*Genetics* The Basics

Humans have 23 pairs of chromosomes

Let’s Examine This Karyotype! 1.Look at pair #19 2.Where do you think both of these chromosomes came from? 3.One from your MOM and one from your DAD! 4.Hair color is determined by genes found on chromosome #19

Alleles…Genes…and Traits oh my!! 1.GENES Chemical factors found in DNA that determine our traits! 2. Traits Characteristics that vary from individual to individual (ex: hair color, eye color, skin color, widow’s peak.) 3. Alleles Are different forms of genes. BLACK HAIR vs RED HAIR

Alleles are represented in Biology by LETTERS. Let’s Use Letter “B” right now! (B)BIG LETTERS represent Dominant Traits Black hair is dominant (b)LITTLE LETTERS represent Recessive Traits Red hair is recessive Dominant RECESSIVE

Each Person has 2 Alleles for each trait! Question? Where did these 2 alleles come from? Answer: 1 came from MOM and 1 came from DAD BB bb

Let’s Remember This Karyotype! 1.Look at pair #19 2.Keanu got one B allele for hair color from his MOM and one B from his DAD BB

GENOTYPE vs PHENOTYPE Genotype =the genetic makeup of an organism (THE LETTERS) There are only 3 options: BB, Bb, bb Homozygous- both alleles same Heterozygous- alleles are different Phenotype = the physical characteristic of the organism (WHAT YOU SEE) Tell me what you see!

A Widow’s Peak is a dominant trait! Let’s represent it with a W W=widow’s peak (D) w=no widow’s peak (R) Question: What is the baby’s PHENOTYPE? Widow’s peak! Question: What is the baby’s GENOTYPE? BB or Bb

PRACTICE ONE MORE TIME! Question: What are the phenotypes of these girls? Left and Right. Left-rolls tongue Right-no rolling Question: There is only one girl that I know the EXACT genotype. Which one is it? Right girl=rr Tongue Rolling is a Dominant Trait! R=rolling tongue (D) r=no rolling (R)

Dominant traits show up more often! 2 Possible Genotypes for a dominant trait RR or Rr Only 1 possible genotype for a recessive trait rr Question? If you were Rr, what does that mean for your kids?

Keanu Reeves has black hair and a widow’s peak Let’s say Keanu is homozygous dominant (BB) for his black hair but he is heterozygous (Ww)for his widow’s peak. What traits could he give to his kids?

Segregation Segregation is the separation of alleles during gamete formation Gametes are specialized cells involved in sexual reproduction Ww When Keanu makes his sex cells (sperm) his alleles for widow’s peak will separate W w Can Keanu give both his alleles to his kids?

LAW OF INDEPENDENT ASSORTMENT Is Keanu’s black hair trait hooked to his widow’s peak trait? NO WAY! Principle of Independent Assortment Genes for different traits can segregate independently during the formation of gametes

Keanu’s Black Hair 1 B 2 B Keanu’s Widow’s Peak 3 W 4 w There are 4 options! 1 with 3 BW 1 with 4 Bw 2 with 3 BW 2 with 4 Bw Is it possible for Keanu to have kids that have red hair? What about a widow’s peak ?

Probability and Punnet Squares Punnet Squares can be used to predict the outcomes of genetic crosses. Probability is the likelihood that a particular event will occur.

LET’S PREDICT PROBLEM: A mom and a dad decide to have a baby. Both mom and dad are HETEROZYGOUS for a widow’s peak. *first you musts figure out the genotype of the parents!!!! What are their chances (%) of having a child who has a widow’s peak? What are the chances of having a child who doesn’t have a widow’s peak?

W W w w WW Ww wwWw 75% Widow’s peak 25% No widow’s peak