Introduction to Genetics. Biology. Genetics – the study of patterns of inheritance and how traits or characteristics are passed on from parent to offspring. Gregor Mendel. Gregor Mendel – the father of genetics. He used pea plants to study patterns of inheritance.
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Gregor Mendel – the father of genetics. He used pea plants to study patterns of inheritance.
RR x rr
Genotypic ratio-compares possible genotypes
# homozygous dominant: # heterozygous: #homozygous recessive
In Ex. #1 it is 1:2:1
In Ex. #2 it is 0:4:0
Phenotypic ratio-compares possible phenotypes
# with Dominant trait: # with recessive trait
In Ex. #1 it is 3:1
In Ex. #2 it is 4:0
Percentages-% chance of something occuring
In Ex. #1 there is a 75% chance the plant will be tall and a 25% chance the plant will be short.
Complete Dominance: In the heterozygous individual, only the dominant allele is expressed, the recessive allele is present but unexpressed.
What is the phenotypic ratio?
What is the genotypic ratio?
Genotypic ratio: 1:2:1
Phenotypic ration is 3:1
Find genotypic ratio the same way we did for complete dominance
Now there are 3 phenotypes so the ratio is
# Dom: # Heterozygous: # Rec
Find Genotypic ratio and phenotypic ratio for the previous problem
Genotypic ratio: 0:4:0
Phenotypic ratio: 0:4:0
WW = White
RW = Roan
Genotypic Ratio- #RR: #RW: #WW
Phenotypic Ratio- #red: #roan: #white
Go to Section:
1st letter with 3rd letter
1st letter with 4th letter
2nd letter with 3rd letter
2nd letter with 4th letter
6. Fill in the Punnett Square
-keep like letters together
-capital always goes first
1st trait dominant, 2nd trait dominant:
1st trait dominant, 2nd trait recessive:
1st trait recessive, 2nd trait dominant:
1st trait recessive, 2nd trait recessive
In previous example, the phenotypic ratio is 9:3:3:1
Sex-linked traits are determined by genes found only on the sex “X” chromosome
EX. Red-Green Colorblindess
Possible female Genotypes
Possible male genotypes
What is the % chance they will have a colorblind son?
Multiple Alleles: Having more than 2 alleles for a trait.
Ex. Human blood type
3 alleles: A, B, and O
A and B are codominant
O is recessive
AA-homozygous dominant Type A
BB-homozygous dominant Type B
AO-heterozygous Type A
BO-heterozygous Type B
AB-codominant Type AB
OO-homozygous recessive Type O
Answer: Type A and Type B (both are heterozygous)
Polygenic traits: stature, body shape, hair and skin color
Pedigree: diagram that shows how a trait is inherited over several generations.
Diamond: unknown sex
Karyotype-picture of an individual’s chromosomes
-Review of chromosome structure
-Each pair of chromosomes are called homologous chromosomes
Use a Punnett Square for the following cross:
XX (mom) x Xy (dad)
What is the % chance for a girl? Boy?
Ex. Down’s Syndrome (trisomy 21)