Heredity

by Evangeline Narciso

 Heredity: Inheritance and Variation of Traits​

​Many times you may have heard other people tell you that you have your mother’s eyes or your father’s height. You know that these are characteristics you inherited from your parents. What, then, is actually inherited? How are these traits inherited? Do they follow a certain unique pattern?

​Inheritance is the process by which genetic information is passed on from parent to child. This is why members of the same family tend to have similar characteristics. 

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Heredity refers to the passing of genetic factors from parents to offspring or from one generation to the next.

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Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.

Open Ended

Make a list that people tell you that you inherit to your parents.

Multiple Choice

Heredity is the passing of traits  from _____ to _______.

• predators to prey

• water to rain

• fungi to protists

• parents to offsprings

Multiple Choice

______ is the study of how traits are passed on, or inherited.

• dominant traits

• phenotype

• ratio

• genetics

Multiple Choice

The traits of an organism are passed to its offspring on small coded strands of DNA material called?

• genes.

• recessive traits.

• meiosis

• heredity

Multiple Choice

One trait that is ALWAYS present and causes the other traits to disappear is a ________________________

• recessive trait

• absent trait

• aggressive trait

• dominant trait

Multiple Choice

During sexual reproduction, each parent contributes...

• a double helix of chromosomes.

• one strand of chromosomes, or half of the new organism's DNA

• a dominant gene and a recessive gene.

• multiple mutated cells.

Multiple Choice

A ________________________ is used to predict the possible genotype from certain parents.

• Mendel Grid

• Punnett Square

• Genetic Tic Tac Toe

• Pedigree Plot

Multiple Choice

______________________ is the mathematical chance that something will happen

• division

• ratio

• probability

• selective breeding

​Invention of microscope lead to discovery of chromosomes.

​What is the link between chromosomes and genetics?

​The human body is made up of trillion of cells. Found tightly packed in the nucleus of eukaryotic cells are the chromosomes. Chromosomes are carriers of genes, the unit determiners of hereditary characteristics. The genes in turn are made up of DNA molecules. The chromosomes number varies depending on the species.

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​Eukaryote, any cell or organism that possesses a clearly defined nucleus. The eukaryotic cell has a nuclear membrane that surrounds the nucleus, in which the well-defined chromosomes (bodies containing the hereditary material) are located.

selective breeding

​The number of chromosomes is crucial to the survival of the organisms. Any increase or decrease in the number of chromosomes of any species of organism can cause mutation or in viability that can lead to the death of the organisms.

​Karyotype is the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

​Each chromosome is made up of two long strands of DNA molecule, the blueprint of life or the genetic plan of the organism. The entire DNA in the body cells makes up what is called the human genome. The set of chromosomes that compose a particular species of organism though basically are similar in appearance and slightly differ in size and shape.

​At one point along the chromosome’s length is a constriction, called the centromere. The centromere divides the chromosomes into two arms: a long arm region ( also called q arm ) and a short arm (also called p arm region). Take note that the 22 pairs of chromosomes also vary in the position of the centromere and that the centromere of the pair of chromosomes is in the same position.

​Humans have 46 or 23 pairs of chromosomes. The mother contributes 23 chromosomes through the egg cell and the father contributes the other 23 chromosomes through the sperm cell. In all eukaryotes, chromosomes come in pairs and because the chromosomes come in pairs, the genes they contain also come in pairs. Take note that from among the 46 chromosomes, 22 pairs have almost the same size and shape and they have the same genes on them (Refer to Figure 1). Chromosomes that have the same size and shape and have the same genes on them are called homologous chromosomes.

Diagram of homologous chromosomes​

​When the chromosomes are stained, they show distinctive patterns of Light and dark  bands which enable geneticists to distinguish different chromosomes and pair them up based on the banding pattern. The pair of chromosomes also exhibits similar banding patterns.

​ The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes. 

​Sex Chromosome & Gender Determination

​Humans have 22 pairs of autosomes, which are the same in both male and female. The last two chromosomes were given letter designations X and Y. They are the sex chromosomes. Sex chromosomes determine the gender of the organism. The X and Y chromosomes differ in size and shape. The Y chromosomes contains the genes that trigger the development of specific male characteristics. Females have two identical sex chromosomes designated as XX and males have two non-identical sex chromosomes designated as X and Y chromosomes. Thus, all of the human female eggs in the ovaries contain X chromosomes (homogametic); while in male humans 50% of the sperm in the testes carry the X chromosome and other 50% carry the Y chromosome.

Open Ended

What will happen if an organism inherits a structurally altered or missing one or more chromosomes or extra copy of chromosomes?

​NON-MENDELIAN GENETICS

​Incomplete Dominance:

There are two alleles for a gene, but neither is dominant or recessive. When both alleles are present (the heterozygous condition), the phenotype is a blend of the two alleles. This is seen in flower color in snapdragons. In these plants, one homozygous genotype produces red flowers, the other homozygous genotype produces white flowers, but the heterozygous genotype produces pink flowers.

​INCOMPLETE Dominance

Neither the ​red trait ( R allele) nor the white trait ( r allele) is completely dominant in a heterozygous (Rr) individual. Having only one R allele in heterozygotes produces only enough pigment to make the plant's flowers pink, not enough to make them red.

​Co-dominance 

In some cases, the heterozygous characteristics are both fully expressed in the F1 offspring in a phenomenon called codominance as in coat color in cattle. Both red and white coat color are dominant. When a homozygous red-coat colored cow (RR) is crossed with a homozygous white coat colored cow (WW), the F1 offspring are all heterozygous, roan coat(fur) colored cattle (RW). A roan coat color  is one in which the coat color is the mixture of the red and white coat color.

​Codominance

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​Codominance

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​Sex Linked Traits

     Sex-linked traits are traits that are controlled by the genes found in the sex chromosomes (both X and Y). Sex-linked traits are recessive. In most cases, the recessive gene or allele was inherited from one or both of the parents. Sex-linked traits affects mostly male offspring. This is because they have only one X chromosome, which they inherit from their mother. If the X chromosome carries a genetic disorder, such disorder will be expressed in them. In contrast, the two X chromosomes of the female offspring should both carry the disorder before it can be expressed. Examples of sex-linked traits carried by the genes in the X chromosome are color blindness and Hemophilia (also called bleeder’s disease).