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GeneticsGenetics
• Heredity – characteristics inherited from parents to offspring through genes
• Genetics - The study of genes and heredity
Traits • Characteristics that are inherited through genes– Genes are a portion
of an organism’s DNA– Each organism has
two copies of each gene
– Genes have different forms called alleles
Gregor Mendel• A monk in the 1800s• First to identify
heredity• Studied the traits in
garden peas– Tall/short– Round/wrinkled– Green/yellow pods– Purple/white flowers
• Why peas???
Parent or “P” Generation
• The 2 organisms that are used to reproduce
F1 Generation
• The offspring - babies
F2 generation• The babies of the F1 or the
grandchildren of the P generation– Mendel noticed that in his peas, the
white trait that disappeared with the F1 generation reappeared, but in a very small ratio compared to the purple trait
The Rule of Dominance• There are two contrasting traits/alleles
– Ex: tall or short– Another example pod color – green/yellow
• Alleles can be either dominant or recessive (strong or weak)– Dominant alleles are observable– Recessive alleles are not observable when
the dominant allele is present – they are hidden (masked) by the dominant allele
The Law of Segregation• The two allleles for a gene
separate when forming a sperm and egg
Law of Independent assortment
• Alleles for different genes are distributed to sperm and egg independently and randomly– Different alleles do not affect
each other• Could be
– tall and fat– Short and thin– Tall and thin– Short and fat
• Why all siblings do not look exactly alike
Genotype• Created after fertilization of an egg
by sperm• The copies of alleles or genes that
an organism has• Genetic make-up• ontrols the phenotype• Ex: BB, Bb, bb
Phenotype• The way an organism physically
looks– Ex: Brown hair, tall– Determined by the genotype
How can three genotypes only produce two phenotypes?
Homozygous – (Homo: same)
• Pure/true breeding• When an organism has 2 copies of
the same allele• BB – homozygous dominant• bb – homozygous recessive
Heterozygous (Hetero: different)
• Hybrid• When an organism has 2 different
alleles for a gene• one capital; one lower case• Bb, Gg etc.
Punnett Square
• A chart used to predict the probability of traits represented among offspring
• Why it is only a prediction?
Monohybrid
• One cross because you are looking at only one trait
Monohybrid Punnett Square Problems
• Height – tall is dominant to short• Symbol for tall _______• Symbol for short _____• Phenotype –
– Homozygous tall male X short female
• Genotype– Male _____ X Female ______
P1 Punnett Square
– F1 genotype ratio
– F1 phenotype ratio
Monohybrid Punnett Square Problems
• Height – tall is dominant to short• Symbol for tall _______• Symbol for short _____• Phenotype –
– Heterozygous male and female
• Genotype– Male _____ X Female ______
F1 Punnett Square
– F2 genotype ratio
– F2 phenotype ratio
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