Mendelian Genetics Professor Janaki Natalie Parikh [email protected].

Mendelian Genetics

Professor Janaki Natalie [email protected]

Human Traits- Tongue Rolling

• Let’s try a human trait: Tongue Rolling• Note on conventions: typically use a capital letter

to denote dominant & lwr case for recessive allele• Letter “R” used for tongue rolling (arbitrary)• 2 alleles: R, r inherited as a dominant trait• Genotypes: Phenotypes

RR tongue rollerRr tongue rollerrr non roller, can’t tongue roll

Human Traits- Tongue Rolling

• Punnett square scenario: couple considering having kids, he’s a tong. Roller & she’s not, will their kids be able to roll? (Given: his mom is not a roller) (rememb. 1st step)

• ♀ & ♂ genotypes?

• ♀: rr, & ♂ must be Rr? Why? Since his mom cannot roll, she must be rr). Now to setup the square…

r r

R

r

Now, let’s interpret…

Rr Rr

rr rr

Human Traits

• Dimples: not these, but, rather, these• Letter D is utilized, inherited as a recessive• 2 alleles: D, d. Combos: DD, Dd, dd• Scenario: Couple, neither have dimples, but they want

to know if their kids can inherit them (Given: his dad has dimples & her mom does too)

• 1st step?• ♀: Dd ♂: Dd

D d

D D d

(Interpret &…)

DD Dd

Dd dd

Multi-allelic system

• Ready to throw in an additional allele?• Multi-allelic system (genetic menage a trois• ABO blood group, only O is a recessive here,

notice the effect this has on phenotypes:• AA: blood type A• AO: blood type A• BB: blood type B• BO: blood type B• OO: blood type O any more?• AB: blood type AB

Blood Groups

• Relationship btwn A & B is such that it creates a reaction (agglutination), thus a person w/ A cannot be given B & vice versa

• Thus AB blood type has an advantage, known as?• Universal Recipient, can be given any of the types• & type O is important to commty, known as?• Universal Donor, utilized in emergencies when

typing cannot be done• Extra credit: https://www.givelife.org/index_flash.cfm

Blood Type Punnetts

• Scenario: A woman has a baby & has identified 2 men as potential fathers. Can we rule anyone out based on blood type? ♀: blood type O, Baby: blood type A, ♂ #1: blood type AB, ♂ #2: blood type O

• Genotypes?

• ♀: OO, ♂ #1: AB, ♂#2: OO

A B O O

O O

O O

Interpret:

AO BO

AO BO

OO OO

OO OO

Chromosomes & Reproduction

• Cells: basic unit of life• Organelles: carry out

a specific function• Our focus: • Nucleus: DNA is

housed inside it• Mitochondria: Pwrhouse• Inherited from whom?• Ribosome: site of

protein manufacture

Chromosomes

• human cells are eukaryotic: DNA in the nucleus• DNA packaged into chromosomes• Human cells have how many chromosomes?• 46 chromosomes in 23 homologous pairs• Chromosome # is arbitrary, not related to sz.,

complexity or intelligence• Ex: Mosquito: 6 chrom.• White Oak Tree: 24 chrom.• Turkey: 82 chrom.

Chromosomes

• Gene locus (loci): specific location of a gene• Homologous pairs: corresponding gene loci• Per pair, 1 chromosome from each parent• Pairs 1-22: autosomes• Pair 23: sex chromosomes

Mitosis a.k.a. Cell Divisiona.k.a. asexual reproduction

• Cells: somatic cells & gametes• Somatic cells: diploid chrom. #46• Gamete,sex cell: haploid chrom #23• Somatic cells replenished via mitosis• 1 exception: once maturity reached,

no more are made, what type?• Mitosis yields: 2 daughter cells,

identical to orig. parent cell

Meiosis a.k.a production of gametesa.k.a. sexual reproduction

• Begins w/ a diploid cell• However, cleavage division

takes place twice • Notice: DNA replication only happens once• Meiosis results: 4 end products: haploid gametes• This specific example must be spermatogenesis

Spermatogenesis

• Why? The other type of meiosis (oogenesis) plays out difftly, sperm only requires genetic info, sugar & a tail for motility

• Results: Spermatogenesis: 4 haploid gametes• Where does this process take place?• In the testes. When does it begin?• W/ the onset of puberty, prior to

that no sperm are produced.

Oogenesis

• Oogenesis: production of oocytes. Involves anan assymetric cleavage division. The smaller section is referred to as a polar body.Results: each fullprocess only yields1 viable oocyte &3 polar bodies,which are geneticwaste

Oogenesis

• Where does this take place?• In the ovaries. When?• Previously thought solely in utero, new evidence

suggests that it continues during a ♀s lifetime

• Why is oogenesis so difft?

• In addition to genetic info, oocytes also require organelles to sustain life. Each living thing inherits its orig. set of organelles from mom’s oocyte. Thus, mitochondria (which have their own separate DNA) are passed on from mother to her offspring

Mendelian Principles

• Princ. Of Segregation: in the production of gametes, homologous chromosomes segregate into separate gametes, a gamete will receive only 1 of the 2 homologous chromosomes

• Princ. Of Independent Assortment: whichever of 2 homologous chromosmes is contributed to a gamete is independent of whichever of any 2 other homologous chromosomes thatis contributed to the same gamete

Mendelian Principles

Mendelian Principles

Genetic Recombination

• These 2 principles contribute to a seemingly endless # of possible combinations of the same orig. set of genetic material: genetic recombination,the reason why you & your siblings don’t look alike

Sex Chromosomes

• Like the autosomes, code for norm. body traits, however, also determine a person’s biological sex

• Size differential btwn the 2 sex chromosomes• Typical pairings: XX, yielding?• Biological female. & XY, yielding?• Biological male• As a result, there are many alleles

located on the X chromosome forwhich the Y does not provide acorresponding allele

http://www.newscientist.com/article/dn12971-diet-may-influence-your-babys-gender.html

Sex Linked Traits

• Due to sz. diffc. there are many traits for which ♂s only inherit 1 single allele, located on their X chromosome

• These traits are called “sex-linked” or “X-linked” • For sex linked traits, ♂s are hemizygous, meaning

they have only 1 allele XY: ♂

XX: ♀

Sex Linked Traits

• This also makes them more susceptible to X linked recessive conditions

• Normally, to inherit a recessive condition, requires how many alleles?

• 2, one from ea. parent. Not for sex linked traits• What are some examples?• Pattern balding, red-green color blindness,

hemophilia, fragile X syndrome, etc…• http://anthro.palomar.edu/biobasis/bio_4.htm

Human Traits

• http://www.nerdmodo.com/wp-content/uploads/2009/05/5391701_std11.jpg