The science of heredity Frank Gregorio Genetics The science of heredity Frank Gregorio
GREGOR MENDEL – Father of Genetics He experimented with pea plants. They worked well because they reproduce quickly and create a large number of offspring in one generation.
Heredity- The passing on of characteristics from parents to offspring. Traits- Characteristics that are inherited. Ex: Brown or Blue Eyes
DOMINANT GENE –Stronger gene – This trait will show up if it is present in an organism. (CAPITAL LETTER) RECESSIVE GENE – Weaker gene. This trait will be hidden in the organism. (LOWER CASE LETTER) Each organism receives 2 genes (alleles) from each parent.
HOMOZYGOUS DOMINANT OR PUREBRED HOMO = The same 2 Recessive Genes The Rules: 2 Dominant Genes ex) B B (capital letters) HOMOZYGOUS DOMINANT OR PUREBRED HOMO = The same 2 Recessive Genes ex) b b HOMOZYGOUS RECESSIVE OR PUREBRED RECESSIVE
1 Dominant gene and 1 Recessive gene ex) B b = HETEROZYGOUS OR HYBRID. HETERO = Different CAPITAL LETTER ALWAYS GOES FIRST
PHENOTYPE – The trait expressed (observed) in an organism PHENOTYPE – The trait expressed (observed) in an organism. The physical trait. GENOTYPE – The two genes that determine a specific inherited trait.
STRAIGHT: HAIR TEXTURE Example STRAIGHT: HAIR TEXTURE DOMINANT TRAIT RECESSIVE SYMBOL CURLY x C STRAIGHT X c WHAT ARE POSSIBLE COMBINATIONS OF GENOTYPES AND PHENOTYPES FOR HAIR TEXTURE (CURLY/STRAIGHT)?
ANSWER GENOTYPE PHENOTYPE CC---------- CURLY---- HOMOZYGOUS DOMINANT Cc----------- CURLY-- HETEROZYGOUS cc---------- STRAIGHT-- HOMOZYGOUS RECESSIVE
Review Genotype – Genetic makeup Ex. Bb, Gg, Tt Phenotype – physical appearance as the result of the genotype. Ex: Brown vs. blue, Green vs. yellow, Tall vs. short. Dominant – Traits that are expressed Recessive – Traits that are hidden. Hybrid/Heterozygote – The offspring resulting from a cross with parents with contrasting traits. Ex: Brown and Blue eyed parents (BB vs bb = Bb)
P GenerationF1 Generation Mendel selected a 6 ft tall pea plant and a 2 ft tall pea plant for the parent generation. All of the offspring (F1 generation) were tall.
F1 Generation Mendel let the tall F1 pea plants (offspring of P generation) pollinate with themselves. Ex: F1 x F1 The offspring (F2 generation) were ¾ tall and ¼ short. This makes a 3:1 ratio of Dominant:Recessive
Test Cross – Crossing a homozygous recessive allele with an unknown dominant genotype. TT x tt = 100 % Tall Tt x tt = 50 % Tall, 50 % short
Monohybrid cross – hybrid cross, because only one pair of contrasting traits is being studied. Dihybrid cross – crossing two different traits.
Punnett Squares
Example 1 BB x bb
Example 2 Black hair x White hair Rabbit Bb x bb
Example 3 Widow’s Peak x Widow’s Peak WW x Ww
Mendel’s Laws Law of Dominance- When an organism is hybrid for a pair of traits, only the dominant trait can be seen in the hybrid. Ex. Brown Eyes (BB) x Blue Eyes (bb) = Brown Eyed offspring (Bb)
Mendel’s Laws 2. Law of Segregation- Every gene has 2 alleles and when gametes are produced, each gamete receives one of these alleles. A a A a
Mendel’s Laws 3. Law of Independent Assortment-Different traits are not inherited together. -Ex: No connection between Pea color, Pea shape, Pod Shape, Flower Color. All are inherited separately. One does not affect the other being inherited.
Pedigree - a table or chart recording a line of ancestors.
Incomplete Dominance – Heterozygotes have an intermediate phenotype. Ex. Crossing white and red flowers.
Codominance – Two dominant alleles are expressed equally at the same time.
Co-Dominance
Multiple alleles – Traits with more than two alleles. Ex. ABO blood type.
Linked Genes- Genes that are typically inherited together. Example: Red hair and freckles
Sex-linked Trait- Traits controlled by genes located on sex chromosomes (X and Y). Ex: Red-Green Color Blindness, Hemophilia
Sex-Linked Inheritance: Men are likely to be affected (only 1 X chromosome) Woman are likely to be carriers (2 X chromosomes)
Polygenic Inheritance- The inheritance of a trait that is controlled by two or more genes. Ex: Skin color, Hair Color, Height
The Environment Influences Gene Expression, too! External Environment Influences: Temperature Nutrition Light Chemicals Infectious Agents (Viruses, Bacteria, Parasites)
Internal Environment Influences: Ex: Hormones, Body Differences Female or Male Ex: Hormones, Body Differences