Psychology Study Material: Genes May be Dominant or Recessive

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Genes May be Dominant or Recessive

  • A dominant gene means that its characteristics will dominate those of the recessive one e. g. if father has brown eyes and mother has black eyes, and if the father՚s genes dominate then the baby will have brown eyes.
  • Each zygote՚s 46 chromosomes contain about 30,000 segments strung along its beads i.e.. , “genes”
  • Genes, made up of Deoxyribonucleic Acid (DNA,) determine all our heredity.

Prenatal Stages

EMBRYO: A developed zygote with a heart, a brain and other organs.

Prenatal Stages

Fetus: A developing child; 9 weeks after conception till birth.

Determination of the Sex of the Embryo

  • A combination of chromosomes from the parents determines sex.
  • An XX pair means a female will be born An XY pair means a male will be born.
  • The mother՚s sex chromosome is always and ‘X’ , but the father may be either ‘X’ or ‘Y’ . If X chromosome is being contributed by the father՚s side, then the new being has to be a female; and if the father is contributing a ‘Y’ chromosome then the new being is going to be a male

Genotype and Phenotype

  • Genotype: genetic composition of a person.
  • Phenotype: observable characteristics.
  • The characteristics that can be observed and seen, make up our “phenotype” . They may not always be the same e. g. person may have brown eyes (phenotype) but carry genes for both brown and blue eyes (genotype) ________ dominant gene is brown


This difference in colour is due to the fact that genes come in alternative forms called “Alleles” (alternative forms of a gene) . When alleles are identical, a person is homozygous for a trait; when alleles are dissimilar the person is heterozygous

Patterns of Transmission of Characteristics

Homozygous and Heterozygous

  • When the person inherits identical alleles, he is said to be “homozygous” (possessing two identical alleles for a trait) . When he inherits two different alleles then the person is “heterozygous” (possessing two different alleles for a trait) .
  • Example: when a person is homozygous for brown eyes then he will transmit only genes for brown eyes to his offspring and if heterozygous for blue and brown eyes then although dominant one is brown, but he will transfer his both alleles to his offspring.

Autosomal Dominant Inheritance

Patterns of inheritance in which a specific gene is dominant; if it is inherited; it manifests itself in the person.

Autosomal Recessive Inheritance

Patterns of inheritance in which trait appears only if a person inherits two genes for it, one from each parent. If the person inherits only one gene for a trait, it will not appear in a person but may be passed on to his children.

Multi- Factorial Inheritance

  • Patterns of inheritance in which a trait is expressed either by a combination of several genes or through the interaction of genes with environmental factors.
  • More complicated combination of genes or an interaction between genetic predispositions and environmental factors that bring them out.
  • Some characteristics follows one of these patterns, other genes another.
  • Hair type (curly or straight) is either autosomal dominant or autosomal recessive, baldness is sex-linked; height and weight are probably multi- factorial.

Some diseases and birth defect are inherited according to these patterns. Most prominent examples are:

  • Achondroplasia: a kind of dwarfism that is inherited by autosomal dominance.
  • Tay- Sachs disease: body՚s inability to break down fat; results into death by 3 - 4 years of age
  • Huntington՚s disease: 99.9 % correlation between having the identified gene and the disease.
  • The blood- clotting disorder haemophilia is a sex- linked condition.
  • Spina bifida: a defect in the closure of the vertebral canal, that is believed to be the condition transmitted by sex- linked inheritance

The Process of Development Continues Throughout the Life Span

While considering aspects of development, individuality and interactions are the key terms in understanding it. All beings bring their unique genetic package into this world and have unique sets of experiences too. An individual՚s strengths, abilities, and predispositions are affected by the influence of environment. These influences make a person act in ways that elicit new experiences.