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Mendelian Genetics
Professor Janaki Natalie Parikh
[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:
tongue roller
tongue roller
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…
Now, let’s interpret…
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
(Interpret &…)
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
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
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.
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 Division
a.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 gametes
a.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
• 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: production of oocytes. Involves an
an assymetric cleavage division. The smaller
section is referred
to as a polar body.
Results: each full
process only yields
1 viable oocyte &
3 polar bodies,
which are genetic
• 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 that
is 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 for
which the Y does not provide a
corresponding allele
Sex Linked Traits
• Due to sz. diffc. there are many traits for which
♂s only inherit 1 single allele, located on their X
• 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…
Human Traits