Intro to Genetics

1. GENETICS
I. GREGOR MENDEL (1822-1884)
General
Monk
Worked with pea plants
Self-fertilization
Simple traits
Used Statistics
Looked at 1 trait at a time

2. A. Experiment – example
Parents purple flower x white flower
F1 100% purple
F2 75% purple 25% white
WHAT HAPPENED?

3. II. MENDELIAN GENETICS
A. . DEFINITIONS
Gene – a segment of
DNA that codes for a
specific trait. It is
found at a specific
locus (location) on a
chromosome

4. Chromosome – A
condensed structure
made of one or two
DNA molecules with
genes.
2 chromatids 1 chromatid
Allele – A form of a
gene. T or t

5. Dominant – Allele that
T
is expressed when
present.
Recessive – Allele t
expressed when the
dominant is not
present.

6. Co-dominant – Alleles for ABO Blood
the same gene that both
express themselves
when present.
Incomplete dominance – RR Rr rr
The heterozygous Red Pink
White
genotype results in a
phenotype between the
two homozygous
genotypes.

7. Genotype – The alleles
TT Tt tt
an organism/cell has.
Phenotype – The
Tall Tall Short
physical expression
of a gene.

8. Homozygous – The TT or tt
homologous pair has
the same alleles for
the same gene.
Heterozygous – The
Tt
homologous pair has
different alleles for the
same gene.

9. Diagram
Gene – Coat Color
Chromosome
Allele
Dominant
Recessive
Genotype Bb
Phenotype black

10. B. Monohybrid Cross –
Look at one gene at a time
1. Principle of Segregation
Every individual (diploid) has 2 copies
(alleles) of a gene (one from the female and one from
the male) for every trait.
In the production of gametes (by Meiosis)
these alleles are separated randomly and come back
together in the formation of a zygote (fertilization).

11. 2. Example – Coat Color in Labrador
B = black (dominant) b = brown (recessive)
Phenotype: Black Black Brown
Parent Genotype: BB Bb bb
Parent gametes: B B B b b b

12. Example of the cross
Male Female
Bb Bb
gametes B b B b
B b
Genotype
Punnett B BB Bb 1BB:2Bb:1bb
square
Phenotype
b Bb bb 3black:1brown

13. C. DIHYBRID CROSS – When look at two
genes at a time.
Linked genes are when genes are on
the same chromosome.
Example

14. 1. PRINCIPLE OF INDEPENDENT
ASSORTMENT
Genes on different chromosomes (so are not linked)
randomly assort into gametes during Meiosis and have an
equal chance for any combination.
Meiosis I or Meiosis I

15. 2. Example Gene Alleles
ear lobes E=free e=attached
freckles F=have f=none
Parent Genotypes EeFf EeFf
Gametes EF Ef eF ef EF Ef eF ef
EACH GAMETE MUST CONTAIN ONE COPY OF EACH GENE (in
this case each must have an E/e and a F/f)

16. Free earlobes, freckles EF Ef eF ef
Free earlobe, none EEFF EEFf EeFF EeFf
EF
Attached, freckles
Attached, none
EEFf EEff EeFf Eeff
Ef
EeFF EeFf eeFF eeFf
eF
EeFf Eeff eeFf eeff
ef

17. SEX-LINKED
• Gene is on the X chromosome (usually).
Male XY
Ex. Recessive trait - XHY or X hY
Female XX
Ex. Recessive trait – XHXH or XHXh or X hX h

18. Co-dominant
When more than one allele for any given gene are
both dominant and express themselves if present.
Example:ABO Blood
Phenotype Genotype
A blood IAIA or IAi
B blood IBIB or IBi
AB blood IAIB
O blood ii

19. ABO are sugar antigens on the surface of
the red blood cells (rbc)
Rh factors are proteins on the surface of
rbc.

20. Incomplete dominance
The heterozygote has a phenotype between
the two homozygous genotypes
GENOTYPES RR RR’ R’R’
PHENOTYPES red pink white

21. III. Pedigree
A tool used to track a genetic history. Used
for a family for some specific trait.
without trait with trait
Female
Male
mated
offspring

22. GENETIC PROBLEMS
MONOHYBRID
In silkworms yellow cocoon is dominant to white cocoon.
Two silkworms are mated (one heterozygous and the
other homozygous recessive).
Find the: parent genotype and phenotype
gametes produced
Punnett Square
Offspring genotype
Offspring phenotype

23. Albinism is inherited as a recessive trait.
a. A heterozygous female has children by a
homozygous normal male. What % of their
offspring will be carriers for albinism?
b. A normally pigmented man whose mother was
albino marries a homozygous normal woman.
What % of their offspring will be homozygous
normal?
c. A heterozygous male marries an albino female.
What percentage of their offspring will be
albino?

24. DIHYBRID
In hogs, a gene that produces a white belt around the
animal’s body is dominant over its allele for a uniformly
colored body. Another independent gene produces fusion
of the two hooves on each foot (an instance of syndactyly).
It is dominant over its allele, which produces normal
hooves.
Supposed a uniformly colored male hog
homozygous for syndactyly is mated with a
normal-footed female hog homozygous for the
belted character.

25. CO-DOMINANCE
In cattle, red is not dominant to white. When the
two colors are crossed, the claves have both red
and white hairs, called roan.
A rancher mates a red bull and white cow.
Show Punnett Square and label
phenotypes.

26. INCOMPLETE DOMINANCE
In four o’ clock flowers there are red, white and
pink petal colors. Pink petals is a heterozygous
condition resulting from a cross of red and white.
Cross two pink plants

27. BLOOD TYPE AND SEX-LINKED
A normal visioned female has type A blood.
Her father was colorblind with type O blood
and her mother had AB blood. She marries
a man who is colorblind and has type B
blood (whose mother had normal vision and
O blood and whose father had normal vision
and B blood).