genetics: patterns of inheritance. allele one of the two or more forms of the gene for a specific...
TRANSCRIPT
GENETICS: PATTERNS OF INHERITANCE
ALLELE
• One of the two or more forms of the gene for a specific trait
• Represented by letters
S – Smooth seed
s – wrinkled seed
AUTOSOMES
The first 22 sets of of chromosomes are called
autosomes.
CHROMOSOME
A strand of DNA carrying many different genes.
CODOMINANCE
Case in which both alleles contribute to the phenotype of the
offspring
Hybrid pink and white azalea
(Rhododendron sp., fam. Ericaceae)
CROSSING-OVER
Homologous chromosomes within the tetrad exchange portions of their chromatids, occurs during
Prophase 1
DIPLOID
• Two sets of chromosomes
DIHYBRID CROSS (Two-Factor Cross)
A genetic cross in which two pairs of contrasting
traits are studied.
DOMINANT
The trait that hides the expression of another
trait.
T
F1 GENERATION
The first filial generation that results from a cross between two purebred
parents.
F2 GENERATION
When flowers of the F1
generation were allowed to self-pollinate, their offspring became the
second filial generation or F2 generation
GAMETE
Sex cells (egg or sperm)
GENE
A unit of DNA that produces a specific trait
in an individual.
GENETICS
The scientific study of heredity
GENOTYPE
The genetic makeup of an organism
TT
GREGOR MENDEL
• Austrian monk who studied mathematics and science
• As a boy he could predict the possible types of flowers and fruits that would result from crossbreeding two plants in his father’s garden
GREGOR MENDEL cont’d
• Curiosity about the connection between the color of a pea flower and the type of seed that same plant produced inspired him to begin experimenting with garden peas in 1856.
• Made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next.
HAPLOID
• One set of chromosomes
HETEROZYGOUS
Having two different alleles for a trait.
HOMOZYGOUS
Having two identical alleles for a trait.
HOMOLOGOUS CHROMOSOMES
Human Chromosomes
Humans have 46 pairs of chromosomes:
23 from the father
+ 23 from the mother
HYBRID
An individual that is heterozygous for a
specific trait.
INCOMPLETE DOMINANCE
Cases in which one allele is not completely
dominate over another; the offspring will have a phenotype between that
of its parents
MEIOSIS
• The process of cell division that leads to gamete formation
• During meiosis, the number of chromosomes per cell is cut in half.
MONOHYBRID CROSS(One-Factor Cross)
A genetic cross in which only one pair of
contrasting traits is studied
NONDISJUNCTION
• During nondisjunction, the chromosomes fail to divide properly during meiosis.
• Abnormal numbers of chromosomes may find their way into gametes.
PEDIGREES
• A “family tree”
• Constructed by studying the phenotypes of family members from one generation to the next.
EXAMPLE OF A PEDIGREE
P GENERATION
The parental generation with two pure-bred
parents
PHENOTYPE
The physical traits that appear in an organism as a
result of it genes.
White hair
Principle of Dominance
The principle of dominance states that
some alleles are dominant and others are
recessive.
Principle of Independent Assortment
The principle of independent assortment states that
genes for different traits can segregate
independently during the formation of gametes.
Principle of Probability
The principles of probability can be used to predict the outcomes
of genetic crosses.
PROBABILITY
The likelihood that a particular event will occur
PUNNETT SQUARE A diagram used to predict the
probability that certain traits will be inherited by offspring
RECESSIVE
• The trait that is hidden
• Recessive traits only appear when homozygous.
t
SEGREGATION
The separation of alleles during gamete formation
SEX CHROMOSOMES
The last pair of chromosomes in the
karyotype are called sex chromosomes because
they determine a whether a person will be male (xy)
or female (xx).
TEST CROSS
A genetic cross between an unknown genotype for a trait and a homozygous recessive genotype for the same trait;
the phenotypes of the resulting generation reveal
the unknown genotype.
TETRAD
The pairing of homologous chromosomes, occurs during
Prophase 1
TRAIT
A genetically determined characteristic, such as
eye color.
Mendel’s 7 garden pea traits.
TRUE-BREEDING
Plants that when crossed produce offspring
identical to themselves every time.