Heredity notes

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General information

We have 46 chromosomes - 22 pairs of homologous chromosomes. *22 are maternal and 22 are paternal. 2 pairs of sex chromosomes.

Meiosis: is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information.

Asexual reproduction:

Mitosis - 2 identical daughter cells (diploids "2n") -- 46 chromosomes, 22 pairs of autosomes and 2 sex of chromosomes

Sexual reproduction:

Parent - offspring - Fertilization - Meosis - 4 different haploid cells ("n") - 23 chromosomes

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Blended inheritance

Genetics is fluid and we are a mix of our parents.

It doesn’t make sense.

The variability is reduced, because if we follow what this theory says at the end we will be really similar, which is not correct.

Blended inheritance:

1. It didn't always happen.

2. It goes against the increase variability

Mendelian traits

Genes are discrete units

Rules of Mendel:

1. Dominance:

Dd= heterozygote

phenotype = dominant

2. Segregation:

Each diploid organism by the process of meiosis separates in two haploids. The with fertilization a new diploid is created.

3. independent assortment:

each trait is inherited separately.

linkage group: all genes on one chromosome.

sometimes exception.

sometimes the two traits are near the nucleus, so

if I take two dominant traits

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Mendel's Laws

1. Law of segregation: each parent give offspring 1 copy of each gene. Each offspring has then 2 copies of each gene.

2. Law of dominance: in the presence of a dominant allele, the recessive allele will not appear in phenotype.

Monohybrid crosses: they cross and create the probability of a offspring to receive an specific trait. They just cross 1 trait.

The Law of Segregation establishes how pairs of gene variants are separated into

reproductive cells. Mendel crossed two heterozygous pea plants, this means that

each plant had two different alleles at a particular genetic site. He discovered that

the pair of alleles encoding the traits in each parental plant had segregated from one

another during the reproductive cells, additionally he found that the traits in the

offspring in the crosses did not always match the traits in the parental plants.

Consequently, Mendel established the Law of Segregation formulating that each

individual has a pair of alleles passed by their parents, for a particular trait.

3. Law of dependent assortment: each trait (gene) is independently inherited.

After Mendel established the Law of Segregation, he discovered and consequently

created the Law of Independent Assortment where after performing dihybrid crosses

in plants that had two traits, for example seed color and pod color, which differed

from one another, this allowed Mendel to conclude that the traits were transmitted to

offspring independently. In conclusion, Mendel formulated that the allele gamete

receives one gene and this does not influence the allele received for another gene.

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Example #1

h/. h/.

H/ Hh Hh

h/ hh. hh.

genotype of offspring:

- 50% homozygous recessive

- 50% heterozygous

phenotype:

-50% white

-50 black

Hh x Hh

h/. h/.

H/ HH. Hh

h/ Hh. hh.

3 :1 phenotype

1:2:1 genotype

E black

e red

HhEe x HhEe

HE He hE he

HE HHEE. HHEe. HhEE. HhEe

He HHEe HHee HhEe Hhee

hE. HhEE HhEe hhEE hhEe

he HhEe. Hhee. hhEe. hhee

9:3:3:1

197/ 19 : 19/19 : 27/ 19 : 85/19

15 : 1 : 1,4 : 4,5

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Vocabulary

inheritance: the reception of genetic qualities or traits from past generations (parents), due to offspring.

allele: version of a gene (base pair substitution)

gene: segment DNA that codes for a trait.

dominant: a trait that is always present in phenotype (G).

recessive: a trait that can be masked or hidden (g).

homozygous: both alleles are dominant or recessive (they are the same) *Purebreed*

heterozygous: each allele is different (one dominant/recessive) *Hybrid*

homolugous pairs: pair of chromosomes that contain the same genes (femenine or masculine)

homozygous recessive: gg

heterozygous: Gg