Presentation on theme: "Vocabulary C12L03C12. dominant & recessive Allele - alternative form that a single gene may have for a particular trait (dominant & recessive) e.g. flower."— Presentation transcript:
dominant & recessive Allele - alternative form that a single gene may have for a particular trait (dominant & recessive) e.g. flower color & plant height Dihybrid – a genetic cross to examine the possible inheritance of two specific alleles (traits) (e.g. flower color & plant height) R Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R). Masks recessive alleles. e.g. a cross between a red cow (RR) and a white cow (WW) produce red a white (RW) spotted cows Codominance – Pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles for a gene are equally expressed. (e.g. a cross between a red cow (RR) and a white cow (WW) produce red a white (RW) spotted cows)
F 1 generation - the first-generation offspring in a breeding experiment. your parents (1st filial generation, your parents) F 2 generation - the second-generation offspring in a breeding experiment. you (2nd filial generation, you) Gene - a unit of heredity; a sequence of DNA nucleotides that determines a single characteristic. Genetics - science of heredity
e.g. RR, Rr, rr Genotype – gene or allele combination for a trait. This is the letter combination for the genes. (e.g. RR, Rr, rr) Heredity - passing of traits from parent to offspring Heterozygous or Hybrid - gene combination of one dominant & one recessive allele e.g. Rr (e.g. Rr) e.g. RR or rr Homozygous or true breeding (pure) -gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr)
Parents = Red Flower (RR), and White Flower (rr); Offspring are all Rr with Pink flowers Incomplete Dominance – Pattern where one allele is not completely dominant over the other. Generally displays a new trait. (Parents = Red Flower (RR), and White Flower (rr); Offspring are all Rr with Pink flowers) Law of Independent Assortment - Mendelian law stating that a random distribution of alleles occurs during the formation of gametes. Law of Segregation - Mendelian law stating that two alleles for each trait separate during meiosis Monohybrid – a genetic cross involving a single trait e.g. flower color
your grandparents Parental P 1 Generation - the parental generation in a breeding experiment.(your grandparents) Pedigree – Graphic representation of genetic inheritance used by geneticists to map genetic traits. e.g. red, white Phenotype – Physical expression of the gene. The observable characteristic that is expressed as a result of genotype (e.g. red, white) Polygenic Traits – traits controlled by two or more genes; genes may be on the same or different chromosomes
Punnett Square - a diagram used to analyze the possible gene combinations of the offspring between two individuals. genotypes and phenotypes ( genotypes and phenotypes) r Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r). Is not seen if a dominant allele is present. Sex Linked Traits – traits controlled by genes located on sex chromosomes X and Y chromosomes ( X and Y chromosomes) Trait — characteristic that is inherited; can be either dominant or recessive
Known as the “father of genetics” Austrian Monk Studied the inheritance of traits in pea plants Developed the rule of dominance and laws of inheritance Mendel's work was not recognized until the turn of the 20th century
Can be grown in a small area Produce lots of offspring very quickly Produce pure plants when allowed to self- pollinate several generations Can be artificially cross – pollinated
(R) (r) 1. Seed shape --- Round (R) or Wrinkled (r) (Y) (y) 2. Seed Color ---- Yellow (Y) or Green (y) (S) (s) 3. Pod Shape --- Smooth (S) or Wrinkled (s) (G) (g) 4. Pod Color --- Green (G) or Yellow (g) (G) (g) 5. Seed Coat Color ---Gray (G) or White (g) (A) (a) 6. Flower position ---Axial (A) or Terminal (a) (T) (t) 7. Plant Height --- Tall (T) or Short (t) (P) (p) 8. Flower color --- Purple (P) or white (p) He studied only one trait at a time to control variables, and he analyzed his data mathematically. Phenotype Genotype
Pollen contains sperm which is produced by the stamen Ovary (found inside the flower) contains eggs stamen pistol ovary Pollen carries sperm to the eggs for fertilization Self-fertilization can occur in the same flower Cross-fertilization can occur between flowers
Mendel cross- pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination He traced traits through the several generations
Mendel produced pure strains by allowing the plants to self- pollinate for several generations
Mendel’s first experiments are called monohybrid crosses because mono means “one” and the two parent plants differed from each other by a single trait like height
When recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. When recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. The dominant allele is always written first. The dominant allele is always written first. Tall plant TT T T Short plant tt t t
Mendel cross-pollinated a tall pea plant with pollen from a short pea plant TT t t Short pea plant Tall
All of their offspring were as tall or taller than the parent plants. TT t t TtTt TtTt Short pea plant Tall
These plants were allowed to self pollinate Tt T t Tall pea plant Tall
Three-fourths of the plants were as tall as the tall plants in the parent and first generations and One-fourth of the offspring were as short as the short plants in the parent generation. Tt T t T T T t tt Tall pea plant Tall
P1P1P1P1 Short pea plant Tall pea plant F1F1F1F1 All tall pea plants F2F2F2F2 3 tall: 1 short Parent generation (P1) Parent generation (P1) produced all tall pea plants. (F1) Short phenotype disappeared First generation (F1) First generation (F1) A cross of two offspring from P1 Produce F2 Second generation (F2) Second generation (F2) Short phenotype reappears
In every case, he found that one trait of a pair seemed to disappear in the F 1 generation, only to reappear unchanged in one-fourth of the F 2 plants. Mendel concluded that each organism has two factors that control each of its traits. We now know that these factors are genes and that they are located on chromosomes.
An organism’s two alleles are located on different copies of a chromosome—one inherited from the female parent and one from the male parent. Mendel called the observed trait dominant and the trait that disappeared recessive.
Mendel’s experiments helped him formulate the 2 laws of inheritance. 1. The law of segregation And 2.The law of independent assortment
States that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles. During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.
TALL SHORT Tt Tt Tt TtTT tt T T t t Female Parent Male Parent Male Gametes Female Gametes
MOM DAD Genotype: Uu Phenotype: two eyebrows YOU
States that genes (traits) for different traits—for example, seed shape and seed color—are inherited independently of each other. This law can be illustrated using dihybrid crosses.