Introduction to Genetics- Phenotype SJCHS

Genes Offspring get half of their genes from either parent; inheritance is random Phenotype: traits of an organism (determined by proteins produced) Phenotype depends on type of inheritance

Complete Dominance 2 different kinds of alleles Dominant allele: Determines the phenotype NOT THE MOST COMMON ALLELE Wild type: Most common allele Recessive allele: No affect on phenotype if dominant allele present

Incomplete Dominance Incomplete dominance: the combination of two different alleles in a heterozygote Heterozygote still has 2 alleles, not a new or different allele

Example Snap dragons 2 alleles for color: red or white If a flower has one of each allele, phenotype will be pink

Example Human Hair: 2 alleles 1 allele for curly hair 1 allele for straight hair Heterozygote (1 curly hair allele and 1 straight hair allele) results in wavy hair

Multiple Alleles Multiple Alleles: Some genes have more than 2 alleles Can have multiple dominant or recessive alleles Codominant: When two dominant alleles are present, both phenotypes are equally expressed

Example In rabbits, there are 4 different alleles that control coat color Order of alleles from most dominant to most recessive Brown, Chinchilla, white with black tips, white

Example Human blood type is determined by carbohydrates on surface of cell 2 dominant alleles code for A carbohydrate, B carbohydrate Type AB means person has both carbohydrates (and both dominant alleles) Type O- no carbohydrates (recessive)

Polygenic Polygenic: A single trait can be influenced by more than one gene

Example Bell Pepper color: Controlled by 3 genes Gene 1 controls timing of chlorophyll elimination Y- early, y normal Gene 2 controls coloring of pigments R- red, r-yellow Gene 3 controls amount of pigments C- normal, c1, c2 less Different combinations of alleles result in different colors

Sex Linked Genes Sex Linked Genes: Genes located on X or Y chromosome X linked genetic disorders are more common in males

Example Color Blindness Several X linked genes 20 times more often in males

Lethal Genes When 2 Lethal genes are inherited, results in an abnormal embryo that does not survive

Example Manx gene in cats Recessive: Normal Heterozygous dominant: No tail Homozygous dominant: Abnormal embryo

Environment “ Nature versus Nurture ” : Does the environment or genetics influence certain traits more? Studies usually use twins or siblings

Behavioral Traits Is blood type inherited? YES

Behavioral Traits Is risk taking inherited? Study of unrelated subjects showed that “ novelty seeking ” is associated with a particular allele Study of twins found no association between “ novelty seeking ” and having a particular allele

Behavioral Traits Is musical skill inherited? “ Absolute Pitch ” : The ability to name a note after hearing the sound Study showed that absolute pitch occurs in more often in people with certain genetic disorders are more likely to have it Study showed that those who grew up in East Asia were more likely to have it Study showed that professional musicians with early musical training were more likely to have absolute pitch as opposed to professional musicians without early musical training

Behavioral Traits Is intelligence inherited? Studies show that identical twins not raised by the same family tend to have similar IQs (more so than non-identical siblings raised by the same family) Studies have shown that children adopted into families that value education will have increased IQ scores as opposed to children adopted into families that do not value education

Environment Some traits not influenced by environment, others are a mix of environment and genetics

Epigenetics Epigenetics: Study of heritable genetic changes that do not involve DNA; involves gene expression

Epigenetic video

Phenotype Inheritance of most traits are complex (a combination of several types of phenotype inheritance)

Example Human eye color Iris- colored part of eye Made of cells containing a pigment holding organelle (melanosome) Amount of pigment in melanosomes and number of melanosomes determine eye color Pigments act the same as pigments in plants (light that is reflected is the color we see)

Example Eye color cannot be explained by simple complete dominance Humans have many eye color genes (polygenic) that produce different pigments Order of alleles from most dominant to most recessive Brown, Green, Blue 2 allele for blue eyes (multiple alleles) Genes located different chromosomes

Example When considering inheritance of eye color, must consider both genes that control eye color and if parents are heterozygous or homozygous for a trait

Example Unanswered questions Number of genes that control eye color Amount of pigment produced can change over time (eye color can change in a person ’ s lifetime) Grey, hazel eye color inheritance cannot be explained Parents with blue eyes can produce offspring with green or brown eyes