haploid (N)
Phases of Meiosis
• Meiosis—2-phase process that cuts the
number of chromosomes per cell in half
• Occurs in sperm & egg cells
Meiosis I
• Prophase I—homologous chromosomes line
up as a tetrad—4 chromatids
• Crossing-over exchanges genetic material
• Metaphase I—tetrads line up at center of cell
• Anaphase I—tetrads separate
• Each separated homologous chromosome moves to
opposite ends of cell
• Telophase I & cytokinesis—2 cells separate
Meiosis II
• Involves 2 cells from meiosis I
• Prophase II—chromosomes become visible
• Metaphase II—chromosome line up at center
of cell
• Anaphase II—chromatids separate
• Telophase II & cytokinesis—both cells separate
& form 4 new cells
• Each cell has half the set of chromosomes (haploid)
Karyotypes
• Genome—full set of genetic information that
an organism carries in its DNA
• Karyotype—shows the complete diploid set of
chromosomes
• Grouped in pairs, arranged by size
• Human cells contain 46 chromosomes (23
pairs)
• Haploid sperm combines with haploid egg
• Sex chromosomes determine an individual’s
sex
• Females = XX, males = XY
• Remaining 44 human chromosomes are
autosomes
Transmission of Human Traits
• Many human traits follow a pattern of
dominance
• Ex: hair & eye color, vision
• Some alleles are codominant
• Ex: blood typing (A, B, AB, O)
• Sex-linked gene—located on X or Y
chromosome
• Genes on Y chromosome only seen in males
• Ex: color blindness
Human Pedigrees
• Pedigree—chart that shows relationships &
patterns of inheritance
• Shows presence/absence of traits
• Pedigrees can determine genotypes of family
members
• Also determines if allele for a trait is dominant or
recessive, or sex-linked
• Sickle cell disease
• Defective allele causes red blood cells to become
sickle-shaped
• Causes clumping of red blood cells
• Cystic fibrosis (CF)
• Caused by deletion of 3 bases
• Causes production of thick mucus
• Having an allele for a disorder may prevent
other diseases
• Ex: allele for sickle cell causes resistance to malaria
Chromosomal Disorders
• Nondisjunction—
homologous
chromosomes fail to
separate during meiosis
• Causes gametes with
abnormal numbers of
chromosomes
• Ex: trisomy 21 (Down
syndrome), XXY, XXX, XO
Manipulating DNA
• Restriction enzymes—cut DNA into smaller
fragments for better study
• Gel electrophoresis—separates & analyzes
DNA fragments
• Causes a series of bands based on fragment size
Gel electrophoresis animation
The Human Genome Project
• Human Genome Project worked to sequence
all 3 billion base pairs of human DNA
• Completed in 2003
• Helped create the field of genomics—the
study of whole genomes
• Also helped identify genes associated with
diseases and disorders
Selective Breeding
• Selective breeding—allowing only organisms
with wanted characteristics to breed
• Hybridization—crossing dissimilar organisms
• Offspring often hardier than parents
• Ex: fruit, mules
• Inbreeding—continued breeding of individuals
with similar characteristics
• Ensures characteristics are preserved
• Increased risk for genetic disorders
• Ex: dog breeding
• Biotechnology—application of technology to a
living organism
• Includes selective breeding, production of
mutations
• Scientists can
produce DNA
molecules in the
lab and insert
them into living
cells
(recombinant
DNA)
• Can change
genetics of living
organisms
• Clone—genetically identical cells produced
from a single cell
• Single-celled organisms easily clone
• Clones of animals have been produced
Agriculture & Industry
• Genetically modified (GM) plants compose
majority of crops grown in the U.S.
• Produce toxins in insects, have higher yields,
resistance to herbicides
• GM animals produce more milk, leaner meat,
grow quicker
• Use of cloned animals may increase (duplicate
required traits)
Health & Medicine
• Uses of recombinant DNA
• Crops developed to prevent disease
• Treating disease through gene therapy—changing a
gene to treat a medical disease or disorder
• Genetic testing for diseases or disorders
Personal Identification
• DNA fingerprinting identifies individuals using
hair, blood, or bodily fluids