If you do, your chromosomes could look like this… Do you have dimples? Dimples are caused when a person inherits at least 1 dominant allele from the parents. If you do, your chromosomes could look like this… Dimples No dimples OR

Mendelian Genetics

Key Terms in Mendelian Genetics Phenotype: observable traits Brown eyes, yellow flower, dimples Genotype: the actual combination of alleles inherited Examples: BB, dd, Ff Phenotype: dimples This is the trait that is expressed. What could be this girl’s genotype? She could be DD or Dd.

A person’s genotype could be… Homozygous: having 2 identical alleles for a trait TT or tt “homo” means “same” Heterozygous: having 2 different alleles for a trait Tt “hetero” means “different” This person has a widow’s peak. Genotype: could be Aa or AA This person could be homozygous dominant (AA) or heterozygous (Aa) for the widow’s peak trait.

Let’s say Kourtney & Scott decide to have a baby Let’s say Kourtney & Scott decide to have a baby. Will the baby have a widow’s peak? We can use our knowledge of genetics & meiosis to make a prediction!

Meiosis & Sexual Reproduction During meiosis, our bodies make egg & sperm cells. Egg & sperm cells contain ½ the amount of DNA as other cells. WHY?

Meiosis & Sexual Reproduction Each parent donates 23 chromosomes to a baby, for a total of 46 chromosomes (23 pairs). Let’s follow 1 gene – the gene for widow’s peak. A = widow’s peak, a = no widow’s peak A a

Kourtney & Scott’s Genotypes Kourtney’s Phenotype: widow’s peak What would be her genotype? Could be Aa or AA. Let’s assume she is heterozygous, Aa. Scott’s Phenotype: no widow’s peak What would be his genotype? MUST be homozygous recessive, aa.

During meiosis, these 2 alleles separate into different egg cells. Kourtney is heterozygous, meaning she carries a dominant & a recessive allele (Aa). During meiosis, these 2 alleles separate into different egg cells. SO, there is a 50% chance that she will pass on the widow’s peak allele (A) to her baby. There’s also a 50% chance she will pass on the normal allele (a) to her baby. OR

Scott is homozygous recessive, meaning he carries 2 copies of the recessive allele (aa). The ONLY allele that Scott can pass down to his baby is the recessive allele (no widow’s peak), because that’s all he has!

a a A Aa Aa a aa aa Punnett Squares Diagrams we can draw to help us predict the genotypes & phenotypes of offspring. a a A Aa Aa a aa aa

Start with a blank box with 4 empty squares. Add the genotype of each parent to the top & left side of the box (outside). Father is on top & mother is on the left side. a a A a

a a A Aa Aa a aa aa Fill in the squares. Remember that each parent only passes on 1 allele to the baby. a a A Aa Aa a aa aa

Remember, alleles are a version of a gene.

What do the results of the Punnett square mean? Kourtney & Scott will have 4 children Two children will look like Kourtney, & two will look like Scott. There is chance that a baby will have a widow’s peak, but there is also a chance that the baby won’t have a widow’s peak.

A = widow’s peak a = no widow’s peak What phenotype will the baby have if it inherits these alleles?

50% What are the chances that the baby will have a widow’s peak? 25% 75% 50% No chance 50%

In guinea pigs, long hair (H), is dominant to short hair (h). A heterozygous long haired pig mates with a short haired pig. Complete a punnett square to determine what the genotype and phenotype ratios would be for their offspring.

In fruit flies, long wings (L) are dominant to short wings (l). A true-breeding long wing female mates with a true-breeding short wing male. Complete a punnett square to determine what the genotype and phenotype ratios would be for their offspring.