Homozygotic genotype homozygote: homozygotic genotype homozygote

homozygotic genotype - homozygote:

• homozygotic genotype - homozygote:

• individual, that inherited from both the parents the same allele of the same gene (AA, aa, BB, bb)

• heterozygotic genotype - heterozygote

• Individual with two different alleles of the same gene ( Aa, Bb)

• Parental generation => P

• Direct descendants => first filial generation F1

• next generation => second filial generation F2,F3,..

hereditary features contained in autosomes

• hereditary features contained in autosomes

• without reference to gene binding

• by every diploid descendant allele pair consists of:

• 1) one father´s allele

• 2) one mother´s allele

• transfer of alleles on descendants is subject to basic rules of combinatorics

• the first solving this matter - Mendel

• => combinational (Mendelian) squares

• 3 Mendel´s laws

I. law about uniformity F1 (1st filial = first generation of descendants)

• I. law about uniformity F1 (1st filial = first generation of descendants)

• by reciprocal crossing of 2 homozygotes originate descendants genotypically and phenotypical uniform

• If there are 2 different homozygotes descendants are always heterozygotic hybrids

II. Law about coincidential gene segregation into gametes

• II. Law about coincidential gene segregation into gametes

• by the crossing of 2 heterozygotes can each of two alleles (dominant and i recessive) be given to the descendant with the same probability

• so it comes to genotypic and also phenotypic splitting = segregation

Probability for the descendant is :

• Probability for the descendant is :

• 25% (homozygotic dominant individual) : 50% (heterozygote) : 25% (homozygotic recessive individual)

• genotype splitting relation 1:2:1.

• phenotype splitting relation 3:1

• If there is a codominance relation between alleles, phenotypic splitting relation corresponds with genotypic splitting relation (1:2:1).

III. Law about independent combinability of alleles

• III. Law about independent combinability of alleles

• by observation of 2 alleles simultaneously there happens the same regular segregation 2 dihybrids AaBb can each of them form 4 different gametes (AB, Ab, aB, ab)

• by the reciprocal crossing of these 2 gametes are formed 16 various zygotic combinations

• 9 various genotypes (relation 1:2:1:2:4:2:1:2:1)

• phenotype splitting relation je 9:3:3:1.

• the law is in force if :

• observed genes occur on different chromosomes

• gene binding is so weak that it cannot prevent their free combinability

Complete dominance and recessivity

• Complete dominance and recessivity

• in heterozygotic genotype occurs only a dominant allele
• Recessive does not occur
• allele A determines red colour of the flower
• allele a determines white colour
• individual with genotype Aa will be red

incomplete dominance and recessivity

• incomplete dominance and recessivity

• both alleles take part in the formation of a feature, usually in unequal degree

• individual with heterozygotic genotype differs from both homozygotes
• A special case– intermediarity (both proves in the same degree)
• allele A determinates red colour of the flower, allele a white, individual with genotype Aa will be pink

codominance

• codominance

• in heterozygotic genotype occur both alleles next to each other
• they do not suppress each other
• e.g. blood groups of the system AB0

  Example 1.

•   Example 1.

• The gene for the formation of black colour in cattle is dominant over the gene for red color (they are two different alleles of the same gene).

• What posterity (F 1) will be obtained after crossing purebred, i.e. homozygous black bull with red cow?

• What will be the composition of the posterity of hybrids obtained by crossing each other (in F 2)?

• And what calves will be obtained by crossing with red bull F1 hybrid cows from?

For tomatoes, the gene responsible for the red colour of the fruit is dominant over the gene for yellow colour (they are two different alleles of the same gene).

• For tomatoes, the gene responsible for the red colour of the fruit is dominant over the gene for yellow colour (they are two different alleles of the same gene).

• What colour will the fruits of plants obtain by crossing homozygous red-fruit with homozygous yellow-fruit plants?

• What plants will bear fruit in the F 2?

• Specify the posterity obtained by crossing plants of red-fruit plants of F 2 with a hybrid plant of F1? Will be composition of posterity of such crosses always equal, or will it be different by some red-fruit plants of F2?

• What colour will have plants in the posterity of the reciprocal crossing of yellow-fruit plants between each other?

A blue-eyed man, whose parents both have brown eyes, married a girl who has brown eyes and whose father was blue-eyed, while his mother was brown-eyed.

• A blue-eyed man, whose parents both have brown eyes, married a girl who has brown eyes and whose father was blue-eyed, while his mother was brown-eyed.

• Their only child so far has brown eyes.

• What are the genotypes of the child, the parents and all the grandparents, if you know that brown eye colour is dominant over blue?

KUBIŠTA, Václav. Obecná biologie: úvodní učební text biologie pro 1. ročník gymnázií. 3. upr. vyd. Praha: Fortuna, c2000, 103 s. ISBN 80-716-8714-6.

• KUBIŠTA, Václav. Obecná biologie: úvodní učební text biologie pro 1. ročník gymnázií. 3. upr. vyd. Praha: Fortuna, c2000, 103 s. ISBN 80-716-8714-6.