Genetics Or…..Who’s Yo Daddy?!?

Warm-up Essential Question What are “sex cells”? How are genes passed from parents to offspring?

Terms Homologous –describes the matching chromosome from each parent (one male / one female) Diploid – term used to describe a cell that contains both sets of homologous chromosomes – 2N Haploid – term used to describe a cell that contains only a single set of chromosomes – N

Terms Gamete – specialized cell involved in sexual reproduction - sperm or egg haploid

Meiosis process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell process by which gametes are formed 1 cell becomes 4 gametes 2 phases: I and II

Heredity- passing of characteristics (traits) from parent to offspring. Traits- examples: shape of nose, size of lips, dimples Traits- passed on in packets of DNA called genes.

Genes All genes are not created equal!! Stronger genes for the same trait are called “dominant” Weaker genes for the same trait are called “recessive” Dominant genes are always expressed over recessive Abbreviate capital letter for dominant, lower case for recessive. Ex: brown hair is dominant over blonde so brown = B and blonde = b. Must be the same letter!

Allele = the same kind of gene on homologous chromosomes Ex: The gene for different eye colors is on the same place in all normal chromosomes

Everyone has two alleles for a trait (one from mom and one from dad) Karyotype is a picture of chromosomes

What you see is what you got?!? No! What alleles you have inside your chromosomes is your “genotype” Example: BB or Bb or bb for brown or blond hair (B= dominant trait for brown and b= recessive trait for blonde) The expression of your DNA (what you see) is called your “phenotype” Example: BB and Bb both make brown hair, while bb makes blond.

Types of Genotypes Homozygous = when you have two alleles of the same kind (BB or bb) Homozygous dominant (BB) Homozygous recessive (bb) Heterozygous = when you have two different alleles (Bb) AKA hybrid

Punnett Square Useful for calculation % chance and ratios Rules: Always take the first letter of dominant gene (ex tall vs short = T and t) Stick with one letter! So if short is recessive it’s t not s Dominant always comes first

50% chance for offspring to have brown hair Your turn! What is the chance that the kid will be short even though the parents are tall?

Ratios The relative amount of each kind Genotypic ratio = number of offspring with each of the three possible genotypes (homozygous dominant, heterozygous, homozygous recessive) Phenotypic ratio = number of offspring with each of the physical traits expressed

Blending AKA “Incomplete Dominance” Not all traits are dominant/ recessive, some “blend” both genes. Example: size of eyes- large and small make medium sized.

Co-Dominance Some traits are both dominant and can share dominance. Both genes are expressed as in the case of black and white rabbits

Practice A plant species has two alleles for flower color: Red (R) and White (r). The Red (R) allele exhibits complete dominance. One parent is heterozygous and the other is homozygous recessive. What are the parent’s genotypes and phenotypes? What is the probability that an offspring will be homozygous dominant? What are the genotypic and phenotypic ratios?

More Practice Let's say that in seals, the gene for the length of the whiskers has two alleles. The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers. What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous? If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?