Genetics, a la Garrett

1. Genetics, a la Garrett

2. Human Perspective • Normal Patterns of Inheritance • AKA “Mendelian Genetics”

3. Body cells are called “somatic cells” and have 46 chromosomes. Body cells are all the cells that make up our body, except egg or sperm cells

4. Sex cells (sperm cells or egg cells) are called “gametes” and have 23 chromosomes.

5. Egg cells and sperm cells have 23 chromosomes, because there should be 46 if fertilization occurs.

6. The fertilized egg is called a zygote. (It’s like when you were an itty, bitty, teeny, tiny single-celled you!) Remember, you can’t control or predict which 23 chromosomes will go into a particular gamete!! Randomness Rules!!

7. Most genes come in 2 forms called “alleles”. Have freckles/ have no freckles Free earlobes/ attached earlobes Can roll tongue/ can’t roll tongue

8. Dominant alleles If you get this type of allele from either parent, the trait (characteristic) that it codes for will show up in your physical characteristics.

9. We call your Physical characteristics, Physical appearance, What you physically show… Your phenotype. phhhhhhhhhhh

10. We really don’t know WHY an allele is dominant or not, we just know that if you get it, you show it!

11. Recessive alleles You must get a recessive allele from both parents for a recessive trait to show up in your phenotype.

12. This is why you sometimes see two parents with free earlobes having a child with attached earlobes!

13. Should two freckle-faced folks fret over having a freckleless kid---NO! They each gave him a recessive allele!! It’s all good!

14. The genes you inherit are called your genotype. If you read the syllables backwards, it tells you the meaning of the words! Genotype type-o-genes So, the genotype is the type of genes you have!

15. For most traits, mom and dad each give us one allele. Whew! That makes it easy!!

16. Three types of allele combinations… You need to know 2 prefixes… HETERO means “different” HOMO means “same”

17. If you get a dominant allele from each parent, your genotype is called homozygous dominant for that trait Homo=same both alleles are the same and they are both dominant

18. If you get a recessive allele from each parent, your genotype is called homozygous recessive for that trait. Homo=same both alleles are the same and both are recessive.

19. If you get a dominant allele from one parent and a recessive allele from the other, your genotype is called heterozygous for that trait. Hetero=different both alleles are different (one dominant and one recessive)

20. If there is at least one dominant allele in the genotype, the Dominant trait shows up in the phenotype!!

21. If you know the genotypes of the parents for a particular trait, you can predict the genotypes & phenotypes of their potential offspring.

22. Choose a letter to stand for the gene Example: Rolling the tongue I choose “R” You will always be told which traits are dominant & which are recessive!

23. Capitalize the letter for the dominant allele R Write it in lower case for the recessiver So… for tongue rolling Homozygous dominant RR Homozygous recessive rr Heterozygous Rr You use the same letter, because you are showing different forms of the same gene!!

24. Based upon information you are given, write the parents’ genotypes For our example problem, let’s say Mom is heterozygous for tongue rolling and dad is heterozygous, too. ___Rr_______ x ___Rr______ Mom’s genes Dad’s genes Mom can roll her tongue. Dad can roll his tongue.

25. We use a Punnett Square to predict all of the possible outcomes of this cross Draw a 4 square Write Mom’s genes on top (one per box) & Dad’s genes on the left side (one per box)

26. R r R r Write the letters from the top & the left into each box. If there is one big & one little, write the big letter first.

27. R r R RR Rr rr r Rr The letters in the boxes are the possible genotypes of potential offspring. The boxes represent babies! Potential ones!

28. Next, make 3 columns: genotypesphenotypeschances of phenotype (letters in boxes) ( which trait would show) (out of 4) _____________ _________________ _________________ • Write the letters from each box under genotypes. • Write the trait that will show (if there is 1 dominant, the dominant trait shows!) • Write how many times out of 4 the phenotype shows up GenotypesPhenotypeChances RR can roll ¾ or 75% Rr can roll Rr can roll rr can’t roll ¼ or 25%

29. What these columns tell you is that ANY baby these two folks might make has a 75% chance of being able to roll its tongue and a 25% chance of not being able to roll its tongue.

30. Another example: Having Freckles (F) is dominant over having no freckles (f) Mom is heterozygous and Dad is homozygous recessive Ffff __________________ x ___________________ Mom’s genes Dad’s genes Set up & fill in the Punnett Square

31. F f f ff Ff Ff ff f Make & fill in columns genotypesphenotypeschances of phenotype Ff Freckles 2/4 or 50% Ff Freckles ff no freckles 2/4 or 50% ff no freckles

32. Remember Mom’s on top (of the boxes) Dad’s on the side (left side of the boxes) If there is at least one big letter in a genotype, the dominant trait shows!