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Summary Heredity, Inheritance, and Variation

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Summary of 5 pages for the course Science at Third year / 9th Grade (Unit I, Chapter II)

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Heredity – passing on of traits from parents to offspring.

Genetics – science that deals with the study of heredity

Human Genome Project | HGP (1990–2003) – They mapped out the sequence of genes,
which has helped develop many fields, including medicine and human evolution.

environment may influence the growth and development of an individual

Traits – The observable characteristics determined by genes.

Genes – A specific segment of a deoxyribonucleic acid
– A length of DNA that codes for a particular protein that is responsible for the uniqueness of
each individual and for the similarities shared among family members
-Stores the information

Deoxyribonucleic Acid | DNA – A double helix molecule composed of thin strands made up of
sugar and phosphate molecules arranged like a twisted ladder found inside a chromosome.
– They make up the chromosomes found inside the nucleus of a cell.

Chromosomes – They replicate before a cell divides to make sure that each daughter cell
contains a complete set of it.

Insulin – A hormone that controls the level of glucose in the blood.

sex cells or gametes undergo cell division to maintain the chromosome number of their
species.

Meiosis – The process by which sex cells divide and shuffle their genetic material. – It takes
place in the production of sperm and egg cells of animals, and in the anther and ovaries of
flowering plants.

Haploid | n – Sex cells that carry only half of the complete set of chromosomes. (add to itself to
get diploid)

Diploid | 2n – Cells that carry the complete set of chromosome

A human has 23 pairs of chromosomes – the first 22 pairs are body chromosomes or
autosomes, while the 23rd pair makes up the sex chromosome

An egg always carry an X
chromosome, while sperm cells carries both X or Y chromosome

, diploid carries 44 autosomes and the last two chromosomes are sex chromosomes.
It is said the Y chromosome is one factor that proves men live shorter than women. The Y
chromosome is smaller than the X chromosome.

crossing-over takes place and allows the exchange of a part of a chromosome with another
part from its homologous chromosome.

Chiasmata | Chiasma – The points where chromosomes cross over.

Segregation – This allows homologous chromosomes to separate so that they will have an
equal chance of being passed on to the next generation.

Alleles – Two or more variations of genes.

Genotype – An organism’s actual set of genes.

Phenotype – The expression or manifestation of an organism’s genotype.

Homozygous – When an individual’s inherited alleles for a trait are the same.

Heterozygous – When an individual’s inherited alleles for a trait are different.

Dominant Allele – It expresses itself and masks the effect of the other allele for the same trait.

Recessive Allele – It is the one that is masked by the presence of the other allele and will only
manifest if the organism is homozygous for that allele.

Polygenic Traits – Traits that arise from the interaction of multiple pairs of genes.

Polygenic Inheritance – The cumulative action of many different genes each with small
individual effects that determine the inheritance of a characteristic.

Mutation – A permanent change in DNA sequence that causes variation

Somatic Mutation – It occurs in any body cell except the reproductive cells. – It is not passed
on to the offspring and will cease to exist when the parent organism dies.

Germline Mutation | Germinal Mutation | Hereditary Mutation – It occurs in reproductive
cells and is transmitted to the offspring.
– It may be passed on from one generation to another

Mutagens – Agents of mutation.

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