Presentation on theme: "Genetics The study of potentials of passing information from one generation to the next."— Presentation transcript:
Genetics The study of potentials of passing information from one generation to the next
Gregor Mendel “Father” of genetics Studied pea plants Used contrasting features Parents “bred true” Kept good records Studied one trait at a time
Mendel’s pea experiment True breeding purple flower plants True breeding white flower plants F1 generation F2 generation
Terminology Gene – unit of inheritance made of DNA Genes occur in pairs except in the egg and sperm An allele is a different form of the same gene Black hair and brown hair are alleles of the hair color gene
Genes Dominant gene is one that can overshadow another gene. Signified with capital letter, e.g. “A” Recessive gene is the subordinate gene that can be suppressed by the dominant gene. Signified with a lower-case letter, e.g. “a”
Genes Homozygous – since genes occur in pairs, this is when both genes for the trait are the same AA is homozygous dominant aa is homozygous recessive
Genes Heterozygous – genes are alleles or different for a given trait Aa is heterozygous Carrier is sometimes used to indicate that someone is heterozygous
Genes Genotype is your genetic makeup For example, you might be heterozygous for hair color, Bb, one gene for black hair, and one for blonde hair
Genes Phenotype is your physical appearance Your phenotype for hair color may be brown
One gene problem Let P = Purple flower plants, or Let p = white flower plants, or The parent generation included true breeding purple flower plants that must have been PP (homozygous dominant) in genotype The parent generation included true breeding white flower plants that must have been pp (homozygous recessive) in genotype
Parents PP plant can only make a gamete with the first “P” gene, or the second “P” gene (See example using E instead of P) pp plant can only make a gamete with its first “p” gene, or the second “p” gene (See example using e instead of P)
F1 generation If these two parents fertilize to create offspring, F1, or first generation, what genotypes and phenotypes would be possible in the F1 generation? Use a mathematical Punnet square to find the probabilities
F1 generation Gamete with “P” gene – parent 1 Gamete with “p” gene – parent 2 Offspring is heterozygous – “Pp” Gamete with “p” gene – parent 2 Offspring is heterozygous – “Pp”
F1 generation 100% of the offspring would have a genotype of Pp, or be heterozygous 100% of the offspring would have a phenotype of purple flowers, since purple is dominant over white
F2 generation If you take two plants from the F1 generation (Pp) and cross them, what would be the genotypic and phenotypic ratios of the next, or F2 generation?
F2 generation Gamete with “P” gene – parent 1 Gamete with “p” gene – parent 1 Gamete with “P” gene – parent 2 Offspring is homozygous dominant – “PP” Offspring is heterozygous – “Pp” Gamete with “p” gene – parent 2 Offspring is heterozygous – “Pp” Offspring is homozygous recessive – “pp”
F2 generation Note that the four squares in the Punnet square do not represent four different offspring, but rather the statistical chances that any ONE offspring has a given trait Genotypic ratios are 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive Phenotypic ratios are 3 purple : 1 white
Try this problem E = unattached earlobes e = attached earlobes Problem one: Both parents have unattached earlobes. However, they had a son with attached earlobes. What are the chances that their next child will have unattached earlobes?
Try this problem E = unattached earlobes e = attached earlobes Problem two: One parent has unattached earlobes and the other has attached earlobes. They had a daughter with attached earlobes. What are the genotypes of the parents? What are the chances that their next child will have unattached earlobes?
Autosomal Dominant The trait or disease is the result of a dominant gene
Autosomal Recessive The trait or disease is the result of a recessive gene (e.g. cystic fibrosis)
Incomplete dominance The dominant gene is not strong enough to completely overshadow the recessive gene Example: If a red flower plant (dominant) crosses with a white flower plant (recessive) and the offspring have pink flowers (heterozygous).
Codominance No clear dominant or recessive gene Genes are equal, or codominant If genes for blood type A and blood type B are codominant and you have one gene of each, your blood type is AB
Blood typing practice Genes for blood types A and B are dominant over type O Genes for blood types A and B are codominant with each other If mom has blood type A and dad has blood type B, and they have a son with blood type O, what are the genotypes of these 3 people? What are the statistical chances that their next child has blood type AB?
Sex-Linked traits The sex of the person has not mattered up until this point working on the genetics problems. Now it does. These sex-linked problems are such that the gene for the particular trait is located on the X chromosome only. Recall that males are XY and females are XX.
Colorblindness is sex linked Colorblind is a recessive trait Carried on the X chromosome only Let B = normal vision and b = color blind Mom and dad both have normal vision. However, their second child was a colorblind son. What are the genotypes of the parents and what are the chances that their next son/daughter is colorblind?