Homologous chromosomes are composed of one chromosome from the mother and the other one from the father. Each metaphase chromosome has two identical sister chromatids. Below you will find different examples.
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Since I do not have the genotypes for each parent, I will propose different genotypes and draw the chromosomes.
You can follow the same reasoning to draw the chromosomes using the genotypes from task 1.
Remember that the chromosome is condensed chromatin associated with histones proteins.
We are going to draw metaphase chromosomes, which are composed of two sister chromatids.
The chromosome is composed of
- Arms ⇒ long arms and short arms
- Centromere ⇒ primary constriction
- Kinetochore ⇒ area of the centromere where spindle fibers join
- Sister chromatids ⇒ identical chains carrying information of one parent
- Genes ⇒ in each chromosome in their different alternative forms ⇒ Alleles
Homologous chromosomes compose a pair of chromosomes, each coming from a different parent - one from the mother and one from the father-. They carry information for the same traits.
Possible genotypes for an individual
ONE GENE
H0m0zyg0us dominant AA
- After replication, each sister chromatid has an A allele.
- Each homologous chromosome has an A allele because both of them carry information for the same trait, and both of them carry the same dominant allele.
H0m0zyg0us recessive aa
- After replication, each sister chromatid has an a allele.
- Each homologous chromosome has an aA allele because both of them carry information for the same trait, and both of them carry the same recessive allele
Heter0zyg0us Aa
- One chromosome of the homologous pair has a dominant allele and the other one a recessive allele ⇒ the dominant allele comes from one parent and the recessive allele comes from the other parent.
- After replication, both sister chromatids have an identical allele. One of the chromosomes has two chromatids with the dominant allele and the other chromosome has chromatids with the recessive allele.
- Homologous chromosomes carry information for the same trait but in different states of the gene.
TWO GENES
⇒ AABB
- After replication, each chromatid sister will have A and B alleles.
- Homologous chromosomes will be equal.
⇒ aabb
- After replication, each chromatid sister will have recessive alleles.
- Homologous chromosomes will be equal.
⇒ AAbb or aaBB
- Each homologous chromosome has A and b alleles, or a and B alleles.
⇒ AaBb
- There are two options for homologous chromosomes. One of them might carry both dominant alleles, and the other one both recessive alleles. Or each chromosome might carry one dominant allele and one recessive allele.
- Chromatid sisters will be identical.
⇒ AABb
- The two homologous chromosomes will have the A dominant allele
- One homologous chromosomes will have the B allele, and the other homologous chromosome will have the recessive b allele.
- Chromatid sisters will be identical.
⇒ AaBB
- The two homologous chromosomes will have the B dominant allele
- One homologous chromosome will have the A allele, and the other homologous chromosome will have the recessive a allele.
- Chromatid sisters will be identical.
Following this same combination reasoning, you can add as many genes as you want to each chromosome.
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You can learn more about homologous chromosomes at
https://brainly.com/question/24874991?referrer=searchResults
https://brainly.com/question/7904813?referrer=searchResults
