Chromosomes

• Locus


  A specific point on a chromosome where a particular gene or DNA sequence is located
• The centrioles are responsible for the formation of spindle fibres during cell division.
• Chromosomes contain millions of genes that are located in specific areas
• An allele


  An alternative form of the same gene.
• Dominant allele refers to an allele that overrides another allele.
• Number of alleles in a gene

  A gene has 2 alleles, which can be identical (homozygous) or two different (heterozygous)
• Heterozygous refers to having different alleles at one locus.
• Homozygous refers to having two identical alleles at one locus.
• Recessive allele refers to an allele that only shows its effect when it is paired with another recessive allele.
• Recessive traits can only be expressed when two recessive alleles are present.
• Homozygous Dominant


  A genotype with two copies of the same dominant allele e.g BB
• Homozygous Recessive 


  A genotype with two copies of the same recessive allele e.g bb
• Heterozygous 


  A genotype with two different alleles (one recessive, one dominant) e.g Bb
• In heterozygous genotypes, the dominant allele overpowers and masks the recessive allele meaning the dominant allele’s trait is shown.
• Brown eyes (AA, Aa) are dominant to blue eyes (bb)

  
• Phenotype refers to an organism's observable characteristics or traits, while genotype refers to its genetic makeup.
• The Punnett square shows all possible combinations of genes from both parents.
• Genotype


  The complete set of genes an individual inherits from their parents
• Phenotype


  The physical and behavioral characteristics of an individual, determined by both genotype and environmental factors
• Number of Human Chromosomes

  23 pairs of chromosomes, total of 46
• Genotype vs. Phenotype


  Genotype: genetic makeup; Phenotype: physical and behavioral characteristics
• Example of Punnett Square


  A table with rows and columns labeled with the possible alleles, used to predict genotype combinations and probabilities of traits in offspring
• Brown eyes (BB) are dominant to blue eyes (bb):

  Parent‘s Cross: BB x bb

  Offspring -

  Genotype: Bb, 100%

  Phenotype: Brown eyes, 100%
• Chromosome Function 1


  Genetic Information Storage
• Autosomal


  Chromosomes outside of sex chromosomes (X and Y); numbered 1-22 in human body cells
• Autosomal Chromosomes


  22 pairs of chromosomes excluding sex chromosomes (X and Y), influencing physical traits like eye and hair color, and height
• Sex-Linked Traits


  Traits influenced by genes on X and Y chromosomes, often recessive and linked to the sex of an individual
• X-Linked Traits


  Traits influenced by genes on the X chromosome, often recessive and affecting females more frequently
• XX vs XY Chromosomes

  Females have two X chromosomes (XX), while males have one X and one Y (XY) affecting trait expression and dosage
• Y-Chromosome Traits


  Traits influenced by genes on the Y chromosome, including male development, testosterone production, fertility, and sperm production
• Who has XX?


  Females, including humans and many other animals, have two X chromosomes (XX)
• Who has XY?


  Males, including humans and many other animals, have one X and one Y chromosome (XY)