Genetics

vocabulary dominant – written as a capital letter, this trait will show in Mendelian genetics   recessive – written as a lower case letter; only will show if two recessive alleles are present homozygous – SAME alleles; TT or tt heterozygous – DIFFERENT alleles; Tt genotype – letter combination that show the genes; TT, Tt, tt phenotype – physical description; tall or short

47 In a genetics laboratory, two heterozygous tall plants are crossed. If tall is dominant over short, what are the expected phenotypic results? Tt x Tt T t T t Phenotype: 75% TALL TT, Tt 25 % SHORT tt 3:1  TT Tt tt

R Tt Tt tt tt x Tt t t T t 50% short 50% tall 1:1 If one homozygous short plant is crossed with a heterozygous tall plant, what percentage of the offspring will be short? tt x Tt t t T t 50% short 50% tall 1:1  Tt Tt tt

RRdd x RrDD Rd Rd Rd Rd RD rD RRDd RrDd

Genotypes: RRDd-50% RrDd-50% Phenotypes: 100% red eyes and dark fur

Incomplete dominance the two traits blend when both are present RW x RW Two pink flowers are crossed R W R W 25% RED-RR 50% PINK-RW 25% WHITE-WW RR RW WW

Co-Dominance Both traits show up when both are present A A A B 50% AA IA IA IA IB

Explain how it is possible for a man with type a blood and a woman with type b blood have a child with type o blood. O (i) blood is recessive, so if the male is AO and the female is BO then a child could have OO

#51 Sex linked traits are carried on the sex chromosome X Males have one X, females have two X’s Therefore a male only needs one allele to have the trait, but females need 2 alleles to have the trait. This makes is more rare for a female to have a sex linked trait. But females can be carriers

#53 Sample Sex-linked trait Question: Color blindness is a sex-linked recessive trait. A mother with normal color vision and a color blind father have a color blind daughter. Which of the following statements is correct? All of their daughters will be color blind. The mother is a carrier of the color blindness gene. All of their sons will have normal color vision. All of their sons will be color blind.