Heredity Review

*Genes create your traits because your DNA is a ‘recipe’ for making your proteins. Your proteins cause your traits. *Genetic variation among different organisms of the same species results from three factors; 1-new combinations of DNA created by the process of meiosis and fertilization, 2-mutations in DNA occurring during DNA replication, 3-mutations in DNA caused by environmental factors (such as UV light, temperature, toxins, etc)

*You have two genes for each trait because you got one set of chromosomes from your mom’s gamete (egg) and one set from your dad’s gamete (sperm). *When your body makes gametes (sex cells; sperm or egg), half of your gametes get one of your alleles for a trait and the other half of your gametes get the other allele for a trait (so if you have an allele for freckles and an allele for no freckles, half of your egg/sperm cells get the gene for having freckles and half of your egg/sperm cells get the gene for not having freckles.

Alleles Different types of genes for a trait are called alleles. Ex: for the trait of eye color, there is a gene for blue eyes, a gene for green eyes, a gene for brown eyes, etc. The difference in each gene results in a different in the proteins that cause eye color. Each different type of gene for this trait is called an allele. Some alleles are dominant and some alleles are recessive. If a person inherits a dominant allele from one parent and a recessive allele from another parent, the cells will only express the gene of the dominant allele (meaning, it only makes proteins from the dominant gene). The recessive allele’s gene is not used to make proteins, even though it is still in the cell. We abbreviate alleles with letters. Use the same letter for the different alleles of the same trait, but use capital for the dominant and lower case for the recessive. Ex: The allele for wet earwax is dominant to the allele for dry earwax, so E=wet earwax and e=dry earwax

The alleles an individual inherits are referred to as the organism’s genotype. The way the trait is expressed (often, how it looks) is called the phenotype. Example: If F=purple flowers and f = white flowers, the ff genotype will result in a phenotype of White flowers ff Phenotype Genotype

Heterozygous – genotype with two different alleles (Bb) Vocabulary Review: Dominant – ‘stronger’ allele Recessive – ‘weaker’ allele (Dominant allele is used to make protein and recessive is not) Phenotype – The way the trait is expressed (often, how it looks) Ex-Bob would have brown eyes Genotype – The alleles inherited Ex-Bob inherits a dominant allele for brown eyes and a recessive allele for blue eyes. If we use B’s, his genotype is Bb. Homozygous – genotype with two of the same alleles (BB or bb) Heterozygous – genotype with two different alleles (Bb)

Mendelian Genetics: genotype: PP genotype: pp genotype: Pp Only the dominant allele is expressed in the phenotype. genotype: PP genotype: pp genotype: Pp phenotype: purple phenotype: white phenotype: purple

Review Problem: P P p PP Pp Pp pp In pea plants, purple flowers (P) are dominant over white flowers (p). Show the cross between two heterozygous plants. P p OFFSPRING P p purple = ? white = ? purple = 75% white = 25% PP Pp Pp pp

Incomplete Dominance *Neither allele is completely dominant, so heterozygous (hybrid) genotype results in a phenotype that shows NEITHER allele, it shows something in-between. RR = red rr = white Rr = pink

Incomplete Dominance Review Problem: Show the cross between a red flower and a white flower. R R Offspring: Red = 0% Pink = 100% White = 0% Red = ? Pink = ? White = ? Rr Rr r Rr Rr

Incomplete Dominance Review Problem: Show the cross between a two pink flowers. R r PHENOTYPES: Red = ? Pink = ? White = ? Red = 25% Pink = 50% White = 25% RR Rr R r Rr rr

Codominance Both alleles are equally dominant, so a heterozygous (hybrid) genotype results in a phenotype that shows BOTH alleles. RR = red WW = white RW = red/white speckled

Codominance Example: BB = black feathers WW = white feathers BW = black & white speckled feathers Notice – NO GRAY! NO BLEND! Each feather is either black or white

Codominance Review Problem: Cross a chicken with black feathers with a chicken with white feathers B= black feathers W= white feathers B B W OFFSPRING: Black = ? Speckled = ? White = ? OFFSPRING: Black = 0 % Speckled = 100 % White = 0 % BW BW BW BW

Sex-linked Traits: Some genes are on the sex chromosomes. These are called sex-linked traits. The Y chromosome is a different chromosome than the X and contains different genes for different traits. WOMEN have two X chromosomes, so they get 2 alleles for these traits, while MEN only have one X chromosome, so they only get one allele for these traits.

Sex-Linked Traits The gene for one form of colorblindness is located on the X chromosome Females get TWO alleles for this trait and males get one. Red-Green Colorblind gene B = normal vision, b = colorblind (Normal is dominant) Normal vision Female = XBXB Female carrier = XBXb (normal vision) Colorblind Female = XbXb Normal vision Male = XBY Colorblind Male = XbY

A female child has ____ % chance of being colorblind. Colorblind Review Problem: *Cross a colorblind female with a normal-vision male Xb Xb XB Y A female child has ____ % chance of being colorblind. A male child has ____ % chance of being colorblind. XBXb XBXb XbY XbY 100