INHERITANCE

Inheritance

Where ADN and genetics become real!

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What is it?

ALLELES

What was the puzzle he solved?

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Intro video

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GENES

How did they find out?

And his secret?

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His experiments!

Now let´s understand it better

Dominant and Recessive Alleles

• There are two alleles for a given gene characteristic (such as flower color)

Let P stand for the purple flower alleleLet p stand for the white flower allele

• Every cell in a pea plant carries two alleles per characteristic (either the same or different)

• The particular combination of the two alleles carried by an individual is called the genotype (PP, Pp, or pp)
• The physical expression of the genotype is known as the phenotype (e.g. purple or white flowers).
• In this example case, The phenotype of the homozygous genotype PP is purple flowers
• The phenotype of the homozygous genotype pp is white flowers.

Dominant and Recessive Alleles

• The phenotype of Pp is purple flowers.
• The P allele masks the presence of the p allele
• P is the dominant allele while p is recessive
• The dominant allele is always written with a capital letter while the recessive allele is written in lower case

What is the phenotype of genotype Pp?

Mendel’s Law of Segregation

The two alleles for a characteristic separate during gamete formation (meiosis).

Let´s look the experiment deeper

Let´s look the experiment deeper

Let´s look the experiment deeper

What happened?

The F1 offspring were all heterozygous (Pp) for flower color When the F1 offspring were allowed to self-fertilize, four types of gametes were produced from the Pp parents Sperm: P p Eggs: P p

What happened?

Combining these four gametes into genotypes in every possible way produces offspring PP, Pp, Pp, and pp Can also be tabulated by the genotypic fraction of total offspring: ¼ PP, ½ Pp, and ¼ pp.

Punnett Squares

Punnett Square Method predicts offspring genotypes from combinations of parental gametes

How to solve them

1. First assign letters to the different alleles of the characteristic under consideration (uppercase for dominant, lowercase for recessive) 2. Determine the gametes and their fractional proportions (out of all the gametes) from both parents… 3. Write the gametes from each parent, together with their fractional proportions, along each side of a 2 x 2 grid (Punnett square) 4. Fill in the genotypes of each pair of combined gametes in the grid, including the product of the fractions of each gamete (e.g. ¼ P with ½ p = 1/8 Pp)… 5. Add together the fractions of any genotypes of the same kind (1/4 Pp + ¼ pP = ½ Pp total) 6.From the sums of all the different kinds of offspring genotypes, create a genotypic ratio 1/4 PP, ½ Pp, ¼ pp is in the ratio 1PP: 2Pp: 1pp 7. Based on dominant and recessive rules, determine the phenotypic ratio A genotypic ratio of 1PP: 2Pp: 1pp yields 3 purple flower plants: 1 white flower plant

Ratios?

And then?

Traits Are Inherited Independently

Mendel performed genetic crosses in which he followed the inheritance of two traits at the same time. Let´s have a look.

Traits Are Inherited Independently

Traits Are Inherited Independently

Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were the characteristics studied. The allele symbols were assigned: Y = yellow (dominant), y = green (recessive) S = smooth (dominant), s = wrinkled (recessive)

Traits Are Inherited Independently

Two trait cross was between two true breeding varieties for each characteristic P: SSYY x ssyy

Mendel’s Law of Independent Assortment

Genes of pea color and pea shape (S, s and Y, y) separate independently during meiosis. Possible gametes of parent SSYY are SY, SY, SY, and SY (each S can combine with each Y) Possible gametes of parent ssyy are sy, sy, sy, and sy (each s and combine with each y)

Traits Are Inherited Independently

Punnett Square from SSYY x ssyy cross

Gametes

sy

sy

sy

sy

1/4

1/4

1/4

1/4

1/16

1/16

1/16

1/16

SY

1/4

1/16

1/16

1/16

1/16

SY

1/4

1/16

1/16

SY

1/16

1/16

1/4

1/16

1/16

1/16

SY

1/16

1/4

Traits Are Inherited Independently

Punnett Square from SSYY x ssyy cross

Mendel’s Law of Independent Assortment

Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy Gametes are ¼SY, ¼Sy, ¼sY, ¼sy from each parent

Traits Are Inherited Independently

Punnett Square from SsYy x SsYy cross

Gametes

1/4

1/4

1/4

1/4

1/4

1/4

1/4

1/4

DIHYBRID CROSS