Do We Need Some Review??

Draw a punnett square for a di-hybrid cross between RrYy and RRyy

Draw a punnett square for a di-hybrid cross between TtGg and ttgg

Draw a punnett square for a di-hybrid cross between EeJj and EeJj

The Generations The original pair (the parents) in the cross is known as the parent generation. The offspring from those parents are known as the F1 generation.

We know that the dominant alleles over power the recessive alleles, but the recessive alleles are still present. Recessive alleles are expressed only when the genes are homozygous recessive.

Parent Generation RR X rr Let’s draw a punnett square for this cross.

F1 Fertilization Rr X Rr Let’s draw a punnett square for this cross.

The Recessive Allele Throughout the generations, the recessive allele was still present, just not expressed until the alleles were homozygous recessive In order for this to happen, the alleles need to separate.

Law of Segregation The separation of alleles occurs during the formation of gametic cells. What are gametic cells, again?

Let’s Draw It! Parent Generation Gametes RR x rr

F1 Generation Gametes Rr x Rr

Independent Assortment During segregation, when alleles separate, different alleles for different genes don’t need to separate to the same gamete.

Independent Assortment The alleles for hair color and eye color separate independently. Just because an offspring gets blonde hair, it doesn’t mean it will have blue eyes.

Heredity is a little more complicated than just Dominant and Recessive…

Co-Dominance What does “co” mean? – Co-Author – Co-Chair – Co-Director – Co-teach – Cooperate

Codominance Neither allele is more dominant than the other. Both phenotypes are expressed.

“Erminette”

Let’s Make a Punnett Square Roan

Let’s Make a Punnett Square

Incomplete Dominance Neither allele is dominant or recessive. Heterozygous phenotype is a combination of the two homozygous phenotypes.

4 o’clock Flowers

Codominance or Incomplete Dominance?

Worksheet

Multiple Alleles So far we have talked about genes with only two alleles…. Some genes can have more than two alleles that express a certain trait

Multiple Alleles While there are multiple alleles available in a population; each individual still only has two alleles in their DNA Still follows Dominant and Recessive rule – Spectrum

Let’s Draw a Spectrum Most Dominant Least Dominant

Polygenic Traits Look at the term “polygenic” – Poly=?? – Genic=??

Polygenic Traits Traits that are controlled by 2 or more genes Results in a wide range of phenotypes – Skin color (4 + genes) Comes more into play in evolution

Sex Linked Genes Remember gametes?? They are determined by “sex chromosomes” (23 rd pair); all other chromosomes are called “autosomes” (1- 22) Sex chromosomes are labeled X or Y – XX- female – XY- male

Fertilization Every Egg (female gamete) gives 1 X Sperm (male gamete) gives either an X or Y

Sex Linked Genes Genes that are on a sex chromosome (X or Y). – Only males have a Y chromosome, which is inherited from their dad – A gene only carried on the Y chromosome will show up only in males – Males only have one X chromosome

Sex Linked Genes Females receive two X chromosomes, one from their mother and one from their father. – Have a “back up” X chromosome if a gene on the x chromosome is defective – Most sex linked disorders are found on the X chromosome

Sex Linked Genes Color Blindness (the genes reside on the X chromosome) Hemophilia Fragile X Syndrome

Let’s Draw a Punnett Square