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Understanding Genetics: Traits, Alleles, and Their Role in Inheritance

This concise introduction to genetics covers the essential concepts of traits, chromosomes, and heredity. Traits are inherited characteristics, such as eye color, passed down from parents through genes located on chromosomes. With 23 pairs of chromosomes in each human cell, genes code for specific proteins that determine traits. The difference between dominant and recessive alleles is explained, along with genotypes and phenotypes, which illustrate how genetic information is expressed. Additionally, karyotypes are discussed, highlighting their role in identifying chromosomal abnormalities.

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Understanding Genetics: Traits, Alleles, and Their Role in Inheritance

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Presentation Transcript

  1. INTRODUCTION TO GENETICS Ms. Wassum

  2. Traits • Traits are the different forms of a characteristic that you may exhibit • Ex: Blue or Brown Eyes • Traits are inherited from our parents • Therefore, when we talk about genetics, we are talking about sexual reproduction

  3. Chromosomes • Every cell in a human body has 23 pairs of chromosomes – half from our mother, half from our father • Genes are found on chromosomes • We have about 20,000-25,000 genes • Each gene holds a code that tells our body to make a certain protein • The protein that is made determines a Specific trait. Ex: Blue eye pigment or Brown eye pigment

  4. Alleles • The different forms of a gene that can exist • Ex: Curly hair gene or straight hair gene • Dominant – ‘Strongest Allele’ – If it is present, you will have that trait. We use upper case letters for dominant alleles • Recessive – ‘Weakest Allele’ – This won’t show up unless there are two of them. We use lower case letters for recessive alleles

  5. Genotype • The actual alleles you have for a trait • Ex: For eye color, you inherit B from dad and b from Mom • Your genotype is Bb • If there is a dominant allele, the genotype is written with the upper case first. (Never write bB) • Your genotype is the genesyou have

  6. Genotype (Cont’d) • If you have two copies of the same allele for a trait (BB or bb), then you are HOMOZYGOUS for that trait • If you have two different alleles for a trait (Bb), then you are HETEROZYGOUS for that trait

  7. Phenotype • How the genes actually show up, or how they are expressed • So, if your genotype is Bb, • Where B is brown • And b is blue • The phenotype would be Brown eyes • Phenotype is the physical appearance

  8. Karyotype-Normal A picture of the chromosomes found in an individual. Used to determine abnormalities.

  9. Karyotype - Abnormal There are three copies of chromosome 21 – there should only be two copies. This is a karyotpe of a female with Down’s Syndrome.

  10. Quiz Time • You inherit the gene for freckles (F) from dad, and the gene for no freckles (f) from mom 1. What would your genotype be? • Ff 2. What would your phenotype be? • You would have freckles • Which allele is dominant? • F (freckles)

  11. Quiz Time • You inherit the gene for no allergies (a) from dad, and the gene for allergies (A) from mom 1. What would your genotype be? • Aa 2. What would your phenotype be? • You would have allergies • Which allele is dominant? • A (allergies)

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