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Heredity The passing of traits from parent to offspring. Genetics The study of heredity Gregor Mendel is known as the “Father of Genetics”. In 1866 – Gregor Mendel, an Austrian monk, published his findings about the inheritance in garden pea plants. .
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GeneticsThe study of heredityGregor Mendel is known as the “Father of Genetics”
In 1866 – Gregor Mendel, an Austrian monk, published his findings about the inheritance in garden pea plants.
Mendel noticed that certain types of garden pea plants produced specific forms of a trait, generation after generation. He noticed some plants always produced green seeds and others always produced yellow seeds. He called these “true-breeding”.
Mendel performed cross pollination by transferring the male gametes from the flower of a yellow-seed plant to the female organ of a green-seed plant. Mendel called the green-seed plant and yellow seed plant the Parent Generation (P generation). X Parent Generation: Yellow Peas (male) Green Peas (female)
When Mendel grew the seeds from the cross between the green-seed and yellow-seed plants all of the offspring had yellow seeds. The offspring of the P generation were called the first filial generation (F1 generation)
Parent Generation: X Yellow Peas (male) Green Peas (female) F1 Generation: All Yellow Peas
Mendel wanted to know whether the trait was no longer present, or whether it was hidden or masked. He planted the F1 generation of yellow-seeds and allowed them to grow and self-fertilize, then examined the seeds from that cross.
The offspring from the F1 generation were called the second filial generation (F2 generation). The F2 generation had 6022 yellow seeds and 2001 green seeds, which is almost a perfect 3:1 ratio.
P Generation: X Yellow Peas (male) Green Peas (female) F1 Generation: All Yellow Peas SELF FERTILIZATION F2 Generation: 6022 Yellow Peas 2001 Green Peas 3:1 Ratio
Mendel concluded that there must be 2 forms of the seed trait in the pea plants – yellow seed and green seed – and that each was controlled by a factor, which we now call an allele.
AlleleAn alternative form of a single gene passed from generation to generation ex. The gene for yellow seeds and the gene for green seeds are just different forms of a single gene.
Mendel said the 3:1 ratio he saw in his pea plant experiments could be explained if the alleles were paired in each of the plants. Mendel called the form of the trait he saw in the F1 generation dominant(yellow) and the form of the trait that was masked in the F1 generation recessive (green).
DominantTrait that appears in the F1 generation, and masks or hides the expression of the recessive geneIndicated by a capital letter.
RecessiveTrait that is masked in the F1 generation by the dominant trait. Indicated by a lowercase letter.
In Mendel’s experiment the yellow-seed form of the trait is dominant, so it is represented by a capital Y. The green-seed form was recessive, so it is represented by a lowercase y.
If an organism has two of the same alleles for a trait it is homozygous. Ex. Homozygous yellow seeds are YY. Homozygous green seeds are yy.
HomozygousAn organism with two of the SAME alleles for a specific trait. YY or yy
An organism can have two different alleles for a trait, and when this happens they are heterozygous. Ex: Yy The dominant trait observed in heterozygous organisms, which means it will be yellow in this case.
HeterozygousAn organism with two DIFFERENT alleles for a specific trait. Yy
Were the yellow plants in the F1 generation of Mendel’s experiments homozygous or heterozygous?The yellow plants could have been homozygous OR heterozygous. The outward appearance of an organism does not always indicate which pair of alleles is present.
GenotypeThe genetic make-up of the alleles. Ex. YY or yy or Yy in Mendel’s plants
PhenotypeThe physical appearance or expression of an allele. Ex. The phenotype of plants with the genotype yy will be green plants.
Mendel used homozygous yellow seed and homozygous green seed plants in his P generation. Each gamete from the yellow plant contains one Y. Each gamete from the green plant contains one y.
Mendel’s Law of Segregation says that two alleles for each trait separate during Meiosis, and during fertilization two alleles for that trait unite.
HybridAn organism that is heterozygous for a specific trait. Ex. The F1 generation in Mendel’s experiments were hybrids. (Yy)
When Mendel allowed the Yy plants (F1 generation) to self-fertilize he performed a monohybrid cross.
Monohybrid CrossA cross that involves hybrids for a single trait. Results: Genotypic Ratio – 1:2:1Phenotypic Ratio – 3:1
Punnett SquareA visual summary of the possible alleles for any given trait. Shows all the possible combinations of genetic traits that results from the crossing of the parent organims.
Once Mendel knew how a single trait was inherited using a monohybrid cross he could look at two or more traits in the same plant.
In Garden Pea Plants round seeds (R) are dominant to wrinkled seeds (r), and yellow seeds (Y) are dominant to green seeds (y).
If Mendel crossed homozygous yellow, round seed pea plants with homozygous green, wrinkled pea plants the cross would result in all YyRr, yellow, round pea plants (F1 generation).The F1 generation are called DIHYBRIDS because they are heterozygous for both traits. You can cross dihybrids using a dihybrid cross.
Dihybrid CrossA cross that involves two dihybrids. Results in a phenotypic ratio of 9:3:3:1.
From Mendel’s dihybrid cross he came up with the Law of Independent Assortment.
Law of Independent AssortmentAlleles randomly distribute during gamete formation. Genes on separate chromosomes sort independently during meiosis.
The law of independent assortment says that any four of these combinations are equally likely.
Genetic RecombinationThe new combination of genes produced by crossing over and independent assortment.
To calculate the possible combinations of genes due to independent assortment you use the formula 2n. n = the number of chromosomesThe possible # of combinations after fertilization for humans would be: 223 X 223 = over 70 trillion
Genes that are close to each other on the same chromosome are said to be “linked”. They usually travel together during gamete formation.
Gene LinkageGenes located close to one another on the same chromosome that usually travel together and do not segregate independently. Linked genes are an exception to Mendel’s Law of Independent Assortment.
Most species have diploid cells (2n), but some have polyploidy cells.
PolyploidyThe occurrence of 1 or more extra sets of all chromosomes in an organismEx. Sugar Cane (8n)Oats (6n)Strawberries (8n)
If an organism has a heterozygous genotype the phenotype will be the DOMINANT trait. BUT…. There’s an exception to that….