1. Theoretical genetics
Ms. Jackie

2. Important definitions
Genotype- the alleles possesed by an organism
Phenotype- all the characteristics of an organism.
Dominant allele- an allele which has the same effect on the phenotype whether it is present in the homozoygous or heterozygous state
Recessive allele- an allele which only has an effect on the phenotype when present in the homozygous state

3. Important definitions
Codominant alleles- alleles which only has an effect on the phenotype when present in heterozygous but a greater effect in homozygous individuals.
Locus- The particular position of a gene on homologous chromosomes.
Homozygous- two identical alleles of a gene
Heterozygous- having two different alleles of a gene
Carrier- an individual that has a recessive allele of a gene that does not have an effect on the phenotype
Test cross- testing a suspected heterozygote by crossing with a known homozygous recessive.

4. Construction of Punnett grids
Way of finding he expected ratio of the offspring, giving certain parental phenotypes

5. Punnett grids Tall TT or Tt Short tt Tt
Example using characteristics used by Mendel
He study the size of pea plants and found that tall is dominant over short
Lets start with two pure breeding (homozygous) plants with contrasting traits (tall and short)
F1 generation will have the dominant phenotype tall but will be heterozygous.
Phenotypes
Corresponding genotypes
Tall
TT or Tt
Short tt
T T Tt t

6. Punnett grids
T t
IF the F1 generation self fertilized we will obtained F2:
¾ tall
¼ short
3:1
1TT:2Tt:1tt TT Tt tt T t

7. Lets practice
IF a tall garden pea is crossed with a dwarf garden pea, the F1 are all tall. Predict the result of self fertilization of the F1, using a Punnett square.

8. Pedigree chart
Used to show the inheritance of certain traits over several generations of humans
Example Queen Victoria hemophilic condition
Males are normal or affected
Females normal or carriers
Hemophilia allele is homozygous lethal as well as sex linked since it is carried on the X chromosome
Males can be XHY (normal) or XhY (affected)
Females can be XHXH (normal) or XHXh (carrier)

9. Queen Victoria and hemophilia
Affected male
Affected female
Normal female
Normal male
Victoria Albert
Victoria Edward Alice Alfred Helena Louise Arthur Leopold Beatrice
George V 3
Irene Frederick Alexandra NicholasII
Duke of Windsor
George VI 3
Alexis
Elizabeth Margaret

10. Multiple alleles Some genes have more than two alleles
Multiple alleles can be found in blood groups

11. ABO blood groups Based on 4 different phenotypes (A;B;AB and O)
Caused by different combinations of 3 different alleles
Phenotypes
Genotypes A
IAIA or IAi B
IBIB or IBi AB
IAIB ii

12. ABO blood groups
Using a Punnett Grid work out the possible combinations of blood groups of a male with blood group B and a female with blood group
Using a Punnett Grid explain why a female with blood group O and a male with blood group AB cannot have children with either pf the parents´ blood group.

13. How sex chromosomes determine gender
Gender determination
Decided by sex chromosomes
Females has two X chromosomes
Males have one X and one Y chromosome

14. Genes in X and Y chromosomes
The X chromosome is relatively large
Y chromosome is much smaller
Several genes are located on the X chromosome
Sex linked examples
Colorblindness
hemophilia
Few genes on the Y
Hairy ears

15. Define sex linkage and state two examples
Genes carried on the sex chromosomes, most often on the X chromosome.
Examples
Color blindness
Certain colors cannot be distinguished, and is most commonly due to an inherited condition. Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.
Depending on just which figures you believe, color blindness seems to occur in about 8% - 12% of males of European origin and about one-half of 1% of females. Total color blindness (seeing in only shades of gray) is extremely rare.
There is no treatment for color blindness, nor is it usually the cause of any significant disability.

16. Define sex linkage and state two examples
Hemophilia
Blood condition in which an essential clotting factor is either partly or completely missing.
This causes a person with hemophilia to bleed for longer than normal.
Cuts and grazes are not great problems as a little pressure and a plaster are usually enough to stop bleeding.
The main problem is internal bleeding into joints, muscles and soft tissues.
Hemophilia is a lifelong inherited genetic condition, which affects females as carriers and males who inherit the condition.

17. Human females can be homozygous, hetero with respect to sex linked genes
Human males cannot be heterozygous since they only have one copy of one allele
Example
Colorblindness
Existing alleles
XB for normal vision
Xb for colorblindness
A female can be
XBXB or XBXb
XbXb
A male can be
XBY
XbY

18. Female carriers are heterozygous for X linked recessive alleles
Human females can be homozygous, hetero with respect to sex linked genes
Hemophilia example
Existing alleles
XH for normal
Xh for hemophilia
A female can be
XHXH or XHXh
XhXh (not exist)
A male can be
XHY
XhY
Homozygous lethal
Female carriers are heterozygous for X linked recessive alleles
They will not show the disease but can pass it on to the next generation

19. Heterozygous females for sex linked traits
Explain that female carriers are heterozygous for X-linked recessive alleles
Heterozygous females for sex linked traits
Are said to be carriers
They will not show the disease
Can pass the disease to the next generation

20. Calculate and predict the genotypic and phenotypic ratios of monohybrid crosses
Involves the cross between two individuals to study the inheritance of one gene
Example
Character: Tongue Rolling
Gene: R
Alleles: R, r
Genotypes: RR, Rr, rr
Phenotypes: rollers, non rollers
Cross:
Heterozygous X Heterozygous
Rr X Rr
Gametes R, r X R, r
Punnett square
R r RR Rr rr R r
Ratio 3:1

21. Calculate and predict the genotypic and phenotypic ratios of monohybrid crosses
In your notebooks calculate the genotypic and phenotypic ratios of a cross between a heterozygous tongue roller and a recessive individual for tongue rolling

22. Calculations and codominance
Type pf inheritance in which the two alleles of the gene are equally dominant and so they are both expressed in the heterozygous genotype.
Alleles
R red
W white
RR red
WW white
RW- pink

23. Calculations and codominance
The two alleles are equally dominant
This kind of inheritance produces more variation.
Example
Phenotypes of parents Red X White
Genotypes of parents RR X WW
Gametes R and W
F1- RW all pink
Perform a self cross between the F1 generation

24. Deduce the genotypes or phenotypes of individuals in pedigree charts
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Answer exercises 2 and 4