Gregor Mendel’s Peas

Gregor Mendel’s Peas • Gregor Mendel’s Peas • Genetics is the scientific study of heredity. • Gregor Mendel was an Austrian monk. • Mendel studied garden peas

Gregor Mendel’s Peas • Mendel knew that • the male part of each flower produces pollen, (containing sperm). • the female part of the flower produces egg cells. • Together they make a new plant

Gregor Mendel’s Peas • Pea flowers are self-pollinating. (Pollen can fertilize the flower it was made on) • Self-pollination results in the offspring getting all its DNA from 1 organism.

Gregor Mendel’s Peas • Mendel used True-Breeding Pea plants • Plants that were homozygous for a trait • To prevent Self pollination- Mendel removed either the male or the female parts from each flower.

Gregor Mendel’s Peas • Mendel took a brush and cross-pollinated the flowers by hand! • Mendel was able to produce seeds that had two different parents.

Genes and Dominance • Genes and Dominance • A trait is a specific characteristic that varies from one individual to another.

Genes and Dominance • Each original pair of plants is the P (parental) generation. • The offspring are called the F1, or “first filial,” generation. • The offspring of crosses between parents with different traits are called hybrids. • The F1 hybrid plants all had the character of only one of the parents.

Genes and Dominance • Genes and Dominance • Mendel studied seven pea plant traits, each with two contrasting characters. • He crossed plants with each of the seven contrasting characters and studied their offspring.

Genes and Dominance Mendel’s F1 Crosses on Pea Plants

Genes and Dominance Mendel’s Seven F1 Crosses on Pea Plants Mendel’s F1 Crosses on Pea Plants

Genes and Dominance • Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. • We call these factors GENES

Genes and Dominance • Mendel luckily chose traits controlled by a single gene with different forms. • The different forms of a gene are called alleles(ah-le-eels).

GENOTYPE vs PHENOTYPE • GENOTYPE – are the actual DNA coded genes or instructions that make you. • PHENOTYPE – The express or what the genotype looks like in the physical world. For short – What you look like.

Genes and Dominance • The principle of dominance states that some alleles are dominant and others are recessive.

Genes and Dominance • Dominant alleles – Only need one for this form to show in the phenotype Possible Genotype – (DD or Dr) • Recessive – Need two alleles for this one to show in the phenotype Possible Genotype– (rr)

Segregation • Segregation • Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation. • The traits controlled by recessive alleles reappeared in one fourth of the F2 plants.

Segregation • The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated, from the allele for tallness.

Segregation • During the formation of GAMETES (sex cells) – Alleles are separated (segregated) into different resulting daughter cells.

Segregation • Alleles separate during gamete formation.

Using a Punnett Square

What is a PUNNETT SQUARE? • A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine • A way to show phenotype & genotype • A chart that shows all the possible combinations of alleles that can result when genes are crossed

What is a PUNNETT SQUARE? • Letters stand for dominant and recessive alleles • An uppercase letter stands for a dominant allele • Lowercase letters stand for recessive alleles

Using a PUNNETT SQUARE To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

Using a PUNNETT SQUARE Now you need two parents to mate, ones with a known genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

Using a PUNNETT SQUARE Place one of the parents on top, and one on the left. You should get a something similar to this:

Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

Using a PUNNETT SQUARE • The two-letter combinations are the possible genotypes of offspring • They are: Rr, Rr, rr, and rr genotypes • From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)

Gregor Mendel’s Peas