Download Mendelian Genetics

Unit 5 Notes: Mendelian Genetics Name:_________________________________________ Date: ___________
Genetics: the branch of biology that studies heredity
Heredity: Is the passing on of characteristics from parents to offspring
Trait: A characteristic coded for by a gene.
˃ Height (tall or short)
˃ Color (purple or white)
˃ Shape (smooth or wrinkled)
Inherited traits: Characteristics that are inherited or passed on from parents to
offspring
Acquired traits: characteristics that you get as you go through life (not inherited)
Gregor Mendel: the father of genetics.
˃ Mendelian Genetics
˃ He worked with garden pea inheritance in the 1800’s.
˃ His ideas were not accepted widely until the 1900’s
Scar
Law of Segregation
˃States that every individual has two alleles of each gene and when gametes
are produced, each gamete receives one of these alleles
Pollination: (plants)Is the transfer of pollen from anther (male) to stigma (female)
Gamete: Sex cell (sperm or egg) produced by an organism
˃ The sperm in the pollen grain fertilizes the egg in the female part of the flower (pistil)
Zygote: A fertilized egg; formed when a sperm unites with an egg.
Self Pollination: The transfer of pollen from anther to stigma on the same flower
Cross Pollination: The transfer of pollen from the anther of one flower to the stigma on a different
flower
Chromosome: Dark rod-shaped bodies (coiled up chromatin) inside a cell’s nucleus made of DNA
Unit 5 Notes: Mendelian Genetics Name:_________________________________________ Date: ___________
Gene: A segment of DNA on a chromosome that directs protein production for a
trait
˃ located on the chromosome
˃ exist in alternative forms
Allele: alternate forms of a gene
Monohybrid: Crosses that involve only 1 trait
Monohybrid cross
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P1 = original parents --- grandparents
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P1 x P1 = F1 (F = offspring) --- parents
»F1 x F1 = F2 --- you
Rule of Dominance
Dominant allele: a gene that expresses itself in the presence of a weaker form of the gene
(capital letter- example T = tall)
Recessive allele: a gene that is masked in the presence of a dominant allele
(lowercase letter –example t = short)
Phenotype: the way an organism looks & behaves.
Genotype: the alleles (letters) that determine how an organism looks or behaves.
Homozygous: purebred; having 2 identical alleles
˃ TT – homozygous dominant
˃ tt – homozygous recessive
Heterozygous: hybrid; having 2 different alleles
>
Tt – heterozygous dominant
Punnett Square: Shorthand way of finding the expected
proportions of possible genotypes in the offspring of a cross.
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Devised by Reginald Punnett in 1905
Unit 5 Notes: Mendelian Genetics Name:_________________________________________ Date: ___________
Probability: The chance that an event will occur
˃ Determined by dividing the desired outcomes by the total number of possible outcomes
˃ Expressed as a fraction or a percent
T
t
Cross a heterozygous tall plant with a heterozygous tall parent. Tt x Tt
T
(T= tall) (t=short)
»
»
Genotypic ratio: 1:2:1
Phenotypic ratio: 3:1
t
Cross a homozygous tall plant with a short plant. TT x tt
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»
T
T
TT
T
t
Genotypic ratio: 4:0
Phenotypic ratio: 4:0
t
Cross a plant that is pure tall with a plant that is heterozygous tall. TT x Tt
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»
T
TTT
T
Genotypic ratio: 2:2
Phenotypic ratio: 4:0
t
Independent Assortment
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States that the genes for different traits are inherited independently of each other.
Dihybrid cross: involve two traits
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RrYy X RrYy
RY
Ry
rY
ry
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Genotypic ratio: 1:2:2:4:1:2:1:2:1
Phenotypic ratio: 9:3:3:1
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Unit 5 Notes: Mendelian Genetics Name:_________________________________________ Date: ___________
Cross a cat heterozygous for both traits with a cat homozygous recessive for both traits.
HhTt x hhtt
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Genotypic ratio: 4:4:4:4
Phenotypic ratio: 4:4:4:4
ht
ht
ht
ht
HT
HhTh
HhTh
HhTh
HhTh
Ht
Hhtt
Hhtt
Hhtt
Hhtt
hT
hhTt
hhTt
hhTt
hhTt
ht
hhtt
hhtt
hhtt
hhtt